CONTROL OF LYTIC FUNCTION BY MITOGEN-ACTIVATED PROTEIN KINASE EXTRACELLULAR REGULATORY KINASE-2 (ERK2) IN A HUMAN NATURAL-KILLER-CELL LINE - IDENTIFICATION OF PERFORIN AND GRANZYME-B MOBILIZATION BY FUNCTIONALERK2

The signal pathways that control effector function in human natural ki ller (NK) cells are little known. In this study, we have identified th e critical role of the mitogen-activated protein kinase (MAPK) pathway in NK lysis of tumor cells, and this pathway may involve the mobiliza tion of granule components in NK cells upon interaction with sensitive tumor target cells. Evidence was provided by biological, biochemical, and gene transfection methods. NK cell binding to tumor cells for 5 m in was sufficient to maximally activate MAPK/extracellular signal-regu latory kinase 2 (ERK2), demonstrated by its tyrosine phosphorylation a nd by its ability to function as an efficient kinase for myelin basic protein. MAPK activation was achieved in NK cells only after contact w ith NK-sensitive but not NK-resistant target cells. In immunocytochemi cal studies, cytoplasmic perforin and granzyme B were both maximally r edirected towards the tumor contact zone within 5 min of NK cell conta ct with tumor cells. A specific MAPK pathway inhibitor, PD098059, coul d block not only MAPK activation but also redistribution of perforin/g ranzyme B in NK cells, which occur upon target ligation. PD098059 also interfered with NK lysis of tumor cells in a 5-h Cr-51-release assay, but had no ability to block NK cell proliferation Transient transfect ion studies with wild-type and dominant-negative MAPK/ERK2 genes confi rmed the importance of MAPK in NK cell lysis. These results document a pivotal role of MAPK in NK effector function, possibly by its control of movement of lyric granules, and clearly define MAPK involvement in a functional pathway unlinked to cell growth or differentiation.