Role of constitutive nitric oxide synthase S-nitrosylation in Helicobacter pylori-induced gastric mucosal cell apoptosis: effect of ghrelin. Inflammopharmacology. 2010;18:233-240. [PMID: 20596895 DOI: 10.1007/s10787-010-0051-7]

TBL1XR1 induces cell proliferation and inhibit cell apoptosis by the PI3K/AKT pathway in pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest solid tumors. Identification of diagnostic and therapeutic biomarkers for PDAC is urgently needed. Transducin (β)-like 1 X-linked receptor 1 (TBL1XR1) has been linked to the progression of various human cancers. Nevertheless, the function and role of TBL1XR1 in pancreatic cancers are unclear.

AIM

To elucidate the function and potential mechanism of TBL1XR1 in the development of PDAC.

METHODS

Ninety patients with histologically-confirmed PDAC were included in this study. PDAC tumor samples and cell lines were used to determine the expression of TBL1XR1. CCK-8 assays and colony formation assays were carried out to assess PDAC cell viability. Flow cytometry was performed to measure the changes in the cell cycle and cell apoptosis. Changes in related protein expression were measured by western blot analysis. Animal analysis was conducted to confirm the impact of TBL1XR1 in vivo.

RESULTS

Patients with TBL1XR1-positive tumors had worse overall survival than those with TBL1XR1-negative tumors. Moreover, we found that TBL1XR1 strongly promoted PDAC cell proliferation and inhibited PDAC cell apoptosis. Moreover, knockdown of TBL1XR1 induced G0/G1 phase arrest. In vivo animal studies confirmed that TBL1XR1 accelerated tumor cell growth. The results of western blot analysis showed that TBL1XR1 might play a key role in regulating PDAC cell proliferation and apoptosis via the PI3K/AKT pathway.

CONCLUSION

TBL1XR1 promoted PDAC cell progression and might be an effective diagnostic and therapeutic marker for pancreatic cancer.

Role of LPS-elicited signaling in triggering gastric mucosal inflammatory responses to H. pylori: modulatory effect of ghrelin

Infection with Helicobacter pylori is a primary culprit in the etiology of gastric disease, and its cell-wall lipopolysaccharide (LPS) is recognized as a potent endotoxin responsible for triggering a pattern of the mucosal inflammatory responses. The engagement by the LPS of gastric mucosal Toll-like receptor 4 (TLR4) leads to initiation of signal transduction events characterized by the activation of mitogen-activated protein kinase (MAPK) cascade, induction of phosphoinositide-specific phospholipase C (PLC)/protein kinase C (PKC)/phosphatidylinositol 3-kinase (PI3K) pathway, and up-regulation in Src/Akt. These signaling events in turn exert their influence over H. pylori-elicited excessive generation of NO and PGE2 caused by the disturbances in nitric oxide synthase and cyclooxygenase isozyme systems, increase in epidermal growth factor receptor transactivation, and the induction in matrix metalloproteinase-9 (MMP-9) release. Interestingly, the extent of gastric mucosal inflammatory response to H. pylori is influenced by a peptide hormone, ghrelin, the action of which relays on the growth hormone secretagogue receptor type 1a (GHS-R1a)-mediated mobilization of G-protein dependent transduction pathways. Yet, the signals triggered by TLR-4 activation as well as those arising through GHS-R1a stimulation converge at MAPK and PLC/PKC/PI3K pathways that form a key integration node for proinflammatory signals generated by H. pylori LPS as well as for those involved in modulation of inflammation by ghrelin. Hence, therapeutic targeting these signals' convergence and integration node could provide a novel and attractive opportunities for developing more effective treatments of H. pylori-related gastric disease.

Ghrelin Prevents Cisplatin-Induced Testicular Damage by Facilitating Repair of DNA Double Strand Breaks Through Activation of p53 in Mice

