Naoufal Zamzami, Luigi Ravagnan, Santos A. Susin, Marja Jäättelä, Guido Kroemer, Eric Daugas, Carmen Garrido, Tak W. Mak, Sandeep Gurbuxani, Carine Maisse, Josef M. Penninger, UMR 1599, Centre National de la Recherche Scientifique (CNRS), Institut Gustave Roussy (IGR), U-517, Institut National de la Santé et de la Recherche Médicale (INSERM), CHU Tenon [AP-HP], Sorbonne Université (SU)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP), Department of Medical Biophysics and Immunology, Ontario Cancer Institute, University of Toronto, Amgen Institute, Institute of Cancer Biology, Apoptosis Laboratory, and Danish Cancer Society
Heat-shock protein 70 (Hsp70) has been reported to block apoptosis by binding apoptosis protease activating factor-1 (Apaf-1), thereby preventing constitution of the apoptosome, the Apaf-1/cytochrome c/caspase-9 activation complex [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 (AIF), which is a mitochondrial intermembrane flavoprotein [3,4]. In a cell-free system, Hsp70 prevented the AIF-induced chromatin condensation of purified nuclei. Hsp70 specifically interacted with AIF, as shown by ligand blots and co-immunoprecipitation. Cells overexpressing Hsp70 were protected against the apoptogenic effects of AIF targeted to the extramitochondrial compartment. In contrast, an anti-sense Hsp70 complementary DNA, which reduced the expression of endogenous Hsp70, increased sensitivity to the lethal effect of AIF. The ATP-binding domain of Hsp70 seemed to be dispensable for inhibiting cell death induced by serum withdrawal, 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 AIF.