The Human Papilloma virus is a major risk factor for Oropharyngeal cancers (OPC), with HPV16 being associated with up to 75% of cases. Small non-coding RNAs, such as microRNAs (miRNAs) have been shown to be regulated by HPV16, promoting cancer development. The miRNA expression profile in this cancer type is unique and is key to uncovering what pathways are associated with viral tumorigenesis.
To further our understanding, we investigated the expression levels of miRNAs in OPC HPV16(+) tissue using an LNA miRNA array. miR-33a, miR-210, miR-142-3p and miR-496 were differentially expressed between HPV16(+) and HPV16(-) samples. Of these miR-496 and miR-33a were the most significantly deregulated. Using a bioinformatics approach, we constructed a novel viral/target/miRNA interactome to identify a mechanistic link between miR-33a, SREBF2 and miR-496. Interestingly, SREBF2 harbours miR-33a and we believe there is a correlation whereby E6 and E7 regulates the expression of SREBF2/miR-33a which then impacts of miR-496. TCGA analysis showed that SREBF2 was significantly higher in the HPV(+) OPC and not in cervical samples. We also vetted SREBF2 levels in our OPC cohort. It suggests this pathway is unique to OPCs. We knocked out E7/E6 and SREFB2 using siRNAs alone or in combination and showed that the viral oncogenes can regulate SREBF2/miR-33a and miR-496. In addition, the overexpression of E6/E7 has an effect on SREBF2/miR-33 levels.
This study has identified a specific regulatory pathway involving HPV16 E6/E7 and specific miRNAs. These events may be important for viral replication and transformation of the cell. More so, the construction of viral interactomes combined with in vitro approaches can provide novel insights for discovering mechanistic links not only in OPC but can be extended to other human diseases.