EVIDENCE FOR A MECHANISM OF DEMYELINATION BY HUMAN JC VIRUS - NEGATIVE TRANSCRIPTIONAL REGULATION OF RNA AND PROTEIN-LEVELS FROM MYELIN BASIC-PROTEIN GENE BY LARGE TUMOR-ANTIGEN IN HUMAN GLIOBLASTOMA CELLS

Human JC virus (JCV) is a neurotropic human polyomavirus that was foun d in the plaques and oligodendroglial cells of the brains of patients with the fatal demyelinating disease, progressive multifocal leukoence phalopathy (PML). Transgenic mice expressing JCV large tumor (T)-antig en from integrated DNA showed dysmyelination in the central nervous sy stem. However, the role of T-antigen from episomal DNA in the demyelin ation in PML remains unclear. In this report, we examined the effect o f episomally expressed JCV T-antigen on the expression of myelin basic protein (MBP) in U-87 MG human glioblastoma cells to study the mechan ism of demyelination. Expression assays of the MBP promoter in U-87 MG detected a 2.5-fold reduction in cells expressing intact T-antigen. N ext, U-87 MG expressing T-antigen were examined by RNase protection as says for mRNA accumulation from the endogenous MBP promoter. Also, the expression of the MBP promoter plasmid was determined using in vitro transcription assays with extracts from T-antigen expressing cells. Bo th assays found a similar down-regulation of the MBP promoter by T-ant igen, confirming that negative regulation occurred at the transcriptio nal level for the endogenous and exogenous MBP promoters. Furthermore, in situ immunofluorescence assays and quantitative Western blot analy sis provided convincing evidence of a similar reduction in the level o f MBP produced from the functional endogenous gene in U-87 MG glioblas toma cells expressing T-antigen. Thus, we provide evidence for the rol e of T-antigen in a transcriptional control mechanism for the demyelin ation that is caused by JCV in PML patients. (C) 1996 Wiley-Liss, Inc.