Transmembrane signaling during natural killer cell-mediated cytotoxicity. Regulation by protein kinase C activation

P. J. Leibson, D. E. Midthun, K. P. Windebank, R. T. Abraham

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


NK cells can mediate either FcR-dependent cytotoxicity against antibody-coated target cells or direct cytotoxicity against a variety of tumor cells. We used homogeneous, cloned populations of CD16+/CD3- human NK cells to characterize and compare the transmembrane signaling mechanisms used during these alternative forms of cytotoxicity. Cross-linkage of NK cell FcR with anti-FcR (anti-CD16) mAb or direct binding to NK-sensitive tumor targets resulted in a rapid release of inositol phosphates and increases in [Ca2+](i). The receptor-dependent [Ca2+](i) increase (as monitored in indo-1 loaded NK cells by flow cytometry) consisted of an initial release of calcium from intracellular stores, followed by a sustained influx of calcium across the plasma membrane. To assess the potential regulatory feedback role of protein kinase C (PKC) activation in these proximal signaling events, NK cells were pretreated with either PKC-activating phorbol esters, nonactivating phorbol ester homologs, or synthetic diacylglycerols. Brief pretreatment with activating phorbol esters rapidly inhibited, in a concentration-dependent manner, both phosphoinositide hydrolysis and increases in [Ca2+](i) induced by FcR ligation, whereas pretreatment with an inactive phorbol ester had no effect. This acute inhibitory effect was not explained by FcR down-regulation, which occurred with more prolonged exposure to phorbol esters. In contrast, the phosphoinositide turnover and [Ca2+](i) increase in NK cells stimulated with NK-sensitive tumor targets were not affected by prior exposure to PKC-activating phorbol esters. This differential regulatory effect of phorbol ester on proximal signaling was paralleled by a corresponding effect on cytotoxicity, i.e., phorbol ester-induced activation of PKC inhibited FcR-dependent cytotoxicity, but did not alter direct cytotoxicity against NK-sensitive tumor cells. These results indicate that PKC activation can differentially regulate alternative forms of NK cell-mediated cytotoxicity by rapidly and specifically desensitizing the FcR.

Original languageEnglish (US)
Pages (from-to)1498-1504
Number of pages7
JournalJournal of Immunology
Issue number5
StatePublished - 1990

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology


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