Subunit 6 of the COP9 signalosome promotes tumorigenesis in mice through stabilization of MDM2 and is upregulated in human cancers

Protein neddylation and its role in health and diseases

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

CSN6-SPOP-HMGCS1 Axis Promotes Hepatocellular Carcinoma Progression via YAP1 Activation

Cholesterol metabolism has important roles in maintaining membrane integrity and countering the development of diseases such as obesity and cancers. Cancer cells sustain cholesterol biogenesis for their proliferation and microenvironment reprograming even when sterols are abundant. However, efficacy of targeting cholesterol metabolism for cancer treatment is always compromised. Here it is shown that CSN6 is elevated in HCC and is a positive regulator of hydroxymethylglutaryl-CoA synthase 1 (HMGCS1) of mevalonate (MVA) pathway to promote tumorigenesis. Mechanistically, CSN6 antagonizes speckle-type POZ protein (SPOP) ubiquitin ligase to stabilize HMGCS1, which in turn activates YAP1 to promote tumor growth. In orthotopic liver cancer models, targeting CSN6 and HMGCS1 hinders tumor growth in both normal and high fat diet. Significantly, HMGCS1 depletion improves YAP inhibitor efficacy in patient derived xenograft models. The results identify a CSN6-HMGCS1-YAP1 axis mediating tumor outgrowth in HCC and propose a therapeutic strategy of targeting non-alcoholic fatty liver diseases- associated HCC.

Mechanisms and potential applications of COPS6 in pan-cancer therapy

The COP9 signalosome subunit 6 (COPS6) is abnormally overexpressed in many malignancies, yet its precise role in carcinogenesis is unknown. To gain a better understanding of COPS6's role, the authors conducted a pan-cancer analysis using various bioinformatics techniques such as differential expression patterns, prognostic value, gene mutations, immune infiltration, correlation analysis, and functional enrichment assessment. Results showed that COPS6 was highly correlated with prognosis, immune cell infiltration level, tumor mutation burden, and microsatellite instability in patients with a range of tumor types. This suggests that COPS6 may be a potential target for cancer treatment. Overall, this research provides insight into COPS6's role in cancer development and its potential therapeutic applications.

Friend or foe? Reciprocal regulation between E3 ubiquitin ligases and deubiquitinases

Protein ubiquitination is a post-translational modification that entails the covalent attachment of the small protein ubiquitin (Ub), which acts as a signal to direct protein stability, localization, or interactions. The Ub code is written by a family of enzymes called E3 Ub ligases (∼600 members in humans), which can catalyze the transfer of either a single ubiquitin or the formation of a diverse array of polyubiquitin chains. This code can be edited or erased by a different set of enzymes termed deubiquitinases (DUBs; ∼100 members in humans). While enzymes from these distinct families have seemingly opposing activities, certain E3-DUB pairings can also synergize to regulate vital cellular processes like gene expression, autophagy, innate immunity, and cell proliferation. In this review, we highlight recent studies describing Ub ligase-DUB interactions and focus on their relationships.

Emerging Roles of Cullin-RING Ubiquitin Ligases in Cardiac Development

Heart development is a spatiotemporally regulated process that extends from the embryonic phase to postnatal stages. Disruption of this highly orchestrated process can lead to congenital heart disease or predispose the heart to cardiomyopathy or heart failure. Consequently, gaining an in-depth understanding of the molecular mechanisms governing cardiac development holds considerable promise for the development of innovative therapies for various cardiac ailments. While significant progress in uncovering novel transcriptional and epigenetic regulators of heart development has been made, the exploration of post-translational mechanisms that influence this process has lagged. Culling-RING E3 ubiquitin ligases (CRLs), the largest family of ubiquitin ligases, control the ubiquitination and degradation of ~20% of intracellular proteins. Emerging evidence has uncovered the critical roles of CRLs in the regulation of a wide range of cellular, physiological, and pathological processes. In this review, we summarize current findings on the versatile regulation of cardiac morphogenesis and maturation by CRLs and present future perspectives to advance our comprehensive understanding of how CRLs govern cardiac developmental processes.

Computational exploration of the significance of COPS6 in cancer: Functional and clinical relevance across tumor types

BACKGROUND

The COP9 signalosome subunit 6 (COPS6) has been implicated in cancer progression, while its precise role in most types of cancer remains elusive.

AIM

To investigate the functional and clinical relevance of COPS6 across various tumor types using publicly available databases.

METHODS

We used R software and online analysis databases to analyze the differential expression, prognosis, mutation and related functions of COPS6 in pan-cancer.

RESULTS

Differential expression analysis and survival analysis demonstrated that COPS6 was highly expressed and associated with high-risk profiles in the majority of cancer types. Possible associations between COPS6 expression level and prognostic outcomes were found using data from public databases. Mutational analysis revealed that missense mutations were the predominant type of COPS6 mutation. Additionally, positive correlations were identified between COPS6 expression level and tumor mutational burden and microsatellite instability in most types of cancer. Immune infiltration analysis demonstrated a negative correlation between COPS6 expression level and CD8+ T cell infiltration in certain types of cancer. The correlation between COPS6 expression level and cancer-associated fibroblast infiltration exhibited heterogeneity, in which a positive correlation was found in head and neck squamous cell carcinoma and tenosynovial giant cell tumor, and a negative correlation was identified in diffuse large B-cell lymphoma and thymoma. The correlation between COPS6 expression level and macrophage infiltration was closely related to macrophage type. Gene co-expression and enrichment analysis highlighted transcription elongation factor B polypeptide 2 and G protein pathway suppressor 1 were significantly and positively associated with COPS6 expression level. These genes were predominantly involved in processes, such as ubiquitin-mediated proteolysis and human immunodeficiency virus 1 infection.

CONCLUSION

In conclusion, this study systematically explored the significance of COPS6 across different tumor types, providing a solid foundation for considering COPS6 as a novel biomarker in cancer research.

Genomics of deletion 7 and 7q in myeloid neoplasm: from pathogenic culprits to potential synthetic lethal therapeutic targets

Complete or partial deletions of chromosome 7 (-7/del7q) belong to the most frequent chromosomal abnormalities in myeloid neoplasm (MN) and are associated with a poor prognosis. The disease biology of -7/del7q and the genes responsible for the leukemogenic properties have not been completely elucidated. Chromosomal deletions may create clonal vulnerabilities due to haploinsufficient (HI) genes contained in the deleted regions. Therefore, HI genes are potential targets of synthetic lethal strategies. Through the most comprehensive multimodal analysis of more than 600 -7/del7q MN samples, we elucidated the disease biology and qualified a list of most consistently deleted and HI genes. Among them, 27 potentially synthetic lethal target genes were identified with the following properties: (i) unaffected genes by hemizygous/homozygous LOF mutations; (ii) prenatal lethality in knockout mice; and (iii) vulnerability of leukemia cells by CRISPR and shRNA knockout screens. In -7/del7q cells, we also identified 26 up or down-regulated genes mapping on other chromosomes as downstream pathways or compensation mechanisms. Our findings shed light on the pathogenesis of -7/del7q MNs, while 27 potential synthetic lethal target genes and 26 differential expressed genes allow for a therapeutic window of -7/del7q.

