Subunit 3 of the COP9 signalosome is poised to facilitate communication between the extracellular matrix and the nucleus through the muscle-specific beta1D integrin

COPS3 Promotes Proliferation, Invasion, and EMT of Colorectal Cancer Cells by MEK/ERK Pathway

Colorectal cancer (CRC) is one of the most aggressive cancers with poor prognosis and high mortality. The study of the pathogenesis of CRC is a top priority in providing effective diagnostic and prognostic strategies for CRC. COPS3 protein is a subunit of the COP9 signaling body (CSN), which is closely associated with the development of multiple types of tumors. However, there are few studies on the role of COPS3 in colon adenocarcinoma (COAD). This study investigated the effects of COPS3 on proliferation, motility, and EMT of colorectal cancer cells and related mechanisms. COPS3 was highly expressed in COAD. The depletion of COPS3 suppressed the viability and stimulated the apoptosis of COAD cells. Depletion of COPS3 suppressed the motility and EMT process of COAD cells. Mechanically, we found that COPS3 could mediate MEK/ERK pathway and therefore affected the process of COAD cells. We thought that COPS3 could serve as a promising COAD target.

The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease

The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.

Role of the COP9 Signalosome (CSN) in Cardiovascular Diseases

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is an evolutionarily conserved multi-protein complex, consisting of eight subunits termed CSN1-CSN8. The main biochemical function of the CSN is the control of protein degradation via the ubiquitin-proteasome-system through regulation of cullin-RING E3-ligase (CRL) activity by deNEDDylation of cullins, but the CSN also serves as a docking platform for signaling proteins. The catalytic deNEDDylase (isopeptidase) activity of the complex is executed by CSN5, but only efficiently occurs in the three-dimensional architectural context of the complex. Due to its positioning in a central cellular pathway connected to cell responses such as cell-cycle, proliferation, and signaling, the CSN has been implicated in several human diseases, with most evidence available for a role in cancer. However, emerging evidence also suggests that the CSN is involved in inflammation and cardiovascular diseases. This is both due to its role in controlling CRLs, regulating components of key inflammatory pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and complex-independent interactions of subunits such as CSN5 with inflammatory proteins. In this case, we summarize and discuss studies suggesting that the CSN may have a key role in cardiovascular diseases such as atherosclerosis and heart failure. We discuss the implicated molecular mechanisms ranging from inflammatory NF-κB signaling to proteotoxicity and necrosis, covering disease-relevant cell types such as myeloid and endothelial cells or cardiomyocytes. While the CSN is considered to be disease-exacerbating in most cancer entities, the cardiovascular studies suggest potent protective activities in the vasculature and heart. The underlying mechanisms and potential therapeutic avenues will be critically discussed.

Knockdown of subunit 3 of the COP9 signalosome inhibits C2C12 myoblast differentiation via NF-KappaB signaling pathway

Background

The COP9 signalosome (CSN) is a conserved protein complex composed of 8 subunits designated CSN1-CSN8. CSN3 represents the third subunit of the CSN and maintains the integrity of the complex. CSN3 binds to the striated muscle-specific β1D integrin tail, and its subcellular localization is altered in differentiated skeletal muscle cells. However, the role of CSN3 in skeletal muscle differentiation is unknown. The main goal of this study was to identify whether CSN3 participates in myoblast differentiation and the signalling mechanisms involved using C2C12 cells as a skeletal muscle cell model.

Methods

Small-hairpin (shRNA) was used to knockdown CSN3 in C2C12 cells. Differentiation was evaluated by immunostaining and confocal microscopy. Markers of differentiation, NF-κB signaling and CSN subunits expression, were assessed by immunoblotting and/or immunostaining. Cell proliferation was analysed by cell counting, flow cytometry and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by one or two-way analysis of variance (ANOVA) followed by post-hoc testing.

Results

Transduction of C2C12 cells with two distinct CSN3 shRNAs led to the production of two cells lines expressing 7% of CSN3 protein (shCSN3-Low) and 43% of CSN3 protein (CSN3-Med) compared to controls. Knockdown of CSN3 was accompanied by destabilization of several CSN subunits and increased nuclear NF-κB localization. shCSN3-Med cells expressed less myogenin and formed shorter and thinner myotubes. In contrast, the shCSN3-Low cells expressed higher levels of myogenin prior and during the differentiation and remained mononucleated throughout the differentiation period. Both CSN3 knockdown cell lines failed to express sarcomeric myosin heavy chain (MHC) protein during differentiation. The fusion index was significantly higher in control cells than in shCSN3-Med cells, whereas shCSN3-Low cells showed no cell fusion. Interestingly, CSN3 knockdown cells exhibited a significantly slower growth rate relative to the control cells. Cell cycle analysis revealed that CSN3 knockdowns delayed in S phase and had increased levels of nuclear p21/Cip1 and p27/Kip1.

