Overview of the HERV-loci differentially expressed in SKOV3WT ovarian carcinoma cells treated with the HDACis romidepsin and vorinostat

To check the acetylation levels at the positions harbouring HERV-loci and assess their variation after the treatment with HDACis (Vorinostat, romidepsin), the univocal genomic coordinates of about 3280 HERV-loci have been compared with the position of the H3AcK9 peaks identified by ChIP-seq analysis. The first analysis confirmed that HDACis are able to modulate the acetylation of repetitive elements, including HERV sequences. Subsequently, we considered only the differential peaks (diffpeaks), i.e. the peaks showing significant variation after the treatment with vorinostat and/or romidepsin. Interestingly, even if more than half of HERV-loci co-localised with acetylation peaks after HDACi treatment, only a minority of them (0.9 to 1.9%) co-localised with diffpeaks, showing mostly a reduction in their acetylation levels. Diffpeaks co-localised HERV-loci could be classified into 24 HERV groups and included the ERV-V2 locus. We focused then on the 11 HERV-loci which co-localised with diffpeaks showing an increase in acetylation levels, hence indicating an increased transcriptional activation after HDACi treatment. Remarkably, diffpeaks corresponding to the ERV-V2 locus were identified in all samples and were the most significantly upregulated in both vorinostat and romidepsin treatment. This was in part confirmed by ChIP-qPCR in different OC cells. Beside ERV-V2, only the HML8 sequence at locus 2q11,2 showed increased acetylation levels in all treated samples, independent from the HDACis used, but having lower statistical significance. The analysis revealed that the treatment with HDACis did not only account for the significant increase of ERV-V2 acetylation, but also led to the shift and concentration of acetylation peaks at the 5’ region of the HERV provirus. This observation allows us to hypothesize that HDACi treatment could not only increase ERV-V2 transcriptional activation, but also modify its pattern of expression, and eventually leading to alternative splicing. SKOV3 wt cells were treated with HDACis romidepsin and vorinostat. After 24 h chromatin immunoprecipitation was performed. The harvested DNA was ChIP sequenced and analyzed. *** Submitter declares raw data are unavailable.