The global outbreak of SARS-CoV-2 has resulted in a renewed focus on coronaviruses with the potential for cross-species transmission and mutation risks. In particular, swine acute diarrhea syndrome coronavirus (SADS-CoV), potentially originating from the intermediate horseshoe bat (Rhinolophus affinis), is a novel coronavirus that causes acute diarrhea, vomiting, and high mortality in suckling piglets. Innate immunity plays a crucial role in defending the host against invading pathogens. Previous studies have identified several host factors that inhibit SADS-CoV replication through innate immunity; however, research on SADS-CoV remains insufficient compared to that on other coronaviruses. This study demonstrates that Moloney leukemia virus 10 protein (MOV10) exerts anti-SADS-CoV activity via its N-terminal domain in a helicase activity-independent manner. Mechanistic analysis reveals that MOV10 induces translocation of tripartite motif-containing 24 (TRIM24) from the nucleus to the cytoplasm. The cytoplasmically localized TRIM24 binds to MOV10 and TNF receptor-associated factor 3 (TRAF3) to form a ternary complex. Functional studies demonstrate that MOV10 strengthens the interaction between TRIM24 and TRAF3 in a dose-dependent manner and facilitates TRIM24-mediated K63-linked ubiquitination of TRAF3, thereby activating interferon immune responses. Furthermore, we identify the strategies by which SADS-CoV evades innate immunity. The viral N protein inhibits the antiviral effect of MOV10 by disrupting the interaction between MOV10 and TRAF3 and by promoting K48-linked polyubiquitination of TRAF3, leading to TRAF3 degradation via the ubiquitin-proteasome pathway. Collectively, our findings reveal the role of MOV10 in antiviral immunity and how SADS-CoV evades host immune defense.

Importance: Moloney leukemia virus 10 protein (MOV10), a DExD-box RNA helicase, is a known component of cytoplasmic RNA processing centers known as P bodies. As an interferon-stimulated gene (ISG), MOV10 exhibits broad-spectrum antiviral activity against multiple viruses, including SARS-CoV-2, HIV, HSV-1, IAV, and PRRSV. Here, we identify a novel helicase-independent antiviral mechanism of MOV10 against SADS-CoV. In this study, we show that MOV10 bridges TRIM24 and TRAF3 and facilitates K63-linked ubiquitination of TRAF3 independent of its helicase activity. This process strongly amplifies downstream interferon antiviral responses and suppresses viral replication. Furthermore, the SADS-CoV N protein efficiently antagonizes MOV10-mediated immune defense by disrupting the MOV10-TRAF3 interaction and inducing K48-linked ubiquitination and proteasomal degradation of TRAF3. Collectively, this study establishes a previously uncharacterized MOV10-TRIM24-TRAF3 antiviral regulatory axis, which offers new mechanistic insights into how coronaviruses evade host immune defenses.

Keywords: MOV10; N protein; SADS-CoV; TRAF3; TRIM24; ubiquitination.