Journal
BIOCHEMICAL JOURNAL
Volume 397, Issue -, Pages 329-336Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20052002
Keywords
extracellular-signal-regulated kinase (ERK); H-Ras; nitric oxide synthase (NOS); S-nitrosylation
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Funding
- NCI NIH HHS [CA-10529] Funding Source: Medline
- NIBIB NIH HHS [P41 EB002034, EB-2034] Funding Source: Medline
- NIGMS NIH HHS [R25 GM055036, R25-GM55036] Funding Source: Medline
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nNOS (neuronal nitric oxide synthase) is a constitutively expressed enzyme responsible for the production of NO center dot from L-arginine and O-2. NO center dot acts as both an intra- and an inter-cellular messenger that mediates a variety of signalling pathways. Previous studies from our laboratory have demonstrated that nNOS production of NO center dot blocks Ca2+-ionophore-induced activation of ERK1/2 (extracellular-signal-regulated kinase 1/2) of the mitogen-activated protein kinases through a mechanism involving Ras G-proteins and Raf-1 kinase. Herein we describe a mechanism by which NO center dot blocks Ca2+-mediated ERK1/2 activity through direct modification of H-Ras. Ca2+-mediated ERK1/2 activation in NO-producing cells could be restored by exogenous expression of constitutively active mitogen-activated protein kinase kinase 1. In contrast, exogenous expression of constitutively active mutants of Raf-1 and H-Ras only partially restored ERK1/2 activity, by 50% and 10% respectively. On the basis of these findings, we focused on NO-mediated mechanisms of H-Ras inhibition. Assays for GTP loading and H-Ras interactions with the Ras-binding domain on Raf-1 demonstrated a decrease in H-Ras activity in the presence of NO center dot. We demonstrate that S-nitrosylation of H-Ras occurs in nNOS-expressing cells activated with Ca2+ ionophore. Mutation of a putative nitrosylation site at Cys(118) inhibited S-nitrosylation and restored ERK1/2 activity by constitutively active H-Ras even in the presence of NO center dot. These findings indicate that intracellular generation of NO center dot by nNOS leads to S-nitrosylation of H-Ras, which interferes with Raf-1 activation and propagation of signalling through ERK1/2.
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