Melanoma Review

7/29/2019 Melanoma Review

1/15

Th e n e w e n g l a n d j o u r n a l o fm ed i c i n e

n engl j med 355;1 www.nejm.org july 6, 2006 51

review article

mechanisms of disease

MelanomaArlo J. Miller, M.D., Ph.D., and Martin C. Mihm, Jr., M.D.

From the Dermatopathology Unit, Massa-chusetts General Hospital, and HarvardMedical School both in Boston. Ad-dress reprint requests to Dr. Mihm at theDepartment of Dermatopathology, Massa-chusetts General Hospital, 55 Fruit St.,Warren 827, Boston, MA 02114.

N Engl J Med 2006;355:51-65.Copyright 2006 Massachusetts Medical Society.

Although melanoma accounts foronly 4 percent of all derma-

tologic cancers, it is responsible for 80 percent of deaths from skin cancer;

only 14 percent of patients with metastatic melanoma survive for f ive years.1

The intractability of advanced melanoma shows how much we have to learn about

the changes that facilitate the vertical growth and deep invasion of melanoma and

about the mechanisms that block the effectiveness of chemotherapy.

The Clark model of the progression of melanoma emphasizes the stepwise trans-

formation of melanocytes to melanoma (Fig. 1). The model depicts the proliferation

of melanocytes in the process of forming nevi and the subsequent development of

dysplasia, hyperplasia, invasion, and metastasis.2 Numerous molecular events, manyof them revealed by genomic3 and proteomic4 methods, have been associated with

the development of melanoma. But rather than catalogue all the molecular lesions

in this tumor, we will focus on connections between molecular pathways and risk

factors for melanoma, the different steps of neoplastic transformation, and the

patterns of molecular changes in melanoma (Fig. 2).

Environmental and Genetic Interactions

Risk Factors

The strongest risk factors for melanoma are a family history of melanoma, multiple

benign or atypical nevi, and a previous melanoma. Immunosuppression, sun sensi-

tivity, and exposure to ultraviolet radiation are additional risk factors. Each of these

risk factors corresponds to a genetic predisposition or an environmental stressorthat contributes to the genesis of melanoma. Each factor is understood to various

degrees at a molecular level. For example, 25 to 40 percent of the members of

melanoma-prone families have mutations in cyclin-dependent kinase inhibitor 2A

(CDKN2A)5 (Table 1 lists all genes mentioned in this article), and a few rare kindreds

have mutations in cyclin-dependent kinase 4 (CDK4). There is a rational basis for a

link between susceptibility to melanoma and a mutation in CDKN2Aor CDK4 since

both are tumor-suppressor genes. They will be discussed later in the context of

disease progression. In addition, sensitivity to ultraviolet light is associated with a

polymorphic genetic determinant that affects susceptibility to melanoma, thereby

highlighting an important geneticenvironmental interaction.

Photosensitivity, Tanning, and Melanoma

The effect of exposure to ultraviolet light is governed by variations in particular

genes (polymorphisms) that affect both the defensive response of the skin to ultra-

violet light and the risk of melanoma. Ultraviolet radiation causes genetic changes

in the skin, impairs cutaneous immune function, increases the local production of

growth factors, and induces the formation of DNA-damaging reactive oxygen species

that affect keratinocytes and melanocytes.6,7 The tanning response is a defensive

measure in which melanocytes synthesize melanin and transfer it to keratinocytes,

The New England Journal of Medicine

Downloaded from nejm.org by MAURICIO RIVAS on January 29, 2013. For personal use only. No other uses without permission.

Copyright 2006 Massachusetts Medical Society. All rights reserved.


2/15


n engl j med 355;1 www.nejm.org july 6, 200652

where it absorbs and dissipates ultraviolet energy.7

Clinically, variations in pigmentation and the tan-

ning response to ultraviolet light are associated

with variations in susceptibility to melanoma.8,9

At the molecular level, exposure to ultraviolet

light increases skin pigmentation, in part through

the action of -melanocytestimulating hormone(-MSH) on its receptor, the melanocortin recep-

tor 1 (MC1R) (Fig. 3). Binding of the hormone to

the receptor stimulates intracellular signaling in

melanocytes, and this signaling increases the ex-

pression of enzymes involved in the production

of melanin. Light-skinned and redheaded people

often carry germ-line polymorphisms in the MC1R

gene10,11 that reduce the activity of the receptor.12

Such polymorphisms increase the risk of mel-

anoma considerably.13 In light-skinned people,

therefore, the basis of increased susceptibility to

melanoma is a genetic impairment in the produc-

tion of melanin, the main defense of melanocytesagainst ultraviolet radiation.

Although the tanning response to ultraviolet

radiation appears dose-dependent, the nature of

the exposure is also a factor. Melanoma occurs

most frequently after intermittent exposure to the

sun and in people with frequent sunburns. Epi-

demiologic observations suggest that chronic or

low-grade exposures to ultraviolet light induce

protection against DNA damage, whereas intense,

intermittent exposures cause genetic damage.7

A Molecular Model

of Melanoma Progres sion

The Clark model (Fig. 1) describes the histologic

changes that accompany the progression from

normal melanocytes to malignant melanoma.2

We will relate these histologic changes to particu-

lar gene mutations (Table 1) in melanoma and dis-

cuss how these mutations affect molecular sig-

naling to contribute to the progression from

normal melanocytes to melanoma (Fig. 2).

Hyperplasia and Nevus Formation

In the Clark model, the first phenotypic change

in melanocytes is the development of benign nevi,

which are composed of neval melanocytes (Fig. 1).

The control of growth in these cells is disrupted,

yet the growth of a nevus is limited a nevus

rarely progresses to cancer.2 The absence of pro-

gression is probably due to oncogene-induced

cell senescence, in which growth that is stimulat-

ed by the activation of oncogenic pathways is lim-

ited.14 At a molecular level, abnormal activation

of the mitogen-activated protein kinase (MAPK)

signaling pathway (also called extracellular-related

kinase [ERK]) stimulates growth in melanoma

cells (Fig. 4A).15-17 Activation of this pathway is the

result of somatic mutations of N-RAS, which areassociated with about 15 percent of melanomas,

or BRAF, which are associated with about 50 per-

cent of melanomas. These mutations, which occur

exclusively of each other, cause constitutive acti-

vation of the serinethreonine kinases in the

ERKMAPK pathway.18-20

BRAFmutations occur at a similar frequency

in benign nevi and in primary and metastatic

melanomas.21 Since most nevi cease proliferation

and remain static for decades, these similar fre-

quencies suggest that nevi must acquire addition-

al molecular lesions to free themselves of growth

restraints and become malignant. Experiments inmodel systems support this hypothesis. In zebra-

fish, melanocyte-specific expression of a mutant

BRAF protein causes an ectopic proliferation of

melanocytes, analogous to human nevi.22 In these

fish, the combination of a BRAFmutation and

inactivation of the tumor-suppressor gene p53

causes melanocytes to become malignant.22 In

human melanocytes, mutant BRAF protein induc-

es cell senescence by increasing the expression

of the cell-cycle inhibitor of kinase 4A (INK4A).23

INK4A limits hyperplastic growth caused by a

BRAFmutation. The arrest of the cell cycle caused

by INK4A can, however, be overcome by mutations

in INK4A itself, as well as other cell-cycle factors.

In vitro, depletion of BRAF and N-RAS from

melanoma cells suppresses their growth.24-26

Small molecules that inhibit BRAF are being

tested clinically (BAY 43-9006) but have had only

limited success as single agents.27 In mice, the

Figure 1 (facing page). The Clark Model (Hematoxylinand Eosin).

