Although the inflammatory cytokine interleukin-1 (IL-)is an important regulator of gene expression in vascular smooth muscle (VSM), the signal transduction pathways leading to transcriptional activation upon IL-1stimulation are poorly understood. Recent studies have implicated IL-1-mediated ERK1/2 activation in the upregulation of type II nitric oxide synthase (iNOS) in VSM. In the present study, we report that these events are mediated in a phospholipase C- and protein kinase C-dependent manner utilizing a signaling mechanism independent of p21^ras and Raf1 activation. Stimulation of rat aortic VSM cells with IL-1activated phospholipase C (PLC) and pharmacological inhibition of PLC attenuated IL-1-induced ERK1/2 activation and subsequent iNOS expression. Stimulation with IL-1 activated PKC and , which was blocked using the PLC inhibitor U-73122. Pharmacological studies using isoform specific PKC inhibitors and adenoviral overexpression of constitutively active PKC (caPKC) indicated that ERK 1/2 activation was PKC independent and PKCdependent. Similarly, adenoviral overexpression of caPKCenhanced iNOS expression. IL-1stimulation did not induce either p21^ras (Ras) nor Raf1 activity. The absence of a functional role for Ras and Raf1 related to ERK1/2 activation and iNOS expression was further confirmed by adenoviral overexpression of dominant/negative Ras (RasN17) and treatment with the Raf1 inhibitor GW5074. Taken together, we outlined a novel transduction pathway implicating PKCas a critical component of the IL-1 dependent activation of ERK in VSM cell.