The tetraspanin superfamily: molecular facilitators

428 0892-6638/97/0011 -0428/$01 .50 © FASEB

The tetraspanin superfamily: molecular facilitators

HOLDEN T. MAECKER, SCOTF C. TODD, AND SHOSHANA LEVY’

Department of Medicine/Oncology, Stanford University Medical Center, Stanford, California 94305,USA

ABSTRACT A legacy of molecular evolution is theformation of gene families encoding proteins that of-ten serve related functions. One such family gainingrecent attention is the tetraspanin superfamily, whosemembership has grown to nearly 20 known genessince its discovery in 1990. All encode cell-surfaceproteins that span the membrane four times, forming

two extracellular loops. Some of these genes arefound in organisms as primitive as schistosomes andnematodes. Alternately known as the transmembrane4 (TM4) superfamily or the TM4SF, 4TM, or tetras-pan family, we propose here that the name tetraspan-ins be used for the purpose of standardization. Whatdo the tetraspanins do? Awaiting definitive functionalstudies, we can only put together pieces of a puzzlethat has been built by raising antibodies against theseproteins and looking at their distribution, associa-tions, and functions. A brief overview indicates thatsome tetraspanins are found in virtually all tissues

(CD8 1, CD82, CD9, CD63),whereas others are highlyrestricted, such as CDS7 (B cells) or CD53 (lymphoidand myeloid cells). Many of these proteins have a flairfor promiscuous associations with other molecules,including lineage-specific proteins, integrins, andother tetraspanins. In terms of function, they are in-volved in diverse processes such as cell activation andproliferation, adhesion and motility, differentiation,and cancer. We propose that these functions may allrelate to their ability to act as “molecular facilita-tors,” grouping specific cell-surface proteins and thusincreasing the formation and stability of functionalsignaling complexes.-Maecker, H. T., Todd, S. C.,Levy, S. The tetraspanin superfamily: molecular fa-cifitators. FASEBJ. 11, 428-442 (1997)

Key Words: TM4SF adhesion inlegrins . gene familiesmembrane proteins

THE TETRASPANINS

THE CELL MEMBRANE is rather like an ocean afloatwith many different vessels (cell-surface proteins), somein motion, some anchored to the cytoskeleton. Eachindividual vessel may be capable of executing certaintasks (signaling, adhesion, etc.). But what allows forthe organization of these vessels into floating arma-das, or mobile complexes of many dissimilar proteins,

capable of united functions that they could not carryout as single molecules? We propose here that themembers of an emerging family of proteins, the tet-raspanins, may serve just such an organizing func-tion. Their ability to interact with many othersignaling molecules and participate in activation, ad-hesion, and cell differentiation could all relate to a

role as “molecular facilitators” that bring togetherlarge molecular complexes and allow them, throughstabilization, to function more efficiently.

The tetraspanin superfamily was first recognized in1990, when comparison of the sequences of the newly

cloned CD37, CD81 (TAPA-1), and sm23 genes withthe tumor-associated gene CD63 (ME491) (1) re-

vealed sequence homology and a conserved pre-dicted structure (2-4). The family has now grown toabout 20 known members (Table 1) in species fromSchistosoma to humans. Recently, several genes withhomology to tetraspanins have also been identifiedin the nematode, Caenorhabditis elegans, as part of itsgenome project (5, 6). Some of them have homologyto particular mammalian tetraspanins, suggesting aconserved role for these proteins over great evolu-tionary spans, a role that is only beginning to be ap-preciated.

Defining characteristics of tetraspanins

What makes a tetraspanin? What distinguishes it fromother proteins with four membrane-spanning do-mains? Basic structural motifs include the presenceof four hydrophobic, putative transmembrane do-mains (TM1-TM4), forming a small and a largeextracellular loop (EC1 and EC2), with short intra-cellular amino and carboxyl tails. This predictedmembrane topology (Fig. 1) has yet to be proven by

crystallography studies; however, antibody epitopemapping and glycosylation patterns confirm that thehydrophilic regions are indeed extracellular. In CD9,the small loop (EC1) contains a glycosylation site (7).In CD37, CD53, CD63, and CD82, glycosylation sites

are found in EC2 (8). Finally, epitope mapping ofsm23 (9) and CD53 (10, 11), and epitope mappingas well as protease digestion of CD81 in microsomes(12), are all consistent with the topology shown inFig. 1.

Correspondence.

1c2

N

C

TETRASPANIN SUPERFAMILY 429

Alignment of all 18 tetraspanin amino acid se-quences (Table 1) reveals that much of the homology

between tetraspanins is confined to the transmem-brane domains, which contain a few highly conservedpolar amino acids (an asparagine in TM1 and a glu-tamate or glutamine in TM3 and TM4, Fig. 1). These

charged residues within the membrane may inter-act with each other and may be important for the

stability of protein assembly, as has been demon-strated in T cell receptor (13). There are alsoconserved hydrophobic residues in all four trans-membrane domains; some in TM2 are found in 17/18 tetraspanin sequences (Fig. 1, and see the discus-sion of “Divergent Members” below). The short re-gion between TM2 and TM3 contains two to threecharged residues, including a conserved glutamicacid. These homologies are not shared with otherprotein families that also have four transmembranedomains, such as the ligand-gated ion channels, con-nexins, or CD2O/FcERII3.

There is greater sequence divergence in the extra-cellular loops of tetraspanins. However, three cys-teines in EC2 are located at defined distances from

the TM regions in 16/18 family members. Two ofthese cysteines occur in a conserved CCG motif lo-cated about 50 amino acids past TM3. The third cys-teine is often preceded by a glycine and is fixed at 11amino acids upstream of TM4. A fourth conservedcysteine, frequently found in a PXSC motif, is variablyplaced in EC2.

Disulfide bonding

Binding of antibodies to a number of tetraspanins(CD53, CD81, and sm23) is sensitive to reducingagents (11, 12, 14), indicating that disulfide bondinginvolving at least two of the conserved cysteines inEC2 occurs. Which cysteines are involved is un-known. The a subunits of the acetylcholine receptor,like tetraspanins, contain two adjacent cysteines(aa192 and 193), which are disulfide-bonded to eachother (15). However, such proximal disulfide bondsare rare. In the case of CD81, the region between thetwo fixed cysteine positions marks a subloop that ishypervariable between CD81 sequences from differ-

ent species (16). The significance of this is unknown,although it suggests that conserved CD81 functions(such as ligand binding and signal transduction) areprobably mediated by other domains.

Structural similarity to ion channels

Although there is no significant sequence homologyof tetraspanins with any other known gene families,it has been suggested that some of their structuralfeatures are similar to ligand-gated ion channels (8,17). For example, polar amino acid residues line thepore of ion channels and are also found in the trans-

Figure 1. Schematic structure of tetraspanin proteins. Amino(N) and carboxyl (C) termini and extracellular and trails-membrane domains are indicated in boldface. Highly con-served amino acids (found in at least 12/18 tetraspaningenes) are shown in circles; those found in 14 or more tetra-spanins are shown in boldface circles. The conserved PXSC

motif is located at different positions within EC2 in the varioustetraspanins, and is therefore indicated with floating arrows.

Asterisks indicate conserved charged amino acids within thetransmembrane domains. Patterned after Horesi and Vlcek(17).

membrane domains of tetraspanins. Note the con-served glutamine or glutamate residues, one each inTM3 and TM4, and the asparagine in TMI (Fig. 1).Of course, these charged residues may also be in-volved in stabilizing protein assembly, as noted above.Less striking is the similarity of tetraspanins to ace-tylcholine receptor family members, which also have

four transmembrane domains and form multivalentcomplexes with each other (see “Molecular Associa-tions of Tetraspanins” below).

Divergent members

As with any large family, some of the tetraspanins aremore highly diverged from the others and do notshare certain key features. These distant relatives in-

clude two ocular proteins, peripherin and Rom-l,and the epithelial proteins il-TMP and L6. L6 and il-TMP do not share the CCG motif in EC2 shared byall other members, and their EC2 domains are much

shorter than those of the other tetraspanins. Pert-pherin and Rom-1 have long carboxy-terininal cyto-plasmic tails not found in other family members.Their relationships to each other and to the rest ofthe tetraspanins, based on amino acid homology, are

ce

C.”

C”

a -0’ -

kC t ‘a . -C C 5-I ‘ 5-- 5- -

- - - - - - r, - -

0

cQ_

5)a

VU

Va

-

-as =CSUES) U

S‘ -a E

at 0I_a.[.,, .

U.E a#{128}a ,.

a-a

a.

ES

-,

E- a.95

a a a.0aV9 #{149}a-a

,I,

a.

VUaV

0

a.V

aV

-aa‘5

0

aV

-a0

aCS

0

a

aaa

-aaVSC-a

V

SaC-

V

0

-

9#{149}E a.9

a. ‘aUS

-t#{149}#{149} .9 U

za-a ‘a

aa

.a a ba’E - a-atV v S5)

,a aa -a

. . #{149}!-a 0;V C-’

a‘ a o-a.Eaa v - U #{149}. a s aa- ar-- a -‘ .C ‘a ‘5

aUaaE’5

.S -e-’

aaaaVU

a.-XC.

..aaSC V

- Iaba

-aVaa

‘aaa

- c

aa

CSEC-

aaUaaC-SaU‘5

aEaC-aVaI-,

-a

a

C-

aaaas

-a.aX

CS

EaaUC-55

O

aVOZ

.-t

a

CCC ‘a

a-a

a

‘a

a

a.

aaa

IIE

a

U

-a

aEU-a

a.a CCC

-a’aU‘5

aE

--VbO

--a

I

I

a.‘ a -a. -

C-’

0

a a..S

E Ea a

5-.

C-’C-I

0-0

430 Vol. 11 May 1997 The FASEB journal MAECKER ET AL.

VeS

z

a

VVSa.a0

V

-aSVU

aaaUa

a

Sa, z

-

a

a.

aSEa

=V S

a

n .Elt#{149}- a.“- au E

SaaU V

U-a .

.Ea -ao V

aaa a#{149}-V . U0

V a_ V

a a- V,U....

ba00ba

a E-aa -a

- taaU b.9a aa 1.oa V

S a.LVS -a-a_V aao 0aU OEa .a- #{149}-rI U S ri,VVV-‘ a ‘-‘ a U, -a

#{149}.S: .< tz

a aS S

E Ea a

5-. ce c

C) 0 0

aa

#{149}aS

a vUtS;_

= V

-

,a,a,a..-‘-a

-a

55)

.t

U -

.9 E

a..

aSE a

‘ a a

c’1

0

5-4

-C-I C’)C’-

aC

CS

aUCS

-aaSaaCSSCVC-SCSCCS

V

V

CS

a.‘5VUa

-aa

aC

CS

C-

aCSI.