Melanocytes progress through a series of steps towardmalignant transformation. The frequency of both the

progression of nevi toward becoming malignant and

the regression of nevi is unknown. The model empha-

sizes the histopathological changes that occur in the

progression of melanoma. Normal melanocytes pro-gressively develop a malignant phenotype through the

acquisition of various phenotypic features. The partic-ular histologic features characterizing each step of pro-

gression are the visible manifestations of underlying

genetic changes.





3/15







4/15



growth of melanomas with BRAFmutations can

be suppressed by the inhibition of the down-

stream MEK enzymes, providing a possible target

for treatment.28

Cytologic Atypia and Tumor-Suppressor

Genes

The Clark model suggests that the next step toward

melanoma is the development of cytologic atypia

in dysplastic nevi, which may arise from preex-

isting benign nevi or as new lesions. The molecu-

lar abnormalities at this stage of progression

affect cell growth, DNA repair, and the suscepti-

bility to cell death. In 25 to 40 percent of cases of

familial melanoma,6 a genetic defect inactivates

CDKN2A, a single gene that encodes two tumor-

suppressor proteins, p16INK4A and p19ARF29,30; in

25 to 50 percent of nonfamilial melanoma,31,32 a

different tumor-suppressor gene, phosphatase and

tensin homologue (PTEN) (Fig. 3), is inactivatedby mutation.33,34 In murine models of melanoma,

mutation of either CDKN2Aor PTENalone fails to

cause melanoma, but when combined with each

other or with mutations in other genes,35 mela-

nomas do arise. Mutation ofCDKN2Aor PTEN is

only one molecular step on the path to the devel-

opment of melanoma, but it is unclear precisely

when such mutations occur. The increased sus-

ceptibility to melanoma that is associated with

loss of the germ-line CDKN2Agene suggests that

this genetic lesion increases the probability that

dysplastic nevi will become malignant or increas-

es the rate of the development of new melanomawithout a precursor.

CDKN2A

The G1S checkpoint that governs the commitment

of a cell to DNA replication during the S phase

(synthesis of DNA) is a site where many pathways

that control cell division converge36,37 (Fig. 4B).

In some familial and sporadic cases of melano-

ma,36,37 the CDKN2Alocus is lost by homozygous

deletion of a portion of chromosome 9.36-38 One

of the genes in this locus encodes INK4A,

(p16INK4A), a protein that blocks the cell cycle at

the G1S checkpoint by inhibiting cyclin-depen-

dent kinases. INK4A (an inhibitor of CDK4) sup-

presses the proliferation of cells with damaged

DNA or activated oncogenes and also acts when

cells are old or crowded.39 Mice lacking INK4A

appear normal but are abnormally sensitive to

carcinogens and prone to the development of

tumors.40 The development of melanoma in such

mice requires mutations in other genes, such as

an activating mutation in H-RAS, an upstream

component in MAPK signaling, which triggers

MEK signaling.41 Genes that encode CDK4 and

cyclin D1 (CCND1) encode proteins that act down-

stream of INK4A, and they are also mutated insome melanomas. These targets of INK4A func-

tion together as part of a complex that promotes

the progression of the cell cycle by phosphorylat-

ing retinoblastoma (Rb) protein, a cell-cycle reg-

ulator. Rare melanoma kindreds carry germ-line

mutations in CDK4 that disrupt cell-cycle control

by preventing the molecular interaction that allows

INK4A to repress CDK4.42 Mice that carry the hu-

man CDK4 mutation are prone to melanoma when

exposed to various carcinogens.43

The D-type cyclin CD1 may have an oncogenic

role in acral melanoma, in which amplification of

the CCND1 gene and overexpression of cyclin CD1protein occur more frequently than in melanoma

at other sites.44 Inhibition ofCCND1 (with anti-

sense CCND1) causes apoptosis of human mela-

noma xenografts implanted in immunodeficient

mice, without an apparent effect on normal mela-

nocytes.

Alternative splicing of various exons within

CDKN2Ayields two distinct tumor-suppressor pro-

teins, INK4A and alternate reading frame (ARF)

(Fig. 3).39 The ARF gene (also called p14ARF) de-

rives its name from the use of an alternative

reading frame of the exons it shares with INK4A.

ARF functions as a tumor suppressor by arrest-ing the cell cycle or promoting cell death after

DNA damage or when various oncogenes or loss

of Rb stimulate aberrant cell proliferation. ARF

participates in the core regulatory process that

controls levels of the p53 protein. It acts through

the mouse double minute 2 (MDM2) protein,

which triggers the ubiquination of p53, thereby

instigating its destruction in the proteosome.

ARF binds to MDM2, sequestering it from p53

and in this way causes p53 to accumulate; p53

then arrests the cell cycle at the G2M site, allow-

ing for repair of damaged DNA or the induction

of apoptosis.45,46 In cells, ARF deficiency abro-

gates oncogene-induced senescence and increases

susceptibility to transformation.47 In vitro, im-

mortalization of cells often occurs with the loss

of either ARF or p53.48 In animals, ARF deficiency

shortens the time required for the development

of melanoma after exposure to ultraviolet light;





5/15



when both gene products ofCDKN2A(INK4A and

ARF) are deficient, the latent period is even short-

er.49 These data suggest how ARF facilitates the

progression of melanoma and indicate that the

low frequency of p53 mutations in melanoma is

partly related to loss of ARF, which renders the

p53 pathway inactive.39

PTEN, AKT, and Cell Death

A second chromosomal region that is frequently

affected by homozygous deletion in melanoma

and other cancers is the PTENlocus on chromo-

some 10.33,34,50PTENencodes a phosphatase that

attenuates signaling by a variety of growth factors

that use phosphatidylinositol phosphate (PIP3) as

an intracellular signal. In the presence of such

growth factors, intracellular levels of PIP3

rapidly

increase. This increase triggers the activation of

protein kinase B (PKB, also called AKT) by phos-

phorylation (Fig. 3). Activated AKT phosphory-

lates and inactivates proteins that suppress the

cell cycle or stimulate apoptosis, thereby facilitat-

ing the proliferation and survival of cells. PTEN

normally keeps PIP3

levels low; in its absence,

Figure 2. Biologic Events and Molecular Changes in the Progression of Melanoma.At the stage of the benign nevus, BRAFmutation and activation of the mitogen-activated protein kinase (MAPK) pathway occur. The cy-

tologic atypia in dysplastic nevi reflect lesions within the cyclin-dependent kinase inhibitor 2A (CDKN2A) and phosphatase and tensinhomologue (PTEN) pathways. Further progression of melanoma is associated with decreased differentiation and the decreased expres-

sion of melanoma markers regulated by microphthalmia-associated transcription factor (MITF). The vertical-growth phase and meta-

static melanoma are notable for striking changes in the control of cell adhesion. Changes in the expression of the melanocyte-specificgene melastatin 1 (TRPM1) correlate with metastatic propensity, but the function of this gene remains unknown. Other changes include

the loss of E-cadherin and increased expression of N-cadherin, V3 integrin, and matrix metalloproteinase 2 (MMP-2).





6/15



Ta

ble1

.Importan

tGenes

inMe

lanoma.

