Tethering of intercellular adhesion molecule on target cells is required for LFA-1-dependent NK cell adhesion and granule polarization.
Alpha(L)beta(2) integrin (LFA-1) has an important role in the formation of T cell and NK cell cytotoxic immunological synapses and in target cell killing. Binding of LFA-1 to ICAM on target cells promotes not only adhesion but also polarization of cytolytic granules in NK cells. In this study, we tested whether LFA-1-dependent NK cell responses are regulated by the distribution and mobility of ICAM at the surface of target cells. We show that depolymerization of F-actin in NK-sensitive target cells abrogated LFA-1-dependent conjugate formation and granule polarization in primary NK cells. Degranulation, which is not controlled by LFA-1, was not impaired. Fluorescence recovery after photobleaching experiments and particle tracking by total internal reflection fluorescence microscopy revealed that ICAM-1 and ICAM-2 were distributed in largely immobile clusters. ICAM clusters were maintained and became highly mobile after actin depolymerization. Moreover, reducing ICAM-2 mobility on an NK-resistant target cell through expression of ezrin, an adaptor molecule that tethers proteins to the actin cytoskeleton, enhanced LFA-1-dependent adhesion and granule polarization. Finally, although NK cells kept moving over freely diffusible ICAM-1 on a lipid bilayer, they bound and spread over solid-phase ICAM-1. We conclude that tethering, rather than clustering of ICAM, promotes proper signaling by LFA-1 in NK cells. Our findings suggest that the lateral diffusion of integrin ligands on cells may be an important determinant of susceptibility to lysis by cytotoxic lymphocytes.
Gross
Catharina C
CC
Molecular and Cellular Immunology Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
Brzostowski
Joseph A
JA
Liu
Dongfang
D
Long
Eric O
EO
D000199:Actins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism / Q000502:physiology; D002448:Cell Adhesion / Q000276:immunology; D015815:Cell Adhesion Molecules / Q000378:metabolism / Q000502:physiology; D002450:Cell Communication / Q000276:immunology; D045744:Cell Line, Tumor; D016764:Cell Polarity / Q000276:immunology*; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000276:immunology* / Q000378:metabolism*; D003601:Cytotoxicity Tests, Immunologic / Q000379:methods*; D018390:Gene Targeting / Q000379:methods; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism* / Q000502:physiology; D020014:K562 Cells; D007694:Killer Cells, Natural / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism / Q000502:physiology*; D051379:Mice
D000199:Actins; D015703:Antigens, CD; D015815:Cell Adhesion Molecules; C480027:ICAM-2 protein, mouse; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1