ZPR1 Is Dispensable for HPV R-Loop Resolution but Regulates Host R-Loop Dynamics

Abstract

The human papillomavirus (HPV) is a small, non-enveloped virus with a circular double-stranded DNA genome. The HPV genome encodes the E2 activator protein, which is required for viral transcription. R-loops are triple-stranded nucleic acid structures that occur when newly synthesized single-stranded RNA anneals to duplex DNA. These structures form during papillomavirus transcription. We and others have demonstrated that resolution of viral R loops is crucial for HPV episomal maintenance. ZPR1 is a zinc finger protein that can recruit SETX to mammalian R-loops to mediate resolution. E2 binds to and recruits SETX, an R-loop helicase, to the viral promoter. We observed E2 in complex with SETX and ZPR1. However, we found that ZPR1 depletion decreased viral R-loops while enhancing cellular R-loops. ZPR1 depletion also increased SETX binding to the viral promoter. These data suggest that ZPR1 is not required for HPV R-loop resolution, in contrast to what has been observed in mammalian cells. We detected the E2 protein associated with R-loops and found that E2 overexpression increases cell-derived R-loop formation. Analysis of TCGA datasets revealed that ZPR1, but not SETX, mRNA expression is significantly reduced in HPV-positive cervical and head and neck cancers. Together, these findings indicate that while E2 mediates HPV R-loop resolution, it also promotes R-loop accumulation in the host genome, likely through SETX sequestration.