-CS-aEVOUUa’-

a

a

aV-. aC-a.

depicted in Fig. 2. The uroplakins, Ia and lb (and themink epithelial protein TI-i, most likely a specieshomologue of uroplakin ib), are closely related to

each other and segregate further from the other te-traspanin genes in Fig. 2. The remaining 12 tetra-spanins may be considered “core” family members,as they form one major branch of the dendogram ofFig. 2. In this review, we will focus on these 12 coremembers, which include all of those expressed onleukocytes, with limited reference to the more distantrelatives.

Genomic structure

Among the family members whose genomic organi-zation is known (CD37, CD53, CD63, CD81), there isrelatively tight conservation of intron/exon structure(18). Typically, a large intron [8 kb in CD8I (19)]lies between the first and second exons; the remain-ing exons 2-8 are clustered more tightly at the 3’ endof the locus. The gene structure of the distant relativeRom-1 does not conform to this structure (20).

late bloomer

sm23

SAS

CD63

CO-029

CD9

CD81

CDS3

CDS2

CD37

PETA-3

A15

uroplakin Ia

uroplakin lb/TI-i

Rom-1

peripherin

CCCV

S

VC-

aSCCC

cCr) ‘a t-- .-.- -cr

- -CC) CC) r- C-I- - C-I ‘a ‘a ‘a -

S

!VU

SSC

.

.-V

a..aa.V

.EaaC-aa.aa:a,

9C..

5a.

Ua

i-

CU

a.a#{149}

a-a’aaU-V

CC_._ 0‘5Un

aH

-C..

CCC CCC= a

C.. VVU a

-a .-

..a9 . -

CCC ,

a a.a.. -

CCC

a -t. a.

Eaa

- IES . .5.5-

C- SCSCC- a.U an0

aC>- a

- aaa ‘a- -aV V VCCC ‘CCCCC CCC

U aaa. a. aaX )< .aaV

SCa -

-a -t

6ga

-

d.C

V CaU..

E-Caa-a.EV

..UaSC’-’5

Va5.a’’

-

EEV aa

-E VV

V

--E‘5 VC)

VVV-a-a.a

V -a-aV. Ea.z

a aS S

E Ea a

I.V aV 5C)

ESCaCaaa.a

000

0

aC-C)

a. a-

.9.a

aCSC-

aaCCV

VU

E -CC- V

V

a. EV

;:. sCa- EC.E- CCCC UC C-

SUC/CC/)

a5 5V

E Ea a

CC)

CI C-I CCC<EC-’C/C CCC

c-s

-aVC.V

U

-a

aC)UC)

C)aC)SC

aSa.

V

V

Ua

C)a

-aV

-aCS

-a

a

L6

il-TMP

Figure 2. Evolutionary tree of the tctraspanin superfamilydrawn as a dendogram with constant branch lengths. The rel-ative divergence of indisidual members, based on sequencehomology, was determined using the “pileup” multisequenceanalysis and the linked “grow trees” programs in the GCGWisconsin Sequence Analysis software package, version 8.1.

Comparisons are based on the region from the first amino

acid to the cysteine-cysteine-glycine motif in EC2. This limitedanalysis was done because “pileup” of all 18 tetraspanins pro-duces a high frequency of gaps after the CCC motif, does notalign the PXSC motif in EC2, and misaligns TM4 of il-TMP

and L6. The tree does not include several C. elegans tetraspan-ins that were recently identified (6).


432 Vol. 11 May 1997 The FASEB journal MAECKER FT AL.

Chromosomal locations

Many of the tetraspanin genes have been mapped,and they lie on a number of different chromosomes.However, CD81 and CD82 genes are found on hu-man chromosome 11 (lip15.5 and iipii.2, respec-tively); and CD9, CD63, and SAS are found onchromosome 12 (l2pl3, 12ql2-q13, and 12q13-q14,respectively) (1, 21). CD53 is found on chromosome

lpl3 (22) and CD37 on chromosome 19 in humans.In the mouse, CD63 has two loci: one on chromo-some 10 in a region with linkage homology to humanchromosome 12; the other (designated CD63-rs, forCD63-related sequence) maps to chromosome 18(23). There is some evidence for divergence from asingle ancestral locus that can be gleaned from genemapping. In the mouse, CD53 on chromosome 3 and

CD37 on chromosome 7 are surrounded by othergenes that are structurally or functionally related(18). Two of the tetraspanin loci, CD63 and CD81,have been conserved as part of a syntenic group(genes whose chromosomal order is preserved be-

tween species, in this case between mouse and hu-man) (19).

Transcriptional regulation

Limited studies have been done on the regulation oftetraspanin gene transcription. Common features arethe absence of a TATA box and the presence of Spibinding sites, as exemplified by CD9 (24).

In CD63, the promoter region is C-C rich and con-tains three transcription initiation sites, as well as po-tential binding sites for the transcription factors AP-1,Spi, and ETF (25). Some of these features are shared

with other housekeeping and growth-regulatinggenes. A cryptic promoter within the first intron ofCD63 has also been identified (26) and may be a ras-responsive element.

The 5’-flanking region of CD81 is also C-C-richand contains putative Spi binding sites (19). UnlikeCD9 and CD63, it does contain a TATA box at posi-

tion -25.Since many tetraspanins are induced in different

tissues under different conditions, it is not surprisingthat these genes have complex regulatory regionsgoverning their transcription.

Post-translational modifications

Most of the tetraspanins are modified by N-glycosy-lation; some are variably glycosylated or acylated,such as CD9 (27). The glycosylation patterns betweendifferent tetraspanins vary widely, however. Some,like CD81, are not glycosylated. CD9 contains a gly-cosylation site in EC1 (7), whereas most other gly-cosylated tetraspanins contain sites in EC2 (28, 29).Thus, there is no conservation of glycosylation sites

between the different tetraspanin molecules. Withinindividual members, however, most glycosylation

sites are conserved between species. For example,CD9 of mouse, rat, primates, and cow have identicalsingle glycosylation sites, whereas the feline moleculelost this site altogether. In CD63, the glycosylationsites are conserved in the mouse, rat, human, and

rabbit.

EXPRESSION OF TETRASPAN1NS

In considering the expression pattern of tetraspan-ins, the first rule seems to be that there are no rules.Some of these proteins have nearly ubiquitous tissuedistribution (CD9, CD63, CD81, CD82) whereas oth-ers are highly restricted, for example, to lymphoidand myeloid cells (CD53) or mature B cells (CD37).Some members appear to be highly expressed in theimmune system; more recently, their expression inthe nervous system has also been appreciated. Therecent discovery of the late bloomer (Ibi) gene in Dro-

sophila is a case in point (30), as it plays a role in theformation of neuromuscularjunctions. Embryos lack-ing the lbl protein exhibit delayed formation of syn-apses between motoneurons and their targetmuscles, and neighboring motoneurons display ec-topic sprouting.

Expression in development

Late bloomer is not the only tetraspanin potentiallyinvolved in development. CD9 is transiently ex-pressed in developing spinal motoneurons and otherfetal central and peripheral nervous system sites (31).It is present in embryonic and fetal hematopoietic

and other tissues as well (32-34). CD81 is ex-pressed on embryos as early as the preimplantation

stage (35).During T cell development, CD53 expression is

correlated with thymocytes that can proliferate in re-sponse to alloantigen or lectin (36); it is absent on

the vast majority of CD4CD8 thymocytes. However,CD53 expression is dramatically induced upon posi-tive selection (10). Other tetraspanins are expressedonly at certain stages of B cell maturation; e.g., CD9is expressed only during B cell development (7)whereas CD37 is found only on mature B cells (37).

In vitro studies have implicated CD81 in thematuration of thymocytes from CD4CD8 toCD4CD8 (38). However, in vivo T cell develop-ment of CD81 mice is normal (39).

Association with cellular activation

Many tetraspanins are associated with cellular acti-vation. Some are up-regulated on activated cells

[CD9 (7), CD53 (18), CD63 (40), CD82 (41)],


whereas others are down-regulated or associated with

growth arrest [TI-i (42), il-TMP (43), CD37 (44), and

CD53 (18)]. CD81, highly expressed in germinal cen-ter B cells (45), was recently rediscovered as a proteinup-regulated during glial cell mediated repair of neu-ral injury (46).

Expression in tumors

A number of tetraspanins were discovered as tumor-

associated proteins, including CO-029 (47), PETA-3/SFA-1 (48), and SAS (49), which is amplified in asubset of sarcomas. CD9 is expressed on 90% of non-T cell acute lymphoblastic leukemia cells and on 50%of chronic lymphocytic and acute myeloblastic leu-kemias (7). CD63 is expressed in early, but not late-stage melanomas (50).

The relationship of CD9 and CD63 with subsets ofcertain cancers may relate to their association withcell motility and metastasis. For example, CD9 ex-pression induced by transfection of carcinoma cell

lines suppresses motility and metastasis (51). CD9 ex-pression on primary melanomas has also been in-versely correlated with metastatic potential (52).Also, reduction in CD9 expression has been corre-lated with poor prognosis in breast carcinoma (53).For CD63, the story is less clear, but its absence inlate-stage melanomas suggests a similar anti-meta-static property (50). Also, antibodies to CD63 caninfluence adhesion of neutrophils to endothelium(54, 55), suggesting some role for CD63 in cell mo-tility. Perhaps the most dramatic tetraspanin-cancer-metastasis story is that of CD82, which was recentlyrediscovered in a screen for genes that suppressedmetastasis of a prostate cancer cell line (56).

Other disease associations

Two tetraspanin genes have been implicated in hu-man hereditary diseases. The peripherin/RDS locussegregates with autosomal dominant retinitis pig-mentosa, a syndrome associated with progressive vi-sual loss and clumping of retinal pigment (57).Mutations in the peripherin gene have been linkedto this and similar syndromes in a number of families(58-63).

