UBC Theses and Dissertations
The role of talin in LFA-1 function in cell-mediated cytotoxicity Mace, Emily Margaret
Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) are effectors of cell-mediated cytotoxicity towards virally infected and tumourigenic cells. The integrin leukocyte function associated antigen-1 (LFA-1) is required for the adhesion of effector cells to their targets. In addition, LFA-1 transduces signals resulting in actin polymerization. We show that in both CTLs and NK cells, LFA-1 ligand binding results in the recruitment of actin, the cytoskeletal adaptor talin, and the activator of actin nucleation Wiskott-Aldrich Syndrome protein (WASP). We used talin-knockout (KO) NK cells to demonstrate that talin is required for LFA-1 mediated adhesion and polarization towards the target cell. This actin polarization is a prerequisite for subsequent steps leading to cytotoxicity, including the translocation of cytotoxic granules. Further analysis of the LFA-1 mediated signaling that leads to actin polymerization shows that talin recruits proteins that catalyze de novo actin formation. Talin forms a complex with vinculin and the actin-nucleator Arp2/3, and talin is required for the movement of these proteins to LFA-1 following LFA-1 binding to ICAM-1. In addition, talin binds the phosphatidylinositol phosphate kinase PIPKIγ and talin is required for the localized production of phosphatidylinositol 4,5 bisphosphate (PIP₂) following LFA-1 ligation. This production of PIP₂ is required for the recruitment of WASP, which in turn activates Arp2/3 to polymerize actin. Thus we have demonstrated a critical role for talin in the actin polarization that is required for cell-mediated cytotoxicity and elucidated the mechanism of LFA-1 mediated actin polymerization.
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