Molecular basis of the interactions between the p73 N terminus and p300: Effects on transactivation and modulation by phosphorylation

Medical Research Council Centre for Protein Engineering, Hills Road, Cambridge CB2 0QH, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 03/2009; 106(9):3142-7. DOI: 10.1073/pnas.0900383106
Source: PubMed

ABSTRACT The transcription factor p73 belongs to the p53 family of proteins and can transactivate a number of target genes in common with p53. Here, we characterized the interaction of the p73 N terminus with four domains of the transcriptional coactivator p300 and with the negative regulator Mdm2 by using biophysical and cellular measurements. We found that, like p53, the N terminus of p73 contained two distinct transactivation subdomains, comprising residues 10-30 and residues 46-67. The p73 N terminus bound weakly to the Taz1, Kix, and IBiD domains of p300 but with submicromolar affinity for Taz2, in contrast to previous reports. We found weaker binding of the p73 N terminus to the p300 domains in vitro correlated with a significant decrease in transactivation activity in a cell line for the QS and T14A mutants, and tighter binding of the phosphomimetic T14D in vitro correlated with an increase in vivo. Further, we found that phosphorylation of T14 increased the affinity of the p73 N terminus for Taz2 10-fold. The phosphomimetic p73alpha T14D caused increased levels of transactivation.

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    ABSTRACT: p53 protein has about thirty phosphorylation sites located at the N- and C-termini and in the core domain. The phosphorylation sites are relatively less mutated than other residues in p53. To understand why and how p53 phosphorylation sites are rarely mutated in human cancer, using a bioinformatics approaches, we examined the phosphorylation site and its nearby flanking residues, focusing on the consensus phosphorylation motif pattern, amino-acid correlations within the phosphorylation motifs, the propensity of structural disorder of the phosphorylation motifs, and cancer mutations observed within the phosphorylation motifs. Many p53 phosphorylation sites are targets for several kinases. The phosphorylation sites match 17 consensus sequence motifs out of the 29 classified. In addition to proline, which is common in kinase specificity-determining sites, we found high propensity of acidic residues to be adjacent to phosphorylation sites. Analysis of human cancer mutations in the phosphorylation motifs revealed that motifs with adjacent acidic residues generally have fewer mutations, in contrast to phosphorylation sites near proline residues. p53 phosphorylation motifs are mostly disordered. However, human cancer mutations within phosphorylation motifs tend to decrease the disorder propensity. Our results suggest that combination of acidic residues Asp and Glu with phosphorylation sites provide charge redundancy which may safe guard against loss-of-function mutations, and that the natively disordered nature of p53 phosphorylation motifs may help reduce mutational damage. Our results further suggest that engineering acidic amino acids adjacent to potential phosphorylation sites could be a p53 gene therapy strategy.
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    ABSTRACT: p73 is a structural and functional homologue of p53 tumor suppressor protein. Like p53, p73 induces apoptosis and cell cycle arrest and transactivates p53-responsive genes, conferring its tumor suppressive activity. In addition, p73 has unique roles such as neuronal development and differentiation. The importance of p73-induced apoptosis lies in its capability to substitute the pro-apoptotic activity of p53 in various human cancer cells in which p53 is mutated or inactive. Despite the great importance of p73-induced apoptosis in cancer therapy, little is known about molecular basis for the p73-induced apoptosis. In this review, we discuss the p73 structures reported to date, detailed structural comparison between p73 and p53, and current understanding of transcription-dependent and -independent mechanisms of p73-induced apoptosis.
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    ABSTRACT: p53 is an important tumor suppressor gene, which is stimulated by cellular stress like ionizing radiation, hypoxia, carcinogens, and oxidative stress. Upon activation, p53 leads to cell-cycle arrest and promotes DNA repair or induces apoptosis via several pathways. p63 and p73 are structural homologs of p53 that can act similarly to the protein and also hold functions distinct from p53. Today more than 40 different isoforms of the p53 family members are known. They result from transcription via different promoters and alternative splicing. Some isoforms have carcinogenic properties and mediate resistance to chemotherapy. Therefore, expression patterns of the p53 family genes can offer prognostic information in several malignant tumors. Furthermore, the p53 family constitutes a potential target for cancer therapy. Small molecules (e.g., Nutlins, RITA, PRIMA-1, and MIRA-1 among others) have been objects of intense research interest in recent years. They restore pro-apoptotic wild-type p53 function and were shown to break chemotherapeutic resistance. Due to p53 family interactions small molecules also influence p63 and p73 activity. Thus, the members of the p53 family are key players in the cellular stress response in cancer and are expected to grow in importance as therapeutic targets.

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