Pa

thway

Geneor

Pro

tein*

Func

tion

Changes

inMe

lanoma

RASan

dMAPK

N-RAS

Oncogene

Sporadicactivatingmutation

atG13R

BRAF

Oncogene

Sporadicactivatingmutation

atcodonV600Ein

neviandmelanoma

Mitogen-activatedproteinkinaseextracellular-

relatedkinase(MEK)

Signaltransduction

Up-regulatedinradial-growth

andvertical-growth

phases

Extracellular-relatedkinase1or2(ERK1orERK2)

ormitogen-activatedproteinkinase(MAP

K)

Signaltransduction

Increasedactivity

INK4A

,CDK

,an

dRb

Cyclin-dependentkinaseinhibitor2Aorinhib

itor

ofkinase4A(CDKN2AorINK4A)

Tumorsuppressornegativeregulato

rofcellprolif-

eration

Germ-linemutationsinsomefamilialmelanomas;

sporadicdeletions,promoterinactivation,loss

ofheterozygosityinmanymelanomas

Cyclin-dependentkinase4(CDK4)

Promoterofcellproliferation

Proteininsensitivetoinhibiti

onbyINK4Adueto

rarefamilialgerm-linemutationsatR24C

CyclinD1(CCND1)

Promoterofcellproliferation

Sporadicamplificationinacralmelanoma

Retinoblastoma(Rb)

Tumorsuppressornegativeregulato

rofcellprolif-

eration

Phosphorylationleadstopro

gressionfrom

G1toS

ARFan

dp

53

Alternatereadingframe(ARF)

Tumorsuppressor,degradesMDM2

Germ-linemutationsinsomefamilialmelanomas;

sporadicdeletions,promoterinactivation,in

manymelanomas

Tumorprotein53(p53)

Tumorsuppressorthatinducesapop

tosisandsup-

pressedproliferationafterDNAd

amage

Expressionusuallypresentin

melanoma

Mousedoubleminute2(MDM2)

Targeterofp53forubiquinationand

destruction

Up-regulatedinpresenceofARFmutation

BCL-2associatedXprotein(BAX)

Inducerofcelldeath

Variablebutusuallydown-regulated

PTEN

an

dAKT

Phosphataseandtensinhomologue(PTEN)

Tumorsuppressor,repressesPI3K

Sporadicdeletionofchromosomalregion

Phosphatidylinositol3kinase(PI3K)

Signalingmoleculeformanygrowthfactors

ActiveinpresenceofPTENm

utation

ProteinkinaseB(AKTorPKB)

OncogenethatisactivatedbyPI3K,leadingto

increasedcellsurvival

Amplifiedinsomemelanomas

BCL-2antagonistofcelldeath(BAD)

Inducerofcelldeath

Variablebutoftendown-regu

lated

Forkheadreceptor(FKHR)

Growthsupression

ActivatedinresponsetoPI3pathway





7/15



MSH

an

dMITF

Pro-opiomelanocortinor-melanocytestimulating

hormone(POMCor-MSH)

Signalingmoleculeimportantinpigm

entation

Increasedmelanomavertical-growthphase

Melanocortinreceptor1(MC1R)

Receptorfor-MSH

Polymorphicgeneaffectingh

airandskincolor

andresponsetoultravioletradiation

Adenylatecyclase(AC)

ProducerofcyclicAMP

Up-regulated

cAMPresponseelementbindingprotein(CR

EB)

Transcriptionfactor

Up-regulated;affectsMITFandmelanocyte

differentiation

Microphthalmia-associatedtranscriptionfact

or

(MITF)

Transcriptionfactor

Sporadicamplificationofchromosomalregion

Tyrosinase(TYR)

Pigmentsynthesis

Decreasedexpression

Tyrosinase-relatedprotein1(TYRP1)

Pigmentsynthesis

Decreasedexpression

Dopachrometautomerase(DCT)

Pigmentsynthesis

Decreasedexpression

Melan-A(MLANA)

Antigenrecognizedbymelan-Aandm

elanomaanti-

genrecognizedbyT-cells1(MART1)antibodies

Decreasedexpression

Silverhomologue(SILV)

AntigenrecognizedbyHMB-45antib

ody

Decreasedexpression

Melastatin1(TRPM1)

Unknown

Decreasedexpressioninmetastaticmelanoma

BCL-2

Cellsurvival

Variableup-regulationinvariousphasesof

melanoma

Ce

lla

dhes

ion

Wingless-typemammarytumorvirusintegration-

sitefamily(WNT)

Protooncogene,secretedgrowthfactorthatinacti-

vates

GSK3-B

Pathwayup-regulated

Glycogensynthasekinase3(GSK3)

Serinethreoninekinasethattargets-cateninfor

degradation

Variable;affectedbyWNTpathway

-Catenin

Adherensjunctionprotein,transcript

ionalco-

activator

Sporadicstabilizingmutation

s

T-cellfactorlymphoid-enhancingfactor(TCF

LEF)

Transcriptionfactor

Up-regulated

E-cadherin

Cell-adhesionmolecule

Decreasedexpressioninvertical-growthphase

N-cadherin

Cell-adhesionmolecule

Aberrantexpressioninvertical-growthphase

V3integrin

Dimerthatformscell-adhesionmolecule

Aberrantexpressioninvertical-growthphase

*Abbreviatedformsofth

egenearegiveninparentheses.





8/15



levels of PIP3

and active (phosphorylated) AKT in-

crease. Increased AKT activity prolongs cell sur-

vival through the inactivation of BCL-2 antago-

nist of cell death (BAD) protein and increases

cell proliferation by increasing CCND1 expres-

sion, and affects many other cell-survival and cell-

cycle genes through the activation of the forkhead

(FKHR) transcription factor.32,51 AKT activity can

also be increased in cells by mutations that cause

the amplification and overexpression of the pro-

tein. Restoration of PTEN in cultured mouse me-

lanocytes decreases the ability of the cells to form

tumors.52In model systems, suppression of AKT3,

a member of the AKT family, reduces the survival

of melanoma cells and the growth of human mela-

nomas implanted in immunodeficient nude mice.53

Figure 3. Microphthalmia-Associated Transcription Factor (MITF) and -Catenin Pathways.In the MITF pathway, MITF is regulated at both transcriptional and post-translational levels. The post-translational activation can occur

through the ERK component of the MAPK pathway. The chief transcriptional pathways that are activated by extracellular signals are themelanocortin and WNT pathways. The melanocortin pathway regulates pigmentation through the MC1R. MC1R activates the cyclic AMP

(cAMP) response-element binding protein (CREB). Increased expression of MITF and its activation by phosphorylation (P) stimulate the

transcription of tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), and dopachrome tautomerase (DCT), which produce melanin;melan-A, silver homologue, and melastatin 1 (TRPM1) are melanoma markers; inhibitor of kinase 4A (INK4A) leads to cell-cycle arrest,

and BCL-2 suppresses apoptosis. In the -catenin pathway, -catenin plays a central role in cell adhesion and cell signaling. Signals from

WNT ligands block the breakdown of -catenin. When WNT proteins bind the G-proteincoupled receptor (called frizzled), they inacti-vate the kinase GSK3, an enzyme that phosphorylates -catenin and targets it for destruction in the proteosome. Then -catenin accu-

mulates in the cytoplasm and translocates to the nucleus, where it binds to LEFTCF transcription fac tors and increases the expression

of several genes, including MITF, the cell-cycle mediator cyclin D1 (CCND1), and matrix metalloproteinase 7 (MMP-7).





