PKC-δ mediates activation of ERK1/2 and induction of iNOS by IL-1β in vascular smooth muscle cells

Although the inflammatory cytokine interleukin-1 beta (IL-beta) is an important regulator of gene expression in vascular smooth muscle (VSM), the signal transduction pathways leading to transcriptional activation upon IL-1 beta stimulation are poorly understood. Recent studies have implicated IL-1 beta-mediated ERK1/2 activation in the upregulation of type II nitric oxide synthase (iNOS) in VSM. We report that these events are mediated in a phospholipase C (PLC)- and protein kinase C (PKC)- dependent manner utilizing a signaling mechanism independent of p21(ras) (Ras) and Raf1 activation. Stimulation of rat aortic VSM cells with IL-1 beta activated PLC-gamma and pharmacological inhibition of PLC attenuated IL-1 beta-induced ERK1/2 activation and subsequent iNOS expression. Stimulation with IL-1 beta activated PKC-alpha and -delta, which was blocked using the PLC inhibitor U-73122. Pharmacological studies using isoform-specific PKC inhibitors and adenoviral overexpression of constitutively active PKC-delta indicated that ERK1/2 activation was PKC-alpha independent and PKC-delta dependent. Similarly, adenoviral overexpression of constitutively activated PKC-delta enhanced iNOS expression. IL-1 beta stimulation did not induce either Ras or 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 and treatment with the Raf1 inhibitor GW5074. Taken together, we have outlined a novel transduction pathway implicating PKC-delta as a critical component of the IL-1-dependent activation of ERK in VSM cells.