The activating protein 1 (AP-1) family of regulatory proteins is characterized as immediate-early inducible transcription factors which were shown to be activated by a variety of stress-related stimuli and to be involved in numerous biological processes, including cellular and viral gene expression, cell proliferation, differentiation, and tumorigenesis. We have recently demonstrated the involvement of the AP-1 family members c-Jun and c-Fos in transcriptional regulation of the human polyomavirus, JC virus (JCV), genome. Here, we further examined their role in JCV gene regulation and replication through their physical and functional interaction with JCV early regulatory protein large T antigen (T-Ag). Transfection and replication studies indicated that c-Jun and c-Fos can significantly diminish T-Ag-mediated JCV gene transcription and replication. Affinity chromatography and coimmunoprecipitation assays demonstrated that c-Jun and T-Ag physically interact with each other. Results from band shift assays showed that the binding efficiency of c-Jun to the AP-1 site was reduced in the presence of T-Ag. In addition, we have mapped, through the use of a series of deletion mutants, the regions of these proteins which are important for their interaction. While the c-Jun interaction domain of T-Ag is localized to the middle portion of the protein, the T-Ag interacting domain of c-Jun maps to its basic-DNA binding region. Results of transient-transfection assays with various c-Jun mutants and T-Ag expression constructs further confirm the specificity of the functional interaction between c-Jun and T-Ag. Taken together, these data demonstrate that immediate-early inducible transcription factors c-Jun and c-Fos physically and functionally interact with JCV major early regulatory protein large T-Ag and that this interaction modulates JCV transcription and replication in glial cells.

Progressive multifocal encephalopathy (PML) is a fatal demyelinating disease of the CNS, caused by the lytic infection of oligodendrocytes by a human polyomavirus, JC virus. PML is rare disease that mostly develops in patients with underlying immunosuppressive conditions, including Hodgkin’s lymphoma, lymphoproliferative diseases, AIDS and in those undergoing antineoplastic therapy. However, consistent with the occurrence of PML under immunocompromised conditions, this disease seems to also be steadily increasing among patients with autoimmune diseases (e.g., multiple sclerosis and Crohn’s disease) who are treated with antibody-based regimens (natalizumab, efalizumab and rituximab). This unexpected occurrence of the disease among such a patient population reconfirms the existence of a strong link between underlying immunosuppressive conditions and development of PML. These recent observations have generated a new interest among investigators to further examine the unique biology of JC virus.

The activating transcription factor 1 (AP-1) family of proteins consists of a large number of inducible factors that are implicated in many biological processes, including cellular and viral gene expression, cell proliferation, differentiation, and tumorigenesis. Here, we investigated the role of the AP-1 family members c-Jun and c-Fos in transcriptional regulation of the JC virus (JCV) promoter in glial cells. DNA binding studies demonstrated the specific association of c-Jun with its DNA sequences corresponding to the AP-1 site within the JCV promoter. Functional analysis of the promoter showed that ectopic expression of c-Jun and c-Fos results in an additive activation of the JCV early and late promoters. Further functional assays indicated that the JCV AP-1 binding site is sufficient to confer responsiveness to both c-Jun/c-Fos- and UV-induced activation when transposed to a heterologous promoter. Analysis of c-Jun expression during the viral infection cycle by Western blotting revealed that c-Jun is posttranslationally modified by phosphorylation and its protein level is substantially increased at the late phases of infection cycle. Altogether, our findings indicate that AP-1 family members may play a role in the pathogenesis of JCV-induced disease in the human brain by modulating JCV gene transcription.