title: Hypertonic induction of COX-2 expression in renal medullary epithelial cells requires transactivation of the EGFR.
abstract: Hypertonic stress increases expression of cyclooxygenase-2 (COX-2) in renal medullary epithelial and interstitial cells. Because hypertonic COX-2 expression is, in part, sensitive to inhibition of the ERK MAPK, an effector of activated receptor tyrosine kinases such as the EGF receptor, we investigated a role for this receptor in signaling to COX-2 expression. Hypertonic stress increased COX-2 expression at the mRNA and protein levels at 6 and 24 h of hypertonic treatment. Two potent, specific inhibitors of the EGF receptor kinase, AG-1478 and PD-153035, abrogated this effect. These inhibitors also blocked the ability of hypertonic stress to increase PGE2 release; in addition, they partially blocked tonicity-dependent phosphorylation of ERK but not of the related MAPKs, JNK or p38. Pharmacological inhibition of ERK activation partially blocked tonicity-dependent COX-2 expression. Hypertonic induction of COX-2 was likely transcriptionally mediated, as NaCl stress increased luciferase reporter gene activity under control of the human COX-2 promoter, and this effect was also sensitive to inhibition of the EGF receptor kinase. Metalloproteinase action is required for transactivation of the EGF receptor. Pharmacological inhibition of metalloproteinase function blocked tonicity-inducible COX-2 expression. Furthermore, the effect of hypertonicity on COX-2 expression was also evident in the EGF-responsive Madin-Darby canine kidney and 3T3 cell lines but was virtually absent from the EGF-unresponsive (and EGF receptor null) Chinese hamster-derived CHO cell line. Taken together, these data indicate that hypertonicity-dependent COX-2 expression in medullary epithelial cells requires transactivation of the EGF receptor and, potentially, ectodomain cleavage of an EGF receptor ligand.
authors.affiliation: Division of Nephrology and Hypertension, Oregon Health and Science University and the Portland Veterans Affairs Medical Center, Portland, OR 97201, USA.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Tian
authors.forename: Cynthia
authors.initials: C
authors.lastname: Tai
authors.forename: David M
authors.initials: DM
authors.lastname: Cohen
mesh_terms: D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D051546:Cyclooxygenase 2; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D066246:ErbB Receptors / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D007527:Isoenzymes / Q000235:genetics*; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014882:Water-Electrolyte Balance / Q000235:genetics*
chemical_list: D002070:Butadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007527:Isoenzymes; D009570:Nitriles; D012333:RNA, Messenger; D012462:Saline Solution, Hypertonic; C113580:U 0126; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D066246:ErbB Receptors; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one