Bax translocation to mitochondria subsequent to a rapid loss of mitochondrial membrane potential

Abstract

Bax, a pro-apoptotic member of the Bcl-2 family, is a cytosolic protein that inserts into mitochondrial membranes upon induction of cell death. Using the green fluorescent protein fused to Bax (GFP-Bax) to quantitate mitochondrial binding in living cells we have investigated the cause of Bax association with mitochondria and the time course relative to endogenous and induced changes in mitochondrial membrane potential (Δψm). We have found that staurosporine (STS) induces a loss in Δψm before GFP-Bax translocation can be measured. The onset of the Δψm loss is followed by a rapid and complete collapse of Δψm which is followed by Bax association with mitochondria. The mitochondria uncoupler FCCP, in the presence of the F1-F0 ATPase inhibitor oligomycin, can trigger Bax translocation to mitochondria suggesting that when ATP levels are maintained a collapse of Δψm induces Bax translocation. Neither FCCP nor oligomycin alone alters Bax location. Bax association with mitochondrial is also triggered by inhibitors of the electron transport chain, antimycin and rotenone, compounds that collapse Δψm without inducing rapid ATP hydrolysis that typically occurs with uncouplers such as FCCP. Taken together, our results suggest that alterations in mitochondrial energization associated with apoptosis can initiate Bax docking to mitochondria.