title: Bone morphogenetic protein-7 inhibits proximal tubular epithelial cell Smad3 signaling via increased SnoN expression.
abstract: Bone morphogenetic protein-7 (BMP-7) improves outcome in animal models of fibrotic renal disease by opposing transforming growth factor beta1 (TGF-beta)-dependent fibrosis. However, the underlying mechanisms remain obscure. Here, we studied the effect of BMP-7 on response to TGF-beta in the proximal tubular cell line HK-2 (PTC). BMP-7 specifically limited Smad3 but not Smad2 signaling. BMP-7 did not inhibit Smad3 phosphorylation or nuclear accumulation, nor did BMP-7 alter phosphorylated Smad3 dephosphorylation or degradation. However, BMP-7 treatment reduced Smad3 DNA binding to a consensus Smad binding element probe, and chromatin immunoprecipitation showed reduced Smad3 binding to the plasminogen activator inhibitor-1 promoter in PTCs treated with BMP-7 and TGF-beta compared with TGF-beta alone. Degradation of the transcriptional repressor SnoN has recently been shown to be necessary for Smad3 (but not Smad2) signaling. SnoN expression was transiently lost in PTCs after TGF-beta stimulation, but BMP-7 prevented this. Furthermore, BMP-7 had no effect on Smad3 signaling after siRNA-mediated SnoN knockdown, whereas prevention of SnoN degradation with the proteasome inhibitor MG132 reproduced the inhibitory action of BMP-7 on Smad3 signaling. We conclude that BMP-7 prevents TGF-beta-mediated loss of the transcriptional repressor SnoN and hence specifically limits Smad3 DNA binding, altering the balance of transcriptional responses to TGF-beta in PTCs. These results provide an important mechanistic insight into a key regulator of TGF-beta signaling.
authors.affiliation: Institute of Nephrology, School of Medicine, Cardiff University, Heath Park Campus, Cardiff, UK CF14 4XN.
authors.forename: Dong Dong
authors.initials: DD
authors.lastname: Luo
authors.forename: Aled
authors.initials: A
authors.lastname: Phillips
authors.forename: Donald
authors.initials: D
authors.lastname: Fraser
mesh_terms: D055419:Bone Morphogenetic Protein 7 / Q000494:pharmacology*; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D007976:Leupeptins / Q000494:pharmacology; D008954:Models, Biological; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
chemical_list: D055419:Bone Morphogenetic Protein 7; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins; D011518:Proto-Oncogene Proteins; C060615:SKIL protein, human; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D004247:DNA; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde