As an immunosuppressive virus, the occurrence of secondary bacterial infection following porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) infection is widely recognized. The immune escape capability of PRRSV-2 enables the virus to maintain efficient proliferation even within macrophages. In this study, we report that PRRSV-2 infection disrupts the intracellular F-actin, thereby causing the inability of macrophage lysosomes to transport to secondary infected bacteria promptly for bacterial clearance. RhoA is a crucial molecule in the polymerization of G-actin to F-actin within the cell. Silencing RhoA suppresses the production of F-actin in the cell, delays the targeted clearance of bacteria by lysosomes, and leads to an increase in the number of viable bacteria within the cell. Overexpression of RhoA promotes the production of F-actin, accelerates the targeted clearance of lysosomes to bacteria, and effectively reduces the number of viable bacteria. After PRRSV-2 infection, the expression of RhoA protein is down-regulated by nsp5 to inhibit the production of F-actin. Mechanistically, nsp5 interacts with the E3 ubiquitin ligase Smurf1 to mediate K63-linked ubiquitination of RhoA at lysine 187 (K187), which subsequently leads to its degradation via the autophagy-lysosome pathway under the guidance of the selective autophagy receptor TOLLIP. Therefore, our study presents a novel mechanism through which PRRSV-2 reprograms the cytoskeleton to facilitate the survival of bacteria in secondary infections, providing a theoretical foundation and target for the prevention and control of PRRSV-2 secondary bacterial infection.
Zheng et al. (Fri,) studied this question.