Interferon regulator transcription factors (IRF) are a family characterized by a helix-turn-helix DNA binding domain enriched in tryptophan repeats. IRF family members show diverse cellular regulation of interferon-stimulated gene transcription, viral-mediated gene activation, apoptosis, differentiation, and cellular growth. IRF2 functions as a regulator of type I interferons influencing cellular proliferation and immune response through transcriptional regulation. IRF2 competitively inhibits IRF1 gene activation, as well as, stimulating transcription on its own. Human IRF3 is a transcription factor that binds the interferon-sensitive response element (ISRE) and is activated by Toll-like receptors, TLR3 and TLR4.
Interferon regulatory factor 4 (IRF4), also known as MUM1 and LSIRF, is a 51 kDa lymphocyte-restricted transcription factor. It is required for immunoglobulin class switching and terminal differentiation of B cells. IRF4 is overexpressed in multiple myeloma and cooperates with Myc in an autoregulatory loop. In T cells, IRF4 is required for the production of IL-4. IRF4 contains an N-terminal DNA binding domain that is homolgous to that in other IRF proteins. Within the C-terminal domain (aa 130 - 451), human IRF4 shares 90% aa sequence identity with mouse and rat IRF4. Alternate splicing may generate isoforms with N-terminal, C-terminal, or internal deletions.