BCL-2 EXPRESSION CAUSES REDISTRIBUTION OF GLUTATHIONE TO THE NUCLEUS

In this study we used HeLa cells transfected with a conditional Bcl-2 expression construct to study the effects of Bcl-2 on reduced glutathi one (GSH) metabolism, Our previous work demonstrated that depletion of GSH by culturing cells in tissue culture medium lacking the amino aci ds cysteine and methionine, essential for GSH biosynthesis, caused cel ls overexpressing Bcl-2 to become sensitized to apoptotic induction, H ere we report that Bcl-2 also dramatically alters GSH compartmentaliza tion. Cellular distribution of GSH, assayed by confocal microscopy, re vealed that when Bcl-2 expression was suppressed GSH was uniformly dis tributed primarily in the cytosol, whereas overexpression of Bcl-2 led to a relocalization of GSH into the nucleus, Isolated nuclei readily accumulated radiolabeled GSH and maintained higher nuclear GSH concent ration in direct relation to Bcl-2 nuclear protein levels, Moreover, e xogenous GSH blocked apoptotic changes and caspase activity in isolate d nuclei exposed to the pro-apoptotic protease granzyme B, Our results indicate that one of the functions of Bcl-2 is to promote sequestrati on of GSH into the nucleus, thereby altering nuclear redox and blockin g caspase activity as well as other nuclear alterations characteristic of apoptosis, We speculate that this mechanism contributes to the sup pression of apoptosis in cells with elevated Bcl-2 levels.