The E3 ubiquitin ligase ARIH1 promotes antiviral immunity and autoimmunity by inducing mono-ISGylation and oligomerization of cGAS

Abstract

The cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) plays a critical role in antiviral immunity and autoimmunity. The activity and stability of cGAS are fine-tuned by post-translational modifications. Here, we show that ariadne RBR E3 ubiquitin protein ligase 1 (ARIH1) catalyzes the mono-ISGylation and induces the oligomerization of cGAS, thereby promoting antiviral immunity and autoimmunity. Knockdown or knockout of ARIH1 significantly inhibits herpes simplex virus 1 (HSV-1)- or cytoplasmic DNA-induced expression of type I interferons (IFNs) and proinflammatory cytokines. Consistently, tamoxifen-treated ER-Cre;Arih1fl/fl mice and Lyz2-Cre; Arih1fl/fl mice are hypersensitive to HSV-1 infection compared with the controls. In addition, deletion of ARIH1 in myeloid cells alleviates the autoimmune phenotypes and completely rescues the autoimmune lethality caused by TREX1 deficiency. Mechanistically, HSV-1- or cytosolic DNA-induced oligomerization and activation of cGAS are potentiated by ISGylation at its K187 residue, which is catalyzed by ARIH1. Our findings thus reveal an important role of ARIH1 in innate antiviral and autoimmune responses and provide insight into the post-translational regulation of cGAS.

The Ubiquitin–Proteasome System in Tumor Metabolism

“…FAT10 is another Ubl used to modulate substrate degradation by directly binding to substrates; subsequently, FAT10 and its substrates degrade together [ 24 ]. Interferon-stimulating gene 15 (ISG15) not only acts as a cytokine induced by viral infection, but also as a ubiquitin molecule [ 25 ]. It was the first Ubl shown to covalently modify proteins; its enzymatic cascade response is mediated by E1 (UBA7/UBE1L), E2 (UBCH8), and E3 ligases (HERC5 and HERC6) [ 26 ], and it is an antagonist of the ubiquitin pathway, which is abnormally elevated in various human malignancies, showing its potential role in tumor therapies.…”

ISG15 driven cellular responses to virus infection

“…For example, delineating the contribution of free versus conjugated ISG15 in pathological conditions is one such area. Till date, three E3-ligases have been identified for ISG15 conjugation to substrates [9][10][11][12][13]. Of these, while Herc5 is a dedicated ISG15 E3-ligase, Trim25 and ARIH1 can equally function as ubiquitin E3-ligases, begging the question of how many of the ∼700 E3-ligases are able to carry out ISGylation.…”

“…ISG15 is one of the early and most abundant ISGs produced in IFN-stimulated cells. ISG15 can either be secreted out from these cells [5] or be conjugated to substrates via the sequential activity of Ube1L [7], Ubch8 [8] and Herc5 [9,10]/Trim25 [11,12]/ARIH1 [13,14] enzymes.…”

“…The E2 enzyme transfers ISG15 to an E3 ligase (e.g. Herc5 [9,10], Trim25 [11,12], ARIH1 [13,14]), which in turn executes the final step of covalently attaching ISG15 to specific lysine residues of substrates. Like ubiquitylation, ISGylation too is reversible and can be hydrolysed by Usp18 [15], a cysteine protease.…”

ISGylation of the SARS-CoV-2 N protein by HERC5 impedes N oligomerization and thereby viral RNA synthesis

“…For instance, the cytoplasmic-localized dsRNA receptor MDA5 is covalently modified with ISG15 in its CARD domains, which helps the sensor protein to form higher-order assemblies and thereby promotes antiviral gene induction to restrict a range of RNA viruses including SARS-CoV-2 (35). Similarly, cGAS and its adaptor protein STING, as well as the downstream transcription factor IRF3, undergo ISGylation in infected cells, which potentiates antiviral signaling (42)(43)(44)(45). On the other hand, ISG15 in its unconjugated form exerts a proviral activity by dampening signaling by the type I IFN receptor (IFNAR), an effect underlying certain in-born ISG15 deficiencies in humans (40).…”