Hermansky-Pudlak syndrome is characterized byreticuloendothelial cell abnormalities, with lysosomeand dense granule deficiencies. Platelets of patients

with this syndrome are largely devoid of CD63 intheir dense granules (64). However, a locus segre-gating with Hermansky-Pudlak syndrome was re-cently localized to chromosome 10 (65), indicatingthat CD63 is indirectly involved in this syndrome.

Subcellular expression

The expression of CD63 in platelet dense granules

brings up the topic of subcellular localization of te-

traspanins. In addition to CD63, CD9 is highly ex-

pressed in platelet a-granules (66). CD37 is alsohighly expressed in intracellular vesicles (37) as wellas on the cell surface of B cells. Rom-i and peripherinare associated with each other and with intracellularmembranes in the photoreceptor cells of the retina

(67). Finally, the uroplakins Ia and Lb are colocalizedon the asymmetric unit membrane in the apicalplaques of mammalian urothelium (68).

If expression is indicative of function, the tetra-spanins obviously serve many and diverse roles. This

can also be gleaned from the surprising number oftimes some of these genes have been rediscovered byinvestigators working in different fields. CD81, for ex-

ample, has been discovered no less than five times:1) as the target of an anti-proliferative antibody to Bcell lines (4); 2) as the target of a morphology-alter-ing antibody to HIV-infectedJurkat cells (69); 3) asa protein involved in HTLV-1-mediated syncytiumformation (70); 4) as a protein involved in thymocytematuration (38); and 5) as a protein involved in as-trocyte morphology (46). Similar “rediscoveries”have been made for CD9, CD82, CD63, CD53, andPETA-3/SFA-1. The different roles of tetraspanins in

various systems are almost certainly related to theirassociations with a wide variety of other proteins,

many of them tissue-specific. These associations willbe examined in the next section.

MOLECUlAR ASSOCIATIONS OFTETRASPANINS

The tetraspanins have earned a reputation in recent‘ears for promiscuous associations with a wide rangeof other proteins including integrins, coreceptormolecules, and other tetraspanins. In some cases somany associated molecules have been identified fora particular tetraspanin as to cause skepticism about

the genuine nature of the interactions. Yet, like acheerleader who only dates members of the footballteam, there is specificity in the myriad of associations.For a given assay, such as coimmunoprecipitation ofa tetraspanin with other proteins, there need to be(and generally are) a number of other proteins thatserve as negative controls in that they are not copre-cipitated under the same conditions. Likewise, it iscomforting to see that assays done on whole cells,

such as cocapping and fluorescence energy transfer,have confirmed the data obtained by coprecipitation

studies, which could be subject to artifacts due to in-teractions occurring after cell lysis. However, moststudies have not quantitated the associated vs. freemolecular components of a given complex. In gen-eral, the complexes described could he considered“loose” in that they do not involve the entire popli-lation of a cell-surface molecule in the complex; in-

dividual components can also exist as single species.

434 Vol. 11 May 1997 The FASEB Journal MAECKER ET AL.

Consistent with this observation, we postulate that thetetraspanins serve to “facilitate” formation of molec-ular complexes but are not required integral com-ponents of them as is the case, for example, with Tcell receptor-CD3 chains. A brief review of the typesof protein interactions identified for tetraspanins isshown in Table 2, and is summarized below.

Associations with integrins

The discovery of tetraspanin interactions with certain

classes of integrins has come to light largely in thelast 2 years and has been recently reviewed (71).CD81, CD9, CD53, CD63, and CD82 have all beenfound in association with certain integrins in varioustypes of human cells. All of these tetraspanins asso-ciate with the 131 integrins cx3131, a4f31, and a6131 (72-79). Although the 131 chain may play an importantrole in this interaction, there are other 131integrins(a2f31 and a5131) that do not associate with any ofthe tetraspanin proteins tested to date. Some tetra-spanins also interact with certain non-131 integrins.CD81 has been found in complexes with a4137 inte-

TABLE 2. Telraspanin-associated molecules

grin (80), and CD9 has been found to associate with

the 132 integrin LFA-1 (CD11/CD18) (71). The po-tential functional significance of these associations isaddressed in the next section.

Associations with coreceptor molecules

CD81 and CD82, both expressed on T cells, have

been coprecipitated with CD4 and CD8 as well as witheach other (70, 81). Using fusion constructs of CD4and CD2, it was shown that the interaction of CD81with CD4 was dependent entirely on the cytoplasmictail of CD4. Interactions of CD4 with CD82, however,required both cytoplasmic and extracellular do-

mains. The interaction of both tetraspanins with CD4is strongly inhibited by p56-lck binding to CD4 (70);thus, CD4 exists on T cells in distinct complexes withp56-lck or with CD81/CD82. In this instance, the tet-raspanin molecules may serve as barriers to the bind-ing of p56-lck, thus preventing premature activationor otherwise regulating the kinetics of T cell activa-tion.

Tetraspanin Species Cell type Associated molecules References

CD9

CD37

Human

Monkey

RatHuman

Platelets

HeLa cells

NALM-6, HEL cell linesPlateletsVero cells

Schwann cell line S-16B cells

aIIb3 (CD4I/CD61) integrin(mAb-induced association)

a6131integrin, a31 integrinand CD81 or CD63

1 integrins25-26 kDa C-proteinsdiphtheria toxin receptorproHB-EGF and a3131integrina3J31, a6J1 integrinsMHC class II

(91)

(72)

(75)(96)(85)(76, 77)(79)(139)

CD53

CD63

CD8I

Human

RatHuman

RatHuman

Hematopoietic cell linesLymph node; thymoma

B cellsNK cell line, T cellsHematopoietic cell linesHeLa cells, melanoma cell lines

Multiple cell lines

NeutrophilsBasophilic leukemia cell lineB cells

T cellsHematopoietic cell linesHeLa cells

ct4f1 integrinAn unknown phosphataseMHC class IICD2a41 integrin

a31 integrin and CD81 orCD9

a3l and ct61 integrinsLFA-1An unknown phosphataseCD19/CD21/Leu-13 complexMHC class IICD4, CD8, and CD82ct4f31, a47 integrinsa61 integrin, a31 integrin,

and CD9 or CD63

(80)(105)(139)(87)(80)(72, 73)

(74)(55)(105)(82, 140)(45, 139)(70, 81)(80)(72)

CD82

Rom-1

Human

CowHuman

T cellsHematopoietic cell lines

B cellsPhotoreceptor cells

CD4, CD8, and CD81a41 integrina331, a631 integrinsMHC class IIPeripherin

(70, 81)(80)(71)(139)(67)

Peripherin Cow Photoreceptor cells Rom-1 (67)

UPIa Cow Bladder epithelium UPIb, UPII, UPIII (68)UPIb Cow Bladder epithelium UPIa, UPII, UPIII (68)


Associations with other tetraspanins

Many of the associations listed in Table 2 are betweentetraspanins themselves. CD9, CD81, and CD63 canall form heterobimolecular complexes with eachother that also include a3131 and sometimes a6131 in-tegrins (72). CD81 associates with CD82 as well aswith CD4 and CD8 coreceptors (70, 81). Peripherinand Rom-1 are colocalized in photoreceptors of thebovine eye (67), and uroplakin Ia and lb associate inmammalian urothelium (68).

CD19/CD21/CD81/Leu’3 complex

Another “coreceptor” type of interaction involvinga tetraspanin is the binding of CD81 to a signal trans-duction complex consisting of CD19, CD21, andLeu3 (82). This complex lowers the threshold forsignal transduction through the B cell antigen recep-

tor complex (83). The presence of CD21 (comple-ment receptor 2, CR2) in this complex is thought toform a “bridge” between innate and acquired im-munity (84) by allowing complement-coated antigens

to cross-link the CD21 complex with the antigen re-ceptor complex of specific B cells. One role of CD81in this complex may be to facilitate interactions withintegrins, resulting in cell adhesion; another may beto stabilize the CD21/CD19 interaction. Data sup-porting these functions are discussed in the next sec-

tion.Other associations with potential signaling mole-

cules include the association of CD9 with a cell-sur-

face form of epidermal growth factor, proHB-EGF,that acts as the diphtheria toxin receptor (85, 86),and the association of CD53 with CD2 (87).

The varied nature of the myriad complexes de-scribed above has led to the suggestion that tetras-panins may function as “adaptor proteins” (71) thatorganize the relative positions of other cell-surfacemolecules and modulate their function. We agreewith this general interpretation, but note that theterm adapter protein is already used to describe aspecific group of intracellular proteins that containSH2 and SH3 domains. There is no identified do-main (or domains) for interaction of tetraspaninswith other cell-surface proteins; the wide variety ofpartner molecules for tetraspanin association impliesa less rigid interaction. Hence, we favor the term mo-lecular facilitators. We postulate that tetraspaninsmay facilitate the localization of specific proteins intomacromolecular complexes, probably by stabilizingcertain random interactions that occur on the cellmembrane. This in turn will increase the number of

stable, functionally active signal transduction com-plexes and allow for tetraspanins to be coupled with

cell signaling. The exact nature of this signal trans-duction for various tetraspanins is described in thenext section.

TRIGGERING CELL FUNCTIONS BYTETRASPANINS

The regulation of cellular adhesion and migration is

a fundamental requirement of multicellular organ-isms. In mammals, the critical role of adhesion andmigration is well demonstrated by cells of the im-mune system. Among the molecules known to me-

diate lymphocyte adhesion and migration, theselectins, integrins [e.g., LFA-1 (aL/132) and VLA-4(a4/131)], and Ig-superfamily members (e.g., CD2

and ICAMs) are the focus of intense investigation, asrecently reviewed (88, 89). The current model to ex-plain the regulation of lymphocyte adhesion involves

the conversion of integrins, already present on thecell surface, from low to high-affinity status in re-sponse to a variety of stimuli such as engagement of

TCR, MHC-class II, or chemokine receptors. Theconversion of an integrin is thought to involve con-formational changes that increase the affinity of theintegrin for its ligand and allow oligomerization ofintegrins and coupling to cytoskeletal elements,thereby facilitating high avidity binding of the cell to

the integrin-bound substrate. Although the intracel-lular signals resulting from such receptor engage-ment have been characterized, little is known aboutthe mechanisms that allow them to regulate integrinactivity. It is upon this stage that a new cast of char-acters, the tetraspanins, has presented itself.

