A dual role for ER-Golgi cargo receptor LMAN1 in supporting CSFV replication and restraining RLR signaling.

Classical swine fever virus (CSFV) establishes efficient infection by manipulating host factors and intracellular pathways to support viral replication. The host lectin mannose-binding 1 (LMAN1) is a cargo receptor that is involved in the assembly and morphogenesis of several RNA and DNA viruses. However, the function and potential mechanism of LMAN1 in CSFV infection remain elusive. Here, we investigated the LMAN1 expression pattern in CSFV-infected pigs and PK-15 cells, showing upregulation of the protein after CSFV infection. LMAN1 knockdown and overexpression further demonstrated that LMAN1 expression was required for efficient CSFV proliferation. Mechanistically, LMAN1 directly associates with the viral RNA-dependent RNA polymerase NS5B via its carbohydrate recognition domain (CRD), promoting efficient viral replication complex formation. Beyond its vital role in viral RNA replication, LMAN1 also functions as a negative regulator of antiviral signaling. Transcriptomic analyses revealed that LMAN1 deficiency hyperactivates the RIG-I-like receptor (RLR)-MAVS pathway, and further studies confirmed that loss of LMAN1 enhances IRF3 and NF-κB p65 phosphorylation, as well as interferon-β production in response to CSFV. MAVS knockdown reversed the interferon signaling hyperactivation caused by LMAN1 deficiency, and LMAN1 rescue experiments showed that the CRD domain is indispensable for suppression of interferon responses, revealing that LMAN1 modulates antiviral responses via the RLR-MAVS pathway relying on its CRD domain. Overall, our findings uncover LMAN1 as a previously unrecognized host determinant with dual function in CSFV replication and immune evasion, offering new insights into virus-host interactions and revealing a potential antiviral target.IMPORTANCEClassical swine fever virus (CSFV) remains a major threat to global swine health, yet the host factors that the virus exploits to support virus infection and proliferation are not fully understood. Here, we identify the host cargo receptor lectin mannose-binding 1 (LMAN1) as a critical determinant of CSFV infection. LMAN1 directly binds the viral RNA-dependent RNA polymerase NS5B and is recruited to endoplasmic reticulum-derived replication membranes to promote efficient viral RNA synthesis. At the same time, LMAN1 suppresses RIG-I-like receptor signaling, limiting MAVS-mediated activation of IRF3, NF-κB, and downstream antiviral responses. Loss of LMAN1 disrupts CSFV replication complex formation and triggers robust antiviral signaling, revealing that the virus relies on LMAN1 for efficient replication and immune evasion. These findings uncover a novel dual function of a cargo receptor in promoting viral RNA synthesis while simultaneously restraining excessive innate immune responses, highlighting LMAN1 as a potential target for antiviral intervention.