COPS6 promotes tumor progression and reduces CD8+ T cell infiltration by repressing IL-6 production to facilitate tumor immune evasion in breast cancer

Due to poor T cell infiltration, tumors evade immune surveillance. Increased CD8+ T cell infiltration in breast cancer suggests a satisfactory response to immunotherapy. COPS6 has been identified as an oncogene, but its role in regulating antitumor immune responses has not been defined. In this study, we investigated the impact of COPS6 on tumor immune evasion in vivo. Tumor transplantation models were established in C57BL/6 J mice and BALB/c nude mice. Flow cytometry was conducted to identify the role of COPS6 on tumor-infiltrating CD8+ T cells. By analyzing the TCGA and GTEx cohort, we found that COPS6 expression was significantly up-regulated in a variety of cancers. In human osteosarcoma cell line U2OS and non-small cell lung cancer cell line H1299, we showed that p53 negatively regulated COPS6 promoter activity. In human breast cancer MCF-7 cells, COPS6 overexpression stimulated p-AKT expression as well as the proliferation and malignant transformation of tumor cells, whereas knockdown of COPS6 caused opposite effects. Knockdown of COPS6 also significantly suppressed the growth of mouse mammary cancer EMT6 xenografts in BALB/c nude mice. Bioinformatics analysis suggested that COPS6 was a mediator of IL-6 production in the tumor microenvironment and a negative regulator of CD8+ T cell tumor infiltration in breast cancer. In C57BL6 mice bearing EMT6 xenografts, COPS6 knockdown in the EMT6 cells increased the number of tumor-infiltrating CD8+ T cells, while knockdown of IL-6 in COPS6KD EMT6 cells diminished tumor infiltrating CD8+ T cells. We conclude that COPS6 promotes breast cancer progression by reducing CD8+ T cell infiltration and function via the regulation of IL-6 secretion. This study clarifies the role of p53/COPS6/IL-6/CD8+ tumor infiltrating lymphocytes signaling in breast cancer progression and immune evasion, opening a new path for development of COPS6-targeting therapies to enhance tumor immunogenicity and treat immunologically "cold" breast cancer.

eIF3f Mediates SGOC Pathway Reprogramming by Enhancing Deubiquitinating Activity in Colorectal Cancer

Numerous studies have demonstrated that individual proteins can moonlight. Eukaryotic Initiation translation factor 3, f subunit (eIF3f) is involved in critical biological functions; however, its role independent of protein translation in regulating colorectal cancer (CRC) is not characterized. Here, it is demonstrated that eIF3f is upregulated in CRC tumor tissues and that both Wnt and EGF signaling pathways are participating in eIF3f's oncogenic impact on targeting phosphoglycerate dehydrogenase (PHGDH) during CRC development. Mechanistically, EGF blocks FBXW7β-mediated PHGDH ubiquitination through GSK3β deactivation, and eIF3f antagonizes FBXW7β-mediated PHGDH ubiquitination through its deubiquitinating activity. Additionally, Wnt signals transcriptionally activate the expression of eIF3f, which also exerts its deubiquitinating activity toward MYC, thereby increasing MYC-mediated PHGDH transcription. Thereby, both impacts allow eIF3f to elevate the expression of PHGDH, enhancing Serine-Glycine-One-Carbon (SGOC) signaling pathway to facilitate CRC development. In summary, the study uncovers the intrinsic role and underlying molecular mechanism of eIF3f in SGOC signaling, providing novel insight into the strategies to target eIF3f-PHGDH axis in CRC.

FBXW7β loss-of-function enhances FASN-mediated lipogenesis and promotes colorectal cancer growth

Continuous de novo fatty acid synthesis is required for the biosynthetic demands of tumor. FBXW7 is a highly mutated gene in CRC, but its biological functions in cancer are not fully characterized. Here, we report that FBXW7β, a FBXW7 isoform located in the cytoplasm and frequently mutated in CRC, is an E3 ligase of fatty acid synthase (FASN). Cancer-specific FBXW7β mutations that could not degrade FASN can lead to sustained lipogenesis in CRC. COP9 signalosome subunit 6 (CSN6), an oncogenic marker of CRC, increases lipogenesis via interacting with and stabilizing FASN. Mechanistic studies show that CSN6 associates with both FBXW7β and FASN, and antagonizes FBXW7β's activity by enhancing FBXW7β autoubiquitination and degradation, which in turn prevents FBXW7β-mediated FASN ubiquitination and degradation, thereby regulating lipogenesis positively. Both CSN6 and FASN are positively correlated in CRC, and CSN6-FASN axis, regulated by EGF, is responsible for poor prognosis of CRC. The EGF-CSN6-FASN axis promotes tumor growth and implies a treatment strategy of combination of orlistat and cetuximab. Patient-derived xenograft experiments prove the effectiveness of employing orlistat and cetuximab combination in suppressing tumor growth for CSN6/FASN-high CRC. Thus, CSN6-FASN axis reprograms lipogenesis to promote tumor growth and is a target for cancer intervening strategy in CRC.

The RNA binding protein RALY suppresses p53 activity and promotes lung tumorigenesis

The tumor suppressor p53 plays a pivotal role in tumor prevention. The activity of p53 is mainly restrained by the ubiquitin E3 ligase Mdm2. However, it is not well understood how the Mdm2-p53 pathway is intricately regulated. Here we report that the RNA binding protein RALY functions as an oncogenic factor in lung cancer. RALY simultaneously binds to Mdm2 and the deubiquitinating enzyme USP7. Via these interactions, RALY not only stabilizes Mdm2 by stimulating the deubiquitinating activity of USP7 toward Mdm2 but also increases the trans-E3 ligase activity of Mdm2 toward p53. Consequently, RALY enhances Mdm2-mediated ubiquitination and degradation of p53. Functionally, RALY promotes lung tumorigenesis, at least partially, via negative regulation of p53. These findings suggest that RALY destabilizes p53 by modulating the function of Mdm2 at multiple levels. Our study also indicates a critical role for RALY in promoting lung tumorigenesis via p53 inhibition.

COP9 Signalosome Promotes Neointimal Hyperplasia via Deneddylation and CSN5-Mediated Nuclear Export

BACKGROUND

Neointimal hyperplasia (NH) is a common pathological response to vascular injury and mediated primarily by vascular smooth muscle cell (VSMC) migration and proliferation. The COP9 signalosome (CSN) is formed by 8 canonical subunits (CSN1 through CSN8) with its deneddylation activity residing in CSN5. Each or some of CSN subunits may have deneddylation-independent function. Despite strong evidence linking the CSN to cell cycle regulation in cancer cells, the role of the CSN in vascular biology remains obscure.

METHODS

Neointimal CSN5 expression in the lung tissue of pulmonary hypertension (PAH) patients was assessed with immunohistochemistry. Adult mice with smooth muscle cell-restricted CSN5 knockout (CSN5-SMKO) or CSN8 hypomorphism (CSN8-hypo) and cultured mouse VSMCs were studied to determine the role and governing mechanisms of the CSN in NH. NH was induced by ligation of the left common carotid artery (LCCA) and PDGF-BB stimulation was used to mimic the vascular injury in cell cultures.

RESULTS

Remarkably higher CSN5 levels were detected in the neointimal VSMCs of the pulmonary arteries of human PAH. LCCA ligation induced NH and significantly increased the mRNA and protein levels of CSN subunits in the LCCA wall of adult wild type mice. CSN5-SMKO impaired Cullin deneddylation and the nuclear export of p27 in vessel walls and markedly inhibited VSMC proliferation in mice. On the contrary, CSN8-hypo significantly exacerbated NH and VSMC proliferation in vivo and in cellulo . Cytoplasmic CSN5 mini-complexes and the nuclear export of p27 were significantly increased in CSN8-hypo mouse vessels and cultured CSN8-hypo VSMCs. Nuclear export inhibition with leptomycin attenuated the PDGF-BB-induced increases in VSMC proliferation in both CSN8-hypo and control VSMCs. Further, genetically disabling CSN5 nuclear export but not disabling CSN5 deneddylase activity suppressed the hyperproliferation and restored p27 nuclear localization in CSN8 hypomorphic VSMCs. Interestingly, CSN deneddylase inhibition by CSN5i-3 did not alter the hyperproliferation of cultured CSN8-hypo VSMCs but suppressed wild type VSMC proliferation in cellulo and in vivo and blocked neointimal formation in wild type mice.

CONCLUSION

The CSN promotes VSMC proliferation and NH in injured vessels through deneddylation activity and CSN5-mediated nuclear export.

