Selective suppression of IRF5 activity by Lyn in the TLR-MyD88 pathway restrains the development of SLE-like disease,
Tatsuma Ban1, Go Sato1, Akira Nishiyama1, Satoko Matsunaga1, Ayuko Kimura2, Yayoi Kimura2, Hideyuki Yanai3, Yoshiko Matsumoto4, Hiroe Hihara4, Tadashi Yamamoto5, Hisashi Hirano2, Akihide Ryo1, Kappei Tsukahara4, Kentaro Yoshimatsu4, Tadatsugu Taniguchi3, Tomohiko Tamura1, 2
1Yokohama City University Graduate School of Medicine, Yokohama, Japan, 2Advanced Medical Research Center, Yokohama City University, Yokohama, Japan, 3Institute of Industrial Science, The University of Tokyo, Tokyo, Japan, 4Eisai Co., Ltd., Tsukuba, Japan, 5Okinawa Institute of Science and Technology Graduate School, Okinawa, Japan
The transcription factor interferon regulatory factor-5 (IRF5) plays an important role in Toll-like receptor (TLR)-mediated innate immune responses, whereas it contributes to the pathogenesis of systemic lupus erythematosus (SLE). However, little is known about the mechanism regulating the extent of IRF5 activation, especially the negative regulatory mechanism. Lyn, a Src family kinase, is also implicated in human SLE, and Lyn–/– mice develop an SLE-like disease. Here we show that Lyn selectively inhibits the activity of IRF5 in the TLR-MyD88 pathway, thereby restraining the development of autoimmunity. Interestingly, Lyn inhibited IRF5 in a kinase activity-independent manner; it bound to IRF5 and inhibited ubiquitination and phosphorylation of IRF5. Consistently, these post-translational modifications of IRF5 were significantly enhanced in TLR7/9-stimulated Lyn–/– bone marrow-derived dendritic cells (BMDCs), resulting in the boost of IRF5-dependent type-I IFN induction. Moreover, DCs freshly isolated from Lyn–/– mice exhibited phosphorylation and enhanced nuclear translocation of IRF5. These results suggest that IRF5 is constitutively activated in vivo in DCs, if Lyn is lost. Importantly, even monoallelic ablation of the Irf5 gene was sufficient to alleviate the hyper-production of type-I IFNs in TLR7/9-stimulated Lyn–/– BMDCs, and to ameliorate the development of SLE-like symptoms in Lyn–/– mice. Taken together, our results identify Lyn as a critical suppressor of IRF5 in the TLR-MyD88 pathway, and implicate that the selective control of IRF5 activity may contribute to better therapeutics for SLE. We will also show our recent results of high-throughput-screening of small molecular compounds that inhibit IRF5 transcriptional activity.