Human EHMT2/G9a activates p53 through methylation-independent mechanism

p53 is a critical tumor suppressor in humans. It functions mostly as a transcriptional factor and its activity is regulated by numerous post-translational modifications. Among different covalent modifications found on p53 the most controversial one is lysine methylation. We found that human G9a (hG9a) unlike its mouse orthologue (mG9a) potently stimulated p53 transcriptional activity. Both ectopic and endogenous hG9a augmented p53-dependent transcription of pro-apoptotic genes, including Bax and Puma, resulting in enhanced apoptosis and reduced colony formation. Significantly, shRNA-mediated knockdown of hG9a attenuated p53-dependent activation of Puma. On the molecular level, hG9a interacted with histone acetyltransferase, p300/CBP, resulting in increased histone acetylation at the promoter of Puma. The bioinformatics data substantiated our findings showing that positive correlation between G9a and p53 expression is associated with better survival of lung cancer patients. Collectively, this study demonstrates that depending on the cellular and organismal context, orthologous proteins may exert both overlapping and opposing functions. Furthermore, this finding has important ramifications on the use of G9a inhibitors in combination with genotoxic drugs to treat p53-positive tumors.Oncogene advance online publication, 25 July 2016; doi:10.1038/onc.2016.258

Lysine-specific modifications of p53: a matter of life and death?

Post-translational modifications provide a fine-tuned control of protein function(s) in the cell. The well-known tumour suppressor p53 is subject to many post-translational modifications, which alter its activity, localization and stability, thus ultimately modulating its response to various forms of genotoxic stress. In this review, we focus on the role of recently discovered lysine-specific modifications of p53, methylation and acetylation in particular, and their effects on p53 activity in damaged cells. We also discuss a possibility of mutual influence of covalent modifications in the p53 and histone proteins located in the vicinity of p53 binding sites in chromatin and propose important ramifications stemming from this hypothesis

Lysine-specific modifications of p53: a matter of life and death?

Post-translational modifications provide a fine-tuned control of protein function(s) in the cell. The well-known tumour suppressor p53 is subject to many post-translational modifications, which alter its activity, localization and stability, thus ultimately modulating its response to various forms of genotoxic stress. In this review, we focus on the role of recently discovered lysine-specific modifications of p53, methylation and acetylation in particular, and their effects on p53 activity in damaged cells. We also discuss a possibility of mutual influence of covalent modifications in the p53 and histone proteins located in the vicinity of p53 binding sites in chromatin and propose important ramifications stemming from this hypothesis

Histone deacetylase inhibitors cause TP53-dependent induction of p21/Waf1 in tumor cells with TP53 mutations

The p21/Waf1 protein is one of the main regulators of cell cycle arrest and one of the best-known transcriptional targets of the TP53 protein. Here, we demonstrated that there is activation of expression of the p21/Waf1 gene when the cells were treated with sodium butyrate (NaBu), which is a natural histone deacetylase inhibitor, and investigated whether this phenomenon depends on the presence of a functionally active TP53 protein. For this purpose, we compared the effect of NaBu treatment of human cell lines with different TP53 mutation profiles, including wild-type TP53, single nucleotide substitutions, and the complete absence of the TP53 gene. NaBu activated the TP53 protein via hyperacetylation at the lysine residue K382, without significant changes in the level of protein expression. Western blotting showed that the addition of NaBu triggers a significant increase in the p21/Waf1 protein level in both TP53 wild-type cells and in cells with single nucleotide substitutions in the central DNA-binding core domain (DBD) of the TP53 protein. At the same time, no p21/Waf1 protein induction was observed in cells with complete deletion of the TP53 gene. However, NaBu was not able to induce p21/Waf1 production when the expression of TP53 was transiently knocked down by the p53 siRNA. Overall, our results suggest that NaBu-dependent induction of p21/Waf1 does require the presence of TP53 protein, but, unexpectedly, it can occur regardless of mutational changes in the domain responsible for the TP53 binding to DNA. One possible explanations is that NaBu increases the level of TP53 acetylation and the modified protein is able to establish a new network of protein–protein interactions or trigger conformational changes affecting the TP53-dependent transcriptional machinery even when its DNA binding ability is impaired