Identification and characterization of a novel GGA/C-binding protein, GBP-i, that is rapidly inducible by cytokines

Immunosuppressive states with accompanying alterations in cytokine profiles have been postulated to play a vital role in the reactivation of viruses from latency. Cytokines regulate gene express by activating transcription factors via well-characterized signal transduction pathways. In this study, we report the identification of a novel inducible protein, GBP-i, that binds to a double-stranded GGA/C-rich region of the transcriptional control region of the human papovavirus JC virus (JCV), specifically within the origin of viral DNA replication. GBP-i is distinct from previously characterized GC-box-binding proteins with respect to both its sequence specificity and its electrophoretic mobility on native and denaturing gels. GBP-i responds within 90 min to phorbol myristate acetate stimulation; however, unlike typica phorbol myristate acetate-inducible factors, this rapid induction is regulated primarily at the transcriptional level. Further, the induction of GBP-i appears to be widespread and mediated by many inflammatory cytokines, including interleukin-1β, tumor necrosis factor alpha, gamma interferon, and transforming growth factor β. Interestingly, the induced protein acts as a transcriptional repressor in its native context in the JCV_L promoter. However, when its binding sequence is transposed to a heterologous promoter, GBP-i appears to function as a transcriptional activator. The data presented here suggest a role for GBP-i in cytokine-mediated induction of viral and cellular genes.