Porcine Reproductive and Respiratory Syndrome Virus nsp1β Stabilizes HIF-1α to Enhance Viral Replication

Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus that has been devastating the swine industry worldwide since the late 1980s. Severe interstitial pneumonia is the typical pathological characteristic of PRRSV-infected swine. Accumulating evidence has suggested that hypoxia-inducible factor 1 alpha (HIF-1 alpha) plays vital roles in the development of inflammation and the viral life cycle. However, the role and the underlying mechanism of HIF-1 alpha in PRRSV infection remain elusive. Here, we found that PRRSV infection elevated HIF-1 alpha expression. Furthermore, overexpression of HIF-1 alpha increased PRRSV replication, whereas knockdown of HIF-1 alpha inhibited PRRSV infection. Our further mechanistic analysis revealed that PRRSV-encoded nonstructural protein 1b (nsp1b) promoted HIF-1 alpha transcription via its N-terminal nuclease activity and degraded the polyubiquitin chain of HIF-1 alpha via its C-terminal deubiquitylation (DUB) enzyme activity, collectively stabilizing HIF-1 alpha. Meanwhile, nsp1 beta interacted with both HIF-1 alpha and von Hippel-Lindau tumor suppressor (pVHL) to form a ternary complex, which may have hindered pVHL-mediated ubiquitination degradation of HIF-1a by impairing the interaction between HIF-1 alpha and pVHL. Interestingly, pVHL also stabilized nsp1 beta via K63-linked ubiquitination, forming a positive feedback loop to stabilize HIF-1 alpha. Taken together, these results indicate that PRRSV infection stabilizes HIF-1 alpha to facilitate viral proliferation and that viral nsp1 beta plays a vital role in enhancing the expression and stabilization of HIF-1 alpha. The regulation of HIF-1 alpha may have great therapeutic potential for the development of novel drugs against PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) has devastated the swine industry worldwide for over 30 years and shows no signs of slowing down. In this study, we found that PRRSV infection elevated hypoxia-inducible factor 1 alpha (HIF-1 alpha) expression. In addition, overexpressed HIF-1 alpha contributed to PRRSV replication, whereas knockdown of HIF-1 alpha reduced PRRSV growth. The PRRSV-encoded nonstructural protein 1 beta (nsp1 beta) exerted a stabilizing effect on HIF-1 alpha through its nuclease protease and papain-like cysteine protease enzymatic domains. PRRSV nsp1 beta also interacted with von Hippel-Lindau tumor suppressor (pVHL) and HIF-1 alpha, whereby nsp1 beta impaired the interaction between HIF-1 alpha and pVHL. This work deepens our understanding of the molecular mechanisms involved in PRRSV infection and provides new insights for the development of HIF-1 alpha- based anti-PRRSV therapies.

Automated summary

This study reveals that PRRSV infection increases the expression of hypoxia-inducible factor 1 alpha (HIF-1 alpha), and overexpression of HIF-1 alpha promotes PRRSV replication while knockdown of HIF-1 alpha inhibits PRRSV infection. The PRRSV-encoded nonstructural protein 1 beta (nsp1 beta) stabilizes HIF-1 alpha through its nuclease protease and papain-like cysteine protease enzymatic domains. Moreover, nsp1 beta interacts with von Hippel-Lindau tumor suppressor (pVHL) and HIF-1 alpha, impairing the interaction between HIF-1 alpha and pVHL. This study enhances our understanding of the molecular mechanisms involved in PRRSV infection and provides insights for the development of HIF-1 alpha-based anti-PRRSV therapies.