Involvement of Proton-Sensing TDAG8 in Extracellular Acidification-Induced Inhibition of Proinflammatory Cytokine Production in Peritoneal Macrophages

Abstract

Extracellular acidification inhibited LPS-induced TNF-α protein production, which was associated with an inhibition of TNF-α mRNA expression, in mouse peritoneal macrophages. The LPS-induced cytokine production was also inhibited by Gs protein-coupled receptor agonists prostaglandin E1 and isoproterenol. Among OGR1 family proton-sensing GTP-binding regulatory protein-coupled receptors, TDAG8, OGR1, and G2A are expressed in the cells. The inhibitory action by acidic pH on TNF-α production was significantly attenuated in macrophages from TDAG8Tp/Tp mice but not in those from OGR1geo/geo mice. Moreover, small interfering RNA specific to TDAG8, but not to G2A, clearly attenuated the acidification-induced inhibition of TNF-α production. On the other hand, the down-regulation or deficiency of TDAG8 hardly affected prostaglandin E1- or isoproterenol-induced actions. LPS-induced IL-6 production was also inhibited by extracellular acidification in a manner that was sensitive to TDAG8 expression. The acidic pH-induced inhibitory action on the cytokine production was significantly reversed either by a small interfering RNA specific to Gs proteins or by a protein kinase A (PKA)-specific inhibitor H89. Indeed, a PKA-specific cAMP derivative inhibited LPS-induced cytokine production. Moreover, acidification induced cAMP accumulation in a TDAG8-specific way. We conclude that TDAG8, at least partly, mediates the extracellular acidification-induced inhibition of proinflammatory cytokine production through the Gs protein/cAMP/PKA signaling pathway in mouse macrophages.

Emerging roles for the pH-sensing G protein-coupled receptors in response to acidotic stress

“…This cytokine inhibition was shown to occur through the G s -cAMP-protein kinase A (PKA) signaling pathway. 23,27 Treatment with dexamethasone, a potent glucocorticoid, increased GPR65 expression in peritoneal macrophages. Following dexamethasone treatment, there was an inhibition of TNF-α secretion in a manner dependent on increased expression of GPR65.…”

“…GPR4, GPR65, and GPR68 play roles in tumor cell apoptosis, proliferation, metastasis, angiogenesis, and immune cell function. 19,27,32,33,44,45,96,97 GPR4 has had conflicting reports in terms of tumor suppressing or promoting activities. One study demonstrated that GPR4 could act as a tumor metastasis suppressor, when overexpressed and activated by acidic pH in B16F10 melanoma cells, by impeding migration and invasion of tumor cells.…”

Targeting Tumor Microenvironments for Cancer Prevention and Therapy

“…TDAG8, as well as GPR4, exhibited transforming activities when ectopically overexpressed in immortalized cell lines (Sin et al, 2004). Furthermore, the proton-sensing GPCRs have been shown to regulate immune cell function and inflammatory responses (Ichimonji et al, 2010;Mogi et al, 2009;Onozawa et al, 2011). These observations suggest that the proton-sensing GPCRs may represent novel targets for cancer treatment, inflammation inhibition, and chemoprevention.…”

“…Carbonic anhydrases (CA), monocarboxylate transporters (MCT), vacuolar-type H + -ATPase proton pump (V-ATPase), and sodium/hydrogen exchangers (NHE) play important roles in cellular pH regulation (Izumi et al, 2003;Swietach et al, 2010;Webb et al, 2011). Furthermore, recent studies have shown that a family of protonsensing G protein-coupled receptors regulates the behavior of tumor cells, immune cells, and blood vessels (Ludwig et al, 2003;Mogi et al, 2009;Yang et al, 2007). Targeting these pH regulators may be utilized to kill cancer cells or to augment the effects of other anticancer agents.…”

Neonatal high-permeability pulmonary edema based on serial cytokine profiles and KL-6 in serum: case report

“…There are some reports of severe metabolic acidemia possibly having caused abnormal cytokinemia that led to permeability pulmonary edema 15,16) . However, the metabolic acidemia in the present neonate was mild and not so severe for his age.…”