Monoubiquitylation promotes mitochondrial p53 translocation.

A major function of the p53 tumor suppressor is the induction of a pleiotropic apoptotic program in response to stress through transcription-dependent and -independent mechanisms. In particular, this includes a direct apoptotic role of p53 at the mitochondria. Stress-induced p53 translocation to the mitochondria with subsequent outer membrane permeabilization is ...
a common early component in p53-mediated apoptosis in normal and transformed cells. However, the mechanism of p53 delivery to the mitochondria remains unknown. Here, we show that the cytoplasm contains a separate and distinct p53 pool that is the major source for p53 translocation to the mitochondria upon its stress-induced stabilization. Using various manipulations that enhance or diminish p53 ubiquitylation, our data provide evidence that Mdm2-mediated monoubiquitylation of p53 greatly promotes its mitochondrial translocation and thus its direct mitochondrial apoptosis. On the other hand, p53 does not require Mdm2 as a shuttler. Upon arrival at the mitochondria, our data suggest that p53 undergoes rapid deubiquitylation by mitochondrial HAUSP via a stress-induced mitochondrial p53-HAUSP complex. This generates the apoptotically active non-ubiquitylated p53. Taken together, we propose a novel model for mitochondrial p53 targeting, whereby a distinct cytoplasmic pool of stabilized monoubiquitylated p53, generated in resting cells by basal levels of Mdm2-type ligases, is subject to a binary switch from a fate of inactivation via subsequent polyubiquitylation and degradation in unstressed cells, to a fate of activation via mitochondrial trafficking.
Mesh Terms:
Apoptosis, Camptothecin, Cell Line, Tumor, Cytoplasm, Endopeptidases, Humans, Immunoblotting, Immunoprecipitation, Mitochondria, Models, Biological, Protein Transport, Proto-Oncogene Proteins c-mdm2, Tumor Suppressor Protein p53, Ubiquitin, Ubiquitin Thiolesterase
Date: Feb. 21, 2007
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