CircPVT1: a pivotal circular node intersecting Long Non-Coding-PVT1 and c-MYC oncogenic signals

The role of circular RNAs in oncogenesis has begun to be widely studied in recent years, due to the significant impact that these molecules have in disease pathogenesis, as well as their potential for the future of innovative therapies. Moreover, due to their characteristically circular shape, circular RNAs are very resistant molecules to RNA degradation whose levels are easily assessed in body fluids. Accordingly, they represent an opportunity for the discovery of new diagnostic and prognostic markers in a wide range of diseases. Among circular RNAs, circPVT1 is a rather peculiar one that originates from the circularization of the exon 2 of the PVT1 gene that encodes a pro-tumorigenic long non-coding RNA named lncPVT1. There are a few examples of circular RNAs that derive from a locus producing another non-coding RNA. Despite their apparent transcriptional independence, which occurs using two different promoters, a possible synergistic effect in tumorigenesis cannot be excluded considering that both have been reported to correlate with the oncogenic phenotype. This complex mechanism of regulation appears to also be controlled by c-MYC. Indeed, the PVT1 locus is located only 53 Kb downstream c-MYC gene, a well-known oncogene that regulates the expression levels of about 15% of all genes. Here, we review circPVT1 origin and biogenesis highlighting the most important mechanisms through which it plays a fundamental role in oncogenesis, such as the well-known sponge activity on microRNAs, as well as its paradigmatic interactome link with lncPVT1 and c-MYC expression.