Impaired Antiviral Responses to Extracellular Double-Stranded RNA and Cytosolic DNA, but Not to Interferon-α Stimulation, in TRIM56-Deficient Cells

TRIM56 restricts Coxsackievirus B infection by mediating the ubiquitination of viral RNA-dependent RNA polymerase 3D

Coxsackievirus B (CVB) is the major causative pathogen for severe diseases such as viral myocarditis, meningitis, and pancreatitis. There is no effective antiviral therapy currently available for CVB infection primarily due to that the pathogenesis of CVB has not been completely understood. Viruses are obligate intracellular pathogens which subvert cellular processes to ensure viral replication. Dysregulation of ubiquitination has been implicated in CVB infection. However, how ubiquitination is involved in CVB infection remains unclear. Here we found that the 3D protein of CVB3, the RNA-dependent RNA polymerase, was modified at K220 by K48-linked polyubiquitination which promoted its degradation through proteasome. Proteomic analysis showed that the E3 ligase TRIM56 was upregulated in CVB3-infected cells, while the majority of TRIMs remained unchanged. Pull-down and immunoprecipitation analyses showed that TRIM56 interacted with CVB3 3D. Immunofluorescence observation showed that viral 3D protein was colocalized with TRIM56. TRIM56 overexpression resulted in enhanced ubiquitination of CVB3 3D and decreased virus yield. Moreover, TRIM56 was cleaved by viral 3C protease in CVB3-infected cells. Taken together, this study demonstrated that TRIM56 mediates the ubiquitination and proteasomal degradation of the CVB3 3D protein. These findings demonstrate that TRIM56 is an intrinsic cellular restriction factor against CVB infection, and enhancing viral protein degradation could be a potential strategy to control CVB infection.

TRIM56 acts through the IQGAP1-CDC42 signaling axis to promote glioma cell migration and invasion

Diffuse invasion is an important factor leading to treatment resistance and a poor prognosis in gliomas. Herein, we found that expression of the tripartite motif containing 56 (TRIM56), a RING-finger domain containing E3 ubiquitin ligase, was markedly higher in glioma than in normal brain tissue, and was significantly correlated with malignant phenotypes and a poor prognosis. In vitro and in vivo experimental studies revealed that TRIM56 promoted the migration and invasion of glioma cells. Mechanistically, TRIM56 was transcriptionally regulated by SP1 and promoted the K48-K63-linked poly-ubiquitination transition of IQGAP1 at Lys-1230 by interacting with it, which in turn promoted CDC42 activation. This mechanism was confirmed to mediate glioma migration and invasion. In conclusion, our study provides insights into the mechanisms through which TRIM56 promotes glioma motility, i.e., by regulating IQGAP1 ubiquitination to promote CDC42 activation, which might be clinically targeted for the treatment of glioma.