Binbin Ding

Coronaviruses establish infection by reorganizing the host endoplasmic reticulum (ER) to form double-membrane vesicles (DMVs), which function as viral replication platforms. However, the role of other cellular organelles in this process remains incompletely understood. Here, we uncover a self-reinforcing cycle between viral replication organelles and mitochondrial damage that sustains coronavirus replication. We show that DMV formation disrupts ER-mitochondria contact sites (ERMCs), causing mitochondrial damage. This injury initiates a feed-forward mechanism wherein mitochondria release the matrix enzyme ECHS1 into the cytosol. Cytosolic ECHS1 then binds and stabilizes the DMV inducer protein NSP3 by blocking its K963 ubiquitination via the host E3 ligase RBBP6, thereby promoting further DMV formation. Disrupting this cycle, either through enhanced ER-mitochondria tethering or targeted interference with ECHS1-NSP3 binding, effectively suppresses viral replication. Our findings reveal that coronaviruses exploit an inter-organellar feedback loop linking mitochondrial damage to DMV formation, identifying new potential therapeutic targets for inhibition of coronaviral replication.

Lipid droplets (LDs), originating from the ER, play critical roles in lipid metabolism. ER–LD contacts enable lipid exchange and support essential cellular processes. However, how viruses utilize ER–LD coordination remains elusive. Here, we demonstrate that hepatitis C virus (HCV) infection markedly increases LDs abundance and enhances ER–LD contacts. Through a targeted screen of ER–LD tethering proteins, we identified that the NRZ complex, composed of nonsteroidal anti-inflammatory drug-activated gene (NAG), RAD50 interactor 1 (RINT1) and zeste white 10 (ZW10), is essential for HCV-induced ER–LD association and viral infection. Mechanistically, RINT1 and ZW10 interact with the HCV envelope protein E1. Ectopic E1 expression is sufficient to promote ER–LD contacts, which are abolished upon NRZ depletion. NRZ depletion also impairs Dengue virus (DENV) and Zika virus (ZIKV) infection, suggesting its conserved proviral function. Together, this work uncovers a critical mechanism by which host inter-organelle tethering complexes regulate viral infection, offering new insights into virus–host interactions and potential antiviral targets.

Migrasomes are migration-dependent organelles, serving as delivery packets to mediate release of cytoplasmic contents. Tetraspanin 4 (TSPAN4) acts as a marker for migrasomes and is essential for their formation. However, the regulatory mechanism(s) underlying TSPAN4-mediated migrasome biogenesis and its physiological functions remain to be elucidated. Here, we identified AMFR, an ER-resident E3 ligase, regulates migrasome formation through catalyzing the K48-linked polyubiquitination of TSPAN4 for degradation. Further, O-GlcNAcylation of AMFR by OGT at threonine 643 disrupts AMFR-TSPAN4 interactions, thereby stabilizing TSPAN4 and promoting migrasome formation. Additionally, viruses dynamically regulate migrasome formation by modulating AMFR O-GlcNAcylation and TSPAN4 ubiquitination. During the early stages of VSV or HSV-1 infection, viruses enhance migrasome formation and exploit these structures to spread among neighboring cells, whereas abolish migrasome formation during the late stages of infection. Our findings reveal a negatively regulatory mechanism governing migrasome biogenesis, and highlight how VSV and HSV-1 manipulate this process to facilitate their release.

The positive-strand RNA ( + RNA) viruses extensively remodel cellular endomembranes to facilitate viral replication, with coronaviruses forming a specialized viral replication organelle (RO) known as double-membrane vesicles (DMVs). These DMVs serve as platforms for viral replication and shield viral RNA from host immune recognition. However, the biogenesis, structural organization, and physiological properties of DMVs remain poorly understood. In this study, we demonstrate that the coronavirus non-structural protein 6 (nsp6) anchors DMVs to lipid droplets (LDs), hijacks the endoplasmic reticulum (ER)-associated protein degradation (ERAD) machinery to degrade PLIN2, and redirects fatty acids (FAs) from LDs to DMVs, thereby supplying lipids for DMV growth. Furthermore, nsp6 anchors ERAD-derived vesicles to DMVs, directly refurnishing membrane components for DMV expansion. Disruption of lipolysis or ERAD impairs DMV formation and inhibits coronaviral replication. We further validated the antiviral effects of ERAD inhibition in female mice in vivo. Our findings elucidate the mechanisms and functional significance of virus-induced organelle remodeling and DMV biogenesis. Given the conservation of viral ROs across +RNA viruses, these structures represent a promising and attractive target for the development of broad-spectrum antiviral therapies.

