ENHANCEMENT OF PEROXYNITRITE-INDUCED APOPTOSIS IN PC12 CELLS BY FIBROBLAST GROWTH-FACTOR-I AND NERVE GROWTH-FACTOR REQUIRES P21 RAS ACTIVATION AND IS SUPPRESSED BY BCL-2

Extracellular trophic factors can regulate whether cells subjected to oxidative stress will survive to proliferate or else undergo cell deat h. We have previously shown that about 35% of undifferentiated PC12 ce lls undergo apoptosis 18 h after exposure to peroxynitrite and that pr etreatment with nerve growth factor (NGF) protects PC12 cells through activation of phosphatidylinositol (PI) 3-kinase, In contrast, pretrea tment with acidic fibroblast growth factor (FGF-1) approximately doubl ed apoptosis, We report here that NGF added immediately after peroxyni trite treatment no longer protected against apoptosis, but instead enh anced apoptosis to the same extent as FGF, We further investigated whi ch signaling pathways were involved in increasing the level of apoptos is. Overexpression of Bcl-2 blocked the increased apoptosis caused by NGF and FGF-1, but Bcl-2 did not prevent the induction of apoptosis by peroxynitrite alone, The increase in apoptosis caused by the trophic factors was also blocked by the expression of a dominant negative p21R as mutant. Activation of PI 3-kinase by NGF pretreatment completely pr otected against both the enhanced apoptosis induced by FGF-1 pretreatm ent and NGF posttreatment and the apoptosis induced by peroxynitrite a lone. Our results indicate that the enhancement of peroxynitrite-induc ed apoptosis caused by NGF and FGF-1 is dependent on the stimulation o f a proapoptotic pathway involving p21Ras that can be suppressed by Bc l-2. (C) 1998 Academic Press.