IRF9(M87503:9606) is a key transcriptional factor involved in the signaling pathway leading to expression of hundreds of interferon stimulated genes (ISGs). Under normal conditions, IRF9(M87503:9606) exists in a latent form in the cytoplasm. Viral infection triggers the activation of IRF9(M87503:9606) bound to STAT1(M97935:9606) and STAT2(M97934:9606) forming the ISGF3 complex. ISGF3 complex translocates to the nucleus and binds to specific regulatory DNA sequences called IFN-stimulated response elements (ISREs). ISGF3 binding to ISREs initiates the transcription of many IFN-stimulated genes (ISGs).
Several viruses involved in the evasion of the type I and III interferon pathway by inhibiting the interferon regulatory factor-9 protein. The human papillomavirus E7(P03129) oncoprotein abrogates signaling mediated by interferon-alpha. The reovirus µ2(Q00335) protein induces unusual nuclear accumulation of IRF9(M87503:9606) and represses IFN-stimulated gene (ISG) expression.