9/15



As compared with normal melanocytes, increased

levels of the active form of AKT were found in the

radial-growth phase.53

M I T F an d M elan ocyt e

Differentiation

Clark proposed that many nevi regress through

differentiation and that the failure of differentia-

tion is necessary for dysplasia.2 The normal pro-

cess of melanocyte differentiation requires exit

from the cell cycle and the expression of genes

that encode proteins necessary for the produc-

tion of pigment two processes that are de-

regulated in melanoma. The microphthalmia-

associated transcription factor (MITF) regulates

the development and differentiation of melano-

cytes54 and maintains melanocyte progenitor cells

in adults.55,56

MITF in Development

Mice lacking functional MITF are albino because

they lack melanocytes, whereas those with par-

tial MITF function have premature graying owing

to the death of melanocytes. These experiments

show that MITF is important in the differentiation

and maintenance of melanocytes.57,58 MITF ap-

pears to contribute to melanocyte survival by in-

creasing the expression of the BCL-2 gene, a key

antiapoptotic factor.59 In mice, deficiencies of both

MITF and BCL-2 cause gray hair due to a loss of

differentiated melanocytes. The loss of melano-

cytes is due to the apoptosis of melanocyte pro-genitor cells in the hair follicle.55 In melanoma

cell lines, a reduction in BCL-2 protein also causes

cell death, suggesting that the survival of malig-

nant melanocytes depends on BCL-2.60

MITF in Differentiation

MITF functions in a key pathway leading to me-

lanocyte pigmentation (Fig. 3). Intracellular sig-

naling induced by -MSH acting on MC1R in-

creases MITF expression, which in turn increases

the transcription of genes underlying melanin

synthesis: tyrosinase, tyrosinase-related-protein 1,

and dopachrome tautomerase.61 MITF also regu-

lates the transcription of the melanocyte-specific

genes silver homologue (SILV)62,63 and melan-A

(MLANA),62 whose immunohistochemical detec-

tion points to the diagnosis of melanoma. In addi-

tion, MITF causes cell-cycle arrest by the induction

of INK4A.64

MITF in Melanoma

Decreased or absent pigmentation and decreased

or absent expression of SILV and MLANA accom-

pany the progression from nevus to melanoma.

Tumors that are deficient in these proteins have

a poor prognosis.65-68 Expression of the mela-

statin 1 (TRPM1) gene, whose function is unknown,is also controlled by MITF.69 Melanomas that are

deficient in melastatin have a poor prognosis.70

The mechanism of decreased expression of these

genes is a puzzle because MITF is present in nearly

all melanomas.71-73

Although MITF causes differentiation and cell-

cycle arrest in normal melanocytes, melanoma

cells do not have these characteristics. Recently,

a large-scale search for genomic changes in mela-

noma with the use of high-density single-nucleo-

tide polymorphisms (SNPs) found an increased

copy number (4 to 119 copies per cell) of a region

of chromosome 3 that includes the MITFlocus.74This increase was accompanied by the increased

expression of MITF protein. The overexpression

of both MITF and BRAF could transform primary

cultures of human melanocytes, implicating MITF

as an oncogene. Notably, MITFamplification oc-

curs most frequently in tumors that have a poor

prognosis and is associated with resistance to

chemotherapy.74 Interference with MITF function

increased the chemosensitivity of a melanoma

cell line, making MITF a potential target for

treatment.

Cell A dhesion and Invasion

Local invasion and metastatic spread are respon-

sible for the morbidity and mortality in melano-

ma. In the Clark model, invasive characteristics

appear in the vertical-growth phase, when mela-

noma cells not only penetrate the basement mem-

brane but also grow intradermally as an expand-

ing nodule (Fig. 2). Metastatic melanoma develops

when tumor cells dissociate from the primary

lesion, migrate through the surrounding stroma,

and invade blood vessels and lymphatics to form

a tumor at a distant site.75 Clinically, the absolute

depth of local invasion, measured directly by histo-

pathologic analysis (the Breslow index), is the

principal prognostic factor and primary criterion

in melanoma staging.76 Invasion and spread of

melanoma are related to alterations in cell adhe-

sion. Normally, cell adhesion controls cell migra-

tion, tissue organization, and organogenesis,77





10/15



but disturbances in cell adhesion contribute to

tumor invasion, tumorstroma interactions, and

tumor-cell signaling.

Cadherins

Cadherins are multifunctional transmembrane

proteins that sustain cell-to-cell contacts, formconnections with the actin cytoskeleton, and in-

fluence intracellular signaling. The extracellular

domain of cadherins binds to like cadherins on

other cells in regions of cell contacts called adhe-

rens junctions. Cadherins are divided into three

subtypes: E (epithelial), present in polarized epi-

thelial cells in the epidermis, including melano-

cytes and keratinocytes; P (placental); and N (neu-

ral), found in mesenchymal cells in the dermis.

The intracellular domain is associated with a large

protein complex that includes -catenin and forms

structural links with bundles of actin filaments.

Several signaling pathways cause -catenin todissociate from the cell adhesion complex and

transduce signals to the nucleus (Fig. 3). One of

these pathways is called the wingless-type mam-

mary tumor virus integration-site family (WNT)

pathway. WNTs are secreted proteins with impor-

tant functions in development, especially in neu-

ral crest cells like melanocytes. When WNT pro-

teins bind their receptors, they inactivate the

kinase GSK3, an enzyme that phosphorylates

-catenin and targets it for destruction in the pro-

teosome.78,79 Tyrosine phosphorylation of -catenin

disrupts the association between E-cadherin and

-catenin,80 allowing -catenin to translocate tothe nucleus, where it binds to lymphoid enhancer

factorT-cell factor (LEFTCF). Mutations in the

-catenin gene can stabilize the -catenin pro-

tein81 or increase its nuclear localization.82-84 In-

creased levels of nuclear -catenin increase the

expression of MITF85 and CCND1,86 and these in

turn increase the survival and proliferation of

melanoma cells. Alterations in cadherin expres-

sion affect the interaction of melanoma cells with

the environment and alter -catenin signaling.

E-cadherin expression occurs in melanocytes and

keratinocytes in the epidermis and causes mela-

nocytes to associate with keratinocytes.87 In turn,

contacts with undifferentiated keratinocytes from

the basal-cell layer inhibit melanocyte prolif-

eration, suppress the expression of melanoma

Figure 4 (facing page). MAPK and PTEN Pathways and the CDKN2A Tumor-Suppressor Locus.

Panel A shows the pathway associated with N-RAS, BRAF, and mitogen-activated protein kinase (MAPK). MAPKs are involved in signaling from

numerous growth factors and cell-surface receptors. There are many vari-

ations in the components of particular cascades from various cell-surface

receptors. Typically, adapter proteins (not shown) link the growth-factor

receptor to RAS proteins, including N-RAS. When activated, RAS proteinsphosphorylate (P) the mitogen-activated protein kinase (MEK) kinases,

which then act on extracellular-related kinase (ERK) kinases. ERK kinasesphosphorylate many targets in the cytoplasm and interact with other path-

ways, including phosphatidylinositol 3 kinase (PI3K) and MITF. ERK kinases

translocate to the nucleus, where they activate transcription factors thatpromote cell-cycle progression and proliferation by increasing the transcrip-

tion of many genes, including CD1. In survival signaling associated with

phosphatase and tensin homologue (PTEN) and AKT, also known as pro-tein kinase B, PTEN inhibits growth-factor signaling by inactivating phos-

phatidylinositol triphosphate (PIP3) generated by PI3K. A variety of growth

factors (PDGF, NGF, and IGF-1) bind to their respec tive receptor tyrosine

kinases and activate PI3K. The activated molecule converts the plasmamembrane lipid phosphatidylinositol 4,5-bisphosphonate to PIP

3. PIP

3acts

as a second messenger, leading to the phosphorylation and activation of

AKT. AKT is itself a kinase that phosphorylates protein substrates that af-fect the cell c ycle, growth, and survival. Often, these AKT targets are inacti-

vated by phosphorylation. PTEN attenuates this pathway through dephos-

phorylation and inactivation of PIP3, suppressing signaling from growthfactors by blocking the activation of AKT. In Panel B, CDKN2A encodes two

distinct tumor-suppressor genes; separate first exons that are spliced into

alternate reading frames (ARF) of the second and third exons permit theexpression of two different proteins from the same genetic locus. The gene

has 4 exons. Transcription of messenger RNA (mRNA) can be initiated at

either E1B or E1A, and the initiation site determines which gene the locus

will express. RNA that is transcribed from either exon is spliced with the re-maining two exons, E2 and E3, to produce mRNA for either INK4A or ARF.

