The Expression Of P16^INK4a Is Regulated By The Reversible Acetylation

p16^INK4aplays a key role in control of cell cycle progression by negatively regulating theCDK4/6activity. It was shown that histone acetyltransferase p300had a positive effect on theactivation of p16^INK4apromoter, whereas, histone deacetylases HDAC3/4counteracted thep300-mediated activation of p16^INK4apromoter, and decreased the p16^INK4amRNA andprotein levels. We demonstrate that ZBP-89participated in the repression of p16^INK4aexpression in293T cells through an epigenetic mechanism involving histone acetylationmodification. Specifically, HDAC3and HDAC4inhibited the p16^INK4apromoter activity.Chromatin immunoprecipitation （ChIP） tests revealed that HDAC3/4were recruited top16^INK4apromoter by transcription factor ZBP-89and/or YY1to repress the transcription ofp16^INK4a. Overexpression of p300reversed the hypoacetylation status of histones at thep16^INK4apromoter mediated by HDAC3/4.Co-immunoprecipitation assays revealed that thesefour protein factors formed a complex. Moreover, the immunofluorescence study showed thatthe nucleo-cytoplasmic shuttling of HDAC4may play an important role. Furthermore,Western blot and ChIP assays demonstrated that the HDAC inhibitor sodium butyrate （NaBu）enhanced p16^INK4aexpression through inducing histone hyperacetylation. Based on these data,a hypothetical model was proposed for the involvement of reversible histone acetylation intranscriptional regulation of the p16^INK4agene. These data will contribute considerably tounderstand the unique mechanism of p16^INK4atranscriptional control, which is critical to thedevelopment of p16^INK4a-related therapeutic strategies.