PREVENTION OF PC12 CELL-DEATH BY N-ACETYLCYSTEINE REQUIRES ACTIVATIONOF THE RAS PATHWAY

We have shown that N-acetylcysteine (NAC) promotes survival of sympath etic neurons and pheochromocytoma (PC12) cells in the absence of troph ic factors. This action of NAC was not related to its antioxidant prop erties or ability to increase intracellular glutathione levels but was instead dependent on ongoing transcription and seemed attributable to the action of NAC as a reducing agent. Here, we investigate the mecha nism by which NAC promotes neuronal survival. We show that NAG activat es the Ras-extracellular signal-regulated kinase (ERK) pathway in PC12 cells. Pas activation by NAC seems necessary for survival in that it is unable to sustain serum-deprived PC12 MM17-26 cells constitutively expressing a dominant-negative farm of Ras. Promotion of PC12 cell sur vival by NAC is totally blocked by PD98059, an inhibitor of the ERK-ac tivating MAP kinase/ERK kinase, suggesting a required role for ERK act ivation in the NAC mechanism. In contrast, LY294002 and wortmannin, in hibitors of phosphatidylinositol 3-kinase (PI3K) that partially block NGF-promoted PC12 cell survival, have no effect on prevention of death by NAG. We hypothesized previously that the ability of NAC to promote survival correlates with its antiproliferative properties. However, a lthough NAC does not protect PC12 MM17-26 cells from loss of trophic s upport, it does inhibit their capacity to synthesize DNA. Thus, the an tiproliferative effect of NAG does not require Ras activation, and inh ibition of DNA synthesis is insufficient to mediate NAG-promoted survi val. These findings highlight the role of Ras-ERK activation in the me chanism by which NAC prevents neuronal death after loss of trophic sup port.