PDIA3 and CANX counteract EMCV-induced cytosolic calcium elevation by targeting FGFR4 to restrict viral replication

Encephalomyocarditis virus (EMCV) is an important pathogen capable of infecting multiple host species and causing severe myocarditis and neurological dysfunction. EMCV infection induces endoplasmic reticulum (ER) stress, a process closely associated with disruption of intracellular calcium homeostasis. However, the regulatory role of calcium signaling in EMCV replication and the underlying host defense mechanisms remain to be fully elucidated. In this study, Western blotting, quantitative PCR, viral titration, and live‑cell calcium imaging were used to demonstrate how EMCV infection triggers ER calcium release, leading to elevated cytosolic Ca^2 + levels, which in turn promotes viral proliferation. Further investigation revealed that the ER molecular chaperones protein disulfide-isomerase A3 (PDIA3) and calnexin (CANX) effectively counteract virus‑induced cytosolic calcium surge. Proteomic analysis identified fibroblast growth factor receptor 4 (FGFR4) as a key target commonly downregulated by CANX and PDIA3. Overexpression of PDIA3 or CANX suppresses FGFR4 expression at both the mRNA and protein levels, thereby establishing a negative feedback loop that prevents excessive calcium signaling. Of note, FGFR4 acts as a host antiviral restriction factor that becomes activated upon EMCV infection and suppresses viral replication through appropriately induced calcium release. In conclusion, EMCV hijacks ER calcium stores and elevates cytosolic calcium levels to create a microenvironment favorable for its own replication, whereas the host cell counteracts EMCV replication by targeting FGFR4 via PDIA3 and CANX to maintain calcium homeostasis. This study elucidates a novel antiviral mechanism centered on ER molecular chaperones and FGFR4, providing new insights into EMCV-host interactions.