CSN6 Mediates Nucleotide Metabolism to Promote Tumor Development and Chemoresistance in Colorectal Cancer

Metabolic reprogramming can contribute to colorectal cancer progression and therapy resistance. Identification of key regulators of colorectal cancer metabolism could provide new approaches to improve treatment and reduce recurrence. Here, we demonstrate a critical role for the COP9 signalosome subunit CSN6 in rewiring nucleotide metabolism in colorectal cancer. Transcriptomic analysis of colorectal cancer patient samples revealed a correlation between CSN6 expression and purine and pyrimidine metabolism. A colitis-associated colorectal cancer model established that Csn6 intestinal conditional deletion decreased tumor development and altered nucleotide metabolism. CSN6 knockdown increased the chemosensitivity of colorectal cancer cells in vitro and in vivo, which could be partially reversed with nucleoside supplementation. Isotope metabolite tracing showed that CSN6 loss reduced de novo nucleotide synthesis. Mechanistically, CSN6 upregulated purine and pyrimidine biosynthesis by increasing expression of PHGDH, a key enzyme in the serine synthesis pathway. CSN6 inhibited β-Trcp-mediated DDX5 polyubiquitination and degradation, which in turn promoted DDX5-mediated PHGDH mRNA stabilization, leading to metabolic reprogramming and colorectal cancer progression. Butyrate treatment decreased CSN6 expression and improved chemotherapy efficacy. These findings unravel the oncogenic role of CSN6 in regulating nucleotide metabolism and chemosensitivity in colorectal cancer.

SIGNIFICANCE

CSN6 deficiency inhibits colorectal cancer development and chemoresistance by downregulating PHGDH to block nucleotide biosynthesis, providing potential therapeutic targets to improve colorectal cancer treatment.

The COP9 signalosome complex regulates fungal development and virulence in the wheat scab fungus Fusarium graminearum

The COP9 signalosome (Csn) complex is an evolutionarily conserved complex that regulates various important cellular processes. However, the function of the Csn complex in pathogenic fungi remains elusive. Here, the distribution of Csn subunits in the fungal kingdom was surveyed, and their biological functions were systematically characterized in the fungal pathogen Fusarium graminearum, which is among the top 10 plant fungal pathogens. The results obtained from bioinformatic analyses suggested that the F. graminearum Csn complex consisted of seven subunits (Csn1-Csn7) and that Csn5 was the most conserved subunit across the fungi kingdom. Yeast two-hybrid assays demonstrated that the seven Csn subunits formed a complex in F. graminearum. The Csn complex was localized to both the nucleus and cytoplasm and necessary for hyphal growth, asexual and sexual development and stress response. Transcriptome profiling revealed that the Csn complex regulated the transcription abundance of TRI genes necessary for mycotoxin deoxynivalenol (DON) biosynthesis, subsequently regulating DON production to control fungal virulence. Collectively, the roles of the Csn complex in F. graminearum were comprehensively analyzed, providing new insights into the functions of the Csn complex in fungal virulence and suggesting that the complex may be a potential target for combating fungal diseases.

COP9 signalosome deletion promotes renal injury and distal convoluted tubule remodeling

Cullin-RING ligases are a family of E3 ubiquitin ligases that control cellular processes through regulated degradation. Cullin 3 targets with-no-lysine kinase 4 (WNK4), a kinase that activates the Na⁺-Cl^- cotransporter (NCC), the main pathway for Na⁺ reabsorption in the distal convoluted tubule (DCT). Mutations in the cullin 3 gene lead to familial hyperkalemic hypertension by increasing WNK4 abundance. The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) regulates the activity of cullin-RING ligases by removing the ubiquitin-like protein neural precursor cell expressed developmentally downregulated protein 8. Genetic deletion of the catalytically active CSN subunit, Jab1, along the nephron in mice (KS-Jab1^-/-) led to increased WNK4 abundance; however, NCC abundance was substantially reduced. We hypothesized that the reduction in NCC resulted from a cortical injury that led to hypoplasia of the segment, which counteracted WNK4 activation of NCC. To test this, we studied KS-Jab1^-/- mice at weekly intervals over a period of 3 wk. The results showed that NCC abundance was unchanged until 3 wk after Jab1 deletion, at which time other DCT-specific proteins were also reduced. The kidney injury markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin demonstrated kidney injury immediately after Jab1 deletion; however, the damage was initially limited to the medulla. The injury progressed and expanded into the cortex 3 wk after Jab1 deletion coinciding with loss of the DCT. The data indicate that nephron-specific disruption of the cullin-RING ligase system results in a complex progression of tubule injury that leads to hypoplasia of the DCT.NEW & NOTEWORTHY Cullin 3 (CUL3) targets with-no-lysine-kinase 4 (WNK4), which activates Na⁺-Cl^- cotransporter (NCC) in the distal convoluted tubule (DCT) of the kidney. Renal-specific genetic deletion of the constitutive photomorphogenesis 9 signalosome, an upstream regulator of CUL3, resulted in a reduction of NCC due to DCT hypoplasia, which coincided with cortical kidney injury. The data indicate that nephron-specific disruption of the cullin-RING ligase system results in a complex progression of tubule injury leading to hypoplasia of the DCT.

Targeting the COP9 signalosome for cancer therapy

The COP9 signalosome (CSN) is a highly conserved protein complex composed of 8 subunits (CSN1 to CSN8). The individual subunits of the CSN play essential roles in cell proliferation, tumorigenesis, cell cycle regulation, DNA damage repair, angiogenesis, and microenvironmental homeostasis. The CSN complex has an intrinsic metalloprotease that removes the ubiquitin-like activator NEDD8 from cullin-RING ligases (CRLs). Binding of neddylated CRLs to CSN is sensed by CSN4 and communicated to CSN5 with the assistance of CSN6, thus leading to the activation of deneddylase. Therefore, CSN is a crucial regulator at the intersection between neddylation and ubiquitination in cancer progression. Here, we summarize current understanding of the roles of individual CSN subunits in cancer progression. Furthermore, we explain how the CSN affects tumorigenesis through regulating transcription factors and the cell cycle. Finally, we discuss individual CSN subunits as potential therapeutic targets to provide new directions and strategies for cancer therapy.

Roles of Cullin-RING Ubiquitin Ligases in Cardiovascular Diseases

Maintenance of protein homeostasis is crucial for virtually every aspect of eukaryotic biology. The ubiquitin-proteasome system (UPS) represents a highly regulated quality control machinery that protects cells from a variety of stress conditions as well as toxic proteins. A large body of evidence has shown that UPS dysfunction contributes to the pathogenesis of cardiovascular diseases. This review highlights the latest findings regarding the physiological and pathological roles of cullin-RING ubiquitin ligases (CRLs), an essential player in the UPS, in the cardiovascular system. To inspire potential therapeutic invention, factors regulating CRL activities are also discussed.

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 subunit 3 is necessary for early embryo survival by way of a stable protein deposit in mouse oocytes

Investigations of genes required in early mammalian development are complicated by protein deposits of maternal products, which continue to operate after the gene locus has been disrupted. This leads to delayed phenotypic manifestations and underestimation of the number of genes known to be needed during the embryonic phase of cellular totipotency. Here we expose a critical role of the gene Cops3 by showing that it protects genome integrity during the 2-cell stage of mouse development, in contrast to the previous functional assignment at postimplantation. This new role is mediated by a substantial deposit of protein (94th percentile of the proteome), divided between an exceptionally stable cortical rim, which is prevalent in oocytes, and an ancillary deposit in the embryonic nuclei. Since protein abundance and stability defeat prospects of DNA- or RNA-based gene inactivation in oocytes, we harnessed a classical method next to an emerging method for protein inactivation: antigen masking (for functional inhibition) versus TRIM21-mediated proteasomal degradation, also known as 'Trim away' (for physical removal). Both resulted in 2-cell embryo lethality, unlike the embryos receiving anti-green fluorescent protein. Comparisons between COPS3 protein-targeted and non-targeted embryos revealed large-scale transcriptome differences, which were most evident for genes associated with biological functions critical for RNA metabolism and for the preservation of genome integrity. The gene expression abnormalities associated with COPS3 inactivation were confirmed in situ by the occurrence of DNA endoreduplication and DNA strand breaks in 2-cell embryos. These results recruit Cops3 to the small family of genes that are necessary for early embryo survival. Overall, assigning genes with roles in embryogenesis may be less safe than assumed, if the protein products of these genes accumulate in oocytes: the inactivation of a gene at the protein level can expose an earlier phenotype than that identified by genetic techniques such as conventional gene silencing.

