GRAMD4 mimics p53 and mediates the apoptotic function of p73 at mitochondria.
p73, a member of the p53 family, shares high sequence homology with p53 and shows many p53-like properties: it binds to p53-DNA target sites, transactivates p53-responsive genes and induces cell cycle arrest and apoptosis. Apart from this transcription-dependent effect, less is known about the downstream mechanism(s) by which p73 controls cell fate at the mitochondria. We have previously identified GRAMD4 (alias KIAA0767 or Death-Inducing-Protein) as a novel p53-independent pro-apoptotic target of E2F1, which localizes to mitochondria. In this study, we found that p73-induced apoptosis is mediated by GRAMD4 expression and translocation to the mitochondria. We showed that this protein physically interacts with Bcl-2, promotes Bax mitochondrial relocalization and oligomerization, and is highly efficient in inducing mitochondrial membrane permeabilization with release of cytochrome c and Smac. Overexpression of p73α and p73β isoforms, but not p53, leads to direct GRAMD4 promoter transactivation. In addition, GRAMD4 induces changes in Bcl-2 and Bax protein levels. GRAMD4 transcription is activated in response to cisplatin (cDDP) in a manner dependent on endogenous p73. Using solid tumor xenografts, ectopic expression of GRAMD4 together with cDDP resulted in enhanced cancer killing. Our findings demonstrate that p73 is able to trigger apoptosis via the mitochondrial pathway by a new mechanism using pro-apoptotic GRAMD4 as mediator, and strongly support its p53-like function.
Department of Vectorology and Experimental Gene Therapy, Biomedical Research Center, University of Rostock, Schillingallee 69, Rostock, Germany.
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D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology; D004249:DNA Damage / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009368:Neoplasm Transplantation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D055503:Protein Multimerization; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014183:Transplantation, Heterologous; D047368:Tumor Burden / Q000187:drug effects; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays / Q000009:adverse effects; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D000970:Antineoplastic Agents; C494826:BAX protein, human; D004268:DNA-Binding Proteins; C503369:GRAMD4 protein, human; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; C495901:TP53 protein, human; C000606460:TP73 protein, human; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; D008156:Luciferases; D002945:Cisplatin