However, ARF uses a different reading frame of the exon 2 and 3 codons.

In the cell-cycle progression involving INK4A, ARF, and retinoblastoma pro-tein (Rb), a family of cyclins and cyclin-dependent kinases (CDKs) regulate

progression through the cell cycle, and a family of CDK inhibitors opposesthis action. In particular, the two phases of the G1S checkpoint are gov-erned primarily by cyclin D associated with cyclin-dependent kinases 4 and

6 (CDK4 and CDK6) at its early phase and cyclin A or E associated with

CDK2 at the later restriction phase. INK4A encodes a cyclin-dependent ki-nase inhibitor that inhibits CDK4 and CDK6. Ordinarily, these two kinases

associate with D-type cyclins and drive the cell cycle by phosphorylating

Rb, releasing it from its inhibitory interaction with the E2F transcription

factor, thereby allowing the expression of E2F-related genes and progres-sion from G1 to S. The absence of INK4A leads to unopposed CDK4 or

6 activity and increased cell-cycle activity. In response to DNA damage,

mouse double minute 2 (MDM2) protein binds to the transcriptional acti-vation domain of protein 53 (p53), blocking p53-mediated gene regulation

while simultaneously leading to p53 ubiquination, nuclear export, and pro-

teosomal degradation. ARF opposes this action by sequestering MDM2.This disruption of the MDM2p53 interaction stabilizes p53 and increases

p53 activity. Depending on other events, p53 either activates DNA repair

and cell-cycle arrest or causes apoptosis and the formation of BCL-2asso-ciated X protein (BAX). In the absence of ARF, p53 levels are decreased and

the response to DNA damage is blunted.





11/15







12/15



markers, and cause melanocytes to become den-

dritic.88

Progression from the radial-growth phase to

the vertical-growth phase of melanoma is marked

by the loss of E-cadherin and the expression of

N-cadherin89-91 (Fig. 2). N-cadherin is a character-

istic of invasive carcinomas and enables metastaticspread by permitting melanoma cells to interact

with other N-cadherinexpressing cells, such as

dermal fibroblasts and the vascular endothelium.87

Besides these changes in cell adhesion, decreased

E-cadherin expression92 and aberrant N-cadherin

expression increase the survival of melanoma

cells by stimulating -catenin signaling.93,94

Integrins

The integrins mediate cell contacts with fibro-

nectin, collagens, and laminin, components of the

extracellular matrix.95 Transition from radial to

vertical growth of melanoma is associated withthe expression of V3 integrin.96 This integrin

induces expression of matrix metalloproteinase 2,

an enzyme that degrades the collagen in basement

membrane.97-99 In addition, V3 integrin increas-

es expression of the prosurvival gene BCL-2100 and

stimulates the motility of melanoma cells through

the reorganization of melanoma cytoskeleton.101

These observations form a rationale for the de-

velopment of integrin antagonists to treat mela-

noma.102

Patterns of Genetic Alteration

The genetic changes in melanoma can be seen asparticular combinations of molecular lesions that

interrupt a precise set of pathways, each with a

crucial role in the development of melanoma.

The MEK pathway can be activated by a mutation

in either NRAS or BRAF, and an NRAS mutation

can activate both the MEK and PTEN pathways.

Similarly, INK4A, CDK4, and CCND1 function in

a unique pathway that affects the cell cycle; a mu-

tation ofINK4Ahas similar consequences as a

mutation ofCCND1 or CDK4.103-105

There are particular genetic changes in mela-

nomas in different sites, consistent differences

related to ultraviolet exposure on sites that are

chronically exposed (head and neck) or intermit-

tently exposed (chest and back) and in acral and

mucosal skin. For example, CCND1 amplification

occurs predominantly in acral regions,44 whereas

activating mutations in BRAFoccur most frequent-

ly in skin sites of intermittent sun exposure.106

Modeling Mel anoma

Progression

For many of the molecular lesions we have de-

scribed, animal models have provided validation.

A surprising new model is the zebrafish, in which

premalignant and malignant lesions can be cre-

ated by the expression of mutant BRAF with or

without p53 mutation.22 This model is the only

currently tractable system in which genetic

screens can be performed for modifiers of mela-

noma.

Human melanomas that are grafted onto orinjected into nude mice allow measures of the

tumors metastatic potential and have allowed for

the testing of therapeutic interventions. Genetic

manipulation of mice has validated the contribu-

tion of many genetic alterations in melanoma, but

there are fundamental differences between mouse

and human skin. Mouse melanocytes occur in

hair follicles and the dermis, rather than in the

epidermis, as in humans. To circumvent this

problem, human melanocytes can be altered in

cell culture and combined with keratinocytes to

produce graft material. Using this system, the

inactivation of p53 and the simultaneous intro-duction of activated N-RAS, CDK4, and telomer-

ase led to darkly pigmented grafts that became

grossly ulcerated and displayed histologic features

of melanoma, including vertical invasion.107 This

experimental system provides a novel model to

test invasion and metastases of transformed hu-

man melanocytes in a host organism.Supported by a grant (MCM202534) from the Cancer Research

Institute of New York and a grant (T32-GM07753, to Dr. Miller)

from the National Institute of General Medical Science. No other

potential conflict of interest relevant to this article was reported.

We are indebted to Drs. David E. Fisher, Adriano Pi ris, Jenni-

fer Y. Lin, and Jennifer C. Broder for their critical reading of the

manuscript, and to Dr. Claudio Clemente for contributing im-ages for Figure 1.

References

Cancer facts & figures, 2003. Atlanta:

American Cancer Society, 2003.

Clark WH Jr, Elder DE, Guerry D IV,

Epstein MN, Greene MH, Van Horn M.

A study of tumor progression: the precur-

1.

2.

sor lesions of superficial spreading and

nodular melanoma. Hum Pathol 1984;15:

1147-65.

Curtin JA, Fridlyand J, Kageshita T,

et al. Distinct sets of genetic alterations

3.

in melanoma. N Engl J Med 2005;353:

2135-47.

Alonso SR, Ortiz P, Pollan M, et al.

Progression in cutaneous malignant mel-

anoma is associated with distinct expres-

4.





13/15



sion profiles: a tissue microarray-based

study. Am J Pathol 2004;164:193-203.

Aitken J, Welch J, Duffy D, et al. CD-

KN2A variants in a population-based sam-

ple of Queensland families with melano-

ma. J Natl Cancer Inst 1999;91:446-52.

Thompson JF, Scolyer RA, Kefford RF.

Cutaneous melanoma. Lancet 2005;365:

687-701.

