Ubiquitination-dependent degradation of DHX36 mediated by porcine circovirus type 3 capsid protein

Porcine circovirus type 3 (PCV3) is an emerging pathogen that causes porcine dermatitis, and reproductive failure. PCV3 Cap interacts with DExD/H-box helicase 36 (DHX36), a protein that functions primarily through regulating interferon (IFN)-β production. However, how the interaction between DHX36 and PCV3 Cap regulates viral replication remains unknown. Herein, we observed impaired PCV3 proliferation after DHX36 overexpression as indicated by decreased Rep protein expression and virus production. In contrast, PCV3 replication increased upon small interfering RNA-mediated DHX36 depletion. Furthermore, DHX36 positively regulated IFN-β production and interferon-stimulated genes (ISGs) expression. Mechanistically, PCV3 Cap interacted with DHX36, and the PCV3 Cap-NLS and DHX36-NTD were essential for the interaction. Furthermore, DHX36 may get degraded because its binding cellular partners became ubiquitinated and then reduced, and PCV3 Cap-(35-100aa) also promoted the degradation of DHX36 through the K48-linked ubiquitination. Taken together, these results show that DHX36 antagonizes PCV3 replication by interacting with PCV3 Cap and activating IFN-β response, which provides important insight on the prevention and controlling of PCV3 infection.

Importance

Porcine circovirus type 3 (PCV3) is a newly discovered pathogen associated with multiple clinicopathological signs. Clarifying the mechanisms that host factors modulate PCV3 replication helps understanding of the viral pathogenesis. The PCV3 capsid (Cap) protein has been shown to interact with DExD/H-box helicase 36 (DHX36) (Zhou et al., 2022b), a crucial protein that regulates virus replication. Herein, we further demonstrated that DHX36 protein is degraded in PCV3-infected cells and antagonizes the replication of PCV3 and that DHX36 increases interferon-β and interferon-stimulated gene levels by binding to PCV3 Cap. In addition, PCV3 infection could decrease DHX36 expression levels to antagonize its antiviral activity. These results reveal a molecular mechanism by which DHX36 antagonizes PCV3 replication by binding to PCV3 Cap protein and activating IFN signals, thereby providing important targets for preventing and controlling PCV3 infection.