CUL1 exacerbates glucocorticoid-induced osteoporosis by enhancing ASAP1 ubiquitination.

BACKGROUND: Glucocorticoid-induced osteoporosis is a leading secondary cause of osteoporosis. Cullin-1 (CUL1) levels are abnormally elevated in patients with osteoporosis, but the underlying mechanism remains unclear. The purpose of this study was to elucidate the mechanism of action of CUL1 in a glucocorticoid (dexamethasone, Dex)-induced osteoporosis model. METHODS: C57BL/6J mice were intraperitoneally injected with Dex to establish an osteoporosis model. Mouse femur bone injury and bone formation were detected using hematoxylin-eosin or Masson staining. Apoptosis and cell cycle distribution were determined by flow cytometry. Alkaline phosphatase (ALP) activity and calcified nodules were monitored using ALP and Alizarin Red S staining. The molecular mechanism was validated by co-immunoprecipitation (Co-IP) and ubiquitination assays. RESULTS: CUL1 expression was enhanced in the Dex-induced osteoporosis mouse model. CUL1 silencing moderated the Dex-induced cell proliferation and osteogenesis inhibition. Moreover, CUL1 promoted the ubiquitination and degradation of ASAP1 via the SKP1-CUL1-F-box (SCF)-FBXW7 complex. CUL1 induced apoptosis and repressed osteogenesis by ASAP1. CUL1 silencing alleviated the Dex-induced osteoporosis in mice. CONCLUSION: CUL1 suppressed osteoblast proliferation and osteogenesis by promoting ASAP1 ubiquitination via the SCF-FBXW7 complex in glucocorticoid-induced osteoporosis.

SERTAD1 initiates NLRP3-mediated inflammasome activation through restricting NLRP3 polyubiquitination.

We here demonstrate that SERTAD1 is an adaptor protein responsible for the regulation of lysine 63 (K63)-linked NLRP3 polyubiquitination by the Cullin1 E3 ubiquitin ligase upon inflammasome activation. SERTAD1 specifically binds to NLRP3 but not to other inflammasome sensors. This endogenous interaction increases after inflammasome activation, interfering with the interaction between NLRP3 and Cullin1. Interleukin (IL)-1ß and IL-18 secretion, as well as the cleavage of gasdermin D, are decreased in SERTAD1 knockout bone-marrow-derived macrophages, together with reduced formation of the NLRP3 inflammasome complex. Additionally, SERTAD1-deficient mice show attenuated severity of monosodium-uric-acid-induced peritonitis and experimental autoimmune encephalomyelitis. Analysis of public datasets indicates that expression of SERTAD1 mRNA is significantly increased in the patients of autoimmune diseases. Thus, our findings uncover a function of SERTAD1 that specifically reduces Cullin1-mediated NLRP3 polyubiquitination via direct binding to NLRP3, eventually acting as a crucial factor to regulate the initiation of NLRP3-mediated inflammasome activation.

COP9 signalosome-mediated deneddylation of CULLIN1 is necessary for SCFEBF1 assembly in Arabidopsis thaliana.

Functions of the SKP1-CUL1-F box (SCF) ubiquitin E3 ligases are essential in plants. The F box proteins (FBPs) are substrate receptors that recruit substrates and assemble an active SCF complex, but the regulatory mechanism underlying the FBPs binding to CUL1 to activate the SCF cycle is not fully understood. We show that Arabidopsis csn1-10 is defective in SCFEBF1-mediated PIF3 degradation during de-etiolation, due to impaired association of EBF1 with CUL1 in csn1-10. EBF1 preferentially associates with un-neddylated CUL1 that is deficient in csn1-10 and the EBF1-CUL1 binding is rescued by the neddylation inhibitor MLN4924. Furthermore, we identify a subset of FBPs with impaired binding to CUL1 in csn1-10, indicating their assembly to form SCF complexes may depend on COP9 signalosome (CSN)-mediated deneddylation of CUL1. This study reports that a key role of CSN-mediated CULLIN deneddylation is to gate the binding of the FBP-substrate module to CUL1, thus initiating the SCF cycle of substrate ubiquitination.

Exploiting the Cullin E3 Ligase Adaptor Protein SKP1 for Targeted Protein Degradation.

Targeted protein degradation with Proteolysis Targeting Chimeras (PROTACs) is a powerful therapeutic modality for eliminating disease-causing proteins through targeted ubiquitination and proteasome-mediated degradation. Most PROTACs have exploited substrate receptors of Cullin-RING E3 ubiquitin ligases such as cereblon and VHL. Whether core, shared, and essential components of the Cullin-RING E3 ubiquitin ligase complex can be used for PROTAC applications remains less explored. Here, we discovered a cysteine-reactive covalent recruiter EN884 against the SKP1 adapter protein of the SKP1-CUL1-F-box containing SCF complex. We further showed that this recruiter can be used in PROTAC applications to degrade neo-substrate proteins such as BRD4 and the androgen receptor in a SKP1- and proteasome-dependent manner. Our studies demonstrate that core and essential adapter proteins within the Cullin-RING E3 ubiquitin ligase complex can be exploited for targeted protein degradation applications and that covalent chemoproteomic strategies can enable recruiter discovery against these targets.

RNF126, 168 and CUL1: The Potential Utilization of Multi-Functional E3 Ubiquitin Ligases in Genome Maintenance for Cancer Therapy.

