MOLECULAR CHARACTERIZATION OF RESISTANCE TO RADIATION IN A SMALL SUBSET OF TUMOR CELLS INDUCED BY JC VIRUS T-AG IN MICE

JCV is a small, naked tumor polyomavirus with an icosahedral capsids containing a circular, double-stranded DNA genome. Its genome is divided into early and late genes, separated by a non-coding control region (NCCR) containing the promoter, the origin of replication (ORI) and the enhancer elements. Early genes encode for large T antigen, small t antigen and three different T’ proteins called T’135, T’136 and T’165. Late genes encode for the structural proteins VP1, VP2 and VP3, and the non-structural agnoprotein. JCV only replicates in human. In non-permissive cells, they are not able to support viral replication or expression of late genes. In those cells, only the transcription of early genes is observed, such as large T antigen. This leads to genome instability and inactivation of oncosoppressor proteins and eventually tumorigenesis. Cells derived from a murine brain tumor induced by JCV injection have shown different resistance to ionizing radiation. We cultured these BSB8-RR cells and characterized them comparing to the radiation sensitive BSB8 cells. Using MTT assay we showed a resistance to radiation to these cells, compare to the BSB8. We then performed cell-cycle analysis, colony formation assay e soft agar growth assay and we showed that BSB8-RR grow faster and they are more tumorigenic. Since we saw a decrease in the level of large T antigen expression in BSB8-RR, compared to BSB8, we hypothesized an involvement of large T antigen in DNA repair. Using DNA repair assays such as NHEJ and homologous recombination, we suggested that BSB8-RR cells may be resistant to radiation because they have increased homologous recombination activity, compared to the BSB8 cells. We suggested that this increase is due to the lower expression of large T antigen in BSB8-RR, that has been previously reported as inhibitor of homologous recombination. In conclusion, our data showed a more aggressive phenotype of BSB8-RR cells and a resistance to radiation that we suggested is due to the lower level of large T antigen in these cells, compared to BSB8.