Cisplatin administration induces DNA damage resulting in germ cell apoptosis and subsequent testicular atrophy. Although 50 percent of male cancer patients receiving cisplatin-based chemotherapy develop long-term secondary infertility, medical treatment to prevent spermatogenic failure after chemotherapy is not available. Under normal conditions, testicular p53 promotes cell cycle arrest, which allows time for DNA repair and reshuffling during meiosis. However, its role in the setting of cisplatin-induced infertility has not been studied. Ghrelin administration ameliorates the spermatogenic failure that follows cisplatin administration in mice, but the mechanisms mediating these effects have not been well established. The aim of the current study was to characterize the mechanisms of ghrelin and p53 action in the testis after cisplatin-induced testicular damage. Here we show that cisplatin induces germ cell damage through inhibition of p53-dependent DNA repair mechanisms involving gamma-H2AX and ataxia telangiectasia mutated protein kinase. As a result, testicular weight and sperm count and motility were decreased with an associated increase in sperm DNA damage. Ghrelin administration prevented these sequelae by restoring the normal expression of gamma-H2AX, ataxia telangiectasia mutated, and p53, which in turn allows repair of DNA double stranded breaks. In conclusion, these findings indicate that ghrelin has the potential to prevent or diminish infertility caused by cisplatin and other chemotherapeutic agents by restoring p53-dependent DNA repair mechanisms.

Ghrelin in gastrointestinal diseases

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHSR). Upon binding to its receptor, Ghrelin can produce a variety of biological effects, such as promoting the release of growth hormone and maintaining energy balance. Besides, it also promotes gastrointestinal motility, increases gastric acid secretion, and is involved in the genesis of tumors. This article reviews the role of Ghrelin in gastrointestinal system disease.

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

A peptide hormone, ghrelin, is recognized as an important modulator of gastric mucosal inflammatory responses to H. pylori through the regulation of nitric oxide synthase (NOS) system. As cSrc kinase plays a major role in transduction of signals that regulate the activity of NOS isozyme system, we investigated the influence of H. pylori LPS on the processes associated with Src activation in gastric mucosal cells. The LPS-induced drop in constitutive (c) cNOS activity and up-regulation in inducible (i) iNOS was associated with the suppression in cSrc kinase activity that was reflected in a decrease in its phosphorylation at Tyr⁴¹⁶. Further, the countering effect of ghrelin on the LPS-induced changes in cSrc activity and the extent of its phosphorylation was accompanied by a marked reduction in the activity of iNOS and an increase in cNOS activation through phosphorylation at Ser¹¹⁷⁹. Moreover, the effect of ghrelin on cSrc activation and its Tyr⁴¹⁶ phosphorylation was associated with the kinase S-nitrosylation that was susceptible to the blockage by cNOS inhibition. Our findings suggest that up-regulation in iNOS with H. pylori infection leads to disturbances in cNOS phosphorylation that exerts the detrimental effect on the processes of cSrc activation through cNOS-mediated S-nitrosylation. We also show that ghrelin attenuation of H. pylori-induced gastric mucosal inflammatory responses involves the enhancement in cSrc activation, elicited by the kinase S-nitrosylation and the increase in its phosphorylation at Tyr⁴¹⁶.

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

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.

Role of protease-activated receptor-2 on cell death and DNA fragmentation in Helicobacter pylori-infected gastric epithelial cells

Background

Helicobacter pylori (H. pylori) infection is associated with chronic gastritis, peptic ulceration and gastric carcinoma. Protease-activated receptor-2 (PAR-2), which is activated by trypsin, induced the activation of mitogen-activated protein kinases (MAPK), cell proliferation and apoptosis in several cells. Previously, we found that H. pylori induces the expression of PAR-2, which mediates the expression of adhesion molecules integrins in gastric epithelial cells. In the present study, the role of PAR-2 on H. pylori-induced cell death was investigated by determining cell viability, DNA fragmentation, and the activation of MAPK in gastric epithelial AGS cells.

Methods

AGS cells were cultured in the presence of H. pylori transfected with PAR-2 antisense (AS) oligonucleotide (ODN) or treated with a soybean trypsin inhibitor (SBTI). Viable cells and DNA fragmentation were determined by trypan blue exclusion assay and the amount of oligonucleosome-bound DNA, respectively. The activation of MAPK such as extracellular signal-regulated kinases (ERK), p38, and c-Jun N-terminal kinases (JNK), was assessed by Western blotting for phospho-specific forms of MAPK.

Results

H. pylori-induced cell death and DNA fragmentation augmented in the cells transfected with PAR-2 AS ODN or treated with SBTI. The activation of MAPK, induced by H. pylori, were suppressed by transfection with PAR-2 AS ODN or treatment with SBTI.

Conclusion

PAR-2, whose expression is induced by H. pylori, may prevent cell death and DNA fragmentation with the activation of MAPK in gastric epithelial cells.