Gilchrest BA, Eller MS, Geller AC,

Yaar M. The pathogenesis of melanoma

induced by ultraviolet radiation. N Engl J

Med 1999;340:1341-8.

MacKie RM. Risk factors for the de-

velopment of primar y cutaneous malig-

nant melanoma. Dermatol Clin 2002;20:

597-600.

Marks R. Epidemiology of melanoma.

Clin Exp Dermatol 2000;25:459-63.

Naysmith L, Waterston K, Ha T, et al.

Quantitative measures of the effect of the

melanocortin 1 receptor on human pig-

mentary status. J Invest Dermatol 2004;

122:423-8.

Valverde P, Healy E, Jackson I, Rees JL,

Thody AJ. Variants of the melanocyte-

stimulating hormone receptor gene are

associated with red hair and fair skin in

humans. Nat Genet 1995;11:328-30.

Frandberg PA, Doufexis M, Kapas S,

Chhajlani V. Human pigmentation pheno-

type: a point mutation generates non-

functional MSH receptor. Biochem Biophys

Res Commun 1998;245:490-2.

Kennedy C, ter Huurne J, Berkhout M,

et al. Melanocortin 1 receptor (MC1R)

gene variants are associated with an in-

creased risk for cutaneous melanoma

which is largely independent of skin type

and hair color. J Invest Dermatol 2001;

117:294-300.

Braig M, Schmitt CA. Oncogene-

induced senescence: putting the brakes on

tumor development. Cancer Res 2006;66:

2881-4.

Welsh CF, Roovers K, Vil lanueva J, Liu

Y, Schwartz MA, Assoian RK. Timing of

cyclin D1 expression within G1 phase is

controlled by Rho. Nat Cell Biol 2001;3:

950-7.

Brunet A, Roux D, Lenormand P,

Dowd S, Keyse S, Pouyssegur J. Nuclear

translocation of p42/p44 mitogen-activat-

ed protein kinase is required for growth

factor-induced gene expression and cell

cycle entr y. EMBO J 1999;18:664-74.

Lin AW, Barradas M, Stone JC, van

Aelst L, Serrano M, Lowe SW. Premature

senescence involving p53 and p16 is acti-

vated in response to constitutive MEK/

MAPK mitogenic signaling. Genes Dev

1998;12:3008-19.

Albino AP, Nanus DM, Mentle IR, et al.

Analysis of ras oncogenes in malignant

melanoma and precursor lesions: correla-

tion of point mutations with differentia-

tion phenotype. Oncogene 1989;4:1363-74.

Davies H, Bignell GR, Cox C, et al.

Mutations of the BRAF gene in human

cancer. Nature 2002;417:949-54.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

Omholt K, Platz A, Kanter L, Ring-

borg U, Hansson J. NRAS and BRAF

mutations arise early during melanoma

pathogenesis and are preserved through-

out tumor progression. Clin Cancer Res

2003;9:6483-8.

Pollock PM, Harper UL, Hansen KS,

et al. High frequency of BRAF mutations

in nevi. Nat Genet 2003;33:19-20.

Patton EE, Widlund HR, Kutok JL, et

al. BRAF mutations are sufficient to pro-

mote nevi formation and cooperate with

p53 in the genesis of melanoma. Curr Biol

2005;15:249-54.

Michaloglou C, Vredeveld LC, Soen-

gas MS, et al. BRAFE600-associated se-

nescence-like cell cycle arrest of human

naevi. Nature 2005;436:720-4.

Eskandarpour M, Kiaii S, Zhu C, Cas-

tro J, Sakko AJ, Hansson J. Suppression of

oncogenic NRAS by RNA interference in-

duces apoptosis of human melanoma

cells. Int J Cancer 2005;115:65-73.

Hingorani SR, Jacobetz MA, Robert-

son GP, Herlyn M, Tuveson DA. Suppres-

sion of BRAF(V599E) in human melano-

ma abrogates transformation. Cancer Res

2003;63:5198-202.

Hoeflich KP, Gray DC, Eby MT, et al.

Oncogenic BRAF is required for tumor

growth and maintenance in melanoma

models. Cancer Res 2006;66:999-1006.

Lyons JF, Wilhelm S, Hibner B, Bollag

G. Discovery of a novel Raf kinase inhibi-

tor. Endocr Relat Cancer 2001;8:219-25.

Solit DB, Garraway LA, Pratilas CA, et

al. BRAF mutation predicts sensitivity to

MEK inhibit ion. Nature 2006;439:358-62.

Kamb A, Gruis NA, Weaver-Feldhaus J,

et al. A cell cycle regulator potentially in-

volved in genesis of many tumor types.

Science 1994;264:436-40.

Nobori T, Miura K, Wu DJ, Lois A,

Takabayashi K, Carson DA. Deletions of

the cyclin-dependent kinase-4 inhibitor

gene in multiple human cancers. Nature

1994;368:753-6.

Flores JF, Walker GJ, Glendening JM,

et al. Loss of t he p16INK4a and p15INK4b

genes, as well as neighboring 9p21 mark-

ers, in sporadic melanoma. Cancer Res

1996;56:5023-32.

Wu H, Goel V, Haluska FG. PTEN sig-

naling pathways in melanoma. Oncogene

2003;22:3113-22.

Li J, Yen C, Liaw D, et al. PTEN, a pu-

tative protein tyrosine phosphatase gene

mutated in human brain, breast, and pros-

tate cancer. Science 1997;275:1943-7.

Steck PA, Pershouse MA, Jasser SA, et

al. Identification of a candidate tumour

suppressor gene, MMAC1, at chromosome

10q23.3 that is mutated in multiple ad-

vanced cancers. Nat Genet 1997;15:356-

62.

You MJ, Castrillon DH, Bastian BC, et

al. Genetic analysis of Pten and Ink4a/Arf

interactions in the suppression of tumori-

genesis in mice. Proc Natl Acad Sci U S A

2002;99:1455-60.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

Kamb A, Shattuck-Eidens D, Eeles R,

et al. Ana lysis of the p16 gene (CDKN2) as

a candidate for the chromosome 9p mela-

noma susceptibility locus. Nat Genet 1994;

8:23-6.

Hussussian CJ, Struewing JP, Gold-

stein AM, et al. Germline p16 mutations

in familial melanoma. Nat Genet 1994;8:

15-21.

Pollock PM, Trent JM. The genetics of

cutaneous melanoma. Clin Lab Med 2000;

20:667-90.

Sharpless E, Chin L. The INK4a/ARF

locus and melanoma. Oncogene 2003;22:

3092-8.

Serrano M, Lee H, Chin L, Cordon-

Cardo C, Beach D, DePinho RA. Role of

the INK4a locus in tumor suppression

and cel l morta lity. Cel l 1996;85:27-37.

Chin L, Pomerantz J, Polsky D, et al.

Cooperative effects of INK4a and ras in

melanoma susceptibility in vivo. Genes

Dev 1997;11:2822-34.

Zuo L, Weger J, Yang Q, et al. Germ-

line mutations in the p16INK4a binding

domain of CDK4 in familial melanoma.

Nat Genet 1996;12:97-9.

Sotillo R, Garcia JF, Ortega S, et al.

Invasive melanoma in Cdk4-targeted mice.

Proc Natl Acad Sci U S A 2001;98:13312-

7.

Sauter ER, Yeo UC, von Stemm A, et

al. Cyclin D1 is a candidate oncogene in

cutaneous melanoma. Cancer Res 2002;

62:3200-6.

