Beta human papillomavirus 8E6 promotes alternative end-joining

Double strand breaks (DSBs) are one of the most lethal DNA lesions in cells. Previous studies show that the E6 protein of beta-human papillomavirus (HPV8 E6) impairs two major DSB repair pathways homologous recombination (HR) and non-homologous end-joining (NHEJ). However, HPV8 E6 delays but does not eliminate DSB repair capability of cells. How DSBs are repaired in cells with HPV8 E6 remains to be studied. We hypothesis that HPV8 E6 promotes a backup DSB repair pathway, alternative end-joining (Alt-EJ). Using CAS9 based Alt-EJ reporters, we show that HPV8 E6 promotes Alt-EJ. Further, using small molecule inhibitors, CRISPR/CAS9 gene knockout, and HPV8 E6 mutant, we find that HPV8 E6 promotes Alt-EJ by binding p300, an acetyltransferase that facilitates DSB repair by HR and NHEJ. Finally, we analyzed whole genome sequencing data from genomes of human foreskin keratinocytes expressing HPV8 E6 and found they displayed an increased frequency of deletions bearing the microhomology signatures of Alt-EJ. This study fills the knowledge gap how DSB is repaired in cells with HPV8 E6 and the mutagenic consequences of HPV8 E6 mediated p300 destabilization. Broadly, this study supports the hypothesis that beta-HPV promotes cancer formation by increasing genomic instability.