Hypoxia death stimulus induces translocation of p53 protein to mitochondria - Detection by immunofluorescence on whole cells

Evidence suggests that p53 induces cell death by a dual mode of action invo lving activation of target genes and transcriptionally independent direct s ignaling. Mitochondria are major signal transducers in apoptosis, We recent ly discovered that a fraction of induced p53 protein rapidly translocates t o mitochondria during p53-dependent apoptosis, but not during p53-independe nt apoptosis or p53-mediated cell cycle arrest. Importantly, specific targe ting of p53 to mitochondria was sufficient to induce apoptosis in p53-defic ient tumor cells, This led us to propose a model where p53 exerts a direct apoptogenic role at the mitochondria, thereby enhancing the transcription-d ependent apoptosis of p53, Here we show for the first time that mitochondri al localization of endogenous p53 can be visualized by immunofluorescence o f whole cells when stressed by hypoxic conditions. Suborganellar localizati on by limited trypsin digestion of isolated mitochondria from stressed cell s suggests that a significant amount of mitochondrial p53 is located at the surface of the organelle, This mitochondrial association can be reproduced in vitro with purified p53. Together, our data provide further evidence fo r an apoptogenic signaling role of p53 protein in vivo at the le, el of the mitochondria, (C) 2001 Federation of European Biochemical Societies, Publi shed by Elsevier Science B.V. All rights reserved.