PURPOSE: Tripartite-motif-containing protein 56 (TRIM56) has been found to exhibit a broad antiviral activity, depending upon E3 ligase activity. Here, we attempted to evaluate the function of TRIM56 in multiple myeloma (MM) and its underlying molecular basis. MATERIALS AND METHODS: TRIM56 expression at the mRNA and protein level was measured by qRT PCR and western blot analysis. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry analysis was performed to investigate the effect of TRIM56 on MM cell proliferation and apoptosis. The concentrations of interferon (IFN)-β, interleukin (IL)-6, and tumor necrosis factor-α in MM cell culture supernatants were detected with respective commercial ELISA kits. Western blot was employed to determine the effect of TRIM56 on toll-like receptor 3 (TLR3)/toll-IL-1 receptor (TIR) domain-containing adaptor inducing IFN-β (TRIF) signaling pathway. RESULTS: TRIM56 expression was prominently decreased in MM cells. Poly (dA:dT)-induced TRIM56 overexpression in U266 cells suppressed proliferation, induced apoptosis, and enhanced inflammatory cytokine production, while TRIM56 knockdown improved growth, diminished apoptosis, and inhibited inflammatory cytokine secretion in RPMI8226 cells. Moreover, TRIM56 knockdown blocked TLR3 signaling pathway. Furthermore, poly (I:C), a TLR3 agonist, markedly abolished TRIM56 depletion-induced increase of proliferation, decrease of apoptosis, and reduction of inflammatory factor in MM cells. CONCLUSION: TRIM56 may act as a tumor suppressor in MM through activation of TLR3/TRIF signaling pathway, contributing to a better understanding of the molecular mechanism of TRIM56 involvement in MM pathogenesis and providing a promising therapy strategy for patients with MM.
Adaptor Proteins, Vesicular Transport/metabolism ; Apoptosis/drug effects ; Cell Line, Tumor ; Cell Proliferation/drug effects ; Cytokines/secretion ; Disease Progression ; Down-Regulation/drug effects ; Gene Knockdown Techniques ; Humans ; Multiple Myeloma/metabolism ; Multiple Myeloma/pathology ; Poly I-C/pharmacology ; Signal Transduction/drug effects ; Toll-Like Receptor 3/metabolism ; Tripartite Motif Proteins/deficiency ; Tripartite Motif Proteins/metabolism ; Ubiquitin-Protein Ligases/deficiency ; Ubiquitin-Protein Ligases/metabolism

RING finger protein 13 (RNF13) is a newly identified E3 ligase reported to be functionally significant in the regulation of cancer development, muscle cell growth, and neuronal development. In this study, the function of RNF13 in cardiotoxin-induced skeletal muscle regeneration was investigated using RNF13-knockout mice. RNF13(-/-) mice exhibited enhanced muscle regeneration-characterized by accelerated satellite cell proliferation-compared with wild-type mice. The expression of RNF13 was remarkably induced in macrophages rather than in the satellite cells of wild-type mice at the very early stage of muscle damage. This result indicated that inflammatory cells are important in RNF13-mediated satellite cell functions. The cytokine levels in skeletal muscles were further analyzed and showed that RNF13(-/-) mice produced greater amounts of various cytokines than wild-type mice. Among these, IL-4 and IL-6 levels significantly increased in RNF13(-/-) mice. The accelerated muscle regeneration phenotype was abrogated by inhibiting IL-4/IL-6 action in RNF13(-/-) mice with blocking antibodies. These results indicate that RNF13 deficiency promotes skeletal muscle regeneration via the effects on satellite cell niche mediated by IL-4 and IL-6.
Animals ; Cell Proliferation ; Inflammation ; pathology ; Interleukin-4 ; metabolism ; Interleukin-6 ; metabolism ; Macrophages ; metabolism ; Mice ; Mice, Knockout ; Muscle, Skeletal ; metabolism ; pathology ; physiopathology ; Regeneration ; Satellite Cells, Skeletal Muscle ; metabolism ; pathology ; Ubiquitin-Protein Ligases ; deficiency ; metabolism

RING finger protein 13 (RNF13) is a novel E3 ubiquitin ligase whose expression is associated with cancer development. However, its specific role in cancer progression and metastasis remains unclear. Here, a B16F10/LLC experimental pulmonary metastatic model was developed to examine the formation of metastatic foci in the lung. A greater number of tumor colonies were observed in the lungs of RNF13-knockout (KO) mice than in their wild-type (WT) littermates, whereas no significant differences in tumor size were observed between the two groups. In short-term experiments, the number of fluorescently-labeled B16F10 cells increased remarkably in RNF13-KO lungs at early time points, whereas clearance of tumor cells from the blood was not affected. These results indicated that RNF13 may inhibit the colonization of B16F10 cells in the lung. Assessment of the concentration of various cytokines in tumor bearing lungs and blood did not detect significant differences between the blood of RNF13-KO and WT mice; however the levels of GM-CSF were significantly reduced in RNF13-KO tumor bearing lungs, which may have guided more B16F10 cells to migrate to the lungs. This was confirmed by lower GM-CSF concentrations in conditioned media from the culture of RNF13-KO lung slices. Collectively, our results suggest that host RNF13 affects the concentration of GM-CSF in tumor-bearing lungs, leading to a reduction in the colonization of metastatic tumor cells in the lung.
Animals ; Cell Line, Tumor ; Gene Knockout Techniques ; Granulocyte-Macrophage Colony-Stimulating Factor ; metabolism ; Lung ; metabolism ; pathology ; Lung Neoplasms ; pathology ; Mice ; Mice, Knockout ; Neoplasm Invasiveness ; Neoplasm Metastasis ; Ubiquitin-Protein Ligases ; deficiency ; genetics