vIRF3 encoded by Kaposi's sarcoma-associated herpesvirus inhibits T-cell factor-dependent transcription via a CREB-binding protein-interaction motif.

Kaposi's sarcoma-associated herpesvirus (KSHV) is an etiological agent of Kaposi's sarcoma and primary effusion lymphoma. Like other herpesviruses, KSHV has two distinct life cycles: latent and lytic. Among KSHV latent genes, viral interferon regulatory factor 3 (vIRF3), which shares homology with cellular IRFs, is a multifunctional protein. To identify unknown functions of vIRF3, we performed luciferase-reporter assays in the presence of vIRF3. These analyses revealed that overexpression of vIRF3 inhibited T-cell factor (TCF)-dependent transcriptional activity. This TCF-dependent transcription was associated with the Wnt signaling pathway, which normally regulates embryonic development, but contributes to oncogenesis under dysregulated conditions. Using a mutagenesis analysis, we identified a CREB-binding protein-interaction motif (LXXLL) in vIRF3 as an important region for its inhibitory activity. Collectively, our findings provide insight into the dysregulation of host signaling pathways in KSHV-infected cells.