Inhibition of the Neddylation Pathway Suppresses Enterovirus Replication

Cullin 3-mediated ubiquitination restricts enterovirus D68 replication and is counteracted by viral protease 3C

Enterovirus D68 (EV-D68) has emerged as a significant threat to public health because of its association with respiratory illnesses and neurological complications, including acute flaccid myelitis. However, the molecular mechanisms underlying EV-D68 replication and pathogenesis remain unclear. Here, we revealed a novel interaction between EV-D68 and the host Cullin-RING E3 ligase system, specifically Cullin 3, which was reported to restrict viral replication. We initially demonstrated that proteasome inhibition enhanced EV-D68 replication, suggesting an important role for the ubiquitin-proteasome system in viral restriction. Cullin 3 was further identified as a key factor that inhibits EV-D68 replication, and the downregulation of its expression increased viral titers. Mechanistically, Cullin 3 was observed to target the viral capsid protein VP1 for ubiquitination and degradation. However, EV-D68 was determined to utilize its protease 3C to cleave Cullin 3 at the Q681 residue, thereby inhibiting E3 ligase activity and facilitating resistance to Cullin 3-mediated VP1 degradation. This study uncovered a host-virus arms race, wherein the ubiquitin-proteasome system of the host actively targets viral proteins for degradation, and viral proteases counteract this defense mechanism. Accordingly, these findings could lead to more effective antiviral treatments.

IMPORTANCE

The ubiquitin-proteasome system (UPS) is a critical cellular pathway involved in the regulation of protein stability and has been implicated in the regulation of viral infections. However, its role in EV-D68 infection has not been extensively explored. Our study proves that the host UPS, through the scaffold protein Cullin 3, can restrict EV-D68 replication, representing a previously unrecognized antiviral mechanism. Furthermore, we describe a viral strategy used to evade this host defense mechanism comprising Cullin 3 cleavage, which has broad implications for understanding virus-host interactions and could inform the development of novel therapeutic strategies against EV-D68 and other enteroviruses.

Effects of neddylation on viral infection: an overview

Neddylation is a post-translational modification that plays an important role not only in cancer development but also in regulating viral infection and replication. Upregulation of neddylation occurs in viral infections, and inhibition of neddylation can suppress viral replication. Neddylation is thought to enhance viral protein stability and replication. Neddylation has been reported to enhance the stability of the regulatory hepatitis B virus (HBV) X protein, modulate viral replication, and enhance hepatocarcinogenesis. Inhibition of neddylation using the NEDD8-activating enzyme E1 inhibitor MLN4924 inhibits viral replication, including that of HBV. Understanding of the role of neddylation in viral infections is critical for developing new therapeutic targets and potential treatment strategies. In this review, we discuss recent progress in the understanding of the effects of neddylation during viral infection, particularly in HBV infection, and strategies for curing viral infection by targeting the neddylation pathway.

Association Between Neddylation and Immune Response

Neddylation is a ubiquitin-like post-translational protein modification. It occurs via the activation of the neural precursor cell expressed, developmentally downregulated protein 8 (NEDD8) by three enzymes: activating enzyme, conjugating enzyme, and ligase. NEDD8 was first isolated from the mouse brain in 1992 and was initially considered important for the development and differentiation of the central nervous system. Previously, the downregulation of neddylation was associated with some human diseases, such as neurodegenerative disorders and cancers. In recent years, neddylation has also been proven to be pivotal in various processes of the human immune system, including the regulation of inflammation, bacterial infection, viral infection, and T cell function. Additionally, NEDD8 was found to act on proteins that can affect viral transcription, leading to impaired infectivity. Here, we focused on the influence of neddylation on the innate and adaptive immune responses.

Neddylation of Enterovirus 71 VP2 Protein Reduces Its Stability and Restricts Viral Replication

Posttranslational modifications (PTMs) of viral proteins play critical roles in virus infection. The role of neddylation in enterovirus 71 (EV71) replication remains poorly defined. Here, we showed that the structural protein VP2 of EV71 can be modified by neural precursor cell-expressed developmentally downregulated protein 8 (NEDD8) in an E3 ligase X-linked inhibitor of apoptosis protein (XIAP)-dependent manner. Mutagenesis and biochemical analyses mapped the neddylation site at lysine 69 (K69) of VP2 and demonstrated that neddylation reduced the stability of VP2. In agreement with the essential role of VP2 in viral replication, studies with EV71 reporter viruses with wild-type VP2 (enhanced green fluorescent protein [EGFP]-EV71) and a K69R mutant VP2 (EGFP-EV71-VP2 K69R) showed that abolishment of VP2 neddylation increased EV71 replication. In support of this finding, overexpression of NEDD8 significantly inhibited the replication of wild-type EV71 and EGFP-EV71, but not EGFP-EV71-VP2 K69R, whereas pharmacologic inhibition of neddylation with the NEDD8-activating enzyme inhibitor MLN4924 promoted the replication of EV71 in biologically relevant cell types. Our results thus support the notion that EV71 replication can be negatively regulated by host cellular and pathobiological cues through neddylation of VP2 protein. IMPORTANCE Neddylation is a ubiquitin-like posttranslational modification by conjugation of neural precursor cell-expressed developmentally downregulated protein 8 (NEDD8) to specific proteins for regulation of their metabolism and biological activities. In this study, we demonstrated for the first time that EV71 VP2 protein is neddylated at K69 residue to promote viral protein degradation and consequentially suppress multiplication of the virus. Our findings advance knowledge related to the roles of VP2 in EV71 virulence and the neddylation pathway in the host restriction of EV71 infection.