IDENTIFICATION OF A NOVEL MECHANISM FOR LFA-1 ORGANIZATION DURING NK CYTOLYTIC RESPONSE

Abstract

The elimination of transformed and viral infected cells by natural killer (NK) cells requires the formation of a specialized junction between NK and target cells, generally denominated immunological synapse (IS). After initial recognition, the IS enables the directed secretion of lytic granules content into the susceptible target cell. The lymphocyte function-associated antigen (LFA)-1 regulates NK effector function by enabling NK-IS assembly and maturation. The pathways underlying LFA-1 accumulation at the IS in NK cells have not been elucidated so far. A kinase anchoring protein 350 (AKAP350) is a centrosome/Golgi associated protein with a central role in the regulation of Golgi organization and microtubule dynamics. In T cells, AKAP350 participates in LFA-1 activation by mechanisms that remain elusive. We first investigated AKAP350 participation in NK cytolytic activity. Our results showed that the decrease in AKAP350 levels by expression of specific shRNAs (AKAP350KD) inhibited NK-YTS cytolytic activity, without affecting NK:target cell conjugate formation. The impairment of NK effector function in AKAP350KD cells correlated with decreased LFA-1 clustering and defective IS maturation. AKAP350KD cells that were exclusively activated via LFA-1 showed impaired LFA-1 organization and deficient lytic granule translocation as well. In NK AKAP350KD cells, activation signaling through Vav1 was preserved up to 10 min of interaction with target cells, but significantly decreased afterwards. Experiments in YTS and in ex vivo NK cells revealed the existence of an intracellular pool of LFA-1 vesicles, which partially associated with the Golgi apparatus. Upon NK cell activation, this LFA-1 pool redistributed to the IS in a Golgi-AKAP350-dependent manner. Disruption of Golgi integrity or alteration of microtubule dynamics impaired LFA-1 localization at the IS. Therefore, this study reveals the existence of a Golgi/AKAP350 dependent trafficking pathway for LFA-1, which is relevant for LFA-1 organization at NK-lytic IS and, concomitantly, for NK cytolytic function.