High expression of JC polyomavirus-encoded microRNAs in progressive multifocal leukoencephalopathy tissues and its repressive role in virus replication

JC polyomavirus (JCPyV, JCV) causes progressive multifocal leukoencephalopathy (PML) in immunocompromised hosts. JCPyV replicates in oligodendrocytes within the brain tissue of patients with PML. The JCPyV genome encodes a microRNA (miRNA) in the region encoding the large T antigen. JCPyV-encoded miRNA (miR-J1) has been detected in the tissue and cerebrospinal fluid samples of patients with PML; however, there are no reports describing the localization of polyomavirus-encoded miRNA in histological samples of patients with virus-associated diseases. In the present study, we detected high miR-J1 expression in the nuclei of JCPyV-infected cells in PML tissue samples via in situ hybridization. Additionally, in situ hybridization also revealed the expression of BK polyomavirus (BKPyV, BKV)-encoded miRNA in lesions of BKPyV-associated nephropathy. In situ hybridization for miR-J1-5p and -3p showed positive signals in 24/25 (96%) of PML tissues that were positive for JCPyV by immunohistochemistry. Higher copy numbers of miR-J1 were detected in PML tissues than in non-PML tissues by real-time reverse transcription PCR. Next generation sequencing showed that miR-J1-5p, a mature miRNA of primary miRNA, was predominant in the lesions compared with miR-J1-3p, another mature miRNA. Deletion or mutation of miR-J1 in recombinant JCPyV promoted the production of JCPyV-encoded proteins in cells transfected with JCPyV DNA, suggesting that polyomavirus-encoded miRNA may have a repressive role in viral replication in PML tissues. In situ hybridization for viral miRNA may be a useful diagnostic tool for PML.
Author summary JCPyV causes PML in immunocompromised hosts. In patients with PML, JCPyV replicates in the oligodendrocytes of brain tissue. A JCPyV-encoded miRNA, miR-J1, has been detected by real-time PCR in the brain tissue and cerebrospinal fluid of patients with PML; however, there are no reports describing the localization of polyomavirus-encoded miRNA in histological samples of patients with virus-associated diseases. In this study, in situ hybridization clearly showed that miR-J1 was highly expressed in the nuclei of JCPyV-infected cells within PML tissue samples. A high level of BKPyV-encoded miRNA expression was also found in BKPyV-associated nephropathy. The results of experiments with recombinant JCPyV demonstrate that a defect of miR-J1 promotes JCPyV replication in cells transfected with JCPyV DNA. The observed high expression of viral miRNA, which has a repressive role in virus replication, suggests an autoregulation mechanism in virus replication as well as the possibility that viral miRNA may be a new therapeutic tool for PML.