Monocytes use pattern recognition receptors (PRRs) to detect invading pathogens, initiating either an antiviral type I interferon (IFN) response or proinflammatory cytokine production. Cytosolic PRRs like RIG-I and cGAS play key roles in recognizing viral nucleic acids and triggering the type I IFN response via TBK1/IKK kinases or NFκB signaling. Recently, hnRNPM, a member of the RNA-binding heterogeneous nuclear ribonucleoprotein family, has been identified as a positive regulator of IRF3 phosphorylation downstream of RIG-I and cGAS. The RNA-binding protein ELAVL1 interacts with hnRNPM and both host proteins were observed to form a complex with TBK1 and NF-κB p65, linking the cGAS-STING and RIG-I-MAVS pathways.
Numerous viruses target these innate recognition mechanisms, and it is known that hnRNPM is targeted by 3C proteases of coxsackievirus B3 and poliovirus to enhance viral replication. To investigate whether this pathway is involved in the modulation of influenza A virus (IAV) infection, HEK293FT cells were co-transfected with plasmids encoding Luciferase-tagged IAV proteins and Flag-tagged forms of hnRNPM or ELAVL1. Immunoprecipitation experiments using magnetic anti-Flag beads showed that IAV NS1 and NP proteins could both associate with host hnRNPM or ELAVL1 proteins as evidenced by robust luciferase activity in the immunoprecipitates, suggesting that they were possible interaction partners. The association of the IAV proteins with hnRNPM and ELAVL1 was further confirmed by western blotting. Further immunoprecipitation experiments with hnRNPM deletion mutants identified the glycerol-rich domain (GMG) and RNA-binding domain 2 (RRM2) as critical for interaction with both NS1 and NP IAV proteins. Therefore, our preliminary data indicate that IAV proteins interact with hnRNPM and ELAVL1, possibly modulating the host IFN response. Virus infection experiments will further clarify these interactions, potentially uncovering novel therapeutic targets to enhance antiviral responses and limit viral evasion strategies.