Early evidence of a relationship between the tet-raspanins and adhesion came from studies showingthat anti-CD9 mAb induce platelet aggregation (90).Since that time, triggering of nearly every tetraspaninhas been shown to influence adhesion or motility ina variety of cells including platelets, B cells, T cells,prostate carcinoma, breast cancer, melanoma, orSchwann cells. Because of the diversity of cell typesand the array of adhesion mechanisms involved,these studies may best be considered separately foreach individual tetraspanin, remembering that inmany cells more than one member of this family isexpressed and that they are frequently found in as-sociation with each other.

CD9

After the demonstration that anti-CD9 antibodiestrigger platelet aggregation, it was reported that the

antibodies induce association of CD9 with the inte-grin aIIb/1311I (GPIIb/IIIa; CD4I/CD61) on plate-lets and that the triggering of platelet aggregation ismediated by GPIIb/IIIa (91). In fact, injection ofanti-CD9 into monkeys causes lethal thrombocyto-penia within 5 mm of injection, which is preventedby pretreatment of the monkeys with anti-aIIb/13 an-tibodies (92). CD9-mediated platelet activation, likethe activation induced by anti-ctllb/f3III antibodies,can be blocked by antibodies to FcyRII suggesting

436 Vol. 11 May 1997 The FASEB Journal MAFCKER ET AL.

that the activation is mediated by the FcyRlI. Indeed,antibodies to several platelet proteins, including thetetraspanin PETA-3, induce platelet aggregation thatis inhibited by Fc receptor blockade. However, evenin the absence of Fc engagement, treatment of plate-lets with immobilized anti-CD9 F(ab’)2 increasesplatelet activation (93). More recently it has beenshown that triggering platelets with F(ab’)2 increasestyrosine phosphoiylation of p72syk (94). The in-crease in tyrosine phosphomylation is lower than thatseen in the presence of the whole antibody, indicat-ing suboptimal triggering by the F(ab’)2 fragment.Full activation of the kinase is seen only upon persis-tent binding to the Fc receptor, which can be blockedby anti-FcyRH antibody. In addition to the increasesin protein tyrosine phosphomylation, the signals ini-tiated upon treatment of platelets with various anti-CD9 antibodies include increases in intracellularCa2 and production of diacylglycerol and inositol1,4,5-triphosphate, leading to activation of protein ki-nase C (95). Evidence also suggests GTP exchange byactivation may be mediated, in part, by low molecularweight GTP binding proteins (96).

In addition to its effects on platelets, anti-CD9 in-duces aggregation of pre-B cell lines in a manner thatshares many features of integrmn mediated adhesionbut is independent of LFA-1 (aL/f32; CDila/CD18)(97). Subsequent studies have shown that anti-CD9antibodies induce pre-B cell adhesion to bone mar-row fibroblasts via VLA-4-and VLA-5-mediated bind-ing to fibronectin (98). Transfection of CD9 into apoorly motile CD9-negative B cell line (Raji) en-hances cell migration across fibronectin and laminin.The migration is inhibited by anti-VLA4 and VLA6mAb, suggesting that CD9 and these 131 integrins areinvolved in cell motility functions in this cell line(99). Transfection of CD9 into nonlymphoid, motile

cell lines inhibits their motility, indicating that CD9can also down-regulate motility functions (51). Thismay be explained by the fact that integrin activationof high avidity results in arrest of motion whereas in-termediate avidity facilitates migration. CD9 has beenshown to play a role in the adhesion and migrationof Schwann cells, which is accompanied by a rise inintracellular calcium and by enhanced protein tyro-sine phosphorylation (100). CD9 is also involved inadhesion of neutrophils to endothelial cells sincetreatment of endothelial cells with anti-CD9 antibod-ies induces neutrophils, which do not express CD9,to rapidly adhere to the endothelium (101). Mostrecently anti-CD9 was reported to provide a co-stimulatory signal to T cells in the absence of antigen-presenting cells. This costimulatoiy signal is as potent

as the one induced by anti-CD28 mAb. However, it isindependent of CD28 as shown in T cells obtainedfrom CD28 deficient-mice (102). Finally, CD9 hasbeen shown to be required for susceptibility of cellsto canine distemper virus (103). Thus, it is evident

that CD9 is involved in a myriad of activation, adhe-sion, and cell motility functions, as well as cell-cellinteractions.

CD53

An anti-CD53 mAb (7D2) was functionally isolated byits ability to activate a phosphatidylinositol signaling

pathway in a rat NK cell line (87). Treatment of thecells with the intact antibody increased intracellularCa2 and protein tyrosine phosphorylation. These

changes were similar to those induced by cross-link-ing CD2; indeed, it was found that the two moleculesassociate in T cells. The 7D2 mAb induced prolifer-ation in splenic T cells and augmented the responseto a TCR mAb (87). In rat macrophages the mAb wasalso shown to increase intracellular Ca2 accompa-nied by increases in inositol triphosphate and di-acylglycerol. Activation of protein kinase C wasobserved in mAb-treated macrophages as well as anincrease in nitric oxide synthase and nitric oxiderelease (104). CD53-induced signaling may be

mediated by tyrosine phosphorylation and dephos-phorylation, as an unidentified tyrosine phosphatasewas shown to be associated with rat CD53 (105). Ty-rosine phosphorylation is also triggered by anti-CD53in the oxidative burst of human monocytes and isinhibited by blockers of tyrosmne phosphorylation.Cross-linking CD53 on these cells induces a strongincrease in intracellular Ca2, whereas a modest in-crease is seen in B lymphocytes (106). In resting Bcells the molecule transmits a costimulatory signaland promotes activation through the Ig receptor(107). CD53 may also be involved in T cell matura-tion, since in the mouse it is expressed on earlyCD4CD8 thymocytes and is down-regulated in

CD4CD8 cells. The molecule is re-expressed uponpositive selection (10).

CD63

Like CD9 and PETA-3, CD63 was identified as a plate-let-activating antigen. In platelets, the molecule wasindependently identified as a dense granule protein(granulophysin). Involvement of CD63 in cell adhe-sion was demonstrated by antibodies to CD63, whichinhibit the binding of monocytes to serum-coatedplastic and prevent the adhesion of neutorophils toendothelial cells (54, 108). In endothelial cells, CD63was identified as a component of the Weibel-Paladebodies. These secretory granules exocytose upon in-flammatory stimulation. The adhesion protein P-se-lectin and the von Willebrand factor colocalize withCD63 in these granules (109).

Recent studies demonstrated that antibodies toCD63 induce neutrophil adhesion to HUVEC andthat the adhesion is probably mediated by LFA-1

- 2± ‘+since antibodies to LFA-l and Ca (but not Mg-


depletion block CD63-mediated adhesion. LFA-1 isup-regulated in CD63-activated neutrophils, which al-lows binding to HUVEC, whereas L-selectin is

down-regulated. In these studies, LFA-1 as well as sev-

eral protein kinases were shown to associate withCD63 by immunoprecipitation studies (55).

Other integrin molecules, \TLA-3 and VLA-6 (a3/131 and a6/131), associate with CD63 in a humanerythroleukemia cell line and colocalize in cellular

footprints suggesting involvement in cell motility(74). In the rat, CD63 was originally identified by anmAb (A.D1) that inhibits IgE-mediated histamine re-lease in basophilic cell lines. The molecule was shownto be in close proximity to the FcERI, since severalanti-FcERI mAb inhibit binding of AD1 to the cells,and immunoprecipitation studies demonstratedphysical association of CD63 with FcERI (110). Al-

though little is known about intracellular signalinginduced by cross-linking CD63, the molecule copre-cipitates a phosphatase activity in a rat cell line (105).

CD81

Anti-CD81 mAb have been shown to induce homo-typic aggregation of a variety of hematolymphoid celllines. Aggregation induced by the 5A6 mAb is tem-perature-dependent and is not blocked by the re-moval of divalent cations or by anti-LFA-l antibodies(4). Similarly, aggregation induced byJKT.M1 mAb,although divalent cation-dependent, is not inhibitedby antibodies to LFA-1, VLA-4, CD43, and CD44 (69).Treatment of B cell lines with anti-CD81 activatesVLA-4-mediated binding to fibronectin, allowing ad-hesion of the cells to interfollicular stroma of frozenhuman tonsil sections (78). Anti-CD81 induces cell-cell adhesion of human thymocytes, which is medi-

ated by LFA-1 and not VLA-4 despite expression ofVLA4 on these cells (111). Together these findingsillustrate that the functional relationship of CD81

with integrins may be cell type-specific.Anti-CD81 mAb have also been shown to induce

changes in cell morphology (46, 69) and to inhibitsyncytium formation (70, 112). However, it is un-known whether these effects are integrin-mediated.

Anti-CD81 mAb also induce an antiproliferative ef-fect in B cell lines that is probably independent ofcell adhesion. The antiproliferative, but not cell ad-hesion, effects of anti-CD81 mAb can be preventedby an increase in intracellular thiol levels (113). Theantiproliferative effect is initially reversible, but even-tually leads to cell death. Protection from cell deathis correlated with inhibition of protein tyrosine phos-phorylation (113).

The antiproliferative effect induced in B cell linesupon cross-linking CD81 on their surface is probablytriggered as a result of engaging the CD19/CD21/

CD81/Leu complex (83), since triggering multi-ple members of this complex leads to cell death. In

vitro, this B cell complex was shown to decrease the

threshold of Ig binding necessary for the activationof normalB lymphocytes (114). In vivo, it was shownto reduce the threshold for activating HEL-specific

Ig-expressing B cells. Moreover, fusing the HEL an-tigen to the C3d component of complement reducedby several logs the immunogen dose needed to elicitan immune response (84). In this B cell complex,CD19 is thought to mediate intracellular signaling,CD21 to bind complement, and CD81 to trigger cel-lular adhesion (probably via integrin activation).

Leu3, an interferon-inducible molecule (115), maybe involved in the response to viral attack, but its pre-cise role in the complex is not known. CD81 may be

seen as a facilitator molecule in this complex, bring-ing an already large group of proteins into functional

association with another set of proteins, the integrins.Since CD81-null mice exhibit reduced CD19 levels(39), CD81 may stabilize the association of CD19 andCD21.

