The E3 Ubiquitin Ligase AMFR and INSIG1 Bridge the Activation of TBK1 Kinase by Modifying the Adaptor STING

Abstract

Stimulator of interferon genes (STING, also known as MITA, ERIS, or MPYS) is essential for host immune responses triggered by microbial DNAs. However, the regulatory mechanisms underlying STING-mediated signaling are not fully understood. We report here that, upon cytoplasmic DNA stimulation, the endoplasmic reticulum (ER) protein AMFR was recruited to and interacted with STING in an insulin-induced gene 1 (INSIG1)-dependent manner. AMFR and INSIG1, an E3 ubiquitin ligase complex, then catalyzed the K27-linked polyubiquitination of STING. This modification served as an anchoring platform for recruiting TANK-binding kinase 1 (TBK1) and facilitating its translocation to the perinuclear microsomes. Depletion of AMFR or INSIG1 impaired STING-mediated antiviral gene induction. Consistently, myeloid-cell-specific Insig1(-/-) mice were more susceptible to herpes simplex virus 1 (HSV-1) infection than wild-type mice. This study uncovers an essential role of the ER proteins AMFR and INSIG1 in innate immunity, revealing an important missing link in the STING signaling pathway.

Polycomb subunit BMI1 determines uterine progesterone responsiveness essential for normal embryo implantation

“…In this regard, we observed a comparable expression level of PR proteins upon the loss of Bmi1, pointing toward a disassociation of PR ubiquitination by the BMI1-PR-E6AP complex from the process of PR protein turnover. This is consistent with previous reports showing that posttranslational protein modifications by ubiquitin proteins are vital for functional activation of modified proteins, independent of proteasome-mediated degradation mechanisms (33). Collectively, our findings with respect to BMI1 add a potentially new regulatory layer contributing to the complexity and preciseness of PR transcriptional activation.…”

Ubiquitin chain diversity at a glance

“…A second report connects K27 linkages to host immune responses that are triggered by microbial DNA (Wang et al, 2014). Invading nucleic acids trigger the activation of the interferon regulatory factor-3 (IRF-3) and/or NF-κB signaling pathways, thus inducing expression of type-I interferons (IFNs) and proinflammatory cytokines.…”

“…Insulininduced gene 1 (INSIG1) targets the E3 ligase autocrine motility factor receptor (AMFR, also known as gp78) to the STING protein complex upon microbial DNA invasion. Subsequently, AMFR catalyzes K27-linked polyubiquitylation of STING, which serves as a scaffold for the recruitment and activation of TBK1 (Wang et al, 2014). Of note, it has been shown that AMFR interacts with the E2 enzyme UBE2G2 through a specialized binding region on AMFR, and that this interaction is a prerequisite for processive assembly of K48-linked ubiquitin chains on ER-associated degradation (ERAD) substrates (Das et al, 2013(Das et al, , 2009).…”

Activation and Regulation of DNA-Driven Immune Responses

“…Subsequently, TRIM32 was also demonstrated to mediate K63-linked ubiquitination of STING at several lysine residues, including K150 (55), which was associated with elevated IFN-␤ expression. Most recently, the endoplasmic reticulum (ER)-associated E3 ubiquitin ligase AMFR was reported to interact with STING and catalyze K27-linked polyubiquitination, in a manner dependent on insulin-induced gene 1 (56). This modification of STING facilitated the recruitment of TBK1.…”