PERTUSSIS-TOXIN-SENSITIVE GTP-BINDING PROTEINS REGULATE ACTIVATION-INDUCED APOPTOTIC CELL-DEATH OF HUMAN NATURAL-KILLER-CELLS

Apoptosis of natural killer (NK) cells can be induced by non-specific physical damage (UV irradiation, heat shock) or by simultaneous ligati on of the CD16 and the interleukin-2 receptor (IL-2R) molecules, but n ot with either anti-CD1G or IL-2 alone. Whereas blockade of GTP-bindin g protein (G protein)-mediated signal transduction using ADP-ribosylat ing bacterial toxins or the GTPase-resistant GTP analog guanosine 5'-0 -(3-thiotriphosphate (GTP gamma S) does not affect non-specific induct ion of NK cell apoptosis, such interventions do inhibit induction of a poptosis by anti-CD16/IL-2. The G proteins involved in the regulation of activation-induced NK apoptosis are sensitive to pertussis toxin (P TX) and to the non-specific GTP analog GTP gamma S but not to cholera toxin, Pseudomonas exotoxin A or diphtheria toxin. A pertussis toxin m utant that lacks ADP-ribosylating activity, but conserves the membrane translocating and T cell-mitogenic effects of the native molecule, fa ils to inhibit NK apoptosis. To exert their apoptosis-inhibitory effec t, PTX and CTP gamma S must be employed before cells are activated. La ter addition has no effect, suggesting the implication of G proteins i n the transmission of apoptosis-inducing signals, but not in the effec tor stage of apoptosis. Pre-incubation with PTX or GTP gamma S does no t affect the activation of NK cells by CD16 cross-linking, IL-2 stimul ation - or both, as assessed by the induction of CD69 expression, prot ein tyrosine phosphorylation and calcium mobilization. Moreover, neith er PTX nor GTP gamma S compromise the effector function of NK cells or the susceptibility of target cells to NK-mediated lysis. These data s uggest apoptosis as a novel mechanism by which NK responses may be con trolled in vivo, as well as an experimental and therapeutical strategy to counteract endogenous down-regulation of NK responses.