UV-dependent phosphorylation of COP9/signalosome in UV-induced apoptosis

COPS4 is a novel prognostic biomarker and potential therapeutic target involved in regulation of immune microenvironment in numerous cancers

CHOL, HNSC, ESCA, and LIHC are among the most aggressive and fatal malignancies worldwide. Despite their clinical burden, these cancers still lack dependable biomarkers for early detection, prognosis, and therapeutic targeting. The COP9 signalosome (COPS), a key regulator of the ubiquitin proteasome pathway, has been shown to be aberrantly expressed in various cancer types and is thought to contribute to tumor development and progression. Among its subunits, COPS4 plays an essential role in maintaining the functional integrity of the complex. However, its prognostic significance and clinicopathological relevance in cancer remain poorly understood. This study adopted a comprehensive, integrative bioinformatics framework grounded in TCGA-derived datasets, incorporating analytical platforms encompassing UALCAN, GEPIA, MEXPRESS, OncoDB, UCSC Xena, ENCORI, TIMER, GeneMANIA, TNMplot, and TISIDB. Through this strategy, the investigation delineated the transcriptional landscape, genomic aberrations, immunological associations, and putative functional roles of COPS4 across CHOL, HNSC, ESCA, and LIHC. Virtual screening and molecular dynamics simulations were performed to explore its druggable potential. COPS4 expression was significantly upregulated in tumor tissues and exhibited strong associations with key clinical parameters, including pathological stage, histological grade, nodal involvement, and metastatic status. IHC analysis further validated elevated protein levels in tumor specimens compared to adjacent non-neoplastic tissues. Genomic alterations were frequent, with predominant mutations in LIHC, amplifications in CHOL, and both amplifications and deletions in HNSC and ESCA. COPS4 expression showed positive associations with subset of oncogenes and inverse correlations with tumor suppressors. Notably, NUP54 and HELQ emerged as consistent co-targets. Immune analysis revealed strong positive correlations between COPS4 and infiltrating immune cells, including CD8+ and CD4+ T cells, B cells, macrophages, neutrophils, and dendritic cells. Somatic copy number variations of COPS4 also influenced immune cell infiltration and patient survival outcomes. Promoter hypomethylation and gene amplification were identified as mechanisms driving its overexpression. Finally, virtual screening and molecular dynamics simulations identified FDA-approved drugs interacting with COPS4, emphasizing its oncogenic role and therapeutic potential.

Regulatory Mechanism of the Constitutive Photomorphogenesis 9 Signalosome Complex in Response to Abiotic Stress in Plants

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is a highly conserved protein complex that regulates signaling pathways in plants under abiotic stress. We discuss the potential molecular mechanisms of CSN under abiotic stress, including oxidative stress with reactive oxygen species signaling, salt stress with jasmonic acid, gibberellic acid, and abscisic acid signaling, high-temperature stress with auxin signaling, and optical radiation with DNA damage and repair response. We conclude that CSN likely participates in affecting antioxidant biosynthesis and hormone signaling by targeting receptors, kinases, and transcription factors in response to abiotic stress, which potentially provides valuable information for engineering stress-tolerant crops.

Analysis of expression profiles and prognostic value of COP9 signalosome subunits for patients with head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) has been associated with poor prognosis, due to its strong invasive ability and resistance to chemotherapy. Thus, there is an urgent requirement to identify effective biomarkers for the early diagnosis and prognostic evaluation of HNSCC. COP9 signalosome (COPS) regulates numerous cancer-associated biological processes in various malignancies. The aim of the present study was to investigate the association between COPS and HNSCC. The mRNA expression profiles of COPS in HNSCC were analyzed using UALCAN, Oncomine and UCSC Xena databases. The association between overall survival time in patients with HNSCC and the COPS genes was investigated using the Kaplan-Meier plotter database. The CERES score was obtained and evaluated to determine the importance of the COPS genes for survival of the HNSCC cell lines. Functional analysis for Gene Ontology and Gene Set Enrichment Analysis (GSEA) was performed using The Database for Annotation, Visualization and Integrated Discovery and GSEA software, respectively. After knocking down COPS5 and COPS6, cell Counting Kit-8 and wound healing assays were used to detect cell growth and migration of the CAL27 and SCC25 cell lines, respectively. Among the 10 COPS genes examined, most COPS subunits were upregulated in HNSCC samples compared with that in normal tissues, except for COPS9. Increased mRNA expression level of COPS5, COPS6, COPS7B, COPS8 and COPS9 was associated with TNM stage in patients with HNSCC. High mRNA expression level of COPS2, COPS5, COPS6, COPS7A, COPS7B, COPS8 and COPS9 had prognostic significance of patients with HNSCC. Knockdown of COPS5 and COPS6 inhibited cell growth and migration of the CAL27 and SCC25 cell lines. The results from the present study suggested that COPS subunits could be potential biomarkers in patients with HNSCC. COPS5 and COPS6 were important for cell survival and migration of the HNSCC cells.

