Beta Human Papillomavirus 8E6 Attenuates Non-Homologous End Joining by Hindering DNA-PKcs Activity

Abstract

Cutaneous viral infections occur in a background of near continual exposure to environmental genotoxins, like UV radiation in sunlight. Failure to repair damaged DNA is an established driver of tumorigenesis and substantial cellular resources are devoted to repairing DNA lesions. Beta-human papillomaviruses (β-HPVs) attenuate DNA repair signaling. However, their role in human disease is unclear. Some have proposed that β-HPV promotes tumorigenesis, while others suggest that β-HPV protects against skin cancer. Most of the molecular evidence that β-HPV impairs DNA repair has been gained via characterization of the E6 protein from β-HPV 8 (β-HPV 8E6). Moreover, β-HPV 8E6 hinders DNA repair by binding and destabilizing p300, a transcription factor for multiple DNA repair genes. By reducing p300 availability, β-HPV 8E6 attenuates a major double strand DNA break (DSB) repair pathway, homologous recombination. Here, β-HPV 8E6 impairs another DSB repair pathway, non-homologous end joining (NHEJ). Specifically, β-HPV 8E6 acts by attenuating DNA-dependent protein kinase (DNA-PK) activity, a critical NHEJ kinase. This includes DNA-PK activation and the downstream of steps in the pathway associated with DNA-PK activity. Notably, β-HPV 8E6 inhibits NHEJ through p300 dependent and independent means. Together, these data expand the known genome destabilizing capabilities of β-HPV 8E6.

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

“…β-HPV8 E6 expression was confirmed in these cells by probing for p300. As previously reported [9], U2OS β-HPV8 E6 cells had less p300 than β-HPV8 E6 obtains most of its known DNA repair inhibitory effects by binding p300. This includes its ability to impair the HR and NHEJ pathways [7,9].…”

“…β-HPV8 E6 attenuates the overall efficiency of both NHEJ and HR [7,9]. While β-HPV8 E6 does not cause any known defects in NHEJ or HR initiation, it prevents resolution of pDNA-PKcs and RAD51 repair complexes by destabilizing p300 [7,9]. These observations are consistent with the hypothesized ability of some β-HPV infections to promote skin cancer, by making UV damage more mutagenic [42,43].…”

“…DSBs are typically repaired in human foreskin keratinocytes within two to eight hours after they occur [7]. However, β-HPV8 E6 causes DSBs to persist for at least twenty-four hours by delaying the resolution of HR (RAD51) and NHEJ (pDNA-PKcs) repair complexes [7,9]. These studies demonstrate that β-HPV8 E6 attenuated HR and NHEJ repair.…”

“…HPV replication requires actively proliferating cells and the replication machinery of the host cells, which puts β-HPV infections in conflict with the cell cycle arrest associated with the repair of UV photolesions [3][4][5][6]. Potentially as a mechanism to counter cell cycle arrest, some β-HPVs hinder the cellular response to DNA damage [7][8][9]. The E6 gene from β-HPV type 8 (β-HPV8 E6) dysregulates the cellular response to DNA damage by binding and destabilizing p300, a histone acetyltransferase that regulate transcription by chromosome remodelling [10][11][12].…”

“…β-HPV8 E6 attenuates the overall efficiency of both NHEJ and HR [7,9]. While β-HPV8 E6 does not cause any known defects in NHEJ or HR initiation, it prevents resolution of pDNA-PKcs and RAD51 repair complexes by destabilizing p300 [7,9].…”