ATG14 is a core subunit of the class III phosphatidylinositol 3-kinase complex I (PtdIns3K-C1) for macroautophagy/autophagy initiation and also binds to the STX17 to promote autophagosome-lysosome fusion. Our recent work found that ATG14 also targets lipid droplets (LDs) and interacts with mammalian Atg8-family proteins (ATG8s) to mediate lipophagy (selective autophagic degradation of lipid droplets). We also demonstrated that STX18 (syntaxin 18) acts as a negative regulator that disrupts the interactions of ATG14-ATG8s and the formation of the PtdIns3K-C1 through binding to ATG14. Furthermore, we found that knockdown of STX18 induces LD-associated anti-viral protein RSAD2/Viperin degradation dependent on ATG14-mediated lipophagy. Additionally, coronavirus M protein hijacks STX18 to induce lipophagy and degrade RSAD2, facilitating virus production. In summary, our findings reveal new roles of ATG14 in lipid metabolism and viral replication as an autophagic receptor.

Lipid droplets (LDs) are dynamic lipid storage organelles that can be degraded by autophagy machinery to release neutral lipids, a process called lipophagy. However, specific receptors and regulation mechanisms for lipophagy remain largely unknown. Here, we identify that ATG14, the core unit of the PI3KC3-C1 complex, also targets LD and acts as an autophagic receptor that facilitates LD degradation. A negative regulator, Syntaxin18 (STX18) binds ATG14, disrupting the ATG14-ATG8 family members interactions and subverting the PI3KC3-C1 complex formation. Knockdown of STX18 activates lipophagy dependent on ATG14 not only as the core unit of PI3KC3-C1 complex but also as the autophagic receptor, resulting in the degradation of LD-associated anti-viral protein Viperin. Furthermore, coronavirus M protein binds STX18 and subverts the STX18-ATG14 interaction to induce lipophagy and degrade Viperin, facilitating virus production. Altogether, our data provide a previously undescribed mechanism for additional roles of ATG14 in lipid metabolism and virus production.

Lipid droplets (LDs) are dynamic lipid storage organelles that can sense and respond to changes in systemic energy balance. The size and number of LDs are controlled by complex and delicate mechanisms, among which, whether and which SNARE proteins mediate LD fusion, and the mechanisms governing this process remain poorly understood. Here we identified a SNARE complex, syntaxin 18 (STX18)–SNAP23–SEC22B, that is recruited to LDs to mediate LD fusion. STX18 targets LDs with its transmembrane domain spanning the phospholipid monolayer twice. STX18–SNAP23–SEC22B complex drives LD fusion in adiposome lipid mixing and content mixing in vitro assays. CIDEC/FSP27 directly binds STX18, SEC22B, and SNAP23, and promotes the lipid mixing of SNAREs-reconstituted adiposomes by promoting LD clustering. Knockdown of STX18 in mouse liver via AAV resulted in smaller liver and reduced LD size under high-fat diet conditions. All these results demonstrate a critical role of the SNARE complex STX18–SNAP23–SEC22B in LD fusion.

Emerging pathogen infections, such as Zika virus (ZIKV), pose an increasing threat to human health, but the role of mechanobiological attributes of host cells during ZIKV infection is largely unknown. Here, we reveal that ZIKV infection leads to increased contractility of host cells. Importantly, we investigated whether host cell contractility contributes to ZIKV infection efficacy, from both the intracellular and extracellular perspective. By performing drug perturbation and gene editing experiments, we confirmed that disruption of contractile actomyosin compromises ZIKV infection efficiency, viral genome replication and viral particle production. By culturing on compliant matrix, we further demonstrate that a softer substrate, leading to less contractility of host cells, compromises ZIKV infection, which resembles the effects of disrupting intracellular actomyosin organization. Together, our work provides evidence to support a positive correlation between host cell contractility and ZIKV infection efficacy, thus unveiling an unprecedented layer of interplay between ZIKV and the host cell.

Lipid droplets (LDs) form inter-organelle contacts with the endoplasmic reticulum (ER) that promote their biogenesis, while LD contacts with mitochondria enhance β-oxidation of contained fatty acids. Viruses have been shown to take advantage of lipid droplets to promote viral production, but it remains unclear whether they also modulate the interactions between LDs and other organelles. Here, we showed that coronavirus ORF6 protein targets LDs and is localized to the mitochondria-LD and ER-LD contact sites, where it regulates LD biogenesis and lipolysis. At the molecular level, we find that ORF6 inserts into the LD lipid monolayer via its two amphipathic helices. ORF6 further interacts with ER membrane proteins BAP31 and USE1 to mediate ER-LDs contact formation. Additionally, ORF6 interacts with the SAM complex in the mitochondrial outer membrane to link mitochondria to LDs. In doing so, ORF6 promotes cellular lipolysis and LD biogenesis to reprogram host cell lipid flux and facilitate viral production.