In T cell lines, CD81 associates with the lineage-specific molecules CD4 and CD8. These associationsmay play a role in signaling since lck-engaged CD4

molecules do not associate with CD81 (81). In hu-man thymocytes, engagement of CD81 provides acostimulatoty signal with anti-CD3 that promotes IL-2-driven proliferation of these cells (111). CD8I hasalso been shown to play a role in antigen specific B-Tcell interactions, since addition of anti-CD81 mAb tothe interacting cells results in a shift in cytokine pro-duction toward a Th2 profile (116). A striking effectof an anti-mouse CD81 mAb in fetal thymic organculture is the inhibition of maturation of double-neg-ative a13 T cells to the CD4CD8 phenotype (38).This effect was presumed to be mediated throughCD81 on thymic epithelial cells, which stain brightlyfor CD81. However, human (111) and mouse (39)thymocytes have also been shown to express CD81,so this effect may be mediated by direct binding tothe thymocytes. Upon removal of the anti-CD81mAb, the double-negative T cells proceed to mature,

even after a 5 day treatment (38). An antiproliferativeeffect of anti-rat CD81 mAb on astrocytes is also re-versible when the antibody is washed away from theculture (46).

CD82

Several cellular changes induced upon binding CD81were also observed with anti-CD82 mAb. Induction ofdendritic processes was seen when human T cell lineswere treated with immobilized anti-CD82 mAb. Inthese studies, mAb 4F9 and 1A4 also provided a cos-

umulatory signal when immobilized together withanti-CD3 mAb (117, 118). One anti-CD82 mAb wasselected because of its ability to inhibit HTLV-in-

duced syncytium formation; as noted above, an anti-CD81 was also selected by this assay (112). Since


CD81 and CD82 are physically associated on the cellsurface (81) and each molecule is associated with thesame integrins (71) and with CD4 and CD8 in T cells

(81), it is likely that cross-linking either molecule ofthis pair activates a similar signaling cascade. CD82signaling in the absence CD81 expression is seen inU937 cells, where treatment with anti CD82 mAb in-creases intracellular Ca2 (119) and induces proteintyrosine phosphorylation (120). Evidence that themolecule plays a role in motility-related functions

comes from its independent isolation as a metastasissuppressor gene in human prostate cancer (56).

PETA-3/SFA-1

PETA-3 (Platelet-endothelial cell tetraspan antigen)

was identified as a platelet glycoprotein by a mAb thatinduced platelet aggregation (121). The aggregationcould be blocked by the anti-FcyRII antibody (1V.3)or when F(ab’)2 fragments were used, similar to theeffect seen for CD9-mediated platelet aggregation.The same molecule, independently cloned as SFA-1,was shown to be up-regulated in human T cells trans-formed by T cell-leukemia virus type 1 (48).

CD37

Antibody ligation of CD37 has been shown to induce

aggregation of B cell lines and freshly isolated tonsil-lar B cells (122).

Late bloomer

This tetraspanin was recently identified in Drosophila

as a protein involved in contact between motoneu-rons and their muscle targets. In lbt embryos thereis a delay in synapse formation, hence the name (30).Thus, we propose that this tetraspanin also serves amotility-related function.

CONCLUSION

As one considers the barrage of findings outlinedabove, there are general themes that emerge. First,activation of tetraspanins, often found in physicalproximity with integrins, results in changes in cellmorphology, cell-cell and cell-matrix adhesion, andmotility. Second, cross-linking tetraspanin molecules

on the cell surface can provide costimulatory signals,possibly by virtue of their association with lineage-specific signaling molecules. Thus, we hypothesize

that most, if not all, of the observed functions of tet-raspanins relate to their ability to facilitate interac-tions between other proteins, generating functional

complexes. We would propose that the term “molec-ular facilitators” be used to describe this general role

and that the tetraspanins may be considered the pro-totypical examples of such molecules.

REFERENCES

1. Hotta, H., Ross, A. H., Huebner, K., Isobe, M., Wendeborn, S.,Chao, M. V., Ricciardi, R. P., Tsujimoto, Y., Croce, C. M., andKoprowski, H. (1988) Molecular cloning and characterizationof an antigen associated with early stages of melanoma tumorprogression. Cancer Res. 48, 2955-2962

2. Wright, M. D., Henkle, K. J., and Mitchell, G. F. (1990) Animmunogenic !vt 23,000 integral membrane protein of Schis-tosoma mansoni worms that closely resembles a human tumor-associated antigen.j Immunol. 144, 3195-3200

3. Classon, B.J., Williams, A. F., Willis, A. C., Seed, B., and Sta-menkovic, I. (1990) The primary structure of the human leu-kocyte antigen CD37, a species homologue of the rat MRCOX-44 antigen.]. E4. Med. 172, 1007

4. Oren, R., Takahashi, S., Doss, C., Levy, R., and Levy, 5. (1990)TAPA-1, the target of an antiproliferative antibody, defines anew family of transmembrane proteins. Mol. Cell. Biol. 10,4007-4015

5. Tomlinson, M. G., and Wright, M. D. (1996) A new transmem-brane 4 superfamily molecule in the nematode, Caenorhabditiselegans.j Mol. Evol. 43, 312-314

6. Wilson, R., Ainscough, R., Anderson, K., Baynes, C., Berks, M.,Bonfield,J., Burton,J. Connell, M., Copsey, T., Cooper,J., etal. (1994) 2.2 Mb of contiguous nucleotide sequence fromchromosome III of C. elegans. Nature (London) 368, 32-38

7. Boucheix, C., Benoit, P., Frachet, P., Billard, M., Worthington,R. E., Gagnon,J., and Uzan, G. (1991) Molecular cloning ofthe CD9 antigen. A new family of cell surface proteins. j Biol.Chem. 266, 117-122

8. Wright, M. D., and Tomlinson, M. G. (1994) The ins and outsof the transmembrane 4 superfamily. Immunol Today 15, 588-594

9. Reynolds, S. R., Shoemaker, C. B., and Ham, D. A. (1992) Tand B cell epitope mapping of 5M23, an integral membraneprotein of Schistosoma inansoni.j Immunol. 149, 3995-4001

10. Tomlinson, M. C., Hanke, T., Hughes, D. A., Barclay, A. N.,Scholl, E., Hunig, T., and Wright, M. D. (1995) Charactenza-tion of mouse CD53: epitope mapping, cellular distributionand induction by T cell receptor engagement during repertoireselection. Eur. J. Immunol. 25, 220 1-2205

11. Tomlinson, M. C., Williams, A. F., and Wright, M. D. (1993)Epitope mapping of anti-rat CD53 monoclonal antibodies. Im-plications for the membrane orientation of the transmembrane4 superfamily. Eur.]. Immunol. 23, 136-140

12. Levy, S., Nguyen, V. Q.,Andria, M. L., and Takahashi, S. (1991)Structure and membrane topology of TAPA-1 .j Biol. C/tern. 266,14597-14602

13. Cosson, P., Lankford, S. P., Bonifacino, J. S., and Klausner,R. D. (1991) Membrane protein association by potential intra-membrane charge pairs. Nature (London) 351, 414-416

14. Oligino, L. D., Percy, A.J., and Ham, D. A. (1988) Purificationand immunochemical characterization of a 22 kilodalton sur-face antigen from Schi.ctosorna mansoni. Mol Biochem Parasitol28,95-103

15. Kao, P. N., and Karlin, A. (1986) Acetylcholine receptor bind-ing site contains a disulfide cross-link between adjacent half-cystinyl residues. j Biol. Chem. 261, 8085-8088

16. Levy, S., Todd, S. C., and Maecker, H. T. (1997) CD81 (TAPA-1), a molecule involved in signal transduction and cell inter-action in the imune system. Annu. Rev. Immunol. In press

17. Horejsi, V., and Vlcek, C. (1991) Novel structurally distinct fam-ily of leucocyte surface glycoproteins including CD9, CD37,CD53 and CD63. 1EBS LetI. 288, 1-4

18. Wright, M. D., Rochelle,J. M., Tomlinson, M. G., Seldin, M. F.,and Williams, A. F. (1993) Gene structure, chromosomal local-ization, and protein sequence of mouse CD53 (Cd53):evidencethat the transmembrane 4 superfamily arose by gene duplica-tion. mt. Immunol. 5, 209-216


19. Andna, M. L., Hsieh, C. L., Oren, R., Francke, U., and Levy, S.(1991) Genomic organization and chromosomal localization ofthe TAPA-1 gene.j Immunol. 147, 1030-1036

20. Bascom, R. A., Schappert, K., and Mclnnes, R. R. (1993) Clon-ing of the human and murine ROM1 genes: genomic organi-zation and sequence conservation. Human Mo!. Genet. 2, 385-391

21. Boucheix, C., Nguyen van, C., Perrot,J. Y., Foubert, C.. Gross,M. S., Weil, D., Laisney, V. Rosenfeld, C., and Frezal,J. (1985)Assignment to chromosome 12 of the gene coding for the hu-man cell surface antigen CD9(p24) using the monoclonal an-tibody ALB6. Ann. Genet. 28, 19-24

22. Gonzalez, M. E., Pardo-Manuel de Villena, F., Fernandez-Ruiz,E., Rodriguez de Cordoba, S., and Lazo, P. A. (1993) The hu-man CD53 gene, coding for a four transmembrane domainprotein, maps to chromosomal region lpl3. Genomics 18. 725-728

23. Gwynn, B., Eicher, E. M., and Peters, L. L. (1996) Genetic lo-calization of Cd63, a member of the transmembrane 4 super-family, reveals two distinct loci in the mouse genome. Genomics

35, 389-39124. Le Naour, F., Prenant, M., Francastel, C., Rubinstein, E., Uzan,

C.,and Boucheix. C. (1996) Transcriptionalregulationof thehuman CD9 gene: characterizationof the 5’-flankingregion.Oncogene 13, 481-486

25. Hotta, H., Miyamoto, H., Hara, I., Takahashi, N., and Homma,M. (1992) Genomic structure of the ME491/CD63 antigengene and functional analysis of the 5’-flanking regulatory se-quences. Biochem. Biophys. Ret. Commun. 185, 436-442

26. Takahashi, N., Hotta, H., and Homma, M. (1991) Activationand suppression of a cryptic promoter in the intron of the hu-man melanoma-associated ME491 antigen gene. ]pn. j Cancer

Ret. 82, 1239-124427. Seehafer,J. G., Tang, S.C., Slupsky,J. R., and Shaw, A. R. (1988)

The functional glycoprotein CD9 is variably acylated: localiza-tion of the variably acylated region to a membrane-associatedpeptide containing the binding site for the agonistic monoclo-nal antibody 50H.19. Biochim. Biophys. Acta 957, 399-410

