Dependence of both spontaneous and antibody-dependent, granule exocytosis-mediated NK cell cytotoxicity on extracellular signal-regulated kinases

Extracellular signal-regulated kinases (ERK, also known as mitogen-activate d protein kinases) are serine-threonine kinases transducing signals elicite d upon ligand binding to several tyrosine kinase-associated receptors, We h ave reported that ERK2 phosphorylation and activation follows engagement of the low affinity receptor for the Fc portion of IgG (CD16) on NK cells, an d is necessary for CD16-induced TNF-alpha mRNA expression, Here, we analyze d the involvement of ERK in NK cell-mediated cytotoxicity and IFN-gamma exp ression induced upon stimulation with targets cells, coated or not with Abs , Our data indicate that, as with immune complexes, ERK2 phosphorylation oc curs in human primary NK cells upon interaction with target cells sensitive to granule exocytosis-mediated spontaneous cytotoxicity, and that this reg ulates both target cell- and immune complex-induced cytotoxicity and IFN-ga mma mRNA expression. A specific inhibitor of mitogen-activated protein kina se kinase reduced both spontaneous and Ab-dependent cytotoxicity in a dose- dependent manner involving, at least in part, inhibition of granule exocyto sis without affecting effector/target cell interaction and rearrangement of the cytoskeleton proteins actin and tubulin, Involvement of ERK in the reg ulation of Ca2+-dependent cell-mediated cytotoxicity was confirmed, using a genetic approach, in primary NK cells infected with a recombinant vaccinia virus encoding an ERK inactive mutant, These data indicate that the bioche mical pathways elicited in NK cells upon engagement of receptors responsibl e for either spontaneous or Ab-dependent recognition of target cells, altho ugh distinct, utilize ERK as one of their downstream molecules to regulate effector functions.