Natural Killer Cells

Chris Nevares & Michael Murphy

http://www.nida.nih.gov/NIDA_notes/NNvol21N6/killercell.jpg

NK cells have a common precursor to other lymphocytes, but it is not known what causes differentiation of NK cells as opposed to T or B cells.

NK cell eating a tumor

Importance of NK cells

Receptors of NK Cells

NK cells do not possess antigen specific receptors.

• They have two different categories of receptors:– Lectin-like– killer-cell immunoglobulin-like receptors (KIR)

• Though the structure does not define function.

Receptors on NK cells exhibit activation and inhibition functions

– Rather than binding to antigen, NK cells have different types of receptors that activate or inhibit their function.

• Current theory states there are multiple activating and inhibiting receptors on each NK cell

• Activating receptors exhibit immunoreceptor tyrosine activating motifs (ITAM) while inhibition receptors exhibit immunoreceptor tyrosine inhibition motifs (ITIM)

– Basically ITAMs help deliver activation signals, and ITIMs repress them

Involved in activation of NK cells

Involved in inhibition in NK cells

NK cells tend to target cells missing Class I MHC

Activating receptor stimulated

Inhibition receptor stimulated

Result

Yes No Kills cell

No No does not kill cell

Yes Yes Does not kill cell

No Yes Does not kill cell

NK cell receptor stimulations and resulting responses

NK cells also have CD16 receptors (FcR)

NK Cells have similar cytotoxic pathways as CTLs

Perforin and Granzymes are also present in NK cells along with FasL.

http://journals.cambridge.org/fulltext_content/ERM/ERM5_03/S1462399403005623sup013.gif

Granules are composed of perforin and granzymes

Dynamin 2 Regulates Granule Exocytosis during NK

Cell-Mediated Cytotoxicity1

Laura N. Arneson,* Colin M. Segovis,* Timothy S. Gomez,*† Renee A. Schoon,* Christopher J. Dick,* Zhenkun Lou,† Daniel D. Billadeau,2*† and Paul J. Leibson*

What is Dynamin 2?

Dyn2 has five functional domains:

1. GTPase domain

2. Oligomerization domain

3. Pleckstrin homology domain

4. GTPase effector domain

5. Proline-rich domain implicated in in interacting with Src homology 3 (SH3) domains

What does Dyn2 do?

Regulates:

• Endo/exocytosis

• Actin assembly

Interacts with:

• Actin remodeling machineryo Cortactin, Grb2, and Nck

• Vav1 o T-cell activation & actin polymerization

• t-SNARE and Vam3p [Vps1p (yeast homologue)]o Vacuole fusion

Summary of paper findings

1. Dyn2 regulates NK cell-mediated cytotoxicityo Controls exocytosis of lytic granules

2. Suppression of Dyn2 impairs cell-mediated cytotoxicity

3. Dyn2 effects independent of proximal signaling

4. Dyn2 regulates terminal phase of granule release

5. Novel function of protein in exocytosis o Endocytosis well characterized

6. May participate in broader cell regulation

Dyn2 localizes with lytic granules at the NK cytolytic synapse

Dyn2 modulates cell-mediated cytotoxicity

Dyn2 modulates cell-mediated cytotoxicity

Dyn2 does not modulate conjugate formation

Proximal signaling is unchanged by Dyn2

Dyn2 does not effect granule polarization

Dyn2 regulates granule secretion

Discussion

• Surprising role in exocytosis

• Coordination of fission with fusion

• Dyn2 involved in insulin secretion

• CTL homologue Muc 13-4 required for vesicle fusion

• Dyn2 in NK cells not required for secretion

• In absence of Dyn2:

• Initial burst occurs, but subsequent bursts limited• Finite number of granule fission sites at synapse• Ineffective removal of empty lytic vesicles• Kiss-and-run model or cavicapture may explain this

phenomena

Kiss and Run Model

http://www.neuroworld.it/aBC/kis_run.htm

Dyn2 in medicine

• Charcot-Marie-Tooth disease

• One of the most common inherited neurodegenerative diseases

• Centronuclear myopathy

• Improper localization of the nucleus

• X-linked