28. Classon, B. J.,Williams, A. F., Willis, A. C., Seed, B., and Sta-menkovic, I. (1989) The primary structure of the human leu-kocyte antigen CD37, a species homologue of the rat MRCOX-44 antigen [published erratum appears in]. Exp. Med. 1990Sep 1;l72(3):1007].j Exp. Med. 169, 1497-1502

29. Angelisova,P.,Vlcek, C.,Stefanova,I.,Lipoldova,M., and Ho-

rejsi, V. (1990) The human leucocvtesurfaceantigen CD53 isa protein structurally similarto the CD37 and MRC OX-44 an-tigens. mmmunoenesics 32, 281-285

30. Kopczynski, C. C., Davis, G. W., and Goodman, C. S. (1996) Aneural tetraspanin,encoded by latebloomer, that facilitatessynapse formation. Science 271, 1867-1870

31. Tole, S.,and Patterson,P. H. (1993) DistributionofCD9 in thedeveloping and mature ratnervous system.Dee Dyn. 197, 94-106

32. Abe,J., Emura, I.,and Ohnishi, Y. (1989) Morphological andimmunocytochemical examinations on development of B-cellsin human embryonic and fetal liver. Nippon Ketsueki Gakkai Za.s-shi52, 712-720

33. Abe, J. (1989) Immunocytochemical characterization of lym-phocyte development in human embryonic and fetal livers.Uin. Immunol. Immunopathol. 51, 13-21

34. Bri#{232}re,N., and Droz, D. (1990) Expression of differentiationmolecules is preserved in human fetal kidneys during culture.Acta Histochem. 89, 157-166

35. Andria, M. L., Barsh, G. S., and Levy, S. (1992) Expression ofTAPA-l in preimplantation mouse embryos. Biochem. Biophys.R#{128}.s.Commun. 186, 1201-1206

36. Paterson, D.J., Green,J. R.,Jefferies, W. A., Puklavec, M., andWilliams, A. F. (1987) The MRC OX-44 antigen marks a func-tionally relevant subset among rat thymocytes.j Exp. Med. 165.1-13

37. Schwartz-Albiez, R., D#{244}rken,B., Hofmann, W.. and Molden-hauer, G. (1988) The B cell-associated CD37 antigen (gp4O-52). Structure and subcellular expression of an extensively gly-cosylated glycoprotein.j Immunol. 140, 905-9 14

38. Boismenu, R., Rhein, M., Fischer, W. H.. and Havran, W. L.(1996) A role for CD8I in early T cell development. Science 271,198-200

39. Maecker, H. T., and Levy, 5. (1997) Nonnal lymphocyte devel-opment but delayed humoral immune response in CD8I-nullmice.]. Exp. Med. 185, 1505-1510

40. Sohma, Y., Suzuki, T., Sasano, H., Nagura, H., Nose, M., andYamamoto. T. (1994) Increased mRNA for CD63 antigen inatherosclerotic lesions of Watanabe heritable hyperlipidemicrabbits. Cell Struct. Fund. 19, 2 19-225

41. Gaugitsch, H. W., Hofer, E., Huber, N. E.. Schnahl, E., andBaumruker, T. (1991) A new superfamily of lymphoid andmelanoma cell proteins with extensive homology to Schistosoma

mansoni antigen 5m23. Fur.]. Immunol. 21. 377-38342. Kallin, B., de Martin, R., Etzold, T., Sorrentino, V., and Philip-

son, L. (1991) Cloning of a growth arrest-specific and trans-forming growth factor beta-regulated gene, TI I, from anepithelial cell line. Mo!. Cell. Biol. 11,5338-5345

43. Wice. B. M., and Gordon,J. 1. (1995) A tetraspan membraneglycoprotein produced in the human intestinal epithelium andliver that can regulate cell density-dependent proliferation.].Biol. Chem. 270, 21907-21918

44. Schwartz, R., Moldenhauer, G., I)orken, B., Pezzutto, A., Mom-burg, F., and Schirrmacher, V. (1986) In Leukocyle Typing II(Reinherz, E. L., Haynes, B. F., Nadler, L. M., and Bernstein, I.D., eds) pp. 527-540, Springer Verlag, New York

45. Schick, M. R., and Levy, 5. (1993) The TAPA-l molecule is as-sociated on the surface of B cells with HLA-DR molecules. jmmmunol. 151, 4090-4097

46. Geisert. E. E., Yang, L., and Irwin, M. H. (1996) Astrocytesgrowth, reactivity, and the target of antiproliferative antibody,TAPA.J. Neurosci. 16, 5478-5487

47. Sela, B. A., Steplewski, Z., and Koprowski, H. (1989) Colon car-cinoma-associated glycoproteins recognized by monoclonal an-tibodies CO-029 and GA22-2. Hyl’ridoma 8, 481-491

48. Haseg-awa, H., Utsunomiya, Y., Kishimoto, K., Yanagisawa, K.,and Fujita, S. (1996) SFA-1, a novel cellular gene induced byhuman T-cell leukemia virus type I, is a member of the trans-membrane 4 superfamily.]. Viral. 70, 3258-3263

49. Jankowski, S. A., Mitchell, D. S., Smith, S. H., Trent,J. M., andMeltzer, P. S. (1994) SAS, a gene amplified in human sarcomas,encodes a new member of the transmembrane 4 superfamilyof proteins. Oncogene9, 1205-1211

50. Atkinson, B., Ernst, C. S., Christ, B. F.. Herlyn, M., Blaszczyk,M., Ross, A. H., Herlyn, D., Steplewski, Z., and Koprowski, H.(1984) Identification of melanoma-associated antigens usingfixed tissue screening of antibodies. Canc’rR,s. 44,2577-2581

51. Ikeyama, S., Koyama. M., Yamaoko, M.. Sasada, R., and Miyake,M. (1993) Suppression of cell motility and metastasis by trans.fection with human motility-related protein (MRP-l/CD9)DNA.]. Exp. Med. 177, 1231-1237

52. Si, Z., and Hersey. P. (1993) Expression of the neuroglandularantigen and analogues in melanoma. CD9 expression appearsinversely related to metastatic potential of melanoma. mt. ].Cancer 54, 37-43

53. Miyake, M.. Nakano, K., ltoi, S. I., Koh, T., and Taki, T. (1996)Motility-related protein-l (MRP-1/CD9) reduction as a factorof poor prognosis in breast cancer. Cancer Res. 56, 1244-1249

54. Toothill, V.J., Van Mourik,J. A., Niewenhuis, H. K., Metzelaar,M. J., and Pearson. K. D. (1990) Characterization of the en-hanced adhesion of neutrophil leukocytes to thrombin-stimu-lated endothelial cells.]. Immunol. 145, 283-291

55. Skubitz, K. M., Campbell, K. I)., Iida,J., and Skuhitz, A. P. N.(1996) CD63 associates with tyrosine kinase activity and CI) 11/CDI8, and transmits an activation signal in neutrophils.]. Im-munol. 157, 3617-3626

56. Dong. J.T., 1.amb, P. W., Rinker-Schaeffer, C. W., Vukanovic,J., Ichikawa, T., lsaacs,J. T., and Barrett. J. C. (1995) KAII, ametastasis suppressor gene for prostate cancer on human chro-mosome llpll.2. Science268, 884-886

57. Jordan, S.A., Farrar, C. J.,Kumar-Singh, R., Kenna, P., Hum-phries, M., Allamand, V., Sharp, E. M., and Humphries. P.(1992) Autosomal dominant retinitis pigmentosa (adRP; RP6):cosegregation of RP6 and the peripherin-RDS locus in a late-onset family of Irish origin. Am.]. Human Gene!. 50, 634-639

58. Wroblewski,J.J., Wells,J. A. , III, Eckstein, A., Fitzke, F.,Juhh,C., Keen, T. J., Inglehearn, C., Bhattacharya, S., Arden, C. B.,Jay, M., et al. (1994) Macular dystrophy associated with muta-tions at codon 172 in the human retinal degeneration slowgene. Ophthalmology 101, 12-22


59. Kikawa, E., Nakazawa, M., Chida, Y., Shiono, T., and Tamai, M.(1994) A novel mutation (Asn244Lys) in the peripherin/RDSgene causing asitosomal dominant retinitis pigmentosa associ-ated with bull’s-eye maculopathy detected by nonradioisotopicSSCP. Genomics 20, 137-139

60. Wroblewski,J.J., Wells,J. A., III, Eckstein, A., Fitzke, F. W.,Jubb,C., Keen, T. J., Inglehearn, C. F., Bhattacharya, S. S., Arden,C. B., Jay, M. R., et al. (1994) Ocular findings associated with a3 base pair deletion in the peripherin-RDS gene in autosomaldominant retinitis pigmentosa. Br.]. Ophlhalmol. 78, 831-836

61. Gorin, M. B., Jackson, K. E. Ferrell, R. E., Sheffield, V. C. Ja-cobson, S. G., Gass,J. D., Mitchell, E., and Stone, E. M. (1995)A peripherin/retinal degeneration slow mutation (Pro-210-Arg) associated with macular and peripheral retinal degener-ation. Ophthalmology 102, 246-255

62. Kim, R. Y., Dollfus, H., Keen, T.J., Fitzke, F. W., Arden, G. B.,Bhattacharya, S. S., and Bird, A. C. (1995) Autosomal dominantpattern dystrophy of the retina associated with a 4-base pairinsertion at codon 140 in the peripherin/RDS gene. Arch.Ophthalmol. 113, 451-455

63. Nakazawa, M., Kikawa, E., Chida, Y., Wada, Y., Shiono, T., andTamai, M. (1996) Autosomal dominant cone-rod dystrophy as-sociated with mutations in codon 244 (Asn244His) and codon184 (Tyrl 84Ser) of the peripherin/RDS gene. Arch. Ophthalmol.114, 72-78

64. Nishibori, M., Cham, B., McNicol, A., Shalev, A., Jam, N., andGerrard, j. M. (1993) The protein CD63 is in platelet densegranules, is deficient in a patient with Hermansky-Pudlak syn-drome, and appears identical to granulophysm.]. Clin. mnvest.91, 1775-1782

65. Fukai, K., Oh, J., Frenk, E., Almod#{243}var,C., and Spritz, R. A.(1995) Linkage disequilibrium mapping of the gene for Her-mansky-Pudlak syndrome to chromosome 10q23.1-q23.3. Hu-man Mol. Gene!. 4, 1665-1669

