Modulation of gastric mucosal inflammatory responses to <i>Helicobacter pylori</i> by ghrelin: Role of cNOS-dependent IKK-<i>β</i> S-nitrosylation in the regulation of COX-2 activation

Abstract

Disturbances in nitric oxide synthase (NOS) and cyclooxygenase (COX) isozyme systems, manifested by the excessive NO and prostaglandin (PGE 2 ) generation, are well-recognized features of gastric mucosal inflammatory responses to H. pylori infection. In this study, we report that H. pylori LPS-induced enhancement in gastric mucosal inducible (i) iNOS expression and COX-2 activation was accompanied by the impairment in constitutive (c) cNOS phosphorylation, up-regulation in the inhibitory κ B kinase- β (IKK β ) activation and the increase in the transcriptional factor, NF- κ B, nuclear translocation. Further, we show that abrogation of cNOS control over NF- κ B activation has lead to induction of iNOS expression and COX-2 activation through S-nitrosylation. Moreover, we demonstrate that the modulatory effect of peptide hormone, ghrelin, on the LPS-induced changes was reflected in the increase in Src/Akt-dependent cNOS activation through phosphorylation and the suppression of IKK- β activity through cNOS-mediated IKK- β protein S-nitrosylation. As a result, ghrelin exerted the inhibitory effect on NF- κ B nuclear translocation, thus causing the repression of iNOS gene induction and the inhibition in COX-2 activation through iNOS-dependent S-nitrosylation. Our findings point to cNOS activation as a pivotal element in the signaling cascade by which ghrelin exerts modulatory control over proinflammatory events triggered in gastric mucosa by H. pylori infection.