p53-dependent R-loop formation and HPV pathogenesis

Abstract

R-loops are trimeric RNA: DNA hybrids that are important physiological regulators of transcription; however, their aberrant formation or turnover leads to genomic instability and DNA breaks. High-risk human papillomaviruses (HPV) are the causative agents of genital as well as oropharyngeal cancers and exhibit enhanced amounts of DNA breaks. The levels of R-loops were found to be increased up to 50-fold in cells that maintain high-risk HPV genomes and were readily detected in squamous cell cervical carcinomas in vivo but not in normal cells. The high levels of R-loops in HPV-positive cells were present on both viral and cellular sites together with RNase H1, an enzyme that controls their resolution. Depletion of RNase H1 in HPV-positive cells further increased R-loop levels, resulting in impaired viral transcription and replication along with reduced expression of the DNA repair genes such as FANCD2 and ATR, both of which are necessary for viral functions. Overexpression of RNase H1 decreased total R-loop levels, resulting in a reduction of DNA breaks by over 50%. Furthermore, increased RNase H1 expression blocked viral transcription and replication while enhancing the expression of factors in the innate immune regulatory pathway. This suggests that maintaining elevated R-loop levels is important for the HPV life cycle. The E6 viral oncoprotein was found to be responsible for inducing high levels of R-loops by inhibiting p53’s transcriptional activity. Our studies indicate that high R-loop levels are critical for HPV pathogenesis and that this depends on suppressing the p53 pathway.

p53 mediated regulation of LINE1 retrotransposition derived R-loops

“…Genome-wide DRIP-seq studies reveal that cis R-loops are predominantly found in GC-rich regions and promoters 42,43 . The recent findings demonstrate that p53 plays a role in global regulation of cis R-loops and viral proteins induce R-loops in p53 inhibited cells 44,45 . However, the precise mechanism by which p53 regulates L1 derived R-loops has yet to be explored.…”

“…The recent findings demonstrate that p53 play a role in global regulation of. cis R-loops and human papillomaviruses proteins induce R-loops in p53 inhibited cells 44,45 . However, the prcise mechanism by which p53 regulates L1 derived R-loops has yet to be explored.…”