title: Transforming growth factor-beta1 potentiates renal tubular epithelial cell death by a mechanism independent of Smad signaling.
abstract: Tubular atrophy resulting from epithelial cell loss is one of the characteristic features in the development of chronic renal interstitial fibrosis. Although the trigger(s) and mechanism for tubular cell loss remain undefined, the hyperactive transforming growth factor (TGF)-beta1 signaling has long been suspected to play an active role. Here we demonstrate that although TGF-beta1 did not induce cell death per se, it dramatically potentiated renal tubular cell apoptosis initiated by other death cues in vitro. Pre-incubation of human kidney epithelial cells (HKC) with TGF-beta1 markedly promoted staurosporine-induced cell death in a time- and dose-dependent manner. TGF-beta1 dramatically accelerated the cleavage and activation of pro-caspase-9, but not pro-caspase-8, in HKC cells. This event was followed by an accelerated activation of pro-caspase-3. To elucidate the mechanism underlying TGF-beta1 promotion of tubular cell death, we investigated the signaling pathways activated by TGF-beta1. Both Smad-2 and p38 mitogen-activated protein (MAP) kinase were rapidly activated by TGF-beta1, as demonstrated by the early induction of phosphorylated Smad-2 and p38 MAP kinase, respectively. We found that overexpression of inhibitory Smad-7 completely abolished Smad-2 phosphorylation and activation induced by TGF-beta1 but did not inhibit TGF-beta1-induced apoptosis. However, suppression of p38 MAP kinase with chemical inhibitor SC68376 not only abolished p38 MAP kinase phosphorylation but also obliterated apoptosis induced by TGF-beta1. These results suggest that hyperactive TGF-beta1 signaling potentiates renal tubular epithelial cell apoptosis by a Smad-independent, p38 MAP kinase-dependent mechanism.
authors.affiliation: Division of Cellular and Molecular Pathology, Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Chunsun
authors.initials: C
authors.lastname: Dai
authors.forename: Junwei
authors.initials: J
authors.lastname: Yang
authors.forename: Youhua
authors.initials: Y
authors.lastname: Liu
mesh_terms: D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004792:Enzyme Precursors / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010080:Oxazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051899:Smad2 Protein; D051906:Smad7 Protein; D019311:Staurosporine / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: C105138:2-methyl-4-phenyl-(4-pyridyl)oxazole; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004792:Enzyme Precursors; D010080:Oxazoles; D011725:Pyridines; C497782:SMAD2 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; D051906:Smad7 Protein; C508960:TGFB1 protein, human; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine