Abstract

Porcine reproductive and respiratory syndrome (PRRS) is a major economic burden to the global swine industry. Here, we identify the endoplasmic reticulum (ER) translocon component SSR4 as a critical host factor co-opted by PRRSV. We demonstrate that the viral non-structural protein Nsp2 physically interacts with SSR4 via its PLP2 and hypervariable domains and selectively upregulates its expression during infection by prolonging its protein half-life. Functional studies revealed that SSR4 is a proviral factor essential for efficient PRRSV replication. Mechanistically, SSR4 is required for the full activation of the PRRSV-induced ER stress response, specifically modulating the PERK-eIF2α and IRE1α-XBP1 axes of the unfolded protein response. Notably, Nsp2 itself acts as a key inducer of ER stress and mediates the upregulation of SSR4, suggesting a potential feed-forward loop that sustains a virus-favorable ER environment. This relationship is finely balanced, as pharmacological disruption of ER homeostasis using either the inducer tunicamycin (TU) or the chemical chaperone 4-phenylbutyric acid (4-PBA) potently inhibited viral replication. Importantly, TU and another inducer, dithiothreitol, exhibited potent, broad-spectrum antiviral activity against multiple PRRSV genotypes in both cell lines and primary porcine alveolar macrophages. Our study delineates a novel pathogenesis model where PRRSV Nsp2 hijacks SSR4 to engineer a proviral ER stress niche. The Nsp2-SSR4-ER stress axis represents a promising target for the development of broad-spectrum antiviral strategies against PRRS.