Nucleocapsid protein residues 35, 36, and 113 are critical sites in up-regulating the Interleukin-8 production via C/EBPα pathway by highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious and pathogenic agent that causes considerable economic damage in the swine industry. It regulates the inflammatory response, triggers inflammation-induced tissue damage, suppresses the innate immune response, and leads to persistent infection. Interleukin-8 (IL-8), a pro-inflammatory chemokine, plays a crucial role in inflammatory response during numerous bacteria and virus infections. However, the underlying mechanisms of IL-8 regulation during PRRSV infection are not well understood. In this study, we demonstrate that PRRSV-infected PAMs and Marc-145 cells release higher levels of IL-8. We screened the nucleocapsid protein, non-structural protein (nsp) 9, and nsp11 of PRRSV to enhance IL-8 promoter activity via the C/EBP alpha pathway. Furthermore, we identified that the amino acids Q35A, S36A, R113A, and I115A of the nucleocapsid protein play a crucial role in the induction of IL-8. Through reverse genetics, we generated two mutant viruses (rQ35-2A and rR113A), which showed lower induction of IL-8 in PAMs during infection. This finding uncovers a previously unrecognized role of the PRRSV nucleocapsid protein in modulating IL-8 production and provides insight into an additional mechanism by which PRRSV modulates immune responses and inflammation.