Integrated HPV18 acts as enhancer-like RNA and form phase-separated condensates to promote oncogenic genes expression.
Most of the cervical cancers are caused by human papillomavirus (HPV) infection. It has been known that, in HeLa cells, HPV18 viral genome is integrated at chromosome 8q24.21 and activates transcription of proto-oncogene c-Myc. However, the mechanism of how the integrated HPV fragment exhibits transcription activation function has not been fully elucidated. In this study, we found that HPV18 transcripts themselves have an enhancer RNA-like function to activate their proximal genes including CCAT1-5L and c-Myc. We showed that the human genome-integrated HPV18 genes are activated by transcription coregulators BRD4, Mediator. The transcribed HPV18 RNAs form a liquid-like condensate at chromosome 8q24.21 locus, which in turn accumulates RNA polymerase II. Moreover, we identified uncharacterized transcript from Upstream Region of CCAT1-5L, named URC. The URC RNA is transcribed as a chimera RNA with HPV18 and is composed of 3'-untranslated region of HPV18 transcript. We found that the URC contributes to stabilization of HPV18 RNAs by supplying a poly-adenylation site for HPV18 transcript. Our findings suggest that HPV18 integration at 8q24.21 locus causes HPV18-URC chimera RNA and promotes tumorigenesis through RNA-based liquid droplet formation. Overall design: Experiment 1: 4sU-labeled RNA-seq prepaerd from HeLa cells upon treatment with 1,6-hexanediol and non-treat using D. melanogastor S2 cells as spike-in control. Experiment 2: 4sU-labeled RNA-seq in control and URC LNA-transfected HeLa cells.