title: Cyclooxygenase-2 expression and prostaglandin E2 production in response to acidic pH through OGR1 in a human osteoblastic cell line.
abstract: Acidosis has been shown to induce depletion of bone calcium from the body. This calcium release process is thought to be partially cell mediated. In an organ culture of bone, acidic pH has been shown to induce cyclooxygenase-2 (COX-2) induction and prostaglandin E(2) (PGE(2)) production, resulting in stimulation of bone calcium release. However, the molecular mechanisms whereby osteoblasts sense acidic circumstances and thereby induce COX-2 induction and PGE(2) production remain unknown. In this study, we used a human osteoblastic cell line (NHOst) to characterize cellular activities, including inositol phosphate production, intracellular Ca(2+) concentration ([Ca(2+)](i)), PGE(2) production, and COX-2 mRNA and protein expression, in response to extracellular acidification. Small interfering RNA (siRNA) specific to the OGR1 receptor and specific inhibitors for intracellular signaling pathways were used to characterize acidification-induced cellular activities. We found that extracellular acidic pH induced a transient increase in [Ca(2+)](i) and inositol phosphate production in the cells. Acidification also induced COX-2 induction, resulting in PGE(2) production. These proton-induced actions were markedly inhibited by siRNA targeted for the OGR1 receptor and the inhibitors for G(q/11) protein, phospholipase C, and protein kinase C. We conclude that the OGR1/G(q/11)/phospholipase C/protein kinase C pathway regulates osteoblastic COX-2 induction and subsequent PGE(2) production in response to acidic circumstances.
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tomura
authors.forename: Ju-Qiang
authors.initials: JQ
authors.lastname: Wang
authors.forename: Jin-Peng
authors.initials: JP
authors.lastname: Liu
authors.forename: Mayumi
authors.initials: M
authors.lastname: Komachi
authors.forename: Alatangaole
authors.initials: A
authors.lastname: Damirin
authors.forename: Chihiro
authors.initials: C
authors.lastname: Mogi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tobo
authors.forename: Hiromi
authors.initials: H
authors.lastname: Nochi
authors.forename: Koichi
authors.initials: K
authors.lastname: Tamoto
authors.forename: Doon-Soon
authors.initials: DS
authors.lastname: Im
authors.forename: Koichi
authors.initials: K
authors.lastname: Sato
authors.forename: Fumikazu
authors.initials: F
authors.lastname: Okajima
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D017931:DNA Primers; D015232:Dinoprostone / Q000096:biosynthesis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010006:Osteoblasts / Q000378:metabolism*; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; C486281:GPR68 protein, human; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; D051546:Cyclooxygenase 2; D015232:Dinoprostone