Mechanism of apoptotic cell death of human gastric carcinoma cells mediated by transforming growth factor β

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Abstract
Human gastric carcinoma cell line HSC-39 has been shown to undergo apoptotic cell death in response to treatment with transforming growth factor β1 (TGF-β1). To understand better the cell death mechanism in this TGF-β1-mediated apoptosis, we investigated the effect of the expression of TGF-β-stimulated clone 22 (TSC-22) on cell death events. TGF-β1 induced TSC-22 gene expression in HSC-39 cells only when the cells had previously been adapted to the serum-free culture conditions required to undergo TGF-β1-mediated apoptosis. HSC-39 cells transfected with a TSC-22 expression vector showed a significant decrease in cell viability compared with those transfected with a control vector. The cellular events characteristic of apoptosis, chromatin condensation and DNA fragmentation were observed only in cells transfected with a TSC-22 expression vector. On immunostaining of the transfected cells, almost every cell that expressed TSC-22 tagged with influenza virus haemagglutinin exhibited the morphology of an apoptotic cell. Partial protection from the cell death effect of TGF-β1 on HSC-39 cells was observed when cells were treated with acetyl-l-aspartyl-l-glutamyl-l-valyl-l-aspart-1-al (Ac-DEVD-CHO, an inhibitor specific for CPP32-type protease). Protection against cell death by the transfection of a TSC-22 expression vector was also offered by Ac-DEVD-CHO addition. These results suggest that TSC-22 elicits the apoptotic cell death of human gastric carcinoma cells through the activation of CPP32-like protease and mediates the TGF-β1 signalling pathway to apoptosis.