The Involvement of Ubiquitination Machinery in Cell Cycle Regulation and Cancer Progression

The cell cycle is a collection of events by which cellular components such as genetic materials and cytoplasmic components are accurately divided into two daughter cells. The cell cycle transition is primarily driven by the activation of cyclin-dependent kinases (CDKs), which activities are regulated by the ubiquitin-mediated proteolysis of key regulators such as cyclins, CDK inhibitors (CKIs), other kinases and phosphatases. Thus, the ubiquitin-proteasome system (UPS) plays a pivotal role in the regulation of the cell cycle progression via recognition, interaction, and ubiquitination or deubiquitination of key proteins. The illegitimate degradation of tumor suppressor or abnormally high accumulation of oncoproteins often results in deregulation of cell proliferation, genomic instability, and cancer occurrence. In this review, we demonstrate the diversity and complexity of the regulation of UPS machinery of the cell cycle. A profound understanding of the ubiquitination machinery will provide new insights into the regulation of the cell cycle transition, cancer treatment, and the development of anti-cancer drugs.

Saccharomyces cerevisiae as a Toolkit for COP9 Signalosome Research

The COP9 signalosome (CSN) is a highly conserved eukaryotic multi-subunit enzyme, regulating cullin RING ligase activities and accordingly, substrate ubiquitination and degradation. We showed that the CSN complex of Saccharomyces cerevisiae that is deviated in subunit composition and in sequence homology harbors a highly conserved cullin deneddylase enzymatic core complex. We took advantage of the non-essentiality of the S. cerevisiae CSN-NEDD8/Rub1 axis, together with the enzyme-substrate cross-species activity, to develop a sensitive fluorescence readout assay, suitable for biochemical assessment of cullin deneddylation by CSNs from various origins. We also demonstrated that the yeast catalytic subunit, CSN5/Jab1, is targeted by an inhibitor that was selected for the human orthologue. Treatment of yeast by the inhibitor led to the accumulation of neddylated cullins and the formation of reactive oxygen species. Overall, our data revealed S. cerevisiae as a general platform that can be used for studies of CSN deneddylation and for testing the efficacy of selected CSN inhibitors.

Impact of diabetes on promoting the growth of breast cancer

BACKGROUND

Type II diabetes mellitus (DM2) is a significant risk factor for cancers, including breast cancer. However, a proper diabetic breast cancer mouse model is not well-established for treatment strategy design. Additionally, the precise diabetic signaling pathways that regulate cancer growth remain unresolved. In the present study, we established a suitable mouse model and demonstrated the pathogenic role of diabetes on breast cancer progression.

METHODS

We successfully generated a transgenic mouse model of human epidermal growth factor receptor 2 positive (Her2⁺ or ERBB2) breast cancer with DM2 by crossing leptin receptor mutant (Lepr^db/+ ) mice with MMTV-ErbB2/neu) mice. The mouse models were administrated with antidiabetic drugs to assess the impacts of controlling DM2 in affecting tumor growth. Magnetic resonance spectroscopic imaging was employed to analyze the tumor metabolism.

RESULTS

Treatment with metformin/rosiglitazone in MMTV-ErbB2/Lepr^db/db mouse model reduced serum insulin levels, prolonged overall survival, decreased cumulative tumor incidence, and inhibited tumor progression. Anti-insulin resistance medications also inhibited glycolytic metabolism in tumors in vivo as indicated by the reduced metabolic flux of hyperpolarized ¹³ C pyruvate-to-lactate reaction. The tumor cells from MMTV-ErbB2/Lepr^db/db transgenic mice treated with metformin had reprogrammed metabolism by reducing levels of both oxygen consumption and lactate production. Metformin decreased the expression of Myc and pyruvate kinase isozyme 2 (PKM2), leading to metabolism reprogramming. Moreover, metformin attenuated the mTOR/AKT signaling pathway and altered adipokine profiles.

CONCLUSIONS

MMTV-ErbB2/Lepr^db/db mouse model was able to recapitulate diabetic HER2⁺ human breast cancer. Additionally, our results defined the signaling pathways deregulated in HER2⁺ breast cancer under diabetic condition, which can be intervened by anti-insulin resistance therapy.

CSN6 promotes melanoma proliferation and metastasis by controlling the UBR5-mediated ubiquitination and degradation of CDK9

As a critical subunit of the constitutive photomorphogenesis 9 (COP9) signalosome (CSN), CSN6 is upregulated in some human cancers and plays critical roles in tumorigenesis and progression, but its biological functions and molecular mechanisms in melanoma remain unknown. Our study showed that CSN6 expression was upregulated in melanoma patients and cells, and correlated with poor survival in melanoma patients. In melanoma cells, CSN6 knockdown remarkably inhibited cell proliferation, tumorigenicity, migration, and invasion, whereas CSN6 recovery rescued the proliferative and metastatic abilities. Notably, we identified that CSN6 stabilized CDK9 expression by reducing CDK9 ubiquitination levels, thereby activating CDK9-mediated signaling pathways. In addition, our study described a novel CSN6-interacting E3 ligase UBR5, which was negatively regulated by CSN6 and could regulate the ubiquitination and degradation of CDK9 in melanoma cells. Furthermore, in CSN6-knockdown melanoma cells, UBR5 knockdown abrogated the effects caused by CSN6 silencing, suggesting that CSN6 activates the UBR5/CDK9 pathway to promote melanoma cell proliferation and metastasis. Thus, this study illustrates the mechanism by which the CSN6-UBR5-CDK9 axis promotes melanoma development, and demonstrate that CSN6 may be a potential biomarker and anticancer target in melanoma.

Posttranslational modifications as therapeutic targets for intestinal disorders

A variety of biological processes are regulated by posttranslational modifications. Posttranslational modifications including phosphorylation, ubiquitination, glycosylation, and proteolytic cleavage, control diverse physiological functions in the gastrointestinal tract. Therefore, a better understanding of their implications in intestinal diseases, including inflammatory bowel disease, irritable bowel syndrome, celiac disease, and colorectal cancer would provide a basis for the identification of novel biomarkers as well as attractive therapeutic targets. Posttranslational modifications can be common denominators, as well as distinct biomarkers, characterizing pathological differences of various intestinal diseases. This review provides experimental evidence that identifies changes in posttranslational modifications from patient samples, primary cells, or cell lines in intestinal disorders, and a summary of carefully selected information on the use of pharmacological modulators of protein modifications as therapeutic options.

Neddylation, an Emerging Mechanism Regulating Cardiac Development and Function

Defects in protein quality control have been increasingly recognized as pathogenic factors in the development of heart failure, a persistent devastating disease lacking efficacious therapies. Ubiquitin and ubiquitin-like proteins, a family of post-translational modifying polypeptides, play important roles in controlling protein quality by maintaining the stability and functional diversity of the proteome. NEDD8 (neural precursor cell expressed, developmentally downregulated 8), a small ubiquitin-like protein, was discovered two decades ago but until recently the biological significance of NEDD8 modifications (neddylation) in the heart has not been appreciated. In this review, we summarize the current knowledge of the biology of neddylation, highlighting several mechanisms by which neddylation regulates the function of its downstream targets, and discuss the expanding roles for neddylation in cardiac physiology and disease, with an emphasis on cardiac protein quality control. Finally, we outline challenges linked to the study of neddylation in health and disease.

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

EGF Relays Signals to COP1 and Facilitates FOXO4 Degradation to Promote Tumorigenesis

Forkhead-Box Class O 4 (FOXO4) is involved in critical biological functions, but its response to EGF-PKB/Akt signal regulation is not well characterized. Here, it is reported that FOXO4 levels are downregulated in response to EGF treatment, with concurrent elevation of COP9 Signalosome subunit 6 (CSN6) and E3 ubiquitin ligase constitutive photomorphogenic 1 (COP1) levels. Mechanistic studies show that CSN6 binds and regulates FOXO4 stability through enhancing the E3 ligase activity of COP1, and that COP1 directly interacts with FOXO4 through a VP motif on FOXO4 and accelerates the ubiquitin-mediated degradation of FOXO4. Metabolomic studies demonstrate that CSN6 expression leads to serine and glycine production. It is shown that FOXO4 directly binds and suppresses the promoters of serine-glycine-one-carbon (SGOC) pathway genes, thereby diminishing SGOC metabolism. Evidence shows that CSN6 can regulate FOXO4-mediated SGOC gene expression. Thus, these data suggest a link of CSN6-FOXO4 axis and ser/gly metabolism. Further, it is shown that CSN6-COP1-FOXO4 axis is deregulated in cancer and that the protein expression levels of CSN6 and FOXO4 can serve as prognostic markers for cancers. The results illustrate a pathway regulation of FOXO4-mediated serine/glycine metabolism through the function of CSN6-COP1 axis. Insights into this pathway may be strategically designed for therapeutic intervention in cancers.

