JC virus causes the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML) under immunosuppressive states such as AIDS. During the pathogenesis of AIDS, HIV-infected microglia secrete cytokines including interleukin-1 and tumor necrosis factor-alpha (TNF-alpha), which affect neuronal cells resulting in dysfunction of the CNS. We hypothesized that extracellular stimuli released from HIV-infected microglia may reactivate JC virus by affecting neighboring oligodendrocytes. In the present study, we found that phorbol myristate acetate (PMA) and interleukin-1beta (IL-1beta) dramatically increased JC virus transcription in glial cells. Site-directed mutagenesis and gel shift analyses revealed that PMA and IL-1beta strongly induced nuclear factor-1 (NF-1) binding to the JC virus enhancer region, increasing transcriptional activity of the viral early promoter. Additionally, we demonstrated that protein kinase C (PKC) pathways were involved in the PMA/IL-1beta-mediated up-regulation of the JC virus early promoter. These findings may represent one of the possible mechanisms for higher incidence of PML among AIDS patients.