OLFML3 negatively regulates RIG-I signaling in RNA virus infection.

Olfactomedin-like protein 3 (OLFML3) is a secreted glycoprotein that is primarily deemed to be associated with embryonic development, angiogenesis, and tumorigenesis. Recent studies have highlighted the function of OLFML3 as an important regulatory protein in viral and bacterial infections. This study explores the role of OLFML3 in type I interferon (IFN-I) signaling in RNA virus infection and related mechanism of action. RT-qPCR was used to determine the effects of OLFML3 on IFN-I production in the RNA virus infection. Olfml3 -/- mice was used to evaluate the effects of OLFML3 in in vivo viral infection. Western blotting (WB) and immunofluorescence microscropy experiments were conducted to analyze the effects of OLFML3 on retinoic-acid-inducible gene I (RIGI)-mediated IFN-I signaling pathway. Mass spectrometry and co-immunoprecipitation (Co-IP) were used to analyze the partner proteins of OLFML3. Gain-of-function studies by overexpression and loss-of-function studies by gene knockout and knockdown were performed to understand the functions of OLFML3 and TRIM21 in RIG-I-mediated IFN-I signaling pathway. OLFML3 can inhibit IFN-I production in RNA virus infection by suppressing RIG-I signaling. OLFML3 interacts with the PRY/SPRY domain of TRIM21, an E3 ubiquitinligase. OLFML3 can disrupt TRIM21-mediated RIG-I K63-ubiquitination, leading to the destabilization of RIG-I and suppressed IFN-I signaling. OLFML3 functions as a general immunosuppressor in RNA virus infection. These results may help developing OLFML3-targeted antiviral therapeutics for the re-activation of IFN-I signaling.