CSN6-TRIM21 axis instigates cancer stemness during tumorigenesis

Background

Cancer stem cells (CSCs) are responsible for tumour initiation, metastasis and recurrence. However, the mechanism of CSC formation, maintenance and expansion in colorectal cancer (CRC) remains poorly characterised.

Methods

The role of COP9 signalosome subunit 6 (CSN6) in regulating cancer stemness was evaluated by organoid formation and limited dilution analysis. The role of CSN6–TRIM21–OCT1–ALDH1A1 axis in CSC formation was evaluated in vitro and in vivo. The association of CSN6, TRIM21 and ALDH1A1 expression was validated by a tissue microarray with 267 CRC patients.

Results

The results showed that CSN6 is critical for sphere formation and maintaining the growth of patient-derived organoids (PDOs). We characterised the role of CSN6 in regulating cancer stemness, which involves the TRIM21 E3 ubiquitin ligase, transcription factor POU class 2 homeobox 1 (OCT1) and cancer stem cell marker aldehyde dehydrogenase 1 A1 (ALDH1A1). Our data showed that CSN6 facilitates ubiquitin-mediated degradation of TRIM21, which in turn decreases TRIM21-mediated OCT1 ubiquitination and subsequently stabilises OCT1. Consequently, OCT1 stabilisation leads to ALDH1A1expression and promotes cancer stemness. We further showed that the protein expression levels of CSN6, TRIM21 and ALDH1A1 can serve as prognostic markers for human CRC.

Conclusions

In conclusion, we validate a pathway for cancer stemness regulation involving ALDH1A1 levels through the CSN6–TRIM21 axis, which may be utilised as CRC molecular markers and be targeted for therapeutic intervention in cancers.

The Emerging Role of CSN6 in Biological Behavior and Cancer Progress

BACKGROUND

The Constitutive Photomorphogenesis 9 (COP9) signalosome (CSN) subunit 6 (CSN6) noticeably acts as a regulator of the degradation of cancer-related proteins, which contributes to cancerogenesis. The aims of this paper are to expound the research advances of CSN6, particularly focusing on roles of CSN6 in the regulation of biological behavior and cancer progress.

METHODS

Literature from PubMed and Web of Science databases about biological characteristics and application of CSN6 published in recent years was collected to conduct a review.

RESULTS

CSN6, not only the non-catalytic Mpr1p and Pad1p N-terminal (MPN) subunit of CSN, but also a relatively independent protein molecule, has received great attention as a regulator of a wide range of developmental processes by taking part in the ubiquitin-proteasome system and signal transduction, as well as regulating genome integrity and DNA damage response. In addition, phosphorylation of CSN6 increases the stability of CSN6, thereby promoting its regulatory capacity. Moreover, CSN6 is overexpressed in many types of cancer compared with normal tissues and is involved in the regulation of several important intracellular pathways, consisting of cell proliferation, migration, invasion, transformation, and tumorigenesis.

CONCLUSION

We mainly present insights into the function and research development of CSN6, hoping that it can help guide the treatment of developmental defects and improve clinical care, especially in the regulation of cancer signaling pathways.

CSN6: a promising target for cancer prevention and therapy

CSN6 has recently received increased attention as a multifunctional protein involved in protein stability. CSN6 plays an important role in controlling cellular proliferation, apoptosis and metastasis, modulating signal transduction, as well as regulating DNA damage and repair. Most studies have demonstrated that CSN6 is significantly upregulated in human malignant tumors such as cervical cancer, papillary thyroid cancer, colorectal cancer, breast cancer, lung adenocarcinoma, and glioblastoma, and its expression is usually correlated with poor prognosis. In this review, we summarize recent available findings regarding the oncogenic role of CSN6 in tumors, and provide a better understanding of CSN6 function at the molecular level and its potential therapeutic implications in combating human cancers.

Macrophage-derived CCL5 facilitates immune escape of colorectal cancer cells via the p65/STAT3-CSN5-PD-L1 pathway

Infiltrated macrophages are an important constituent of the tumor microenvironment and play roles in tumor initiation and progression by promoting immune evasion. However, the molecular mechanism by which macrophage-derived cytokines foster immune escape of colorectal cancer (CRC) is unclear. Here, we demonstrated that macrophage infiltration induced by lipopolysaccharide (LPS) or a high-cholesterol diet (HCD) significantly promoted CRC growth. Similarly, LPS and poly (I:C) remarkably increased the volume of CT26 cell allograft tumors. C-C motif chemokine ligand 5 (CCL5), which is secreted by macrophages, inhibited T-cell-mediated killing of HT29 cells and promoted immune escape by stabilizing PD-L1 in vitro and in vivo. Mechanistically, CCL5 resulted in formation of nuclear factor kappa-B p65/STAT3 complexes, which bound to the COP9 signalosome 5 (CSN5) promoter, leading to its upregulation. Moreover, CSN5 modulated the deubiquitination and stability of PD-L1. High expression of CSN5 in CRC was associated with significantly shorter survival. Furthermore, compound-15 was identified as an inhibitor of CSN5, and destabilized PD-L1 to alleviate the tumor burden. Our results suggest that the novel CCL5-p65/STAT3-CSN5-PD-L1 signaling axis is significantly activated by LPS or HCD-driven macrophage infiltration in an animal model of CRC, which likely has therapeutic and prognostic implications for human cancers.

Long non-coding RNA KRT19P3 suppresses proliferation and metastasis through COPS7A-mediated NF-κB pathway in gastric cancer

Long non-coding RNAs (lncRNAs) have emerged as critical regulators in gastric cancer (GC). LncRNA expression microarray data indicate that KRT19P3 (Keratin 19 Pseudogene 3) is downregulated in GC samples. However, the expression pattern and molecular mechanism of KRT19P3 in GC have not been characterized. The present study confirmed the downregulation of KRT19P3 in GC tissues and cells. Decreased expression of KRT19P3 was correlated with larger tumor size, advanced TNM stage, Lauren's classification, positive lymph node metastasis, and poor prognosis. Enforced expression of KRT19P3 significantly inhibited cell proliferation, migration, and invasion in vitro, as well as tumorigenesis and metastasis in vivo. Conversely, KRT19P3 knockdown had opposite effects. Mechanistically, RNA pull-down and RNA immunoprecipitation assay revealed that KRT19P3 could directly bind COPS7A. KRT19P3 enhanced COPS7A protein stability in GC cells, and KRT19P3 suppressed GC cell proliferation and metastasis partly through regulation of COPS7A expression. COPS7A could promote deubiquitinylation of IκBα, which was executed by CSN-associated deubiquitinylase USP15, and then KRT19P3 inactivated nuclear factor kappa-B (NF-κB) signaling pathway in a COPS7A-dependent manner. For the first time, we revealed that KRT19P3 could suppress tumor growth and metastasis through COPS7A-mediated NF-κB pathway, which may serve as potential targets for treatment of GC in the future.

CSN6 expression is associated with pancreatic cancer progression and predicts poor prognosis

Constitutive photomorphogenesis 9 (COP9) signalosome 6 (CSN6) plays an essential role in tumor development. The present study aims to demonstrate that CSN6 is an important biomarker and has prognostic value for patients with pancreatic ductal adenocarcinoma (PDAC). We analyzed CSN6 expression levels in PDAC and adjacent non-cancerous tissues using immunohistochemistry (IHC) and quantitative real-time PCR (qPCR) analysis. We found that CSN6 was highly expressed in PDAC tissues, contrasting to adjacent non-cancerous tissues. Interestingly, CSN6 expression was positively associated with proliferating cell nuclear antigen (PCNA) expression. Further investigation indicated that CSN6 knockdown significantly suppressed the proliferation of PDAC cells and decreased the expression levels of PCNA, while CSN6 overexpression increased the proliferation, as well as the expression levels of PCNA in PDAC cells. Furthermore, a χ² test indicated that the expression of CSN6 in PDAC tissues was markedly associated with tumor infiltration and serum carbohydrate antigen 19-9 levels. In addition, univariate and multivariate analyses showed that CSN6 levels were significantly correlated with poor clinical outcomes of patients with PDAC. Kaplan-Meier analysis showed that patients with high expression of CSN6 had shorter overall survival. These results suggest that the expression of CSN6 correlates with the progression of PDAC, resulting in poor prognosis. Thus, CSN6 may play a significant role in the development of PDAC and is a potential target to prevent and treat PDAC.

