The UP1 domain is essential for the facilitation effect of HnRNP A1 on PRRSV-2 replication.

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes reproductive failure and respiratory distress and is a serious threat to the swine industry, given its continuous and rapid emergence. The knowledge of viral-host interaction could facilitate anti-PRRSV drug development. HnRNP A1 is an abundantly expressed protein which associates with RNA metabolic processes and plays multifarious roles during the reproduction cycle of multiple viruses. However, the function of porcine HnRNP A1 in PRRSV-2 replication is still unknown. Herein, HnRNP A1 was identified as a nucleocapsid (N)-binding protein for PRRSV-2. Overexpression of porcine HnRNP A1 promoted the expression of viral RNA, and viral proteins, corresponding to enhanced virus titers. While deletion of the UP1 domain abolished the HnRNP A1-mediated enhancement of PRRSV-2 replication. In addition, HnRNP A1-silencing confirmed its pro-viral effect on PRRSV-2 infectivity in porcine alveolar macrophages (PAMs). RNA pull-down and RNA immunoprecipitation verification confirmed that the UP1 domain is important for the recognition of the guanine-rich sequence (GRS) in PRRSV-2 negative RNA. Eventually, supplementation with TMPyP4, a G4 ligand, efficiently provokes the release of HnRNP A1 from GRS, thereby limiting PRRSV-2 replication. Together, these findings help to inform the mechanism by which HnRNP A1 accelerates PRRSV-2 replication, and facilitate antiviral drug design.