Acquisition of resistance to apoptosis and necrosis by Bcl-xL over-expression in rat hepatoma McA-RH8994 cells

Background: Bcl-xL is the predominant anti-apoptotic Bcl-2 family member in the liver. Suppression of cell death promotes carcinogenesis and contribut es to resistance to radiation and chemotherapeutic agents. Methods: Direct effects of Bcl-xL protein on apoptosis and necrosis were in vestigated in rat hepatoma cells. Rat hepatoma cell line McA-RH8994 cells w ere transfected with expression plasmids containing a whole coding sequence of rat bcl-xL cDNA of sense orientation. Stable transfectant cell lines ex pressing bcl-xL cDNA (designated as RH8994/Bcl-xL-S), or control plasmid DN A (designated as RH8994/pT) were established. Results: Cellular amounts of Bcl-xL in RH8994/Bcl-xL-S cells were demonstra ted to be more than 20-fold that of RH8994/pT and parental cells. Three ind ependent clones of RH8994/Bcl-xL-S were isolated and their susceptibility t o various cell death stimuli was compared with that of the control cells. T ransforming growth factor-beta 1 and tumour necrosis factor-alpha induced a poptosis dose dependently in these cells, but the 50% cytotoxicity concentr ations of these factors in RH8994/Bcl-xL-S cells were more than 10-fold hig her than those in RH8994/pT and parental cells. Similarly, RH8994/Bcl-xL-S cells were shown to be significantly less susceptible to necrotic cell deat h induced by a calcium ionophore, A23187; a mutagen, N-methyl-N'-nitro-N-ni trosoguanidine; and UV-irradiation when compared with the control cells. Conclusions: Over-expression of Bcl-xL was shown to provide protection agai nst apoptotic and necrotic cell death in rat hepatoma cells. (C) 1999 Black well Science Asia Pty Ltd.