CSN6 Promotes the Migration and Invasion of Cervical Cancer Cells by Inhibiting Autophagic Degradation of Cathepsin L

CSN6 is one subunit of the highly conserved constitutive photomorphogenesis 9 (COP9) signalosome (CSN), which is overexpressed in many types of cancers, and has received great attention as a regulator of the degradation of cancer-related proteins, suggesting its importance in oncogenic activity. CSN6 has been shown to be overexpressed in cervical cancer (CC) and associated with CC development. CC remains to be one of the most aggressive cancers affecting women. Cathepsin L (CTSL), significantly associated with the autophagy, plays a critical role in degradation of extracellular matrix for metastasis. However, the detailed biological functions of CSN6 on CTSL in CC metastasis have not been well clarified. Our data has shown that CSN6 and CTSL are positively correlated. The overexpression of CSN6 and CTSL might be a strong indicator for CC enhanced aggressiveness. CSN6 could suppress the degradation of CTSL, then facilitated the migration and invasion of CC cells. Interestingly, our results indicated that autophagy is essential for decreasing CTSL, while CSN6 could inhibit the autophagy ability of CC cells. In addition, blocking of the mammalian target of rapamycin (mTOR) pathway reversed CSN6-mediated autophagy inhibition. We further demonstrated that CSN6 positively regulated CTSL expression through an autophagy-lysosomal system. Taken together, we concluded that CSN6 might promote the migration and invasion of cervical cancer cells by inhibiting autophagic degradation of CTSL and serve as a potential gene therapy target for the treatment of CC metastasis.

Inhibition of neddylation induces mitotic defects and alters MKLP1 accumulation at the midbody during cytokinesis

The cullin-RING E3 ubiquitin ligases (CRLs) play crucial roles in modulating the stability of proteins in the cell and are, in turn, regulated by post-translational modification by the ubiquitin-like (Ubl) protein NEDD8. This process, termed neddylation, is reversible through the action of the COP9 signalosome (CSN); a multi-subunit metalloprotease conserved among eukaryotes that plays direct or indirect roles in DNA repair, cell signaling and cell cycle regulation in part through modulating the activity of the CRLs. Previously, inhibition of CRL neddylation by MLN4924, a small molecule inhibitor of the NEDD8-activating enzyme 1 (NAE1), was shown to induce interphase cell cycle arrest and cell death. Using fixed and living cell microscopy, we re-evaluated the cell cycle effects of inhibition of neddylation by MLN4924 in both asynchronous and mitotic cell populations. Consistent with previous studies, treatment of asynchronous cells with MLN4924 increased CDT1 expression levels, induced G2 arrest and increased nuclear size. However, in synchronized cells treated in mitosis, mitotic defects were observed including lagging chromosomes and binucleated daughter cells. Consistent with neddylation and deneddylation playing a role in cytokinesis, NEDD8, as well as subunits of the CSN, could be localized at the midbody and cleavage furrow. Finally, treatment of mitotic cells with MLN4924 induced the premature accumulation of MKLP1 at the cleavage furrow, a key regulator of cytokinesis, which was concomitant with increased abscission delay and failure. Thus, these studies uncover an uncharacterized mitotic effect of MLN4924 on MKLP1 accumulation at the midbody and support a role for neddylation during cytokinesis.

Abbreviations: CSN, COP9 Signalosome; MKLP1, mitotic kinesin-like protein 1; NEDD8, Neural precursor cell Expressed, Developmentally Down-regulated 8.

Transient inhibition of neddylation at neonatal stage evokes reversible cardiomyopathy and predisposes the heart to isoproterenol-induced heart failure

Alterations in perinatal conditions (such as preterm birth) is linked to adult health and disease, in particular, the cardiovascular system. Neddylation, a novel posttranslational modification through which the ubiquitin-like protein NEDD8 is conjugated to protein substrates, has emerged as an important mechanism regulating embryonic cardiac chamber maturation. However, the importance of neddylation in postpartum cardiac development has not been investigated. Here, we aimed to determine whether transient, postnatal inhibition of neddylation has immediate and prolonged impact on the structure and function of the neonatal and adult hearts. Sprague-Dawley pups were given three intraperitoneal injections of MLN4924 (MLN), a specific neddylation inhibitor, at postnatal days (P)1, 3, and 5. Cardiac structure and function were temporally assessed during aging and after 2 wk of isoproterenol (ISO) infusion in adulthood. MLN treatment resulted in modest reduction of neddylated proteins in neonatal hearts. The MLN-treated rats developed cardiac hypertrophy and dysfunction by P7, which was accompanied by significantly reduced cardiomyocyte proliferation. At 3 mo of age, cardiac contractile function was restored in MLN-treated rats, but MLN-treated hearts displayed hypertrophic phenotype. Whereas ISO infusion triggered compensatory cardiac hypertrophy without impairing cardiac contractility in the control rats, the MLN-treated rats displayed a similar degree of hypertrophy, which quickly progressed to decompensation with ventricular wall thinning, chamber dilatation, and reduced ejection fraction as well as exacerbated pathological cardiac remodeling. Our findings suggest that neddylation is required for postnatal cardiac development and that perturbation of neddylation during development predisposes adult hearts to cardiac failure under stress conditions. NEW & NOTEWORTHY Our study demonstrates that perinatal perturbation of neddylation induces cardiomyopathy, impairs postnatal cardiac development, and increases susceptibility to catecholamine-induced cardiac dysfunction. The results reveal a previously unappreciated role of neddylation in postnatal cardiac maturation and call for close monitoring for the potential cardiotoxicity of MLN4924 (pevonedistat) and other agents that modify neddylation, especially in pregnant women and preadolescents.

Generation of a heterozygous p53 R249S mutant human embryonic stem cell line by TALEN-mediated genome editing

As one of the most essential genome guardians, p53 and its mutants have been suggested associated with many types of cancers. Many p53 mutants function induce unique phenotypes, including carcinogenesis, metastasis, and drug resistance. The p53(R249S) mutation is the most prevalent and specific mutation associated with liver cancer development. Here, we demonstrate the generation of a heterozygous p53(R249S) mutation in the H9 human embryonic stem cell line using TALEN-mediated genome editing. The generated cell line maintains a normal karyotype, a pluripotent state and the in vivo capacity to develop a teratoma containing all three germ layer tissues.

Renal COP9 Signalosome Deficiency Alters CUL3-KLHL3-WNK Signaling Pathway

BACKGROUND

The familial hyperkalemic hypertension (FHHt) cullin 3 (CUL3) mutant does not degrade WNK kinases normally, thereby leading to thiazide-sensitive Na-Cl cotransporter (NCC) activation. CUL3 mutant (CUL3Δ9) does not bind normally to the COP9 signalosome (CSN), a deneddylase involved in regulating cullin-RING ligases. CUL3Δ9 also caused increased degradation of the CUL3-WNK substrate adaptor kelch-like 3 (KLHL3). Here, we sought to determine how defective CSN action contributes to the CUL3Δ9 phenotype.

METHODS

The Pax8/LC1 mouse system was used to generate mice in which the catalytically active CSN subunit, Jab1, was deleted only along the nephron, after full development (KS-Jab1 ^-/-).

