ΔNp63 activates the Fanconi anemia DNA repair pathway and limits the efficacy of cisplatin treatment in squamous cell carcinoma

TP63, a member of the p53 gene family gene, encodes the Delta Np63 protein and is one of the most frequently amplified genes in squamous cell carcinomas (SCC) of the head and neck (HNSCC) and lungs (LUSC). Using an epiallelic series of siRNAs with intrinsically different knockdown abilities, we show that the complete loss of Delta Np63 strongly impaired cell proliferation, whereas partial Delta Np63 depletion rendered cells hypersensitive to cisplatin accompanied by an accumulation of DNA damage. Expression profiling revealed wide-spread transcriptional regulation of DNA repair genes and in particular Fanconi anemia (FA) pathway components such as FANCD2 and RAD18 known to be crucial for the repair of cisplatin-induced interstrand crosslinks. In SCC patients Delta Np63 levels significantly correlate with FANCD2 and RAD18 - expression confirming Delta Np63 as a key activator of the FA pathway in vivo. Mechanistically, Delta Np63 bound an upstream enhancer of FANCD2 inactive in primary keratinocytes but aberrantly activated by Delta Np63 in SCC. Consistently, depletion of FANCD2 sensitized to cisplatin similar to depletion of Delta Np63. Together, our results demonstrate that Delta Np63 directly activates the FA pathway in SCC and limits the efficacy of cisplatin treatment. Targeting Delta Np63 therefore would not only inhibit SCC proliferation but also sensitize tumors to chemotherapy.