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Sheng Wei^*, Ana M. Gamero^*, Jin Hong Liu^*, Angela A. Daulton^*, Nichola I. Valkov^*, Joseph A. Trapani, Andrew C. Larner, Michael J. Weber^||, and Julie Y. Djeu^*

From the ^* Immunology Program, H. Lee Moffitt Cancer Center, University of South Florida College of Medicine, Department of Biochemistry and Molecular Biology, Tampa, Florida 33612; the Cellular Cytotoxicity Laboratory, Austin Research Institute, Heidelberg, Victoria 3084, Australia; the Department of Immunology, Cleveland Clinic Research Foundation, Cleveland, Ohio 44195; and the ^|| Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908

The signal pathways that control effector function in human natural killer (NK) cells are little known. In this study, we have identified the critical role of the mitogen-activated protein kinase (MAPK) pathway in NK lysis of tumor cells, and this pathway may involve the mobilization 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 min was sufficient to maximally activate MAPK/extracellular signal–regulatory kinase 2 (ERK2), demonstrated by its tyrosine phosphorylation and by its ability to function as an efficient kinase for myelin basic protein. MAPK activation was achieved in NK cells only after contact with NK-sensitive but not NK-resistant target cells. In immunocytochemical studies, cytoplasmic perforin and granzyme B were both maximally redirected towards the tumor contact zone within 5 min of NK cell contact with tumor cells. A specific MAPK pathway inhibitor, PD098059, could block not only MAPK activation but also redistribution of perforin/granzyme B in NK cells, which occur upon target ligation. PD098059 also interfered with NK lysis of tumor cells in a 5-h ⁵¹Cr-release assay, but had no ability to block NK cell proliferation. Transient transfection studies with wild-type and dominant-negative MAPK/ERK2 genes confirmed 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 lytic granules, and clearly define MAPK involvement in a functional pathway unlinked to cell growth or differentiation.

Key Words: natural killer cell • mitogen-activated protein kinase • perforin • granzyme B • signal transduction

Abbreviations used: AMAPK, active MAPK; ERK, extracellular signal–regulatory kinase; KD, kinase deficient; MAPK, mitogen-activated protein kinase; MBP, myelin basic protein; MEK, MAPK kinase; PI, phosphatidylinositol; PLC, phospholipase C; TRITC, tetramethyl rhodamine isothiocyanate.

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