In ERa-negative cell lines, a subset of genes is epigenetically silenced, while the majority of genes involved in cell cycle control and proliferation are constitutively 1624602-30-7 expressed. Aberrant gene expression is frequently the result of chromatin 36396-99-3 modifications and composition, including histone posttranslational modifications and/or incorporation of histone variants. In particular, deregulation of enzyme complexes responsible for histone acetylation and deacetylation can be associated with breast cancer progression and an increase in tumor malignancy. Thus, compounds that change chromatin modifications are a promising anti-cancer approach. Histone deacetylase inhibitors, such as Trichostatin A, Suberoylanilide hydroxamic acid, Panobinostat and sodium butyrate can inhibit cancer cell growth in vitro and in vivo as a result of selective induction of endogenous genes that play significant roles in G1-S progression. One of the major regulators of cell cycle progression is the cyclin-dependent kinase inhibitor p21 CIP1/WAF1, a gene of the CIP/KIP family, which inhibits CDK activity. p21 can be stimulated by p53 and its activity results in cell cycle arrest and/ or apoptosis. Much of research on HDAC inhibitors has focused on the upregulation of p21. Activation of p21 involves acetylation of promoter chromatin, but the mechanism remains poorly understood. The histone variant H2A.Z has been shown to bind to the promoter of p21 at the p53 binding sites in p53+/+ cells. In response to stress, H2A.Z is evicted to allow p53 to bind which leads to p21 expression. The p400 complex takes part in this pathway and was proposed to be responsible for H2A.Z deposition into the p21 promoter. Depleting p400 by siRNA increases p21 expression in a p53 dependent manner and induces premature senescence. The mechanism of this activation is unclear. In the ERa-negative breast cancer cell line MDA-MB231 p53 is mutated and non-functional. Here we show that activation of p21 in response to HDACi treatment of these ERa-negative cells requires H2A.Z acetylation and exchange at its transcription start site. Zinc finger nucleases are artificial restriction enzymes that are comprised of custom-designed zinc finger proteins and a nuclease domain derived from the FokI endonuclease. Zinc finge