title: Urea and hypertonicity increase expression of heme oxygenase-1 in murine renal medullary cells.
abstract: Epithelial cells derived from the mammalian kidney medulla are responsive to urea at the levels of signal transduction and gene regulation. Hybridization of RNA harvested from control- and urea-treated murine inner medullary collecting duct (mIMCD3) cells with a cDNA expression array encoding stress-responsive genes suggested that heme oxygenase (HO)-1 mRNA was upregulated by urea. RNase protection assay confirmed this upregulation; hypertonicity also increased HO-1 mRNA expression but neither hypertonic NaCl nor urea were effective in the nonrenal 3T3 cell line. The effect on HO-1 expression appeared to be transcriptionally mediated on the basis of mRNA half-life studies and reporter gene analyses using the promoters of both human and chicken HO-1. Although urea signaling resembles that of heavy metal signaling in other contexts, the effect of urea on HO-1 transcription was independent of the cadmium response element in this promoter. Urea-inducible HO-1 expression was sensitive to antioxidants but not to scavengers of nitric oxide. Urea also upregulated HO-1 protein expression and pharmacological inhibition of HO-1 action with zinc protoporphyrin-sensitized mIMCD3 cells to the adverse effects of hypertonicity but not to urea. Coupled with the prior observation of others that HO-1 expression increases along the renal corticomedullary gradient, these data suggest that HO-1 expression may comprise an element of the adaptive response to hypertonicity and/or urea in renal epithelial cells.
authors.affiliation: Division of Nephrology, Oregon Health Sciences University, Portland, Oregon 97201, USA.
authors.forename: W
authors.initials: W
authors.lastname: Tian
authors.forename: H L
authors.initials: HL
authors.lastname: Bonkovsky
authors.forename: S
authors.initials: S
authors.lastname: Shibahara
authors.forename: D M
authors.initials: DM
authors.lastname: Cohen
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002460:Cell Line; D002645:Chickens; D005452:Fluoresceins / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D006207:Half-Life; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics* / Q000378:metabolism; D051547:Heme Oxygenase-1; D006801:Humans; D015151:Immunoblotting; D007679:Kidney Medulla / Q000201:enzymology*; D008565:Membrane Proteins; D051379:Mice; D018384:Oxidative Stress; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D014162:Transfection; D014508:Urea / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D005452:Fluoresceins; D008565:Membrane Proteins; D012333:RNA, Messenger; D012462:Saline Solution, Hypertonic; D014508:Urea; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse; D001616:beta-Galactosidase; C007740:fluorexon