Pomerantz J, Schreiber-Agus N, Liege-

ois NJ, et al. The Ink4a tumor suppressor

gene product, p19Arf, interacts with MDM2

and neutralizes MDM2s inhibition of

p53. Cell 1998;92:713-23.

Harris SL, Levine AJ. The p53 path-

way: positive and negative feedback loops.

Oncogene 2005;24:2899-908.

Sharpless NE, Ramsey MR, Balasub-

ramanian P, Castrillon DH, DePinho RA.

The differential impact of p16(INK4a) or

p19(ARF) deficiency on cell growth and

tumorigenesis. Oncogene 2004;23:379-85.

Kamijo T, Zindy F, Roussel MF, et al.

Tumor suppression at the mouse INK4a

locus mediated by the alternative reading

frame product p19ARF. Cell 1997;91:649-

59.

Recio JA, Noonan FP, Takayama H, et

al. Ink4a/arf deficiency promotes ultravi-

olet radiation-induced melanomagenesis.

Cancer Res 2002;62:6724-30.

Guldberg P, Thor Straten P, Birck A,

Ahrenkiel V, Kirkin AF, Zeuthen J. Disrup-

tion of the MMAC1/PTEN gene by dele-

tion or mutation is a frequent event in

malignant melanoma. Cancer Res 1997;57:

3660-3.

Cantley LC, Neel BG. New insights

into tumor suppression: PTEN suppresses

tumor formation by restraining the phos-

phoinositide 3-kinase/AKT pathway. Proc

Natl Acad Sci U S A 1999;96:4240-5.

Stahl JM, Cheung M, Sharma A, Trive-

di NR, Shanmugam S, Robertson GP.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.





14/15



Loss of PTEN promotes tumor develop-

ment in malignant melanoma. Cancer

Res 2003;63:2881-90.

Stahl JM, Sharma A, Cheung M, et al.

Deregulated Akt3 activity promotes de-

velopment of malignant melanoma. Can-

cer Res 2004;64:7002-10.

Hodgkinson CA, Moore KJ, Nakaya-

ma A, et al. Mutations at the mouse mi-

crophthalmia locus are associated with

defects in a gene encoding a novel basic-

helix-loop-helix-zipper protein. Cell 1993;

74:395-404.

Nishimura EK, Granter SR, Fisher DE.

Mechanisms of hair graying: incomplete

melanocyte stem cell maintenance in the

niche. Science 2005;307:720-4.

Widlund HR, Fisher DE. Microphtha-

lamia-associated transcription factor: a

critical regulator of pigment cell devel-

opment and survival. Oncogene 2003;22:

3035-41.

Lerner AB, Shiohara T, Boissy RE, Ja-

cobson KA, Lamoreux ML, Moellmann GE.

A mouse model for vitiligo. J Invest Der-

matol 1986;87:299-304.

Steingrimsson E, Moore KJ, Lamor-

eux ML, et al. Molecular basis of mouse

microphthalmia (mi) mutations helps ex-

plain their developmental and phenotypic

consequences. Nat Genet 1994;8:256-63.

McGill GG, Horstmann M, Widlund

HR, et al. Bcl2 regulation by the melano-

cyte master regulator Mitf modulates lin-

eage survival and melanoma cell viability.

Cell 2002;109:707-18.

Banerjee D. Genasense (Genta Inc).

Curr Opin Invest ig Drugs 2001;2:574-80.

Goding CR. Mitf from neural crest to

melanoma: signal transduction and tran-

scription in the melanocyte lineage.

Genes Dev 2000;14:1712-28.

Du J, Miller AJ, Widlund HR, Horst-

mann MA, Ramaswamy S, Fisher DE.

MLANA/MART1 and SILV/PMEL17/GP100

are transcriptionally regulated by MITF in

melanocytes and melanoma. Am J Pathol

2003;163:333-43.

Baxter LL, Pavan WJ. Pmel17 expres-

sion is Mitf-dependent and reveals cranial

melanoblast migration during murine de-

velopment. Gene Expr Patterns 2003;3:703-

7.

Loercher AE, Tank EMH, Delston RB,

Harbour JW. MITF links differentiation

with cell cycle arrest in melanocy tes by

transcript ional activation of INK4A. J Cell

Biol 2005;168:35-40.

Hofbauer GF, Kamarashev J, Geertsen

R, Boni R, Dummer R. Melan A/MART-1

immunoreactivity in formalin-fixed par-

affin-embedded primary and metastatic

melanoma: frequency and distribution.

Melanoma Res 1998;8:337-43.

Salti GI, Manougian T, Farolan M,

Shilkaitis A, Majumdar D, Das Gupta TK.

Micropthalmia transcription factor: a new

prognostic marker in intermediate-thick-

53.

54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

64.

65.

66.

ness cutaneous malignant melanoma. Can-

cer Res 2000;60:5012-6.

Seiter S, Monsurro V, Nielsen MB, et al.

Frequency of MART-1/MelanA and gp100/

PMel17-specific T cells in tumor metasta-

ses and cultured tumor-infiltrating lym-

phocytes. J Immunother 2002;25:252-63.

Takeuchi H, Kuo C, Morton DL, Wang

HJ, Hoon DS. Expression of differentia-

tion melanoma-associated antigen genes

is associated with favorable disease out-

come in advanced-stage melanomas. Can-

cer Res 2003;63:441-8.

Miller AJ, Du J, Rowan S, Hershey CL,

Widlund HR, Fisher DE. Transcriptional

regulation of the melanoma prognostic

marker melastatin (TRPM1) by MITF in

melanocytes and melanoma. Cancer Res

2004;64:509-16.

Duncan LM, Deeds J, Hunter J, et al.

Down-regulation of the novel gene mela-

statin correlates with potential for mela-

noma metastasis. Cancer Res 1998;58:

1515-20.

King R, Weilbaecher KN, McGill G,

Cooley E, Mihm M, Fisher DE. Microph-

thalmia transcription factor: a sensitive

and specific melanocyte marker for mela-

noma diagnosis. Am J Pathol 1999;155:731-

8.

Miettinen M, Fernandez M, Franssila

K, Gatalica Z, Lasota J, Sarlomo-Rikala M.

Microphthalmia transcription factor in the

immunohistochemical diagnosis of meta-

static melanoma: comparison with four

other melanoma markers. Am J Surg

Pathol 2001;25:205-11.

Granter SR, Weilbaecher KN, Quigley

C, Fisher DE. Role for microphthalmia

transcription factor in the diagnosis of

metastatic malignant melanoma. Appl Im-

munohistochem Mol Morphol 2002;10:47-

51.

Garraway LA, Widlund HR, Rubin MA,

et al. Integrative genomic analyses iden-

tify MITF as a lineage survival oncogene

amplified in malignant melanoma. Na-

ture 2005;436:117-22.

Haass NK, Smalley KS, Li L, Herlyn M.

Adhesion, migration and communication

in melanocytes and melanoma. Pigment

Cell Res 2005;18:150-9.

Balch CM, Soong SJ, Gershenwald JE,

et al. Prognost ic factors analysis of 17,600

melanoma patients: validation of the

American Joint Committee on Cancer

melanoma staging system. J Clin Oncol

2001;19:3622-34.

Johnson JP. Cell adhesion molecules

in the development and progression of

malignant melanoma. Cancer Metastasis

Rev 1999;18:345-57.

Bienz M. Beta-catenin: a pivot between

cell adhesion and Wnt signalling. Curr

Biol 2005;15:R64-R67.

