MITOGENIC SIGNALING MEDIATED BY OXIDANTS IN RAS-TRANSFORMED FIBROBLASTS

NIH 3T3 fibroblasts stably transformed with a constitutively active is oform of p21(Ras), H-Ras(V12) (v-H-Ras or EJ-Ras), produced large amou nts of the reactive oxygen species superoxide (. O-2-). . O-2(-) produ ction was suppressed by the expression of dominant negative isoforms o f Ras or Rac1, as well as by treatment with a farnesyltransferase inhi bitor or with diphenylene iodonium, a flavoprotein inhibitor, The mito genic activity of cells expressing H-Ras(V12) was inhibited by treatme nt with the chemical antioxidant N-acetyl-L-cysteine. Mitogen-activate d protein kinase (MAPK) activity was decreased and c-Jun N-terminal ki nase (JNK) was not activated in H-Ras(V12)-transformed cells. Thus, H- Ras(V12)-induced transformation can lead to the production of . O-2(-) through one or more pathways involving a flavoprotein and Rac1. The i mplication of a reactive oxygen species, probably . O-2(-), as a media tor of Ras-induced cell cycle progression independent of MAPK and JNK suggests a possible mechanism for the effects of antioxidants against Ras-induced cellular transformation.