Glial Cell-Specific Regulation of the JC Virus Early Promoter by Large T Antigen

Abstract

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease that results from an oligodendrocyte infection caused by JC virus. The JC virus early promoter directs cell-specific expression of the viral replication factor large T antigen, and thus transcriptional regulation constitutes a major mechanism of glial tropism in PML. We have previously demonstrated that T antigen controls the JC virus basal promoter in a glial cell-specific manner, since T antigen repressed the JC virus and simian virus 40 (SV40) early promoters in glioma cells but induced strong activation of the JC virus early promoter in nonglial cells. To further analyze these findings, T antigen and nuclear extracts from glial and nonglial cells were used to examine DNase I footprints on the proximal promoter. T-antigen binding to site II was more extensive than expected based on sequence homology with SV40, and nuclear proteins protected several regions of the proximal promoter in a cell-specific manner. Multiple Sp1 binding domains were identified. Site-directed mutagenesis revealed that T-antigen-mediated activation required a TATA box sequence, a pentanucleotide repeat immediately upstream of the TATA box, and an Sp1 binding site downstream of the TATA box. When footprints were obtained with mutant promoters which blocked T-antigen-induced transactivation, no change in T-antigen binding was observed. These results suggest that T antigen activates the JC virus basal promoter in nonglial cells by interaction with the transcription initiation complex.The human polyomavirus JC virus is the etiologic agent of progressive multifocal leukoencephalopathy (PML). JC virus selectively destroys oligodendrocytes, leading to multiple areas of demyelination and attendant loss of brain function (3, 31). Once a rare condition, PML is no longer infrequent, occurring in 5% of individuals with AIDS (4). JC virus infection exists in a persistent state in kidney tissue and peripheral blood lymphocytes throughout the life of healthy individuals. In the setting of immunodeficiency, the virus infects and destroys oligodendrocytes, producing patches of myelin loss in subcortical white matter (22). Thus, the neuropathological features suggest that reactivated JC virus infection is specific for glial cells.The JC virus early promoter directs cell-specific expression of the large T antigen, which is required for viral replication, and thus transcriptional regulation constitutes a major mechanism of glial tropism of PML (15). The MH1 form of the JC virus promoter was directly isolated from the brain of a PML patient. Its sequence diverges somewhat from that of the original Mad-1 promoter (11); however, both MH1 and Mad-1 proximal promoters have sequence identity from the initiating codon for T antigen up to a pentanucleotide site just upstream of the viral TATA sequence. The pentanucleotide repeat sequence in MH1 varies by a single base from the perfect repeats seen in the Mad-1 variant of the promoter. This sequence conservation implies that this regi...

Human glial chimeric mice reveal astrocytic dependence of JC virus infection

“…One might then anticipate the emergence and selection of dominant JCV mutants with time during disease progression in any given patient. While JCV mutations have been noted to arise during the course of disease and have been well documented in VP1 (26,27), mutation in JCV's noncoding regulatory regions may be especially critical to disease progression (29)(30)(31). Together, these observations suggest that the clonal selection of more infective mutants may occur naturally in human hosts (8); if so, such clonal evolution might account for the terminal acceleration of demyelination often observed in PML patients.…”

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“…The large T antigen ORI binding function is not necessary for activation of late transcription of SV40 (229). Instead, T antigen promotes late transcription by interacting with components of the basal transcription machinery, including TATA binding protein (TBP), TBP-associated factors (TAFs), and transcription factors, including Sp1 (239). T antigen may also function directly as a TAF (92).…”

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