66. Cramer, E. M., Berger, C., and Berndt, M. C. (1994) Plateletalpha-granule and plasma membrane share two new compo-nents: CD9 and PECAM-1. Blood 84, 1722-1730

67. Moritz, 0. L., and Molday, R. S. (1996) Molecular cloning,membrane topology, and localization of bovine rom-1 in rodand cone photoreceptor cells. mnvest. Ophthalmol. Viz. Sri. 37,352-362

68. Wu, X. R., Medina,J.J., and Stmn,T. T. (1995) Selective inter-actions of UPIa and UPIb, two members of the transmembrane4 superfamily, with distinct single transmembrane-domainedproteins in differentiated urothelial cells. j Biol. Chem. 270,29752-29759

69. Lin, S. L., Derr, D., and Hildreth,J. E. (1992) A monoclonalantibody against a novel 20-kDa protein induces cell adhesionand cytoskeleton-dependent morphologic changes.]. mmmunol.149. 2549-2559

70. Imai, T., and Yoshie, 0. (1993) C33 antigen and M38 antigenrecognized by monoclonal antibodies inhibitory to syncytiumformation by human T cell leukemia virus type 1 are both mem-bers of the transmembrane 4 superfamily and associate witheach other and with CD4 or CD8 in T cells.]. immunol. 151,6470-6481

71. Hemler, M. E., Mannion, B. A., and Berditchevski, F. (1996)Association of TM4SF proteins with integrins: relevance to can-cer. Biochim. Biophys. ArIa 1287, 67-71

72. Berditchevski, F., Zutter, M. M., and Hemler, M. E. (1996)Characterization of novel complexes on the cell surface be-tween integrins and proteins with 4 transmembrane domains(TM4 proteins). Mol. Biol. Cell7, 193-207

73. Radford, K.J., Thorne, R. F., and Hersey. P. (1996) CD63 as-sociates with transmembrane 4 superfamily members, CD9 andCD81. and with beta 1 integnns in human melanoma. Biochem.

Biophys. Res. Commun. 222, 13-2874. Berditchevski, F., Bazzoni, C., and Hemler, M. E. (1995) Spe-

cific association of CD63 with the VLA-3 and VLA-6 integrins.]. Biol. C/tern. 270, 17784-17790

75. Rubinstein, E., Le Naour, F., Billard, M., Prenant, M., andBoucheix, C. (1994) CD9 antigen is an accessory subunit of the\TLA integrin complexes. Fur.]. Immunol. 24, 3005-3013

76. Nakamura, K., Iwamoto, R., and Mekada, E. (1995) Membrane-anchored heparin-binding EGF-like growth factor (HB-EGF)and diphtheria toxin receptor-associated protein (DRAP27)/CD9 form a complex with integrin alpha 3 beta 1 at cell-cellcontact sites.]. Cell Biol. 129, 1691-1705

77. Rubinstein, E., Le Naour, F., Lagaudriere-Gesbert, C., Billard,M., Conjeaud, H., and Boucheix, C. (1996) CD9, CD63, CD81,and CD82 are components of a surface tetraspan network con-nected to HLA-DR and VLA integrins. Eur. j mmmunol. 26,2657-2665

78. Behr, S., and Schriever, F. (1995) Engaging CD19 or target ofan antiproliferative antibody 1 on human B lymphocytes in-duces binding of B cells to the interfollicular stroma of humantonsils via integrin alpha 4/beta 1 and fibronectin.jExp. Med.182, 1191-1199

79. Hadjiargyrou, M., Kaprielian, Z., Kato, N., and Patterson, P. H.(1996) Association of the tetraspan protein CD9 with integrinson the surface of S-16 Schwann cells.]. Neurochem. 67, 2505-2513

80. Mannion, B. A., Berditchevski, F., Kraeft, S-K., Chen, L. B., andHemler, M. E. (1996) Transmembrane-4 superfamily proteinsCD81 (TAPA-1), CD82, CD63, and CD53 specifically associatewith integrin a4bi (CD49d/CD29).]. mmmunol. 157,2039-2047

81. Imai, T.,Kakizaki, M., Nishimura, M., and Yoshie, 0. (1995)Molecular analysesof the association of CD4 with two membersof the transmembrane 4 superfamily, CD81 and CD82. j im-munol. 155, 1229-1239

82. Matsumoto, A. K., Martin, D. R., Carter, R. H., Klickstein, L. B.,Ahearn,J. M., and Fearon, D. T. (1993) Functional dissectionof the CD21/CD19/TAPA-1/Leu-13 complex of B lympho-cytes.]. Exp. Med. 178, 1407-1417

83. Bradbury, L. E., Kansas, G. S., Levy, S., Evans, R. L., and Tedder,T. F. (1992) The CDI9/CD21 signal transducing complex ofhuman B lymphocytes includes the target of antiproliferativeantibody-i and Leu-13 molecules.]. Immunol. 149, 2841-2850

84. Dempsey, P. W., Allison, M. E., Akkaraju, S., Goodnow, C. C.,and Fearon, D. T. (1996) C3d of complement as a molecularadjuvant: bridging innate and acquired immunity. Science 271,348-350

85. Mitamura, T., Iwamoto, R., Umata, T., Yomo, T., Urabe, I., Tsu-neoka, M., and Mekada, E. (1992) The 27-kD diphtheria toxinreceptor-associated protein (DRAP27) from vero cells is themonkey homologue of human CD9 antigen: expression ofDRAP27 elevates the number of diphtheria toxin receptors ontoxin-sensitive cells.]. Cell Biol. 118, 1389-1399

86. Iwamoto, R., Higashiyama, S., Mitamura, T., Taniguchi, N.,Kiagsbrun, M., and Mekada, E. (1994) Heparin-binding EGF-like growth factor, which acts as the diphtheria toxin receptor,forms a complex with membrane protein DRAP27/CD9, whichup-regulates functional receptors and diphtheria toxin sensitiv-ity. EMBO]. 13, 2322-2330

87. Bell, C. M., Seaman; W. E., Niemi, E. C., and Imboden, J. B.(1992) The OX-44 molecule couples to signaling pathways andis associated with CD2 on rat T lymphocytes and a naturalkiller

cell line.]. Exp. Med. 175, 527-53688. Tedder, T. F., Steeber, D. A., Chen, A., and Engel, P. (1995)

The selectins: vascular adhesion molecules. FASEBJ. 9, 866-7389. Butcher, E. C., and Picker, L. J. (1996) Lymphocyte homing

and homeostasis. Science 272, 60-6690. Boucheix, C., Soria, C., Mirshahi, M., Soria, J., Perrot, J. Y.,

Fournier, N., Billard, M., and Rosenfeld, C. (1983) Character-isticS of platelet aggregation induced by the monoclonal anti-body ALB6 (acute lymphoblastic leukemia antigen p 24).Inhibition of aggregation by ALB6Fab. 1EBS LeII. 161,289-295

91. Slupsky, J. R., Seehafer, J. G., Tang, S. C., Masellis-Smith, A.,and Shaw, A. R. (1989) Evidence that monoclonal antibodiesagainst CD9 antigen induce specific association between CD9and the platelet glycoprotein Jib-lIla complex.]. Biol. C/tern.

264, 12289-1229392. Kawakatsu, T., Suzuki, M., Kido, H. Sakane, H., Hada, S., Ya-

maguchi, K., Fukuroi, T., Yanabu, M., Nagata, H., Nomura, S.,et al. (1993) Antithrombotic effect of an anti-glycoprotein IIB/lIlA antibody in primate lethal thrombosis. Thromb. Res7O, 245-254

93. Griffith, L., Slupsky, J., Seehafer, J., Boshkov, L., and Shaw,A. R. (1991) Platelet activation by immobilized monoclonalan-tibody: evidence for a CD9 proximal signal. Blood 78, 1753-1759

94. Ozaki, Y., Satoh, K., Kuroda, K., Qi, R., Yatomi, Y., Yanagi, S.,Sada, K., Yamamura, H., Yanabu, M., Nomura, S., et al. (1995)Anti-CD9 monoclonal antibody activates p72syk in humanplatelets.]. Biol. Chern. 270, 15119-15124


95. Jennings, L. K., Fox, C. F., Kouns, W. C., McKay, C. P., Ballou,L. R., and Schultz, H. E. (1990) The activation of human plate-lets mediated by anti-human platelet p24/CD9 monoclonal an-tibodies.]. Biol. C/tern. 265, 3815-3822

96. Seehafer.J. C., and Shaw, A. R. (1991) Evidence that the signal-initiating membrane protein CD9 is associated with small CTP-binding proteins. Biochern. Biophys. Ret. Commun. 179, 401-406

97. Masellis-Smith, A., Jensen, C. S., Seehafer,J. G., Slupsky,J. R.,and Shaw, A. R. (1990) Anti-CD9 monoclonal antibodies in-duce homotypic adhesion of pre-B cell lines by a novel mech-anism.]. ImmunofT 144, 1607-1613

98. Masellis-Smith, A., and Shaw, A. R. (1994) CD9-regulated ad-hesion. Anti-CD9 monoclonal antibody induce pro-B cell ad-hesion to bone marrow fibroblasts through de novorecognition of fibronectin.]. Immunol. 152,2768-2777

99. Shaw, A. R., Domanska, A., Mak, A., Gilchrist, A., Dobler, K.,Visser, L., Poppema, S., Fliegel, L., Letarte, M., and Willett, B.J. (1995) Ectopic expression of human and feline CD9 in ahuman B cell line confers beta 1 integrin-dependent motilityon fibronectin and laminin substrates and enhanced tyrosinephosphomylation.]. Biol. C/tern. 270, 24092-24099

100. Anton, E. S., Hadjiargyrou, M., Patterson, P. H., and Matthew,W. D. (1995) CD9 plays a role in Schwann cell migration invitro.]. Neurosci. 15, 584-595

101. Forsyth, K. I). (1991) Anti-CD9 antibodies augment neutrophiladherence to endothelium. Immunology 72, 292-296

102. Tal, X. C., Yashiro, Y., Abe, R., Toyooka, K., Wood, C. R., Morris,J.,Long, A., Ono, S., Kobayashi, M., Hamaoka, T., Neben, S.,and Fujiwara, H. (1996) A role for CD9 molecules in T cellactivation.]. Exp. Med. 184, 753-758

103. Loffler, S., Lottspeich, F., Lanza, F., Azorsa, D. 0., ter Meulen,J.,and Schneider-Schaulies, J. (1997) CD9, a tetraspan trans-membrane protein, renders cells susceptible to canine dis-temper virus.]. Virol. 71, 42-49

104. Bose, L., and Lazo, P. A. (1994) Induction of nitric oxide re-lease by MRC OX-44 (anti-CD53) through a protein kinase C-dependent pathway in rat macrophages.]. Exp. Med. 179, 1119-1126

105. Carmo, A. M., and Wright, M. D. (1995) Association of thetransmembrane 4 superfamily molecule CD53 with a tyrosinephosphatase activity. Eur.]. Immunol. 25, 2090-2095

106. Olweus,J., Lund-Johansen, F., and Horejsi, V. (1993) CD5S, aprotein with four membrane-spanning domains, mediates Sig-nal transduction in human monocytes and B cells.]. Immunol.

