AHEART June 47/6

Muniyappa, Ranganath, Rui Xu, Jeffrey L. Ram, and James R. Sowers. Inhibition of Rho protein stimulates iNOS expression in rat vascular smooth muscle cells. Am J Physiol Heart Circ Physiol 278: H1762–H1768, 2000.— Inducible nitric oxide synthase (iNOS) in vascular smooth muscle cells (VSMCs) is upregulated in arterial injury and plays a role in regulating VSMC proliferation and restenosis. Inflammatory cytokines [e.g., interleukin-1b (IL-1b)] released during vascular injury induce iNOS. Small GTPbinding proteins of the Ras superfamily play a major role in IL-1b-dependent signaling pathways. In this study, we examined the role of Rho GTPases in regulating iNOS expression in VSMCs. Treatment of VSMCs with mevastatin, which inhibits isoprenylation of Rho and other small GTP-binding proteins, produced significantly higher amounts of IL-1bevoked NO and iNOS protein compared with control. Similarly, bacterial toxins [Toxin B from Clostridium difficile and C3 ADP-ribosyl transferase (C3) toxin from Clostridium botulinium] that specifically inactivate Rho proteins increased NOS products (NO and citrulline) and iNOS expression. Toxin B increased the activity of iNOS promoterreporter construct in VSMCs. Both toxins enhanced IL-1bstimulated iNOS expression and NO production. These data demonstrate for the first time that inhibition of Rho induces iNOS and suggest a role for Rho protein in IL-1b-stimulated NO production in VSMCs.