Spontaneous neutrophil apoptosis involves caspase 3-mediated activation ofprotein kinase C-delta

Neutrophils are short-lived leukocytes that die by apoptosis, Whereas stres s-induced apoptosis is mediated by the p38 mitogen-activated protein (MAP) kinase pathway (Frasch, S, C., Nick, J, A., Fadok, V, A, Bratton, D, L,, Wo rthen, G, S., and Henson, P, M, (1998) J, Biol. Chem. 273, 8389-8397), sign als regulating spontaneous neutrophil apoptosis have not been fully determi ned. In this study we found increased activation of protein kinase C (PKC)- beta and -delta in neutrophils undergoing spontaneous apoptosis, but we sho w that only activation of PKC-delta was directly involved in the induction of apoptosis, PKC-delta can be proteolytically activated by caspase 3, We d etected the 40-kDa caspase-generated fragment of PKC-delta in apoptotic neu trophils and showed that the caspase 3: inhibitor Asp-Glu-Val-Asp-fluoromet hylketone prevented generation of the 40-kDa PKC-delta fragment and delayed neutrophil apoptosis, In a cell-free system, removal of PKC-delta by immun oprecipitation reduced DNA fragmentation, whereas loss of PKC-alpha, -beta, or -zeta had no significant effect. Rottlerin and LY379196 inhibit PRC-del ta and PKC-beta, respectively. Only Rottlerin was able to delay neutrophil apoptosis, Inhibitors of MAP-ERK-kinase 1 (PD98059) or p38 MAP kinase (SB20 2190) had no effect on neutrophil apoptosis, and activation of p42/44 and p 38 MAP kinase did not increase in apoptotic neutrophils, We conclude that s pontaneous neutrophil apoptosis involves activation of PKC-delta but is MAP kinase-independent.