RESULTS

Western blot analysis demonstrated that Jab1 deletion increased the abundance of neddylated CUL3. Moreover, total CUL3 expression was reduced, suggesting decreased CUL3 stability. KLHL3 was almost completely absent in KS-Jab1 ^-/- mice. Conversely, the protein abundances of WNK1, WNK4, and SPAK kinases were substantially higher. Activation of WNK4, SPAK, and OSR1 was indicated by higher phosphorylated protein levels and translocation of the proteins into puncta, as observed by immunofluorescence. The ratio of phosphorylated NCC to total NCC was also higher. Surprisingly, NCC protein abundance was low, likely contributing to hypokalemia and Na⁺ and K⁺ wasting. Additionally, long-term Jab1 deletion resulted in kidney damage.

CONCLUSIONS

Together, the results indicate that deficient CSN binding contributes importantly to the FHHt phenotype. Although defective CUL3Δ9-faciliated WNK4 degradation likely contributes, dominant effects on KLHL3 may be a second factor that is necessary for the phenotype.

COP9 signalosome subunit 6 mediates PDGF -induced pulmonary arterial smooth muscle cells proliferation

Up-regulation of mammalian COP9 signalosome subunit 6 (CSN6) and consequent reduction of SCF ubiquitin ligase substrate receptor β-transduction repeat-containing protein (β-TrCP) have been shown to be associated with cancer cells proliferation. However, it is unclear whether CSN6 and β-TrCP are also involved in PDGF-induced pulmonary arterial smooth muscle cells (PASMCs) proliferation. This study aims to address this issue and further explore its potential mechanisms. Our results indicated that PDGF phosphorylated Akt, stimulated PASMCs proliferation; while inhibition of PDGF receptor (PDGFR) by imatinib prevented these effects. PDGF further up-regulated CSN6 protein expression, this was accompanied with β-TrCP reduction and increase of Cdc25A. Inhibition of PDGFR/PI3K/Akt signaling pathway reversed PDGF-induced such changes and cell proliferation. Prior transfection of CSN6 siRNA blocked PDGF-induced β-TrCP down-regulation, Cdc25A up-regulation and cell proliferation. Furthermore, pre-treatment of cells with MG-132 also abolished PDGF-induced β-TrCP reduction, Cdc25A elevation and cell proliferation. In addition, pre-depletion of Cdc25A by siRNA transfection suppressed PDGF-induced PASMCs proliferation. Taken together, our study indicates that up-regulation of CSN6 by PDGFR/PI3K/Akt signaling pathway decreases β-TrCP by increasing its ubiquitinated degradation, and thereby increases the expression of Cdc25A, which promotes PDGF-induced PASMCs proliferation.

Csn5 Is Required for the Conidiogenesis and Pathogenesis of the Alternaria alternata Tangerine Pathotype

The COP9 signalosome (CSN) is a highly conserved protein complex involved in the ubiquitin-proteasome system. Its metalloisopeptidase activity resides in subunit 5 (CSN5). Functions of csn5 in phytopathogenic fungi are poorly understood. Here, we knocked out the csn5 ortholog (Aacsn5) in the tangerine pathotype of Alternaria alternata. The ΔAacsn5 mutant showed a moderately reduced growth rate compared to the wildtype strain and was unable to produce conidia. The growth of ΔAacsn5 mutant was not affected in response to oxidative and osmotic stresses. Virulence assays revealed that ΔAacsn5 induced no or significantly reduced necrotic lesions on detached citrus leaves. The defects in hyphal growth, conidial sporulation, and pathogenicity of ΔAacsn5 were restored by genetic complementation of the mutant with wildtype Aacsn5. To explore the molecular mechanisms of conidiation and pathogenesis underlying Aacsn5 regulation, we systematically examined the transcriptomes of both ΔAacsn5 and the wildtype. Generally, 881 genes were overexpressed and 777 were underexpressed in the ΔAacsn5 mutant during conidiation while 694 overexpressed and 993 underexpressed during infection. During asexual development, genes related to the transport processes and nitrogen metabolism were significantly downregulated; the expression of csn1-4 and csn7 in ΔAacsn5 was significantly elevated; secondary metabolism gene clusters were broadly affected; especially, the transcript level of the whole of cluster 28 and 30 was strongly induced. During infection, the expression of the host-specific ACT toxin gene cluster which controls the biosynthesis of the citrus specific toxin was significantly repressed; many other SM clusters with unknown products were also regulated; 86 out of 373 carbohydrate-active enzymes responsible for breaking down the plant dead tissues showed uniquely decreased expression. Taken together, our results expand our understanding of the roles of csn5 on conidiation and pathogenicity in plant pathogenic fungi and provide a foundation for future investigations.

COP9 signalosome subunit CSN5, but not CSN6, is upregulated in lung adenocarcinoma and predicts poor prognosis

Background

The COP9 signalosome (CSN) is an evolutionarily conserved complex composed of eight subunits (CSN1-CSN8). Among the CSN subunits, CSN5 and its dimerization partner CSN6 are the only two MPN (Mpr1-Pad1-N-terminal) domain-containing subunits. These two subunits play essential roles in a variety of biological processes, such as cell cycle progression, protein stability and signal transduction. However, their expression patterns and clinical significance in lung cancer are not completely clear.

Methods

We examined the expressions of both CSN5 and CSN6 in lung adenocarcinoma (LUAD) patients (n=59) using immunohistochemistry analysis, and correlated their expressions with clinicopathological characteristics. MTT cell proliferation assay was performed to determine the effect of CSN5 silencing or overexpression on the growth of lung cancer cells. Knock down or overexpression of CSN5 was confirmed by western blotting.

Results

CSN5 expression was elevated in tumor cells, compared to the stromal compartment and adjacent normal epithelial cells. Interestingly, CSN5 was also expressed in the macrophages and lymphocytes adjacent to the tumors. Surprisingly, CSN6 was barely detected in the tumor cells of LUAD patients. Furthermore, we also demonstrated that higher levels of CSN5 were correlated with high tumor-node-metastasis (TNM) stage and worse clinical outcomes. Multivariate Cox regression analysis revealed CSN5 was an independently prognostic factor for LUAD patients. Additionally, in cellular model, depletion of CSN5 expression significantly suppressed the growth of lung cancer cells.

Conclusions

COP9 signalosome subunit CSN5, but not CSN6, is upregulated in LUAD. Moreover, CSN5 is a critical regulator for the growth of lung cancer and represents an independent prognostic factor and a promising therapeutic target for LUAD patients.

Downregulation of CSN6 attenuates papillary thyroid carcinoma progression by reducing Wnt/β-catenin signaling and sensitizes cancer cells to FH535 therapy

The incidence of thyroid cancer has increased worldwide at a rate higher than that of any other cancer. CSN6 is overexpressed in many types of cancers, and such expression is linked to oncogenic activity. However, the detailed biological functions of CSN6 in papillary thyroid cancer (PTC) have not been well characterized. We investigated CSN6 expression in PTC specimens and cell lines. We used short-hairpin RNA-mediated gene silencing to explore the biological effects of CSN6 depletion in PTC cells. The combined effects of CSN6 silencing and FH535 therapy were assessed in terms of cell viability. The mechanism by which CSN6 regulated β-catenin expression was also analyzed. CSN6 levels were determined by real-time polymerase chain reaction (PCR) (mRNA), Western blotting, and immunochemistry (protein). The CCK-8 and migration assays and orthotopic xenograft transplantation were used to investigate the biological effects of CSN6. We assessed the combined effects of CSN6 silencing and FH535 on cell viability in vitro. We also analyzed the relationship between the CSN6 level and clinical pathological status. CSN6 was overexpressed in human PTCs, and loss of CSN6 attenuated tumor proliferation and migration both in vitro and in vivo. CSN6 stabilized β-catenin and facilitated the epidermal-to-mesenchymal transition (EMT) in PTC cells. CSN6 positively regulated β-catenin expression in a β-Trcp-dependent manner and triggered expression of several EMT-related genes regulated by β-catenin. CSN6 silencing sensitized PTC cells to FH535 therapy via downregulation of the Wnt/β-catenin signaling pathway. Finally, in PTC patients, the level of CSN6 was significantly (inversely) correlated with tumor size, the presence of multifocal lesions, and TNM stage. CSN6 overexpression in PTC is a strong indicator of enhanced tumor aggressiveness. CSN6 promotes PTC progression by inducing the EMT. CSN6 knockdown sensitizes PTC cells to FH535 therapy via downregulation of the Wnt/β-catenin signaling pathway.

