Abstract
Linear ubiquitination is a critical regulator of inflammatory signaling pathways. However, linearly ubiquitinated substrates and the biological significance of linear ubiquitination is incompletely understood. Here, we show that STAT1 has linear ubiquitination at Lys511 and Lys652 residues in intact cells, which inhibits STAT1 binding to the type-I interferon receptor IFNAR2, thereby restricting STAT1 activation and resulting in type-I interferon signaling homeostasis. Linear ubiquitination of STAT1 is removed rapidly by OTULIN upon type-I interferon stimulation, which facilitates activation of interferon-STAT1 signaling. Furthermore, viruses induce HOIP expression through the NF-κB pathway, which in turn increases linear ubiquitination of STAT1 and thereby inhibits interferon antiviral response. Consequently, HOIL-1L heterozygous mice have active STAT1 signaling and enhanced responses to type-I interferons. These findings demonstrate a linear ubiquitination-mediated switch between homeostasis and activation of type-I interferon signaling, and suggest potential strategies for clinical antiviral therapy.
Highlights
Linear ubiquitination is a critical regulator of inflammatory signaling pathways
During the identification of the signaling regulators of the transcription factor signal transducer and activator of transcription 1 (STAT1) activation, we noticed that the ubiquitin E3 ligase RNF31, known as HOIP, was repeatedly observed among the potential STAT1-interacting proteins in mass spectrometry analysis (Fig. 1a and Supplementary Fig. 1a)
Further studies found that deletion of the TAD domain of STAT1 abolished binding of Flag-HOIP (Supplementary Fig. 1b), suggesting that HOIP could interact with the TAD domain of STAT1
Summary
Linear ubiquitination is a critical regulator of inflammatory signaling pathways. linearly ubiquitinated substrates and the biological significance of linear ubiquitination is incompletely understood. We show that STAT1 has linear ubiquitination at Lys[511] and Lys[652] residues in intact cells, which inhibits STAT1 binding to the type-I interferon receptor IFNAR2, thereby restricting STAT1 activation and resulting in type-I interferon signaling homeostasis. Viruses induce HOIP expression through the NF-κB pathway, which in turn increases linear ubiquitination of STAT1 and thereby inhibits interferon antiviral response. HOIL-1L heterozygous mice have active STAT1 signaling and enhanced responses to type-I interferons These findings demonstrate a linear ubiquitination-mediated switch between homeostasis and activation of type-I interferon signaling, and suggest potential strategies for clinical antiviral therapy. Recent progress has revealed a few functions mediated by linear ubiquitination, including activation of signaling proteins[8,9,10], recruitment of regulatory proteins[11], and regulation of protein levels via the proteasome pathway[12]. Interferon regulatory factor 3 (IRF3) linear ubiquitination at both Lys[193] and either
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