title: IGF2BP3 inhibits host antiviral innate immunity against RNA viruses by targeting SOCS3
Creators: name: Liu, Siying
Publisher: name: University of Liverpool Repository
Year: 2026

description: Infectious diseases, especially those caused by RNA viruses, impose a substantial burden on public health and human society. Induction and reactions to type I interferon are essential innate immune responses that play a crucial role in host-virus interactions during viral infections. N6-methyladenosine (m6A) modification is the most abundant modification on RNA and plays a significant role in various biological processes, including anti-viral immune responses and viral processes. However, it remains unclear whether the insulin-like growth factor 2 messenger RNA (mRNA)-binding proteins (IGF2BPs), which have been recognized as m6A recognition proteins, are involved in regulating host-virus interactions. Therefore, this project aims to evaluate the impact of IGF2BPs on the regulation of the host’s innate antiviral responses during RNA viral infections and the underlying molecular mechanisms. By examining the transcriptome data of clinical samples with different RNA viral infections, we observed an increase in the expression of IGF2BP3 during RNA virus infections. Moreover, we found that the replication of vesicular stomatitis virus (VSV) was significantly decreased in IGF2BP3-deficient RAW264.7 cells, bone marrow-derived macrophages (BMDMs), and peritoneal macrophages (PMs). Conversely, VSV replication significantly increased in the IGF2BP3-overexpressing RAW264.7 and A549 cells. Our study also showed the Igf2bp3-/- mice exhibited prolonged survival time when challenged with a lethal dose of VSV and decreased VSV loading in mice organs when challenged with an unlethal dose. Our study also showed that Igf2bp3-/- mice exhibited a prolonged survival time when challenged with a lethal dose of VSV and a decreased VSV load in mouse organs when challenged with an unlethal dose. Taken together, these findings indicate that IGF2BP3 plays a role in promoting the replication of RNA viruses during infection.
Next, we explored the potential regulatory roles of IGF2BP3 in antiviral immunity by examining the gene-expression profiles in IGF2BP3-deficient RAW264.7 cells and PMs using RNA-seq analysis. The results indicated that the genes associated with type I interferon (IFN)-related immune responses were highly and significantly enriched in IGF2BP3-deficient RAW264.7 cells and PMs. We also found that the mRNA levels and protein levels of some antiviral interferon stimulated genes (ISGs), such as Isg15, 2'-5'-oligoadenylate synthetase 2 (Oas2) and Retinoic acid-inducible gene I (Rigi), were significantly increased in IGF2BP3-deficient cells. Meanwhile, the phosphorylation of ISG-regulated protein, signal transducer and activator of transcription 1 (STAT1), was significantly increased in the IGF2BP3-deficient RAW264.7 cells when the cells were infected with VSV or stimulated by IFN-β. These findings reveal that IGF2BP3 is a negative regulator that represses the type I IFN signaling and expression of ISGs, which may be responsible for VSV's escape from antiviral responses.
The analysis of the RNA-seq data also indicated that IGF2BP3 potentially binds to the mRNA of suppressors of cytokine signaling 3 (Socs3). When IGF2BP3 was deficient in VSV-infected cells, the mRNA level of Socs3 significantly decreased, indicating a positive correlation between the expression of Socs3 and Igf2bp3. Additionally, reducing the expression of Socs3 significantly resulted in decreased VSV replication and increased expression of Isg15 in RAW264.7 cells, supporting the immune suppressive role of Socs3 in VSV-infected RAW264.7 cells. However, this suppressive effect was absent in IGF2BP3-deficient RAW264.7 cells, suggesting the importance of IGF2BP3 in the immune suppressive function of SOCS3 during VSV infection. Evidence from RNA immunoprecipitation (RIP) assays suggested that Socs3 mRNA binds to IGF2BP3 Additionally, an RNA decay assay revealed that deficiency in IGF2BP3 led to a decrease in the half-life of Socs3 mRNA in VSV-infected RAW264.7 cells. This indicates that IGF2BP3 binds to and stabilizes the mRNA of Socs3. Furthermore, RIP assay with anti-m6A antibody suggested that mRNA of Socs3 was m6A-containing in VSV-infected RAW264.7 cells. m6A writer inhibitor treatment caused a decrease in Socs3 mRNA levels when the RAW264.7 cells were infected with VSV, but this suppressive effect was absent in IGF2BP3-deficient RAW264.7 cells, implying that m6A-mediated regulation on RNA level of Socs3 in VSV-infected RAW264.7 cells is reliant on IGF2BP3. The level of m6A modification on Socs3 mRNA and affinity of IGF2BP3 with Socs3 mRNA were reduced when RAW264.7 cells were treated with an m6A writer inhibitor, indicating that IGF2BP3 binds to Socs3 mRNA in an m6A-dependent manner. To summarize, our findings represent the initial evidence that IGF2BP3 is capable of stabilizing Socs3 mRNA through an m6A-dependent mechanism in VSV infection. This stabilization hinders the host's immune response to type I interferon, thus promoting VSV virus replication.