Oosenbrug, T. | bioRxiv Science

bioRxiv2025

The ubiquitin E3 ligase Huwe1 facilitates viral and self RNA sensing by RIG-I-like receptors

RIG-I-like receptors (RLRs) are cytoplasmic RNA sensors that promote type I and type III interferon (IFN) production in response to RNA ligands of viral or endogenous origin. The RLR pathway is tightly regulated by dynamic post-translational modifications, including ubiquitination. Huwe1 is a HECT domain-containing giant ubiquitin E3 ligase that has not been implicated in the RLR or IFN pathway. Here, we investigated whether Huwe1 is required for type I IFN induction downstream of RLRs. We demonstrate that loss of Huwe1 severely attenuates the expression of IFN-{beta}, IFN-{lambda}1 and IFN-stimulated genes (ISGs) in ADAR1-deficient human cells and primary murine bone-marrow derived macrophages, in which unedited self RNAs that serve as RLR ligands accumulate. In addition, depletion of Huwe1 reduces the induction of type I and III IFNs upon transfection with synthetic viral RNA mimetics or infection with a picornavirus. Using proteomics, we identified several putative Huwe1 substrates, which include key components of the RLR pathway (MAVS, TRAFs). We demonstrate that these substrates interact with Huwe1 and that Huwe1 is essential for the activity of TRAF5 in type I IFN induction. Collectively, our results put Huwe1 on the map as an important ubiquitin E3 ligase in the RLR pathway and provide new insights into ubiquitin-dependent regulation of cell-intrinsic antiviral immune pathways.

immunology↗

bioRxiv2021

RNA sensing via LGP2 is essential for the induction of a type I IFN response in ADAR1 deficiency

RNA editing by the enzyme Adenosine Deaminase Acting on RNA 1 (ADAR1) is an important mechanism by which cells avoid innate immune responses to some endogenous RNAs. In ADAR1-deficient cells, unedited self RNAs can form base-paired structures that resemble viral RNAs and inadvertently activate antiviral innate immune pathways that lead to the induction of type I interferon (IFN). Rare mutations in ADAR1 cause Aicardi-Goutieres Syndrome (AGS), a severe childhood autoinflammatory syndrome that is characterized by chronic and excessive type I IFN production and developmental delay. Conversely, ADAR1 dysfunction and consequent type I IFN production helps restrict tumor growth and potentiates the activity of some chemotherapy drugs. Induction of type I IFN in ADAR1-deficient cells is thought to be due to triggering of the cytosolic RIG-I-like receptor (RLR), MDA5, by unedited self RNAs. Here, we show that another RLR, LGP2, also has an essential role. We demonstrate that ADAR1-deficient human cells fail to mount a type I IFN response in the absence of LGP2 and this involves the canonical function of LGP2 as an RNA sensor and facilitator of MDA5-dependent signaling. Further, we show that the sensitivity of tumor cells to ADAR1 loss requires the presence of LGP2. Finally, we find that type I IFN induction in tumor cells depleted of ADAR1 and treated with some chemotherapeutics is fully dependent on the expression of LGP2. These findings highlight a central role for LGP2 in self RNA sensing with important clinical implications for the treatment of AGS as well as for the potential application of ADAR1-directed anti-tumor therapy.

immunology↗