Conclusions

This study clarifies the first step toward unrevealing the CSN3/CSN-mediated pathways that controls C2C12 differentiation and proliferation. Further in vivo characterization of CSN/CSN3 may lead to the discovery of novel therapeutic target of skeletal muscle diseases such as muscular dystrophies.

The Role of the COP9 Signalosome and Neddylation in DNA Damage Signaling and Repair

The maintenance of genomic integrity is an important process in organisms as failure to sense and repair damaged DNA can result in a variety of diseases. Eukaryotic cells have developed complex DNA repair response (DDR) mechanisms to accurately sense and repair damaged DNA. Post-translational modifications by ubiquitin and ubiquitin-like proteins, such as SUMO and NEDD8, have roles in coordinating the progression of DDR. Proteins in the neddylation pathway have also been linked to regulating DDR. Of interest is the COP9 signalosome (CSN), a multi-subunit metalloprotease present in eukaryotes that removes NEDD8 from cullins and regulates the activity of cullin-RING ubiquitin ligases (CRLs). This in turn regulates the stability and turnover of a host of CRL-targeted proteins, some of which have established roles in DDR. This review will summarize the current knowledge on the role of the CSN and neddylation in DNA repair.

Dynamic regulation of the COP9 signalosome in response to DNA damage

The COP9 signalosome (CSN) is an evolutionarily conserved protein complex that participates in the regulation of the ubiquitin/26S proteasome pathway by controlling the function of cullin-RING-ubiquitin ligases. Impressive progress has been made in deciphering its critical role in diverse cellular and developmental processes. However, little is known about the underlying regulatory principles that coordinate its function. Through biochemical and fluorescence microscopy analyses, we determined that the complex is localized in the cytoplasm, nucleoplasm, and chromatin-bound fractions, each differing in the composition of posttranslationally modified subunits, depending on its location within the cell. During the cell cycle, the segregation between subcellular localizations remains steady. However, upon UV damage, a dose-dependent temporal shuttling of the CSN complex into the nucleus was seen, accompanied by upregulation of specific phosphorylations within CSN1, CSN3, and CSN8. Taken together, our results suggest that the specific spatiotemporal composition of the CSN is highly controlled, enabling the complex to rapidly adapt and respond to DNA damage.

Breaking down protein degradation mechanisms in cardiac muscle

Regulated protein degradation through the ubiquitin-proteasome and lysosomal/autophagy systems is critical for homeostatic protein turnover in cardiac muscle and for proper cardiac function. The discovery of muscle-specific components in these systems has illuminated how aberrations in their levels are pivotal to the development of cardiac stress and disease. New evidence suggests that equal importance in disease development should be given to ubiquitously expressed degradation components. These are compartmentalized within cardiac muscles and, when mislocalized, can be critical in the development of specific cardiac diseases. Here, we discuss how alterations in the compartmentalization of degradation components affect disease states, the tools available to investigate these mechanisms, as well as recent discoveries that highlight the therapeutic value of targeting these pathways in disease.

Influence of the extracellular matrix and integrins on volume-sensitive osmolyte anion channels in C2C12 myoblasts

The purpose of this study was to determine whether extracellular matrix (ECM) composition through integrin receptors modulated the volume-sensitive osmolyte anion channels (VSOACs) in skeletal muscle-derived C2C12 cells. Cl(-) currents were recorded in whole cell voltage-clamped cells grown on laminin (LM), fibronectin (FN), or in the absence of a defined ECM (NM). Basal membrane currents recorded in isotonic media (300 mosmol/kg) were larger in cells grown on FN (3.8-fold at +100 mV) or LM (8.8-fold at +100 mV) when compared with NM. VSOAC currents activated by cell exposure to hypotonic solution were larger in cells grown on LM (1.72-fold at +100 mV) or FN (1.75-fold at +100 mV) compared with NM. Additionally, the kinetics of VSOAC activation was approximately 27% quicker on FN and LM. These currents were tamoxifen sensitive, displayed outward rectification, reversed at the equilibrium potential of Cl(-) and inactivated at potentials >+60 mV. Specific knockdown of beta(1)-integrin by short hairpin RNA interference strongly inhibited the VSOAC Cl(-) currents in cells plated on FN. In conclusion, ECM composition and integrins profoundly influence the biophysical properties and mechanisms of onset of VSOACs.