Histone deacetylase inhibitors: signalling towards p21cip1/waf1.

Chromatin-modifying enzymes such as histone deacetylases (HDAC) facilitate a closed chromatin structure and hence transcriptional repression. HDAC are commonly affected in human cancer diseases. Thus, inhibition of HDAC represents a novel therapeutic approach. Several studies have shown that HDAC inhibitors strongly activate the expression of the cyclin-dependent kinase inhibitor p21(cip1/waf1) through (i) enhanced histone acetylation around the p21(cip1/waf1) promoter and (ii) the Sp1 sites on the p21(cip1/waf1) promoter releasing the repressor HDAC1 from its binding. p21(cip1/waf1) expression is regulated in a p53-dependent and p53-independent manner. The decision if p21(cip1/waf1) up-regulation results in cell cycle arrest or apoptosis, decides about the therapeutic efficacy of an anti-cancer treatment with HDAC inhibitors.