title: Smad7-dependent regulation of heme oxygenase-1 by transforming growth factor-beta in human renal epithelial cells.
abstract: Heme oxygenase-1 (HO-1), a 32-kDa microsomal enzyme, is induced as a beneficial and adaptive response in cells/tissues exposed to oxidative stress. Transforming growth factor-beta1 (TGF-beta1) is a regulatory cytokine that has been implicated in a variety of renal diseases where it promotes extracellular matrix deposition and proinflammatory events. We hypothesize that the release of TGF-beta1 via autocrine and/or paracrine pathways may induce HO-1 and serve as a protective response in renal injury. To understand the molecular mechanism of HO-1 induction by TGF-beta1, we exposed confluent human renal proximal tubule cells to TGF-beta1 and observed a significant induction of HO-1 mRNA at 4 h with a maximal induction at 8 h. This induction was accompanied by increased expression of HO-1 protein. TGF-beta1 treatment in conjunction with actinomycin D or cycloheximide demonstrated that induction of HO-1 mRNA requires de novo transcription and, in part, protein synthesis. Exposure to TGF-beta1 resulted in marked induction of Smad7 mRNA with no effect on Smad6 expression. Overexpression of Smad7, but not Smad6, inhibited TGF-beta1-mediated induction of endogenous HO-1 gene expression. We speculate that the induction of HO-1 in the kidney is an adaptive response to the inflammatory effects of TGF-beta1 and manipulations of the Smad pathway to alter HO-1 expression may serve as a potential therapeutic target.
authors.affiliation: Department of Medicine, Division of Nephrology, Hypertension and Transplantation, Department of Pediatrics, Department of Neuroscience, University of Florida, Gainesville, Florida 32610, USA.
authors.forename: N
authors.initials: N
authors.lastname: Hill-Kapturczak
authors.forename: L
authors.initials: L
authors.lastname: Truong
authors.forename: V
authors.initials: V
authors.lastname: Thamilselvan
authors.forename: G A
authors.initials: GA
authors.lastname: Visner
authors.forename: H S
authors.initials: HS
authors.lastname: Nick
authors.forename: A
authors.initials: A
authors.lastname: Agarwal
mesh_terms: D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006419:Heme Oxygenase (Decyclizing) / Q000096:biosynthesis* / Q000235:genetics; D051547:Heme Oxygenase-1; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000201:enzymology*; D008565:Membrane Proteins; D012333:RNA, Messenger / Q000032:analysis; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; C497802:SMAD6 protein, human; C497806:SMAD7 protein, human; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1