title: Ectodomain shedding of pro-TGF-alpha is required for COX-2 induction and cell survival in renal medullary cells exposed to osmotic stress.
abstract: In the renal medulla, cyclooxygenase (COX)-2 is induced by osmotic stress as present in this kidney region during antidiuresis. Increasing evidence suggests that EGF receptor (EGFR) signaling is involved in this process. The aim of the present study was to examine the mechanisms responsible for COX-2 expression and PGE(2) production during hypertonic conditions and to identify potential autocrine/paracrine EGFR ligands. Immunohistochemisty and Western blot analysis revealed abundant expression of the pro-EGFR ligand pro-transforming growth factor (TGF)-alpha in renal medullary cells in vivo and in cultured Madin-Darby canine kidney cells. In Madin-Darby canine kidney cells, hypertonicity rapidly increased TNF-alpha converting enzyme (TACE)-dependent ectodomain shedding of pro-TGF-alpha; phosphorylation of EGFR, p38, and ERK1/2; expression of COX-2; and production of PGE(2). Conversely, TACE inhibition prevented TGF-alpha release; EGFR, p38, and ERK1/2 activation; and COX-2 expression. Furthermore, cell survival was reduced substantially, a response that could be reversed by the addition of PGE(2). Simultaneous addition of recombinant TGF-alpha during TACE inhibition restored EGFR and MAPK phosphorylation, COX-2 expression, PGE(2) production, and cell survival during osmotic stress. These results indicate that hypertonicity induces TACE-mediated ectodomain shedding of pro-TGF-alpha, which subsequently activates COX-2 expression in an autocrine/paracrine fashion, via EGFR and MAPKs. We conclude that tonicity-induced TGF-alpha release is required for COX-2 expression, PGE(2) synthesis, and survival of renal medullary cells during osmotic stress.
authors.affiliation: Department of Physiology, University of Munich, Munich, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Küper
authors.forename: Helmut
authors.initials: H
authors.lastname: Bartels
authors.forename: Maria-Luisa
authors.initials: ML
authors.lastname: Fraek
authors.forename: Franz X
authors.initials: FX
authors.lastname: Beck
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Neuhofer
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000072198:ADAM17 Protein; D000818:Animals; D019898:Autocrine Communication / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D015232:Dinoprostone / Q000096:biosynthesis; D004285:Dogs; D066246:ErbB Receptors / Q000378:metabolism*; D005786:Gene Expression Regulation; D054513:Group IV Phospholipases A2 / Q000378:metabolism*; D006982:Hypertonic Solutions; D007679:Kidney Medulla / Q000378:metabolism*; D008024:Ligands; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009997:Osmotic Pressure; D019899:Paracrine Communication / Q000502:physiology; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D017382:Reactive Oxygen Species / Q000378:metabolism; D016211:Transforming Growth Factor alpha / Q000378:metabolism*
chemical_list: D006982:Hypertonic Solutions; D008024:Ligands; D017382:Reactive Oxygen Species; D016211:Transforming Growth Factor alpha; D051546:Cyclooxygenase 2; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D054513:Group IV Phospholipases A2; D051722:ADAM Proteins; D000072198:ADAM17 Protein; D015232:Dinoprostone