TIP60 regulation of DNp63a is associated with cisplatin resistance

DNp63a, a member of the p53 transcription factor family, is overexpressed in non-melanoma skin cancer and regulates cell survival, migration and invasion. TIP60 is histone acetyltransferase (HAT) which mediates cellular processes such as transcription and the DNA damage response (DDR). Previous studies in our lab have shown that overexpression of TIP60 induces DNp63a protein stabilization in a catalytic-dependent manner. Since DNp63a is known to transcriptionally regulate several DDR genes and promote cisplatin resistance, its stabilization by TIP60 may contribute to the failure of platinum-based drugs in squamous cell carcinoma (SCC). We hypothesize that TIP60 regulates the transcriptional activity of DNp63a thereby modulating chemoresistance. In this study, we showed that overexpression of TIP60 in both H1299 and A431 cells led to increase in the levels of DNp63a, while TIP60 silencing in A431 cell lines led to a decrease in endogenous DNp63a transcript and protein levels, thus confirming that TIP60 positively regulates DNp63a in these cell lines. Increased levels of DNp63a and TIP60 were observed in a cisplatin resistant A431 SCC line. Further, stable expression of TIP60 or DNp63a individually promoted resistance to cisplatin, whereas loss of DNp63a and TIP60 sensitized cells to cisplatin. Higher acetylation of DNp63a and TIP60 were seen in cisplatin resistant cells. High-throughput transcriptome sequencing was performed using the Ion ProtonTM AmpliSeq panel to identify downstream mRNA targets of TIP60. An NGS data set generated from Lenti viral transduced A431 cells resulting from overexpression of TIP60 and eGFP as a control identified 228 mRNA showing differential gene expression. Taken together, our data suggest that TIP60-mediated regulation of DNp63a increases cisplatin resistance and has potential implications for cancer treatment and drug design. Additionally, since DNp63a confers cisplatin resistance through regulation of genes involved in DNA damage repair, our findings provide critical insight into the mechanism by which genes involved in cisplatin resistance are regulated and may lead to strategies for treating resistant tumors with increased efficacy.