[Histone deacetylase inhibitors cause the TP53-dependent induction of p21/Waf1 in tumor cells carrying mutations in TP53].

p21/Waf1 protein is one of the main cell cycle arrest regulators and one of the most well-known transcriptional targets of TP53 protein. Here, we demonstrated the activation of expression of the p21/Waf1 gene when the cells were treated to sodium butyrate (NaBu)--one of the natural inhibitors of deacetylase, and investigated whether this phenomenon depends on the presence of functionally active TP53 protein. We compared the effect of the NaBu treatment on the human cell line with different TP53 mutation profile, including: wild-type TP53, single nucleotide substitutions, and the complete absence of TP53 gene. NaBu activated the TP53 protein via hyper acetylation at lysine residue K382, without significant changes in the level of protein expression. Western blotting demonstrated that the addition of NaBu triggers a significant increase in the p21/Waf1 protein level in both the TP53 wild-type cells and in the cells with single nucleotide substitutions in the domain responsible for the binding of TP53 protein to DNA. At the same time, no the p21/Waf1 protein induction was observed in the cells with complete deletion of the TP53 gene. However, NaBu was not able to induce the p2 1/Waf1 production when the expression of TP53 was transiently knocked down by the p53 siRNA. Overall, our results suggest that the 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 of the hypothetical 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 some conformational changes affecting the TP53-dependent transcriptional machinery even when its DNA binding ability is impaired.