Protection against hydrogen peroxide cytotoxicity in Rat-1 fibroblasts provided by the oncoprotein Bcl-2: maintenance of calcium homoeostasis is secondary to the effect of Bcl-2 on cellular glutathione

The oncoprotein Bcl-2 protects cells against apoptosis, but the exact molec ular mechanism that underlies this function has not yet been identified. St udying H2O2-induced cell injury in Rat-1 fibroblast cells, we observed that Bcl-2 had a protective effect against the increase in cytosolic calcium co ncentration and subsequent cell death. Furthermore, overexpression of Bcl-2 resulted in an alteration of cellular glutathione status: the total amount of cellular glutathione was increased by about 60 %, and the redox potenti al of the cellular glutathione pool was maintained in a more reduced state during H2O2 exposure compared with non-Bcl-2-expressing controls. In our cy totoxicity model, disruption of cellular glutathione homoeostasis closely c orrelated with the pathological elevation of cytosolic calcium concentratio n. Stabilization of the glutathione pool by Bcl-2, N-acetylcysteine or gluc ose delayed the cytosolic calcium increase and subsequent cell death, where as depletion of glutathione by DL-buthionine-(S,R)-sulphoximine, sensitized Bcl-2-transfected cells towards cytosolic calcium increase and cell death. We therefore suggest that the protection exerted by Bcl-2 against H2O2-ind uced cytosolic calcium elevation and subsequent cell death is secondary to its effect on the cellular glutathione metabolism.