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