Hydrogen Peroxide Stimulates Transcription of C-jun in Vascular Smooth Muscle Cells: Role of Arachidonic Acid

We reported previously that hydrogen peroxide induces DNA synthesis in rat aortic smooth muscle (RASM) cells. In the present paper we studied the mechanism by which hydrogen peroxide induces c-jun mRNA, an early response gene whose activation is required for mitogen-stimulated cell growth. Hydrogen peroxide induced c-jun mRNA in growth-arrested RASM cells in a time dependent manner. This stimulation was significantly inhibited by mepacrine, a phospholipase A2 (PLA2) inhibitor. Arachidonic acid, a PLA2 product, also increased c-jun mRNA with a time course similar to that of hydrogen peroxide. The increases in c-jun mRNA induced by hydrogen peroxide and arachidonic acid were significantly reduced (55%) by down-regulation of protein kinase C with a phorbol ester. Furthermore, the effect of hydrogen peroxide on c-jun mRNA was also reduced by NDGA, an inhibitor of the lipoxygenase-cytochrome P450 mono-oxygenase system, suggesting that metabolism of arachidonic acid through this pathway is required for the induction of c-jun mRNA by oxidants. Both hydrogen peroxide and arachidonic acid significantly increased c-jun transcription as demonstrated by nuclear run-on assays. Together these observations suggest that: (1) the induction of c-jun mRNA by hydrogen peroxide is mediated by PLA2-dependent arachidonic acid release and metabolism through the lipoxygenase-cytochrome P450 mono-oxygenase system; (2) PKC appears to be involved in this signaling pathway and (3) the induction of c-jun mRNA by hydrogen peroxide in RASM cells is due to increased transcription.