# PRRSV-2 impedes lysosomes from eliminating secondary infected bacteria

## TL;DR

PRRSV-2 weakens the ability of pig immune cells to clear bacteria by disrupting a key structural component of the cell, which could lead to new treatments for secondary infections.

## Contribution

This study reveals a novel mechanism by which PRRSV-2 reprograms the cytoskeleton to facilitate secondary bacterial survival.

## Key findings

- PRRSV-2 disrupts F-actin in macrophages, impairing lysosome transport to bacteria.
- nsp5 protein downregulates RhoA via ubiquitination, leading to F-actin suppression and bacterial persistence.
- Targeting cytoskeletal F-actin could be a new strategy to control secondary bacterial infections.

## Abstract

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.

Since its first discovery in the 1980s, porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) has caused incalculable economic damage to the global pig industry. Due to the immunosuppressive characteristics of PRRSV-2, co-infection with PRRSV-2 and secondary bacteria is frequent and intensifies the production of pro-inflammatory cytokines, resulting in more severe clinicopathological damage. A better understanding of the mechanisms of PRRSV-2 secondary bacterial infection is essential for the development of safe and effective treatments. Here, we report that PRRSV-2 impedes the phagocytic function of lysosomes in macrophages by reprogramming the cytoskeleton F-actin, thereby facilitating the survival of secondary infected bacteria. Our work provides a novel mechanism of secondary bacterial infection with PRRSV-2 and suggests that targeting cytoskeletal F-actin may be a new strategy to control secondary bacterial infection.