Effect of pertussis toxin and herbimycin A on proteinase-activated receptor 2-mediated cyclooxygenase 2 expression in Helicobacter pylori-infected gastric epithelial AGS cells

The PAR2 inhibitor I-287 selectively targets Gαq and Gα12/13 signaling and has anti-inflammatory effects

Protease-activated receptor-2 (PAR2) is involved in inflammatory responses and pain, therefore representing a promising therapeutic target for the treatment of immune-mediated inflammatory diseases. However, as for other GPCRs, PAR2 can activate multiple signaling pathways and those involved in inflammatory responses remain poorly defined. Here, we describe a new selective and potent PAR2 inhibitor (I-287) that shows functional selectivity by acting as a negative allosteric regulator on Gα_q and Gα_12/13 activity and their downstream effectors, while having no effect on G_i/o signaling and βarrestin2 engagement. Such selective inhibition of only a subset of the pathways engaged by PAR2 was found to be sufficient to block inflammation in vivo. In addition to unraveling the PAR2 signaling pathways involved in the pro-inflammatory response, our study opens the path toward the development of new functionally selective drugs with reduced liabilities that could arise from blocking all the signaling activities controlled by the receptor.

Avet et al. characterize I-287, an inhibitor to protease-activated receptor 2 using BRET-assays. They find that I-287 selectively inhibits Gα_q and Gα_12/13 without affecting the activation of G_i/o or the recruitment of βarrestin2 and that it blocks inflammation in vitro and in vivo.

Proteinase activated-receptors-associated signaling in the control of gastric cancer

Gastric cancer (GC) is the fourth most common cancer in the world and the second cause of cancer-related death. Gastric carcinogenesis is a multifactorial process, in which environmental and genetic factors interact to activate multiple intracellular signals thus leading to uncontrolled growth and survival of GC cells. One such a pathway is regulated by proteinase activated-receptors (PARs), seven transmembrane-spanning domain G protein-coupled receptors, which comprise four receptors (i.e., PAR-1, PAR-2, PAR-3, and PAR-4) activated by various proteases. Both PAR-1 and PAR-2 are over-expressed on GC cells and their activation triggers and/or amplifies intracellular pathways, which sustain gastric carcinogenesis. There is also evidence that expression of either PAR-1 or PAR-2 correlates with depth of wall invasion and metastatic dissemination and inversely with the overall survival of patients. Consistently, data emerging from experimental models of GC suggest that both these receptors can be important targets for therapeutic interventions in GC patients. In contrast, PAR-4 levels are down-regulated in GC and correlate inversely with the aggressiveness of GC, thus suggesting a negative role of this receptor in the control of GC. In this article we review the available data on the expression and role of PARs in GC and discuss whether manipulation of PAR-driven signals may be useful for interfering with GC cell behavior.

The phenyl-thiophenyl propenone RK-I-123 reduces the levels of reactive oxygen species and suppresses the activation of NF-κB and AP-1 and IL-8 expression in Helicobacter pylori-infected gastric epithelial AGS cells

OBJECTIVE

To investigate whether the phenyl-thiophenyl propenone RK-I-123 suppresses interleukin-8 (IL-8) expression and activation of mitogen-activated protein kinases (MAPKs) and transcription factors (nuclear factor-κB [NF-κB] and activator protein-1 [AP-1]) by reducing reactive oxygen species (ROS) levels in Helicobacter pylori-infected gastric epithelial cells.

MATERIAL

Helicobacter pylori in Korean isolates, human gastric epithelial AGS cells.

TREATMENT

AGS cells pretreated with or without RK-I-123 were cultured in the presence of H. pylori at a bacterium/cell ratio of 300:1.

METHODS

Reactive oxygen species and IL-8 levels were determined by dichlorofluorescein fluorescence and enzyme-linked immunosorbent assay. The IL-8 mRNA expression was analyzed by the real-time reverse transcription-polymerase chain reaction (RT-PCR). The MAPK and IκBα levels were determined by western blotting. The activation of NF-κB and AP-1 was determined by the electrophoretic mobility shift assay.

RESULTS

Helicobacter pylori induced an increase in ROS and IL-8 expression and activation of MAPKs and transcription factors (NF-κB and AP-1) together with the degradation of IκBα in AGS cells, all of which were inhibited by RK-I-123.

CONCLUSIONS

The RK-I-123 suppressed the H. pylori-induced IL-8 expression and activation of MAPKs, NF-κB, and AP-1 by reducing ROS levels in AGS cells. The RK-I-123 may be a potential candidate for the treatment of H. pylori-induced gastric inflammation.