PRRSV Non-Structural Proteins Orchestrate Porcine E3 Ubiquitin Ligase RNF122 to Promote PRRSV Proliferation

Abstract

Ubiquitination plays a major role in immune regulation after viral infection. An alternatively spliced porcine E3 ubiquitin ligase RNF122 promoted PRRSV infection and upregulated in PRRSV-infected PAM cells was identified. We characterized the core promoter of RNF122, located between −550 to −470 bp upstream of the transcription start site (TSS), which displayed significant differential transcriptional activities in regulating the transcription and expression of RNF122. The transcription factor HLTF was inhibited by nsp1α and nsp7 of PRRSV, and the transcription factor E2F complex regulated by nsp9. Together, they modulated the transcription and expression of RNF122. RNF122 could mediate K63-linked ubiquitination to raise stability of PRRSV nsp4 protein and thus promote virus replication. Moreover, RNF122 also performed K27-linked and K48-linked ubiquitination of MDA5 to degrade MDA5 and inhibit IFN production, ultimately promoted virus proliferation. In this study, we illustrate a new immune escape mechanism of PRRSV that enhances self-stability and function of viral nsp4, thus, regulating RNF122 expression to antagonize IFNα/β production. The present study broadens our knowledge of PRRSV-coding protein modulating transcription, expression and modification of host protein to counteract innate immune signaling, and may provide novel insights for the development of antiviral drugs.

PRRSV degrades MDA5 via dual autophagy receptors P62 and CCT2 to evade antiviral innate immunity

“…The main protein degradation pathways in eukaryotic cells are the ubiquitin-proteasome and autophagy-lysosome pathways. Our previous research has established that PRRSV can regulate the E3 ubiquitin ligase RNF122 to promote the K48 ubiquitination and degradation of MDA5 ( Sun et al., 2022 ). Autophagy can support or hinder viral replication depending on the viruses, cell types, or cellular environments ( Diao et al., 2023 ).…”

N-Acetyltransferase 9 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Proliferation by N-Terminal Acetylation of the Structural Protein GP5

“…PRRSV has evolved and employed various kinds of weapons to antagonize the host defense systems, and disruption of host transcription factors to evade innate immune responses is a common mechanism. Both the nonstructural proteins and structural proteins have been found to regulate different host transcription factors to favor PRRSV proliferation ( 31 , 32 , 44 – 46 ). In this study, we characterized the sequence from −89 to −14 bp upstream from the transcription start site (TSS) as the core promoter of Nat9 by using luciferase assay experiments and found that ETV5 acts as an activator and SP1 acts as a suppressor for the transcription of the Nat9 gene through binding to this region.…”

Research Progress on Porcine Reproductive and Respiratory Syndrome Virus NSP7 Protein

“…An E3 ubiquitin ligase ring finger 122 (RNF122) protein helicase-like transcription factor, which NSP1α and NSP7 downregulate, can inhibit RNF122 promoter activity and promote RNF122 transcription. RNF122 ubiquitinates the pathogen pattern recognition receptor melanoma differentiation-associated gene 5 (MDA5) protein via amino acid residues-K27 and K48, thereby degrading MDA5, inhibiting IFN production, and ultimately promoting virus proliferation [31]. Thus, this study provided new insights into the mechanism of action of NSP7 in viruses.…”