Transcription Factors YY1, ZBP-89 Restrained Cell Senescence Through Repressing The Expression Of P16

As a cyclin-dependent kinase inhibitor,p16^INK4a product plays a key role in cell cycle progression and cellular differentiation by negatively regulating the CDK4/6 activity. Therefore, the regulation of expression of p16^INK4a gene has attracted a great deal of reasearch attention. There has been increasing evidence that the expression of p16^INK4a gene is epigenetically controlled and is closely related with many cancers. Although previous biochemical studies revealed that epigenetic mechanisms such as DNA methylation and histone modifications may be involved in transcription regulation of this gene, a detailed description of the molecular basis for the roles of histone acetylation in p16^INK4a regulation has not been reported.The transcription factor ZBP-89 has been implicated to induce growth arrest and apoptosis. In this report, we demonstrate that ZBP-89 was able to suppress cell senescence through regulating the expression of p16^INK4a, a cyclin-dependent kinase inhibitor, in NCI-H460 cells. We also show that ZBP-89 participated in the repression of p16^INK4a expression in 293T cells through an epigenetic mechanism involving histone acetylation modification. Specifically, HDAC3 and HDAC4 inhibited the p16^INK4a promoter activity. The chromatin immunoprecipitation (ChIP) assays verified that HDAC3 was recruited to p16^INK4a promoter by ZBP-89. Moreover, YY1 was also shown to inhibit the expression of p16^INK4a. Co-immunoprecipitation assays revealed that these four protein factors formed a complex. Furthermore, knockdown of these factors induced cell enlargement and flattened morphology and significantly increased the SA-β-gal activity, a biochemical marker of cell senescence. Overall, data from this study suggest that ZBP-89, YY1, HDAC3 and HDAC4 suppressed cell senescence by repressing p16^INK4a expression through an epigenetic modification of histones. These data will contribute to elucidating the unique mechanisms of p16^INK4a transcriptional control, which is crucial to the development of new therapeutic strategies for p16^INK4a -related gene therapy.