Bcl-xL overexpression restricts heat-induced apoptosis and influences hsp70, bcl-2, and bax protein levels in FL5.12 cells

Although several proteins hare been identified that can inhibit stress-induced apoptosis, the cytoprotective potential of bcl-x(L) against heat shock and its ability to alter hsp70 induction is not known. The current study, using control and bcl-x(L)-overexpressing IL-3-dependent FL5.12 cells, compared the effects of 1 h of acute heat stress (42 degrees C) followed by 1, 4, and 8 h recovery (37 degrees C) on hsp70, bax, bcl-2, and bcl-x(L) protein levels and apoptosis. Less than 0.5% of untreated cells were apoptotic. There was significantly more apoptosis in control (similar to 16%) as compared to bcl-x(L) cells (similar to 3%) 8 h after heat stress. Immunoblotting revealed a time-dependent increase in hsp70 protein levels following 1 h of heat stress in control, but not bcl-x(L)-overexpressing cells, bcl-2 protein levels were lower in bcl-x(L)-overexpressing cells than in controls, but decreased in both cell lines after heat stress. bax protein levels in bcl-x(L)-overexpressing cells were decreased similar to 80% below baseline levels 1 h post heat shock. This decrease was maintained to 8 h. No change in bax protein was observed in control cells up to 8 h post heat shock. These data indicate that bcl-x(L) overexpression mitigates the effects of acute heat stress so that hsp70 induction is eliminated and apoptosis is prevented. The rapid loss of bax protein following heat stress in bcl-x(L)-overexpressing, but not control, cells mag contribute to their resistance to apoptosis. Conversely, the loss of bcl-2 protein following heat stress in control cells may contribute to their susceptibility to apoptosis. (C) 1997 Academic Press.