RESUMO
Interferon regulatory factor-5 (IRF5), a transcription factor critical for the induction of innate immune responses, contributes to the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE) in humans and mice. Lyn, a Src family kinase, is also implicated in human SLE, and Lyn-deficient mice develop an SLE-like disease. Here, we found that Lyn physically interacted with IRF5 to inhibit ubiquitination and phosphorylation of IRF5 in the TLR-MyD88 pathway, thereby suppressing the transcriptional activity of IRF5 in a manner independent of Lyn's kinase activity. Conversely, Lyn did not inhibit NF-κB signaling, another major branch downstream of MyD88. Monoallelic deletion of Irf5 alleviated the hyperproduction of cytokines in TLR-stimulated Lyn(-/-) dendritic cells and the development of SLE-like symptoms in Lyn(-/-) mice. Our results reveal a role for Lyn as a specific suppressor of the TLR-MyD88-IRF5 pathway and illustrate the importance of fine-tuning IRF5 activity for the maintenance of immune homeostasis.
Assuntos
Autoimunidade , Células Dendríticas/imunologia , Fatores Reguladores de Interferon/metabolismo , Lúpus Eritematoso Sistêmico/imunologia , Quinases da Família src/metabolismo , Animais , Células Cultivadas , Citocinas/metabolismo , Humanos , Tolerância Imunológica , Imunidade Inata , Fatores Reguladores de Interferon/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fator 88 de Diferenciação Mieloide/metabolismo , NF-kappa B/metabolismo , Fosforilação , Ligação Proteica , Transdução de Sinais , Receptores Toll-Like/metabolismo , Ativação Transcricional , Ubiquitinação , Quinases da Família src/genéticaRESUMO
Monocytes regulate host defenses, inflammation, and tissue homeostasis. The transcription factor interferon regulatory factor-8 (IRF8) stimulates monocyte/macrophage differentiation, yet genome-wide understanding of the differentiation program initiated by IRF8 is lacking. By combining chromatin immunoprecipitation sequencing with gene expression profiling, we show that during IRF8-dependent monocyte differentiation, IRF8 binding occurs at both promoter-proximal and promotor-distal regions together with the transcription factor PU.1 and is associated with gene induction. Many of the promoter-distal IRF8 binding sites show an increase in histone H3 lysine 4 monomethylation, a signature for enhancers. However, about half the IRF8-induced genes were not bound by IRF8, suggesting the involvement of downstream transcription factors. Analysis of DNA motifs in cis-regulatory elements of these indirect IRF8 target genes predicted that Krüppel-like factor-4 (KLF4)-essential for Ly6C(+) monocyte development-is one such factor. Indeed, monocyte development in Irf8(-/-) mice is as defective as that in Klf4(-/-) chimeric mice. Moreover, Irf8(-/-) monocyte-dendritic cell progenitors do not express Klf4 messenger RNA. Introduction of KLF4 into an Irf8(-/-) myeloid progenitor cell line induced a subset of IRF8 target genes and caused partial monocyte differentiation. Taken together, our present results uncover genome-wide behavior of IRF8 and identify an IRF8-KLF4 axis that operates during monocyte differentiation.