Beta human papillomavirus 8 E6 allows colocalization of non-homologous end joining and homologous recombination repair factors

Abstract

Beta human papillomavirus (β-HPV) are hypothesized to make DNA damage more mutagenic and potentially more carcinogenic. Double strand breaks in DNA (DSBs) are the most deleterious DNA lesion. They are typically repaired by homologous recombination (HR) or non-homologous end joining (NHEJ). HR occurs after DNA replication while NHEJ can occur at any point in the cell cycle. They are not thought to occur in the same cell at the same time. By destabilizing p300, β-HPV type 8 protein E6 (β-HPV8 E6) attenuates both repair pathways. However, β-HPV8 E6 delays rather than abrogates DSB repair. Thus, β-HPV8 E6 may cause DSBs to be repaired through a more mutagenic process. To evaluate this, immunofluorescence microscopy was used to detect colocalization, formation, and resolution of DSB repair complexes following damage. Flow cytometry and immunofluorescence microscopy were used to determine the cell cycle distribution of repair complexes. The resulting data show that β-HPV8 E6 causes HR factors (RPA70 and RAD51) to colocalize with a persistent NHEJ factor (pDNA-PKcs). RPA70 complexes gave way to RAD51 complexes as in canonical HR, but RAD51 and pDNA-PKcs colocalization did not resolve within 32 hours of damage. The persistent RAD51 foci occur in G1 phase, consistent with recruitment after NHEJ fails. Chemical inhibition of p300, p300 knockout cells, and an β-HPV8 E6 mutant demonstrate that these phenotypes are the result of β-HPV8 E6-meidated p300 destabilization. Mutations associated with DSB repair were identified using next generation sequencing after a CAS9-induced DSB. β-HPV8 E6 increases the frequency of mutations (>15 fold) and deletions (>20 fold) associated with DSB repair. These data suggest that β-HPV8 E6 causes abnormal DSB repair where both NHEJ and HR occur at the same lesion and that his leads to deletions as the single stranded DNA produced during HR is removed by NHEJ.