The association of deamidation of Bcl-xL and translocation of Bax to the mitochondria through activation of JNK in the induction of apoptosis by treatment with GSH-conjugated DXR

We investigated the induction of apoptosis via deamidation of Bcl-xL and translocation of Bax to the mitochondria by treatment with GSH-DXR. GSH-DXR treatment of HepG2 cells, which did not express GST P1-1, exhibited deamidation of Bcl-xL, and the degree of deamidation was related to the activation of caspase-3. Overexpression of GST P1-1 in HepG2 cells decreased both the Bcl-xL deamidation and caspase-3 activation induced by treatment with GSH-DXR. Bcl-xL deamidation and caspase-3 activation were also suppressed by co-treatment with SP600125, a specific inhibitor of JNK activity. Overexpression of wild-type Bcl-xL in HepG2 decreased GSH-DXR-induced apoptosis although deamidation was observed. However, expression of the deamidated mutant of Bcl-xL, in which aspartic acid was substituted for both arginine 52 and 66 (N52,66D-Bcl-xL), exhibited high sensitivity for the induction of apoptosis. Expression of the Bcl-xL mutant, in which alanine was substituted for both arginine 52 and 66 (N52,66A-Bcl-xL), suppressed deamidation and showed resistance to the induction of apoptosis by treatment with GSH-DXR. On the other hand, endogenous Bax and overexpressed Flag-Bax were localized in the cytosolic fraction of HepG2 cells. Treatment of the cells with GSH-DXR caused translocation of Flag-Bax to the mitochondrial fraction following the induction of apoptosis. The induced apoptosis was enhanced by the expression of Flag-Bax. Moreover, Flag-Bax was partly located in the mitochondrial fraction in N52,66D-Bcl-xL-expressed cells without the induction of apoptosis. Therefore, the induction of apoptosis by treatment of HepG2 with GSH-DXR was enhanced, thereby facilitating the release of cytochrome c by both deamidated inactivation of Bcl-xL and functional translocation of Bax to the mitochondria via JNK activation. Deamidation of Bcl-xL might be induced in order to translocate Bax to the mitochondria.