Characterization of ALTO-encoding circular RNAs expressed by Merkel cell polyomavirus and trichodysplasia spinulosa polyomavirus

Yang, R.; Lee, E.E.; Kim, J.; Choi, J.H.; Kolitz, E.; Chen, Y.T.; ... ; Wang, R.C. (2021)

Article / Letter to editor

Circular RNAs (circRNAs) are a conserved class of RNAs with diverse functions, including serving as messenger RNAs that are translated into peptides. Here we describe circular RNAs generated by human polyomaviruses (HPyVs), some of which encode variants of the previously described alternative large T antigen open reading frame (ALTO) protein. Circular ALTO RNAs (circALTOs) can be detected in virus positive Merkel cell carcinoma (VP-MCC) cell lines and tumor samples. CircALTOs are stable, predominantly located in the cytoplasm, and N-6-methyladenosine (m(6)A) modified. The translation of MCPyV circALTOs into ALTO protein is negatively regulated by MCPyV-generated miRNAs in cultured cells. MCPyV ALTO expression increases transcription from some recombinant promoters in vitro and upregulates the expression of multiple genes previously implicated in MCPyV pathogenesis. MCPyV circALTOs are enriched in exosomes derived from VP-MCC lines and circALTO-transfected 293T cells, and purified exosomes can mediate ALTO expression and transcriptional activation in MCPyV-negative cells. The related trichodysplasia spinulosa polyomavirus (TSPyV) also expresses a circALTO that can be detected in infected tissues and produces ALTO protein in cultured cells. Thus, human polyomavirus circRNAs are expressed in human tumors and infected tissues and express proteins that have the potential to modulate the infectious and tumorigenic properties of these viruses.Author summaryHuman polyomaviruses (HPyV) have been linked to diseases including Merkel cell carcinoma (MCC), a skin cancer caused by Merkel cell polyomavirus (MCPyV), and skin and hair eruptions caused by trichodysplasia spinulosa polyomavirus (TSPyV). We discover that HPyVs generate single-stranded, circular RNAs (circRNAs) in affected tissues. Both MCPyV and TSPyV generate circRNAs encompassing part of the early region (circALTOs) that can be translated to the alternative large T antigen open reading frame (ALTO) protein in cultured cells. Previously described microRNAs (miRNAs) generated by MCPyV have the ability to inhibit the expression of ALTO. MCPyV circALTOs are enriched in extracellular vesicles produced by MCC cell lines and cells that express circALTO. Finally, we discover that MCPyV ALTO protein enhances transcription from some recombinant promoters and promotes the expression of multiple host cell genes previously implicated in MCPyV pathogenesis. Thus, HPyVs generate circRNAs, including circALTOs that are translated to ALTO protein, and MCPyV ALTO has the ability to regulate transcription.

• All authors: Yang, R.; Lee, E.E.; Kim, J.; Choi, J.H.; Kolitz, E.; Chen, Y.T.; Crewe, C.; Salisbury, N.J.H.; Scherer, P.E.; Cockerell, C.; Smith, T.R.; Rosen, L.; Verlinden, L.; Galloway, D.A.; Buck, C.B.; Feltkamp, M.C.; Sullivan, C.S.; Wang, R.C.
• Date: 2021-05-01
• Journal: PLoS Pathogens
• Volume: 17
• Issue: 5
• DOI: doi:10.1371/journal.ppat.1009582
• Link: https://journals.plos.org/plospathogens/article/file?id=10.1371/journal....