Positive Regulation of Interferon Regulatory Factor 3 Activation by Herc5 via ISG15 Modification

Abstract

Virus infection induces host antiviral responses, including induction of type I interferons. Transcription factor interferon regulatory factor 3 (IRF3) plays a pivotal role and is tightly regulated in this process. Here, we identify HERC5 (HECT domain and RLD 5) as a specific binding protein of IRF3 by immunoprecipitation. Ectopic expression or knockdown of HERC5 could, respectively, enhance or impair IRF3-mediated gene expression. Mechanistically, HERC5 catalyzes the conjugation of ubiquitin-like protein ISG15 onto IRF3 (Lys193, -360, and -366), thus attenuating the interaction between Pin1 and IRF3, resulting in sustained IRF3 activation. In contrast to results for wild-type IRF3, the mutant IRF3(K193,360,366R) interacts tightly with Pin1, is highly polyubiquitinated, and becomes less stable upon Sendai virus (SeV) infection. Consistently, host antiviral responses are obviously boosted or crippled in the presence or absence of HERC5, respectively. Collectively, this study characterizes HERC5 as a positive regulator of innate antiviral responses. It sustains IRF3 activation via a novel posttranslational modification, ISGylation.

We thank Genhong Cheng (University of California), Jon M. Huibregtse (University of Texas), Hongbing Shu (Wuhan University, China), Hong Tang (Institute of Biophysics, CAS), and Zhigao Bu (Chinese Academy of Agricultural Sciences, China) for providing reagents used in this study.

This work was supported by grants from the Ministry of Science and Technology of Shanghai (09XD1404800), the Ministry of Science and Technology of China (2006CB504301, 2007CB914504, and 2009ZX10004-105), and the Chinese Academy of Sciences (KSCX1-YW-R-06).