Abstract
Transforming growth factor beta (TGF-beta) has been implicated in the maintenance of homeostasis in various organs, including the gastric epithelium. In particular, TGF-beta-induced signaling was shown to be required for the differentiation-associated physiological apoptosis of gastric epithelial cells, but its mechanism has not been well understood. In this study, the molecular mechanism of TGF-beta-induced apoptosis was analyzed in a human gastric epithelial cell line, SNU16, as an in vitro model. Expression of Smad7 and Bcl-X(L), but not viral FLIP, was shown to prevent TGF-beta-induced apoptosis, indicating an exclusive requirement of the activation of Smad signaling pathway and mitochondrial dysfunction followed by activation of caspase-9. In addition, treatment with TGF-beta induced binding of Bim, a proapoptotic Bcl-2 homology domain 3 (BH3)-only protein, to Bcl-X(L), which is dependent on the activation of Smad, and reduction in the expression of Bim by RNA interference decreased the sensitivity to TGF-beta-induced apoptosis. Moreover, we found abnormalities in the gastric epithelium of both Bim and caspase-9 knockout mice; these abnormalities were associated with a defect of physiological apoptosis in gastric epithelial cells. These results indicate for the first time that TGF-beta is involved in the physiological loss of gastric epithelial cells by activating apoptosis mediated by Smad, Bim, and caspase-9.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenosine Triphosphate / metabolism
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Animals
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Animals, Newborn
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Apoptosis Regulatory Proteins / metabolism*
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Apoptosis*
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Bcl-2-Like Protein 11
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Blotting, Western
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CASP8 and FADD-Like Apoptosis Regulating Protein
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Caspase 9
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Caspases / metabolism*
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Cell Differentiation
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Cell Line
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Cell Line, Tumor
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Crosses, Genetic
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Cycloheximide / pharmacology
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Epithelium / metabolism*
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Female
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Gastric Mucosa / metabolism*
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Humans
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Immunoprecipitation
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Intracellular Signaling Peptides and Proteins / metabolism
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Male
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Membrane Proteins / metabolism*
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Mitochondria / metabolism
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Protein Binding
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Protein Conformation
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Proto-Oncogene Proteins / metabolism*
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RNA Interference
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Sensitivity and Specificity
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Signal Transduction
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Smad Proteins / metabolism*
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Smad7 Protein / metabolism
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Time Factors
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Transforming Growth Factor beta / metabolism*
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Transforming Growth Factor beta1
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bcl-X Protein / metabolism
Substances
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Apoptosis Regulatory Proteins
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BCL2L11 protein, human
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Bcl-2-Like Protein 11
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Bcl2l11 protein, mouse
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CASP8 and FADD-Like Apoptosis Regulating Protein
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CFLAR protein, human
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Cflar protein, mouse
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins
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Proto-Oncogene Proteins
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Smad Proteins
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Smad7 Protein
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TGFB1 protein, human
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Tgfb1 protein, mouse
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Transforming Growth Factor beta
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Transforming Growth Factor beta1
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bcl-X Protein
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Adenosine Triphosphate
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Cycloheximide
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CASP9 protein, human
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Casp9 protein, mouse
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Caspase 9
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Caspases