Vasodilator Stimulated Phosphoprotein (VASP)-Mediated Actin Polymerization Drives Natural Killer Cell Granule Convergence

Abstract

Abstract Natural killer (NK) cells eliminate transformed and malignant cells through a highly orchestrated series of actin and microtubule cytoskeletal rearrangements, culminating in the secretion of preformed lytic granules. Despite the importance of actin and microtubules, the roles of many molecular cytoskeletal regulators in this process have not yet been ascertained. In this study, we investigated the role of Vasodilator Stimulated Phosphoprotein (VASP), an actin regulatory protein, in NK cell-mediated cytotoxicity. Interestingly, we found that depletion of VASP inhibits NK cell cytotoxicity and that VASP co-localizes with F-actin at the NK cell – target cell cytotoxic synapse. Surprisingly, despite their co-localization, VASP depletion did not affect either F-actin accumulation at the cytotoxic synapse or conjugate formation. Instead, we found that a minority of VASP localized and biochemically co-purified with cytolytic granules. Although VASP knockdown did not affect microtubule organizing center (MTOC) polarization, it did dramatically impact lytic granule convergence to the MTOC. Significantly, VASP depletion decreased F-actin accumulation on cytolytic granules and depolymerization of F-actin with Latrunculin A impaired lytic granule convergence. Taken together, these results demonstrate a novel requirement for VASP-mediated actin polymerization in NK cell granule convergence and cytotoxicity and highlight a role for F-actin in lytic granule convergence.