Gottardi CJ, Gumbiner BM. Adhesion

signaling: how beta-catenin interacts with

its partners. Curr Biol 2001;11:R792-R794.

67.

68.

69.

70.

71.

72.

73.

74.

75.

76.

77.

78.

79.

Brembeck FH, Schwarz-Romond T,

Bakkers J, Wilhelm S, Hammerschmidt

M, Birchmeier W. Essentia l role of BCL9-2

in the switch between beta-catenins ad-

hesive and transcriptional functions. Genes

Dev 2004;18:2225-30.

Rubinfeld B, Robbins P, El-Gamil M,

Albert I, Porfiri E, Polakis P. Stabilization

of beta-catenin by genetic defects in mel-

anoma cell lines. Science 1997;275:1790-

2.

Cowley GP, Smith ME. Cadherin ex-

pression in melanocytic naevi and malig-

nant melanomas. J Pathol 1996;179:183-7.

Rimm DL, Caca K, Hu G, Harrison

FB, Fearon ER. Frequent nuclear/cytoplas-

mic localization of beta-catenin without

exon 3 mutations in malignant melano-

ma. Am J Pathol 1999;154:325-9.

Sanders DS, Blessing K, Hassan GA,

Bruton R, Marsden JR, Jankowski J. Al-

terations in cadherin and catenin expres-

sion during the biological progression of

melanocy tic tumours. Mol Pathol 1999;52:

151-7.

Widlund HR, Horstmann MA, Price

ER, et al. Beta-catenin-induced melanoma

growth requires the downstream target

Microphthalmia-associated transcription

factor. J Cell Biol 2002;158:1079-87.

Shtutman M, Zhurinsky J, Simcha I, et

al. The cyclin D1 gene is a target of the

beta-catenin/LEF-1 pathway. Proc Natl Acad

Sci U S A 1999;96:5522-7.

Hsu M, Andl T, Li G, Meinkoth JL,

Herlyn M. Cadherin repertoire determines

partner-specific gap junctional communi-

cation during melanoma progression.

J Cell Sci 2000;113:1535-42.

Valyi-Nagy IT, Hirka G, Jensen PJ,

Shih IM, Juhasz I, Herlyn M. Undifferent i-

ated keratinocytes control growth, mor-

phology, and antigen expression of normal

melanocytes through cell-cell contact. Lab

Invest 1993;69:152-9.

Danen EH, de Vries TJ, Morandini R,

Ghanem GG, Ruiter DJ, van Muijen GN.

E-cadherin expression in human melano-

ma. Melanoma Res 1996;6:127-31.

Hsu MY, Wheelock MJ, Johnson KR,

Herlyn M. Shifts in cadherin profiles be-

tween human normal melanocytes and

melanomas. J Investig Dermatol Symp

Proc 1996;1:188-94.

Scott RA, Lauweryns B, Snead DM,

Haynes RJ, Mahida Y, Dua HS. E-cadherin

distribution and epithelial basement mem-

brane characteristics of the normal human

conjunctiva and cornea. Eye 1997;11:607-

12.

Gottardi CJ, Wong E, Gumbiner BM.

E-cadherin suppresses cellular transfor-

mation by inhibiting beta-catenin signal-

ing in an adhesion-independent manner.

J Cell Biol 2001;153:1049-60.

Qi J, Chen N, Wang J, Siu CH. Trans-

endothelial migration of melanoma cells

involves N-cadherin-mediated adhesion and

80.

81.

82.

83.

84.

85.

86.

87.

88.

89.

90.

91.

92.

93.





15/15



activation of the beta-catenin signaling

pathway. Mol Biol Cell 2005;16:4386-97.

Li G, Satyamoorthy K, Herlyn M.

N-cadherin-mediated intercellular inter-

actions promote survival and migration

of melanoma cells. Cancer Res 2001;61:

3819-25.

Kuphal S, Bauer R, Bosserhoff AK. In-

tegrin signaling in ma lignant melanoma.

Cancer Metastasis Rev 2005;24:195-222.

Danen EH, Ten Berge PJ, Van Muijen

GN, Van t Hof-Grootenboer AE, Brocker

EB, Ruiter DJ. Emergence of alpha 5 beta

1 fibronectin- and alpha v beta 3 vitronec-

tin-receptor expression in melanocytic tu-

mour progression. Histopathology 1994;24:

249-56.

Brooks PC, Stromblad S, Sanders LC,

et al. Localization of matrix metallopro-

teinase MMP-2 to the surface of invasive

cells by interaction with integrin alpha v

beta 3. Cell 1996;85:683-93.

Felding-Habermann B, Fransvea E,

OToole TE, Manzuk L, Faha B, Hensler

M. Involvement of tumor cell integrin al-

94.

95.

96.

97.

98.

pha v beta 3 in hematogenous metastasis

of human melanoma cells. Clin Exp Metas-

tasis 2002;19:427-36.

Hofmann UB, Westphal JR, Waas ET,

Becker JC, Ruiter DJ, van Muijen GN. Co-

expression of integrin alpha(v)beta3 and

matrix metalloproteinase-2 (MMP-2) co-

incides with MMP-2 activation: correla-

tion with melanoma progression. J Invest

Dermatol 2000;115:625-32.

Petitclerc E, Stromblad S, von Schal-

scha TL, et al. Integrin alpha(v)beta3 pro-

motes M21 melanoma growth in human

skin by regulating tumor cell survival.

Cancer Res 1999;59:2724-30.

Li X, Regezi J, Ross FP, et al. Integrin

alphavbeta3 mediates K1735 murine mel-

anoma cell motility in vivo and in vitro.

J Cell Sci 2001;114:2665-72.

Dechantsreiter MA, Planker E, Matha

B, et al. N-methylated cyclic RGD peptides

as highly active and selective alpha(V)beta(3)

integrin antagonists. J Med Chem 1999;

42:3033-40.

Tsao H, Zhang X, Fowlkes K, Haluska

99.

100.

101.

102.

103.

FG. Relative reciprocity of NRAS and

PTEN/MMAC1 alterations in cutaneous

melanoma cell lines. Cancer Res 2000;60:

1800-4.

Daniotti M, Oggionni M, Ranzan i T,

et al. BRAF alterations are associated

with complex mutationa l profi les in ma-

lignant melanoma. Oncogene 2004;23:

5968-77.

Tsao H, Goel V, Wu H, Yang G,

Haluska FG. Genetic interaction between

NRAS and BRAF mutations and PTEN/

MMAC1 inactivation in melanoma. J Invest

Dermatol 2004;122:337-41.

Maldonado JL, Fridlyand J, Patel H,

et al. Determinants of BRAF mutations in

primary melanomas. J Natl Cancer Inst

2003;95:1878-90.

Chudnovsky Y, Adams AE, Robbins

PB, Lin Q, Khavari PA. Use of human tis-

sue to assess the oncogenic activity of

melanoma-associated mutations. Nat Gen-

et 2005;37:745-9.

Copyright 2006 Massachusetts Medical Society.

104.

105.

106.

107.

JOURNALEDITORIALFELLOWTheJournals editorial office invites applications for a one-year

research fellowship beginning in July 2007 from individuals at any

stage of training. The editorial fellow will work on Journal projects

and will participate in the day-to-day editorial activities of theJournal

but is expected in addition to have his or her own independent

projects. Please send curriculum vitae and research interests

to the Editor-in-Chief, 10 Shattuck St., Boston, MA 02115

(fax, 617-739-9864), by October 1, 2006.


Documents

Melanoma Review