Porcine reproductive and respiratory syndrome virus (PRRSV) non-structural protein (NSP)1 transcriptionally inhibits CCN1 and CCN2 expression by blocking ERK-AP-1 axis in pig macrophages in vitro

Abstract Porcine reproductive and respiratory syndrome virus (PRRSV) is a causative pathogen of PRRS that has generated a serious adverse impact on current global pork production. PRRSV primarily infects pig alveolar macrophages, but poor induction of innate immunity after infection often leads to more severe complications. Defining the functional role of each PRRSV non structural protein (NSP) within host cells might be helpful in understanding how PRRSV induces poor innate immunity in host cells. NSP1 of PRRSV exhibits papain like cysteine protease activity and may therefore modulate host cell signaling by degrading a target protein in host cells during infection. In this study, we demonstrated that NSP1 of PRRSV-2 indirectly blocked extracellular signal-regulated kinase (ERK) signaling in polyriboinosinic polyribocytidylic acid (Poly I:C) stimulated pig macrophages (3D4/31 cells). ERK which belongs to the mitogen-activated protein kinase family mediates many biological processes including inflammatory responses during viral infection. The blocking of ERK signaling by NSP1 of PRRSV-2 further leads to the transcriptional inhibition of inflammatory enhancers, cellular communication network factor 1 and 2 (ccn1 and ccn2) through down-regulation of v-fos FBJ murine osteosarcoma viral oncogene homolog (fos) and fosb, the component of activating protein-1 (AP-1) which is an ERK downstream transcription factor. Therefore, NSP1 of PRRSV-2 inhibited the mRNA transcription of ccn1 and ccn2 by blocking the ERK-AP-1 axis in Poly I:C stimulated pig macrophages. These results provide additional evidence supporting that NSP1 has anti-inflammatory function during PRRSV-2 infection.