JC Polyomavirus in the etiology of brain tumors: reality or random association?

JC Polyomavirus (JCPyV) is a human neurotropic human virus, recognized as the causative agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system (CNS). JCPyV persistence in the brain alongside the experimental evidence of its oncogenic potential suggests a possible involvement in brain tumor development. A key factor in cellular transformation is the Large T Antigen (LTAg), which disrupts several host regulatory pathways. Among them, the Wnt/β-catenin cascade is crucial for neural development, and its dysregulation is a well-established contributor to brain tumorigenesis. In light of these considerations, the current PhD project aimed to elucidate the plausible contribution of JCPyV in brain tumor formation and progression, focusing on the impact of JCPyV infection on the Wnt signaling pathway. Notably, the study was conducted both ex vivo, in a cohort of pediatric patients affected by glioma and in vitro, employing a glioblastoma cell line. The prevalence and molecular state of JCPyV DNA, as well as as viral genes and miRNAs expression were examined in 101 gliomas by PCR assays. In parallel, expression levels of β-catenin and Wnt target genes was assessed by RT-qPCR. For in vitro studies, the human glioblastoma cell line, U87-MG, was infected with supernatants collected from previous transfection experiments and analyzed for JCPyV viral load, LTAg and VP1 genes and viral miRNAs by RT-qPCR. Moreover, the Wnt signalling was explored monitoring the expression levels of target genes and evaluating the subcellular distribution of β-catenin. JCPyV DNA was found in about 31% brain tumors, with archetypal NCCR and canonical VP1. The LTAg gene was reported in all JCPyV-positive tumors. Interestingly, among them, 5 tissues did not express VP1 nor viral miRNAs, supporting a hampering of late region transcription. Over-expression of β-catenin, c-myc, cyclin D1, Fgf20 and Sall4 was observed in JCPyV-positive tissues compared to negative ones. To corroborate the obtained results, an in vitro model was developed using U87-MG cells. Once assessed the capability of this cell line to support viral replication and transcription, the Wnt signalling was explored, revealing higher levels of genes encoding Wnt pathway components, following JCPyV infection. Notably, the observed over-expression was further supported by the predominant nuclear localization of β-catenin in infected cells. In conclusion, this PhD project provides new insights into the potential role of JCPyV in brain tumor development through combined ex vivo and in vitro approaches. Detection of JCPyV in CNS tumors and activation of Wnt signaling observed in virus-positive and supported by evidence in vitro, strongly suggest that the virus may exploit this pathway to manipulate cellular processes, promoting viral replication while driving uncontrolled proliferation and the acquisition of a more malignant phenotype. These findings highlight the need to monitor JCPyV in the CNS and explore its role in gliomagenesis. Although additional studies are needed to clarify virus-host interactions, the in vitro model here developed offers a valuable tool for future mechanistic and therapeutic investigations.