Corrected and Republished from: The COP9 Signalosome Interacts with and Regulates Interferon Regulatory Factor 5 Protein Stability

The transcription factor interferon regulatory factor 5 (IRF5) exerts crucial functions in the regulation of host immunity against extracellular pathogens, DNA damage-induced apoptosis, death receptor signaling, and macrophage polarization. Tight regulation of IRF5 is thus warranted for an efficient response to extracellular stressors and for limiting autoimmune and inflammatory responses. Here we report that the COP9 signalosome (CSN), a general modulator of diverse cellular and developmental processes, associates constitutively with IRF5 and promotes its protein stability. The constitutive CSN/IRF5 interaction was identified using proteomics and confirmed by endogenous immunoprecipitations. The CSN/IRF5 interaction occurred on the carboxyl and amino termini of IRF5; a single internal deletion (Δ455-466) was found to significantly reduce IRF5 protein stability. CSN3 was identified as a direct interacting partner of IRF5, and knockdown of this subunit with small interfering RNAs (siRNAs) resulted in enhanced degradation. Degradation was further augmented by knockdown of CSN1 and CSN3 together. The ubiquitin E1 inhibitor UBEI-41 or the proteasome inhibitor MG132 prevented IRF5 degradation, supporting that its stability is regulated by the ubiquitin-proteasome system. Importantly, activation of IRF5 by the death receptor ligand tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resulted in enhanced degradation via loss of the CSN/IRF5 interaction. This study defines the CSN as a new interacting partner of IRF5 that controls its stability.

The role of deubiquitinases in breast cancer

Although growing numbers of oncoproteins and pro-metastatic proteins have been extensively characterized, many of these tumor-promoting proteins are not good drug targets, which represent a major barrier to curing breast cancer and other cancers. There is a need, therefore, for alternative therapeutic approaches to destroying cancer-promoting proteins. The human genome encodes approximately 100 deubiquitinating enzymes (DUBs, also called deubiquitinases), which are amenable to pharmacologic inhibition by small molecules. By removing monoubiquitin or polyubiquitin chains from the target protein, DUBs can modulate the degradation, localization, activity, trafficking, and recycling of the substrate, thereby contributing substantially to the regulation of cancer proteins and pathways. Targeting certain DUBs may lead to destabilization or functional inactivation of some key oncoproteins or pro-metastatic proteins, including non-druggable ones, which will provide therapeutic benefits to cancer patients. In breast cancer, growing numbers of DUBs are found to be aberrantly expressed. Depending on their substrates, specific DUBs can either promote or suppress mammary tumors. In this article, we review the role and mechanisms of action of DUBs in breast cancer and discuss the potential of targeting DUBs for cancer treatment.

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.

Overexpression of COP9 signalosome subunits, CSN7A and CSN7B, exerts different effects on adipogenic differentiation

The COP9 signalosome (CSN) is an essential regulator of cullin‐RING‐ubiquitin (Ub) ligases (CRLs), which ubiquitinate important cellular regulators and target them for degradation by the Ub proteasome system (UPS). The CSN exhibits deneddylating activity localized on subunit CSN5, which removes the ubiquitin‐like protein Nedd8 from the cullins of CRLs. CSN‐mediated deneddylation is an important step in the process of CRL remodeling, in which new substrate recognition units are incorporated into Ub ligases to meet changed requirements for proteolysis in cells. For instance, extensive CRL remodeling occurs during adipogenic differentiation when new CRL3s are formed. Diversification of CSN complexes during evolution is most likely another adaptation to meet different cellular requirements. Best known CSN variants are formed by different CSN subunit isoforms. For instance, in plant cells, isoforms have been identified for the MPN‐domain subunits CSN5 (CSN5A and CSN5B) and CSN6 (CSN6A and CSN6B) which form four distinct CSN variants. In mammalian cells CSN^CSN7A and CSN^CSN7B variants are generated by CSN7 isoforms. We demonstrate that the two variants coexist in human LiSa‐2 cells and in mouse embryonic fibroblasts. During adipogenic differentiation of LiSa‐2 cells CSN7B increases in parallel with an elevation of the total CSN complex. Permanent overexpression of Flag‐CSN7B but not of Flag‐CSN7A accelerates adipogenesis in LiSa‐2 cells indicating a specific function of the CSN^CSN7B variant in stimulating adipogenesis. Silencing of CSN7A as well as of CSN7B in LiSa‐2 cells and in mouse embryonic fibroblasts (MEFs) reduces adipogenic differentiation demonstrating that both CSN^CSN7A and CSN^CSN7B variants are involved in the process.

Quercetin-induced apoptosis of HT-29 colon cancer cells via inhibition of the Akt-CSN6-Myc signaling axis

Constitutive photomorphogenesis 9 signalosome (CSN) consists of a total of eight subunits (CSN1-CSN8) in mammalian cells. CSN6 may promote carcinogenesis by positively regulating v-myc avian myelocytomatosis viral oncogene homolog (Myc) and MDM2 proto-oncogene stability, and is regarded as a potential target for cancer therapy. Quercetin has a substantial anticancer effect on various human cancer cells. The present study investigated the effects of quercetin on HT-29 human colorectal cancer cell viability, apoptosis and cell cycle arrest using an MTT assay, flow cytometry, transmission electron microscopy and western blotting. It was determined that quercetin inhibited HT-29 cell viability in a dose-dependent manner. Cell shrinkage, chromatin condensation and nuclear collapse were observed in the 50, 100 and 200 µM quercetin groups. The exposure of HT-29 cells to quercetin led to significant cell cycle arrest in the S-phase. Western blot analysis revealed that quercetin reduced the protein expression levels of phosphorylated-Akt and increased CSN6 protein degradation; therefore, affecting the expression levels of Myc, p53, B-cell lymphoma 2 (Bcl-2) and Bcl-2 associated X protein. The overexpression of CSN6 reduced the effect of quercetin treatment on HT-29 cells, suggesting that quercetin-induced apoptosis may involve the Akt-CSN6-Myc signaling axis in HT-29 cells.

COP9 signalosome subunit 6 (CSN6) regulates E6AP/UBE3A in cervical cancer

Cervical cancer is one of the leading causes of cancer death in women. Human papillomaviruses (HPVs) are the major cause in almost 99.7% of cervical cancer. E6 oncoprotein of HPV and E6-associated protein (E6AP) are critical in causing p53 degradation and malignancy. Understanding the E6AP regulation is critical to develop treating strategy for cervical cancer patients. The COP9 signalosome subunit 6 (CSN6) is involved in ubiquitin-mediated protein degradation. We found that both CSN6 and E6AP are overexpressed in cervical cancer. We characterized that CSN6 associated with E6AP and stabilized E6AP expression by reducing E6AP poly-ubiquitination, thereby regulating p53 activity in cell proliferation and apoptosis. Mechanistic studies revealed that CSN6-E6AP axis can be regulated by EGF/Akt signaling. Furthermore, inhibition of CSN6-E6AP axis hinders cervical cancer growth in mice. Taken together, our results indicate that CSN6 is a positive regulator of E6AP and is important for cervical cancer development.

Cops2 promotes pluripotency maintenance by Stabilizing Nanog Protein and Repressing Transcription

The COP9 signalosome has been implicated in pluripotency maintenance of human embryonic stem cells. Yet, the mechanism for the COP9 signalosome to regulate pluripotency remains elusive. Through knocking down individual COP9 subunits, we demonstrate that Cops2, but not the whole COP9 signalosome, is essential for pluripotency maintenance in mouse embryonic stem cells. Down-regulation of Cops2 leads to reduced expression of pluripotency genes, slower proliferation rate, G2/M cell cycle arrest, and compromised embryoid differentiation of embryonic stem cells. Cops2 also facilitates somatic cell reprogramming. We further show that Cops2 binds to Nanog protein and prevent the degradation of Nanog by proteasome. Moreover, Cops2 functions as transcriptional corepressor to facilitate pluripotency maintenance. Altogether, our data reveal the essential role and novel mechanisms of Cops2 in pluripotency maintenance.