Ghrelin suppression of Helicobacter pylori-induced S-nitrosylation-dependent Akt inactivation exerts modulatory influence on gastric mucin synthesis

Abstract

Loss of mucus coat integrity and the impairment in its mucin component as well as the disturbance in nitric oxide (NO) generation are well-recognized features of gastric disease associated with H. pylori infection. As ghrelin plays a major role in the regulation of nitric oxide synthase system, we investigated the influence of this hormone on H. pylori LPS-induced interference with gastric mucin synthesis. The results revealed that the LPS-induced impairment in mucin synthesis and accompanied induction in inducible nitric oxide synthase (iNOS) expression, were associated with the suppression in Akt kinase activity and the impairment in constitutive nitric oxide synthase (cNOS) phosphorylation. The LPS effect on Akt inactivation was manifested in the kinase protein S-nitrosylation and a decrease in its phosphorylation at Ser(473). Further, we show that the countering effect of ghrelin, on the LPS-induced impairment in mucin synthesis was reflected in the suppression of iNOS and the increase in Akt activation, associated with the loss in S-nitrosylation and the increase in phosphorylation, as well as cNOS activation through phosphorylation. Our findings demonstrate that up-regulation in iNOS with H. pylori infection and subsequent Akt kinase inactivation through S-nitrosylation exerts the detrimental effect on the processes dependent on Akt activation, including that of cNOS activation and mucin synthesis. We also show that ghrelin protection against H. pylori-induced impairment in mucin synthesis is intimately linked to the events of Akt activation and reflected in a decrease in the kinase S-nitrosylation and the increase in its phosphorylation.

Ghrelin-induced cSrc activation through constitutive nitric oxide synthase-dependent S-nitrosylation in modulation of salivary gland acinar cell inflammatory responses to <i>Porphyromonas gingivalis</i>

“…Our assertion is further supported by the literature evidence indicating that ascorbate treatment both increases cNOS activity and reduces the enzyme protein Snitrosylation, and that the countering effect of ghrelin on the LPS-induced impairment in cNOS activity is associated with the loss of the enzyme protein S-nitrosylation and the increase in its phosphorylation at Ser 1179 [5,13,32]. Indeed, the accumulating evidence demonstrates that protein modification through targeted S-nitrosylation at the critical cysteine, with the participation of both constitutive and inducible forms of NOS system, is a post-translational event of significance to the regulation of signal transduction pathways by NO [4][5][6][13][14][15]17,32,33].…”

“…Also, as up-regulation in iNOS activity in response to LPS involves transcriptional factor NF-B transactivation of iNOS gene for the induction in the enzyme protein [30][31][32], we analyzed the influence of ghrelin on the acinar cell iNOS protein expression. We found that P. gingivalis LPS induction in iNOS activity was associated with the increase in the enzyme protein expression, while the countering effect of ghrelin, was reflected in a marked inhibition of the iNOS protein expression that was further suppressed in the presence of Src kinase inhibitor, PP2.…”

“…Indeed, the accumulating evidence demonstrates that protein modification through targeted S-nitrosylation at the critical cysteine, with the participation of both constitutive and inducible forms of NOS system, is a post-translational event of significance to the regulation of signal transduction pathways by NO [4][5][6][13][14][15]17,32,33]. Moreover, NO-induced Src S-nitrosylation at the critical cysteine residues located within the C-terminal region of its catalytic domain has been reported to promote cSrc activation through autophosphorylation at Tyr 416 [13][14][15].…”

Role of ghrelin-induced cSrc activation in modulation of gastric mucosal inflammatory responses to Helicobacter pylori

“…Indeed, we found that, in keeping with the documented involvement of cSrc in cNOS activation through phosphorylation (Haynes et al 2003;Xu et al 2008;Slomiany and Slomiany 2010b), the induced up-regulation in cNOS activity by ghrelin was reflected in the increase of enzyme protein phosphorylation at Ser 1179 . Moreover, we have shown earlier that the increase in iNOS activity in response to H. pylori LPS was associated with the induction in the enzyme protein expression, while countering effect of ghrelin, like that of NF-jB inhibitor, PPM-18, was reflected in a marked inhibition of the iNOS protein expression (Slomiany and Slomiany 2011).…”

Circadian phase‐dependent effect of nitric oxide on L‐type voltage‐gated calcium channels in avian cone photoreceptors

“…If inactivation of Akt is caused by the direct S‐nitrosylation from NO (Yasukawa et al . ; Slomiany and Slomiany ), 8‐Br‐cGMP should not be able to mimic the effect of SNAP to inhibit pAkt (Martinez‐Ruiz et al . ).…”