Porcine reproductive and respiratory syndrome virus nsp6 hijacks ATP1B1 antagonizing TRAF6 mediated antiviral innate immunity.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is an immune-suppressive pathogen that poses a significant challenge to the global swine industry. The mechanism by which PRRSV regulating host inflammation to evade innate immunity remains unclear. Here, Na/K-ATPase beta1 subunit (ATP1B1), a pivotal antiviral protein, was shown to interact with PRRSV nsp6, a tiny viral protein encoded by ORF1a. ATP1B1 stabilized the protein level of TRAF6 by downregulating K48-linked ubiquitination of TRAF6, thus triggering NF-κB signaling and inflammatory response. Moreover, PRRSV nsp6 competetively interacted with ATP1B1 via the site of Leu 3 and impaired the formation of ATP1B1-TRAF6 complex, leading to TRAF6 proteasomal degradation and compromised inflammatory response. PRRSV with the corresponding mutation in nsp6 L3S was successfully rescued but presented defective virus growth in the late stage of infection, especially under the inflammation condition induced by either ATP1B1 overexpression or poly (I:C) stimulation. In addition, the halt in PRRSV replication was induced by treatment with autophagy inhibitor BafA1 during virus passage. L3S mutant virus impaired the recovery of virus growth even after the removal of BafA1, indicating the key role of nsp6 in sustaining virus vitality under innate immunity. Taken together, these results elucidate the functional mechanism by which PRRSV alleviates the inflammatory response to promote successful virus proliferation and growth recovery from the host innate immune response.