PREVENTION OF APOPTOSIS BY BCL-2 - RELEASE OF CYTOCHROME-C FROM MITOCHONDRIA BLOCKED

Bcl-2 is an integral membrane protein located mainly on the outer memb rane of mitochondria. Overexpression of Bcl-2 prevents cells from unde rgoing apoptosis in response to a variety of stimuli. Cytosolic cytoch rome c is necessary for the initiation of the apoptotic program, sugge sting a possible connection between Bcl-2 and cytochrome c, which is n ormally located in the mitochondrial intermembrane space. Cells underg oing apoptosis were found to have an elevation of cytochrome c in the cytosol and a corresponding decrease in the mitochondria. Overexpressi on of Bcl-2 prevented the efflux of cytochrome c from the mitochondria and the initiation of apoptosis. Thus, one possible role of Bcl-2 in prevention of apoptosis is to block cytochrome c release from mitochon dria.