title: Functional regulation of MyD88-activated interferon regulatory factor 5 by K63-linked polyubiquitination.
abstract: Interferon regulatory factor 5 (IRF-5) plays an important role in the innate antiviral and inflammatory response. Specific IRF-5 haplotypes are associated with dysregulated expression of type I interferons and predisposition to autoimmune disorders. IRF-5 is activated by Toll-like receptor 7 (TLR7) and TLR9 via the MyD88 pathway, where it interacts with both MyD88 and the E3 ubiquitin ligase, TRAF6. To understand the role of these interactions in the regulation of IRF-5, we examined the role of ubiquitination and showed that IRF-5 is subjected to TRAF6-mediated K63-linked ubiquitination, which is important for IRF-5 nuclear translocation and target gene regulation. We show that while the murine IRF-5 and human IRF-5 variant 4 (HuIRF-5v4) and HuIRF-5v5 are ubiquitinated, an IRF-5 bone marrow variant mutant containing an internal deletion of 288 nucleotides is not ubiquitinated. Lysine residues at positions 410 and 411 in a putative TRAF6 consensus binding domain of IRF-5 are the targets of K63-linked ubiquitination. Mutagenesis of these two lysines abolished IRF-5 ubiquitination, nuclear translocation, and the IFNA promoter-inducing activity but not the IRF-5-TRAF6 interaction. Finally, we show that IRAK1 associates with IRF-5 and that this interaction precedes and is required for IRF-5 ubiquitination and activation. Thus, our findings offer a new mechanistic insight into IRF-5 gene induction program through hitherto unknown processes of IRF-5 ubiquitination.
authors.affiliation: Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, MD 21231, USA.
authors.forename: Mumtaz Yaseen
authors.initials: MY
authors.lastname: Balkhi
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Fitzgerald
authors.forename: Paula M
authors.initials: PM
authors.lastname: Pitha
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000378:metabolism*; D007370:Interferon Type I / Q000235:genetics / Q000378:metabolism; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism*; D025821:Polyubiquitin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination
chemical_list: C431713:IRF5 protein, human; D050835:Interferon Regulatory Factors; D007370:Interferon Type I; C498178:Irf5 protein, mouse; D053594:Myeloid Differentiation Factor 88; D048029:TNF Receptor-Associated Factor 6; D025821:Polyubiquitin; D053592:Interleukin-1 Receptor-Associated Kinases; C507769:Irak1 protein, mouse; D008239:Lysine