title: Cross-talk between ERK MAP kinase and Smad signaling pathways enhances TGF-beta-dependent responses in human mesangial cells.
abstract: Transforming growth factor beta (TGF-beta) stimulates renal cell fibrogenesis by a poorly understood mechanism. Previously, we suggested a synergy between TGF-beta1 activated extracellular signal-regulated kinase (ERK) and Smad signaling in collagen production by human glomerular mesangial cells. In a heterologous DNA binding transcription assay, biochemical or dominant-negative ERK blockade reduced TGF-beta1 induced Smad3 activity. Total serine phosphorylation of Smad2/3, but not phosphorylation of the C-terminal SS(P)XS(P) motif, was decreased by pretreatment with the MEK/ERK inhibitors, PD98059 (10 microM) or U0126 (25 microM). This effect was not seen in the mouse mammary epithelial NMuMG cell line, indicating that ERK-dependent activation of Smad2/3 occurs only in certain cell types. TGF-beta stimulated phosphorylation of an expressed Smad3A construct, with a mutated C-terminal SS(P)XS(P) motif, was reduced by a MEK/ERK inhibitor. In contrast, MEK/ERK inhibition did not affect phosphorylation of a Smad3 construct mutated at consensus phosphorylation sites in the linker region (Smad3EPSM). Constitutively active MEK (caMEK) induced alpha2(I) collagen promoter activity, an effect blocked by co-transfected Smad3EPSM, but not Smad3A. The effects of caMEK and TGF-beta1 on collagen promoter activity were additive. These results indicate that ERK-dependent R-Smad linker region phosphorylation enhances collagen I synthesis and imply positive cross talk between the ERK and Smad pathways in human mesangial cells.
authors.affiliation: Department of Pediatrics, The Feinberg School of Medicine, Northwestern University, W-140, Pediatrics, 303 E Chicago Ave., Ward 12-112, Chicago, Illinois 60611-3008, USA. hayashida@northwestern.edu
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hayashida
authors.forename: Mark
authors.initials: M
authors.lastname: Decaestecker
authors.forename: H William
authors.initials: HW
authors.lastname: Schnaper
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D012694:Serine; D003094:Collagen; D020928:Mitogen-Activated Protein Kinases