title: Extracellular calcium-sensing receptor activation induces vitamin D receptor levels in proximal kidney HK-2G cells by a mechanism that requires phosphorylation of p38alpha MAPK.
abstract: In hypocalcaemia, elevated parathyroid hormone transitorily down-regulates the kidney vitamin D receptor, which returns to normal levels with the rise in serum extracellular calcium [Ca(2+)](e). In this study, we investigated the mechanism that underlies VDR increase in kidney in association with elevated [Ca(2+)](e). Examination of MAP kinase signals in a proximal tubule human kidney (HK-2G) epithelial cell line showed that treatment of [Ca(2+)](e) in the culture medium elevated phosphorylation of both ERK and p38 MAPKs. Blockade of p38 phosphorylation with SB203580 or SB202190 in turn abolished [Ca(2+)](e)-mediated VDR protein increase, while treatment with PD98059 and U0126, specifically blocked ERK phosphorylation, but had no effect on VDR stimulation by [Ca(2+)](e). Furthermore, SB203580 treatment potently repressed [Ca(2+)](e)-mediated activation of VDR promoter. We also demonstrate that si-RNA knock down of p38alpha completely diminished high [Ca(2+)](e)-mediated VDR induction. Direct CaSR involvement was demonstrated by using an si-RNA of CaSR that impeded [Ca(2+)](e)-mediated induction of VDR. In conclusion, a high extracellular [Ca(2+)](e) concentration in the physiological range is capable of directly increasing renal proximal VDR expression, and the induction mechanism requires activation of the CaSR and signal mediation by the p38alpha MAP kinase pathway.
authors.affiliation: Department of Orthopaedic Surgery, Virginia Commonwealth University, Richmond, Virginia 23298-0164.
authors.forename: Aparna
authors.initials: A
authors.lastname: Maiti
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0164.
authors.forename: Nitai C
authors.initials: NC
authors.lastname: Hait
authors.affiliation: Department of Orthopaedic Surgery, Virginia Commonwealth University, Richmond, Virginia 23298-0164; Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298-0164. Electronic address: mjbeckma@vcu.edu.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Beckman
mesh_terms: D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D005110:Extracellular Space / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D047468:Immunoprecipitation; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D018167:Receptors, Calcitriol / Q000378:metabolism*; D044169:Receptors, Calcium-Sensing / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D002070:Butadienes; D005419:Flavonoids; D007093:Imidazoles; D009570:Nitriles; D011725:Pyridines; D034741:RNA, Small Interfering; D018167:Receptors, Calcitriol; D044169:Receptors, Calcium-Sensing; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium