Reversal of drug resistance by disruption of a Gain-of-Function mutant p53 and transcriptional co-activator PC4 interaction

The positive coactivator 4 or PC4 is a chromatin-associated protein whose role in gene regulation by wild-type p53 is now well-known. During tumorigenesis, p53 is often mutated resulting in its loss of function. A sub-class of these mutants gain new pro-proliferation properties which occur largely due to the upregulation of many pro-proliferation genes. Little is known about the roles of PC4 in tumor cells bearing mutant p53 genes. In this article, we show that PC4 associates with one of the tumor-associated gain-of-function p53 mutants, R273H. This association drives its recruitment to two promoters, UBE2C, and MDR1, known to be responsible for imparting aggressive growth and resistance to many drugs. A previously reported peptide that disrupts PC4-wild-type p53 interaction also disrupts the PC4-R273Hp53 protein-protein interaction. The introduction of this peptide to tumor cells bearing the R273HTP53 gene resulted in a lowering of MDR1 expression and abrogation of drug resistance. Interestingly, cells bearing another gain-of-function mutant R248W do not show the same type of response, suggesting that the action of PC4 on mutant p53s may differ for different GOF mutants. The results presented here suggest that PC4-R273H interaction may be a promising target for reducing proliferation and tumor drug resistance.