The COP9 Signalosome: A Multi-DUB Complex

The COP9 signalosome (CSN) is a signaling platform controlling the cellular ubiquitylation status. It determines the activity and remodeling of ~700 cullin-RING ubiquitin ligases (CRLs), which control more than 20% of all ubiquitylation events in cells and thereby influence virtually any cellular pathway. In addition, it is associated with deubiquitylating enzymes (DUBs) protecting CRLs from autoubiquitylation and rescuing ubiquitylated proteins from degradation. The coordination of ubiquitylation and deubiquitylation by the CSN is presumably important for fine-tuning the precise formation of defined ubiquitin chains. Considering its intrinsic DUB activity specific for deneddylation of CRLs and belonging to the JAMM family as well as its associated DUBs, the CSN represents a multi-DUB complex. Two CSN-associated DUBs, the ubiquitin-specific protease 15 (USP15) and USP48 are regulators in the NF-κB signaling pathway. USP15 protects CRL1^β-TrCP responsible for IκBα ubiquitylation, whereas USP48 stabilizes the nuclear pool of the NF-κB transcription factor RelA upon TNF stimulation by counteracting CRL2^SOCS1. Moreover, the CSN controls the neddylation status of cells by its intrinsic DUB activity and by destabilizing the associated deneddylation enzyme 1 (DEN1). Thus, the CSN is a master regulator at the intersection between ubiquitylation and neddylation.

Interaction between NSMCE4A and GPS1 links the SMC5/6 complex to the COP9 signalosome

Background

The SMC5/6 complex, cohesin and condensin are the three mammalian members of the structural maintenance of chromosomes (SMC) family, large ring-like protein complexes that are essential for genome maintenance. The SMC5/6 complex is the least characterized complex in mammals; however, it is known to be involved in homologous recombination repair (HRR) and chromosome segregation.

Results

In this study, a yeast two-hybrid screen was used to help elucidate novel interactions of the kleisin subunit of the SMC5/6 complex, NSMCE4A. This approach discovered an interaction between NSMCE4A and GPS1, a COP9 signalosome (CSN) component, and this interaction was further confirmed by co-immunoprecipitation. Additionally, GPS1 and components of SMC5/6 complex colocalize during interphase and mitosis. CSN is a cullin deNEDDylase and is an important factor for HRR. Depletion of GPS1, which has been shown to negatively impact DNA end resection during HRR, caused an increase in SMC5/6 levels at sites of laser-induced DNA damage. Furthermore, inhibition of the dennedylation function of CSN increased SMC5/6 levels at sites of laser-induced DNA damage.

Conclusion

Taken together, these data demonstrate for the first time that the SMC5/6 and CSN complexes interact and provides evidence that the CSN complex influences SMC5/6 functions during cell cycle progression and response to DNA damage.

Cullin-RING Ligase Regulation by the COP9 Signalosome: Structural Mechanisms and New Physiologic Players

The Cullin-RING E3 ligases (CRLs) are major ubiquitylation machineries regulated by reversible cycles of neddylation and deneddylation. The deneddylase COP9 Signalosome (CSN) terminates CRL catalytic cycle. CSN also provides a docking platform for several kinases and deubiquitinases that might play a role in regulating CRL. Recently, remarkable progress has been made in elucidating the biochemical principles and physiological implications of such exquisite regulation. The cryo-EM structures of CRL-CSN complexes provide the biochemical basis of their cognate interactions and reveal potential regulatory mechanisms during complex disassembly. Moreover, novel players beyond the canonical eight subunits of CSN were identified. This includes CSNAP, a potential 9th CSN subunit with regulatory functions, and the metabolite inositol hexakisphosphate (IP₆), which enhances CRL-CSN complex formation, with IP₆-metabolizing enzymes possibly instilling dynamics to the CRL-CSN system. Here, we review and summarize these new mechanistic insights along with progress in understanding CSN biology based on model organisms with genetically edited CSN subunits.

CSNAP, the smallest CSN subunit, modulates proteostasis through cullin-RING ubiquitin ligases

The cullin-RING ubiquitin E3 ligase (CRL) family consists of ~250 complexes that catalyze ubiquitylation of proteins to achieve cellular regulation. All CRLs are inhibited by the COP9 signalosome complex (CSN) through both enzymatic (deneddylation) and nonenzymatic (steric) mechanisms. The relative contribution of these two mechanisms is unclear. Here, we decouple the mechanisms using CSNAP, the recently discovered ninth subunit of the CSN. We find that CSNAP reduces the affinity of CSN toward CRL complexes. Removing CSNAP does not affect deneddylation, but leads to global effects on the CRL, causing altered reproductive capacity, suppressed DNA damage response, and delayed cell cycle progression. Thus, although CSNAP is only 2% of the CSN mass, it plays a critical role in the steric regulation of CRLs by the CSN.

Roles of Multifunctional COP9 Signalosome Complex in Cell Fate and Implications for Drug Discovery

The eight subunits containing COP9 signalosome (CSN) complex, is highly conserved among eukaryotes. CSN, identified as a negative regulator of photomorphogenesis, has also been demonstrated to be important in proteolysis, cellular signal transduction and cell cycle regulation in various eukaryotic organisms. This review mainly summarizes the roles of CSN in cell cycle regulation, signal transduction and apoptosis, and its potential as diagnostic biomarkers, drug targets for cancer and infectious diseases. J. Cell. Physiol. 232: 1246-1253, 2017. © 2016 Wiley Periodicals, Inc.