title: Cyclooxygenase-2-dependent phosphorylation of the pro-apoptotic protein Bad inhibits tonicity-induced apoptosis in renal medullary cells.
abstract: During antidiuresis, cell survival in the renal medulla requires cyclooxygenase-2 (COX-2) activity. We have recently found that prostaglandin E2 (PGE2) promotes cell survival by phosphorylation and, hence, inactivation of the pro-apoptotic protein Bad during hypertonic stress in Madin-Darby canine kidney (MDCK) cells in vitro. Here we determine the role of COX-2-derived PGE(2) on phosphorylation of Bad and medullary apoptosis in vivo using COX-2-deficient mice. Both wild-type and COX-2-knockout mice constitutively expressed Bad in tubular epithelial cells of the renal medulla. Dehydration caused a robust increase in papillary COX-2 expression, PGE2 excretion, and Bad phosphorylation in wild-type, but not in the knockout mice. The abundance of cleaved caspase-3, a marker of apoptosis, was significantly higher in papillary homogenates, especially in tubular epithelial cells of the knockout mice. Knockdown of Bad in MDCK cells decreased tonicity-induced caspase-3 activation. Furthermore, the addition of PGE2 to cells with knockdown of Bad had no effect on caspase-3 activation; however, PGE2 caused phosphorylation of Bad and substantially improved cell survival in mock-transfected cells. Thus, tonicity-induced COX-2 expression and PGE2 synthesis in the renal medulla entails phosphorylation and inactivation of the pro-apoptotic protein Bad, thereby counteracting apoptosis in renal medullary epithelial cells.
authors.affiliation: Department of Physiology, University of Munich, Munich, Germany. Electronic address: Christoph.Kueper@lrz.uni-muenchen.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Küper
authors.affiliation: Department of Anatomy, University of Munich, Munich, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Bartels
authors.affiliation: Department of Physiology, University of Munich, Munich, Germany.
authors.forename: Franz-X
authors.initials: FX
authors.lastname: Beck
authors.affiliation: Department of Physiology, University of Munich, Munich, Germany; Department of Nephrology, University of Munich, Munich, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Neuhofer
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D003681:Dehydration / Q000201:enzymology / Q000473:pathology; D015232:Dinoprostone / Q000378:metabolism; D004195:Disease Models, Animal; D004285:Dogs; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D007679:Kidney Medulla / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009997:Osmotic Pressure; D010766:Phosphorylation; D034622:RNA Interference; D012462:Saline Solution, Hypertonic; D051025:bcl-Associated Death Protein / Q000378:metabolism*
chemical_list: C494820:Bad protein, mouse; D052246:Cyclooxygenase 2 Inhibitors; D012462:Saline Solution, Hypertonic; D051025:bcl-Associated Death Protein; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; C505409:Casp3 protein, mouse; D053148:Caspase 3; D015232:Dinoprostone