151,707-716107. Rasmussen, A. M., Blomhoff, H. K., Stokke, T., Horejsi, V., and

Smeland, E. B. (1994) Cross-linking of CD53 promotes activa-tion of resting human B lymphocytes.]. Immunol. 153, 4997-5007

108. Smith, D. A., Monk, P. N., and Partridge, L.J. (1995) Antibodiesagainst human CD63 activate transfected rat basophilic leuke-mia (RBL-2H3) cells. Mol. Immunol. 32, 1339-1344

109. Vischer, U. M., and Wagner, D. D. (1993) CD6S is a componentof Weibel-Palade bodies of human endothelial cells. Blood 82,1184-1191

110. Kitani, S., Berenstein, E., Mergenhagen, S., Tempst, P., andSiraganian, R. P. (1991) A cell surface glycoprotein of rat ba-sophilic leukemia cells close to the high affinity IgE receptor(Fe epsilon Ri). Similarity to human melanoma differentiationantigen ME491.]. Biol. C/tern. 266, 1903-1909

ill. Todd, S. C., Lipps, S. G., Crisa, L., Salomon, D. R., and Tsoukas,C. D. (1996) CD81 expressed on human thymocytes mediatesintegrin activation and IL-2-dependent proliferation.]. Exp.Med. 184, 2055-2060

112. Imai, T., Fukudome, K., Takagi, K., Nagira, M., Furuse, M., Fu-kuhara, N., Nishimura, M., Hinuma, Y., and Yoshie, 0. (1992)C33 antigen recognized by monoclonal antibodies inhibitoryto human T cell leukemia virus type i-induced syncytium for-mation isa member of a new family of transmembrane proteinsincluding CD9, CD37, CD53, and CD63.j IrnmunoL 149, 2879-2886

113. Schick, M. R., Nguyen, V. Q., and Levy, S. (1993) Anti-TAPA-lantibodies induce protein tyrosine phosphorvlation that is pre-vented by increasing intracellular thiol levels.].-Immunol. 151,1918-1925

114. Fearon, D. T., and Carter, R. H. (1995) The CD19/CR2/TAPA-1 complex of B lymphocytes: linking natural to acquired im-munity. Annu. Rev. Immunol. 13, 127-149

115. Deblandre,G.A.,Marinx,O.P.,Evans,S.S.,Majjaj,S.,Leo,O.,Caput. D., Huez, C. A., and Wathelet, M. G. (1995) Expressioncloning of an interferon-inducible 17-kDa membrane proteinimplicated in the control of cell growth. ]. Biol. C/tern. 270,23860-23866

116. Secrist, H., Levy, S., DeKruyff, R. H., and Umetsu, I). T. (1996)Ligation of TAPA-i (CDS1) or major histocompatibility com-plex class II in co-cultures of human B and T lymphocytes h-hances interleukin-4 synthesis by antigen-specific CD4 T cells.Eur.]. Immunol. 26, 1435-1442

117. Nojima, Y., Hirose, T., Tachibana, K., Tanaka, T., Shi, I..,Doshen, J.,Freeman, C. J., Schlossman, S. F., and Morimoto,C. (1993) The 4F9 antigen is a member of the tetra spans trans-membrane protein family and functions as an accessory mole-cule in T cell activation and adhesion. Cell. Immunol. 152,249-260

118. Lebel-Binay, S., Lagaudrihre, C., Fradelizi, I)., and Conjeaud,H. (1995) CD82, member of the tetra-span-transmembraneprotein family, is a costimulatory protein for T cell activation.

j Immunol. 155, 101-110119. Gil, M. L., Vita, N., Lebel-Binay, S., Miloux, B., Chalon, P.,

Kaghad, M., Marchiol-Fournigault, C., Conjeaud, H., Caput, D.,Ferrara, P., et al. (1992) A member of the tetra spans trans-membrane protein superfamily is recognized by a monoclonalantibody raised against an HLA class I-deficient, lymphokine-activated killer-susceptible, B lymphocyte line. Cloning and pre-liminary functional studies.]. ImmunoL 148. 2826-2833

120. Lebel-Binay, S., Lagaudriere. C., Fradelizi. C.. and Conjeaud.H. (1995) CD82, tetra-span-transmembrane protein, is a regu-lated transducing molecule on U937 monocytic cell line.]. Leu-

koc. Biol. 57, 956-963121. Fitter, S., Tetaz, T.J., Berndt, M. C., and Ashman, L. K. (1995)

Molecular cloning of eDNA encoding a novel platelet-endothe-hal cell tetra-span antigen. PETA-3. Blood 86, 1348-1355

122. Barrett, T. B., Shu, C., and Clark, E. A. (1991) CD4O signalingactivates CDila/CD18 (LFA-i)-mediated adhesion in B cells.].Immunol. 146, 1722-1729

123. Miyake, M., Nakano, K., Ieki,Y., Adachi, M., Huang, C. L., ltoi,S.,Koh,T.,andTaki,T. (1995) Motilityrelatedprotein I (MRP-l/CD9) expression: inverse correlation with metastases inbreast cancer. Cancer Ret 55, 4127-4131

124. Hadjiargyrou, M., and Patterson, P. H. (1995) An anti-CD9monoclonal antibody promotes adhesion and induces prolif-eration of Schwann cells in vitro.]. Nenrosci. 15, 574-583

125. Willett, B. J., Hosie, M. J.,Jarrett, 0., and Neil, J. C. (1994)Identification of a putative cellular receptor for feline immu-nodeficiency virus as the feline homologue of CD9. Immunology

81, 228-233126. Martin-Alonso,J. M., Hernando, N., Ghosh, S., and Coca-Pra-

dos, M. (1992) Molecular cloning of the bovine CD9 antigenfrom ocular ciliary epithelial cells.]. Bwchee. (Tokyo) 112,63-67

127. Ledhetter,J. A., Shu, C., and Clark, E. A. (1987) . In Leukoc-yte

Typing III: White Cell Dsjferentialion Antigens (McMichael, A. j.,ed) pp. 339-340, Oxford University Press, Oxford,

128. Knol, E. F., Mul, F. P., Jansen, H., Calafat, J., and Roos, I).(1991) Monitoring human basophil activation via CD63 mono-clonal antibody 435.]. Allergy Clin. Immunol. 88, 328-338

129. Nishikata, H., Oliver, C., Mergenhagen, S. E., and Sirag-anian,R. P. (1992) The rat mast cell antigen AD1 (homologue tohuman CD63 or melanoma antigen ME491) is expressed inother cells in culture.]. Immunol. 149,862-g70

130. Takagi, S., Fujikawa, K., Imai, T., Fukuhara, N., Fukudome, K.,Minegishi, M., Tsuchiya. S., Konno, T., Hinuma, Y., and Yoshie,0. (1995) Identification of a highly specific surface marker ofT-cell acute lymphoblastic leukemia and neuroblastoma as anew member of the transmembrane 4 superfamily. In!.]. Cancer

61, 706-715131. Szala, S., Kasai, Y., Steplewski, Z., Rodeck, V., Koprowski. H.,

and Linnenbach, A.J. (1990) Molecular cloning of eDNA forthe human tumor-associated antigen CO-029 and identificationof related transmembrane antigens. Proc. Nail. A cad. Sri. USA87, 6833-6837

132. Roberts,J.J., Rodgers, S. E., Druiy,J., Ashman, 1.. K., and Lloyd,J.V. (1995) Platelet activation induced by a murine monoclonalantibody directed against a novel tetra-span antigen. Br.]. Hae-

matol. 89, 853-860

442 Vol.11 May 1997 The FASEB Journal MAECKER ET AL.

133. Jankowski, S. A., Dejong, P., and Meltzer, P.S. (1995) Genomicstructure of SAS, a member of the transmembrane 4 superfam-ily amplified in human sarcomas. Genomics 25, 501-506

134. Lee, K. W., Shalaby, K. A., Medhat, A. M., Shi, H., Yang, Q.,Karim, A. M., and LoVerde, P. T. (1995) Schislosoma mansonccharacterization of the gene encoding Sm23, an integralmembrane protein. Exp. Para.sitoL 80, 155-158

135. Marken,J. S., Schieven, G. L., Hellstr#{243}m,I., Hellstr#{243}m,K. E.,and Aruffo, A. (1992) Cloning and expression of the tumor-associated antigen L6. Proc. NaIL Acad. Sci. USA 89, 3503-3507

136. Maruyama, M., Kozuka-Hata, K., Sakaguchi-Sanai, A., Shioda,S.,Yamaguchi, N., and Maruyama, K. (1996) The eDNA cloningof the hamster homologue of the human L6 gene. Gene 168,273-274

137. Kaprielian, Z., and Patterson, P. H. (1993) Surface and cyto-skeletal markers of rostrocaudal position in the mammaliannervous system.]. Neurosci. 13, 2495-2508

138. Yu,J., Lin,J. H., Wu, X. R., and Sun, T. T. (1994) UroplakinsIa and lb. two major differentiation products of bladder epi-thelium, belong to a family of four transmembrane domain(4TM) proteins.]. Cell BioL 125, 171-182

139. Angehisova, P., Hilgert, I., and Horejs, V. (1994) Association offour antigens of the tetraspans family (CD37, CD53, TAPA-1,and R2/C33) with MHC class II glycoproteins. Immunogenetics39, 249-256

140. Takahashi, S., Doss, C., Levy, S., and Levy, K. (1990) TAPA-1,the target of an antiproliferative antibody, is associated on thecell surface with the Leu-13 antigen.]. Immunol. 145,2207-2213

Documents

The tetraspanin superfamily: molecular facilitators