Heat-shock protein 70 antagonizes apoptosis-inducing factor

Heat-shock protein 70 (Hsp70) has been reported to block apoptosis by bindi ng apoptosis protease activating factor-1 (Apaf-1), thereby preventing cons titution of the apoptosome, the Apaf-1/cytochrome c/caspase-9 activation co mplex(1,2). Here we show that overexpression of Hsp70 protects Apaf-1(-/-) cells against death induced by serum withdrawal, indicating that Apaf-1 is not the only target of the anti-apoptotic action of Hsp70. We investigated the effect of Hsp70 on apoptosis mediated by the caspase-independent death effector apoptosis inducing factor (AlF), which is a mitochondrial intermem brane flavoprotein(3,4). In a cell-free system, Hsp70 prevented the AIF-ind uced chromatin condensation of purified nuclei. Hsp70 specifically interact ed with AlF, as shown by ligand blots and co-immunoprecipitation. Cells ove rexpressing Hsp70 were protected against the apoptogenic effects of AIF tar geted to the extramitochondrial compartment. In contrast, an anti-sense Hsp 70 complementary DNA, which reduced the expression of endogenous Hsp70, inc reased sensitivity to the lethal effect of AIR The ATP-binding domain of Hs p70 seemed to be dispensable for inhibiting cell death induced by serum wit hdrawal, AIF binding and AIF inhibition, although it was required for Apaf- 1 binding. Together, our data indicate that Hsp70 can inhibit apoptosis by interfering with target proteins other than Apaf-1, one of which is AIR