Ubiquitination is a post-translational modification (PTM) that is involved in proteolysis, protein-protein interaction, and signal transduction. Accumulation of mutations and genomic instability are characteristic of cancer cells, and dysfunction of the ubiquitin pathway can contribute to abnormal cell physiology. Because mutations can be critical for cells, DNA damage repair, cell cycle regulation, and apoptosis are pathways that are in close communication to maintain genomic integrity. Uncontrolled cell proliferation due to abnormal processes is a hallmark of cancer, and mutations, changes in expression levels, and other alterations of ubiquitination factors are often involved. Here, three E3 ubiquitin ligases will be reviewed in detail. RNF126, RNF168 and CUL1 are involved in DNA damage response (DDR), DNA double-strand break (DSB) repair, cell cycle regulation, and ultimately, cancer cell proliferation control. Their involvement in multiple cellular pathways makes them an attractive candidate for cancer-targeting therapy. Functional studies of these E3 ligases have increased over the years, and their significance in cancer is well reported. There are continuous efforts to develop drugs targeting the ubiquitin pathway for anticancer therapy, which opens up the possibility for these E3 ligases to be evaluated for their potential as a target protein for anticancer therapy.

Interaction between dual specificity phosphatase-1 and cullin-1 attenuates alcohol-related liver disease by restoring p62-mediated mitophagy.

Besides abstinence, no effective treatment exists for alcohol-related liver disease (ALD), a dreaded consequence of alcohol abuse. In this study, we assessed the roles on ALD of dual specificity phosphatase-1 (DUSP1), an hepatoprotective enzyme, and Cullin-1 (CUL1), a member of the E3 ubiquitin ligase complex that exerts also transcriptional suppression of mitochondrial genes. Alcohol treatment downregulated hepatic DUSP1 expression in wild-type mice. Notably, DUSP1 transgenic (Dusp1Tg ) mice showed resistance to alcohol-mediated hepatic dysfunction, as evidenced by decreased AST/ALT activity, improved alcohol metabolism, and suppressed liver fibrosis, inflammation, and oxidative stress. Functional experiments demonstrated that DUSP1 overexpression prevents alcohol-mediated mitochondrial damage in hepatocytes through restoring mitophagy. Accordingly, pharmacological blockade of mitophagy abolished the hepatoprotective actions of DUSP1. Molecular assays showed that DUSP1 binds cytosolic CUL1 and prevents its translocation to the nucleus. Importantly, CUL1 silencing restored the transcription of p62 and Parkin, resulting in mitophagy activation, and sustained mitochondrial integrity and hepatocyte function upon alcohol stress. These results indicate that alcohol-mediated DUSP1 downregulation interrupts DUSP1/CUL1 interaction, leading to CUL1 nuclear translocation and mitophagy inhibition via transcriptional repression of p62 and Parkin. Thus, targeting the DUSP1/CUL1/p62 axis will be a key approach to restore hepatic mitophagy as well as alleviate symptoms of ALD.

Inhibitory effect of CUL1 on atherosclerosis through the p53 pathway.

Background: Atherosclerosis (AS) is a serious chronic condition associated with cardiovascular and cerebrovascular diseases. Research on AS is currently lacking, and there is a need to increase research to improve the diagnosis, treatment, and prognosis of AS. Therefore, the aim of the present study was to explore the molecular mechanism and identify potential biomarkers in AS. Methods: First, we downloaded the GSE28829 dataset and screened differentially expressed genes (DEGs). Then, DEGs were analyzed by functional enrichment analysis and protein-protein interaction (PPI) networks to determine hub genes. The key gene for AS was identified following the expression analysis of AS, clinical correlation with immune factors, the gene set enrichment analysis (GSEA) enrichment pathway, and receiver-operating characteristic curve analysis. In functional experiments, correlations between cullin 1 (CUL1), cytokines, and downstream targets in AS were investigated. Results: We identified 595 upregulated and 391 downregulated DEGs enriched in neutrophil degranulation, the B-cell receptor signaling pathway, cell-matrix adhesion, and fatty acid degradation. Through PPI, we identified 7 hub genes for the expression analysis, immunoassay, and GSEA. Finally, CUL1 was identified as the inhibitory gene in AS associated with immune factors, and was found to have a strong prognostic prediction ability. The results indicated that CUL1 upregulated interleukin (IL)-6, IL-1ß, and tumor necrosis factor-α concentrations, and weakened the cell proliferation of AS. It was also found that CUL1 exerted its inhibitory function in AS by the p53 pathway. Conclusions: The findings of the present study indicate that CUL1 is a suppressing gene in AS, and has the potential to be a therapeutic and prognostic biomarker for AS.

A Hypoxia-Induced SCFFBXL1 E3 Ligase Ubiquitinates and Degrades the MEN1 Tumor Suppressor to Promote Colorectal Cancer Tumorigenesis.

PURPOSE: Emerging evidence has shown that SKP1-cullin-1-F-box-protein (SCF) E3 ligases contribute to the pathogenesis of different cancers by mediating the ubiquitination and degradation of tumor suppressors. However, the functions of SCF E3 ligases in the pathogenesis of colorectal cancer (CRC) remain obscure. MATERIALS AND METHODS: The cancerous and adjacent noncancerous tissues from CRC patients were collected, and protein levels were analyzed. Lentiviral short hairpin RNA (shRNA) and plasmid transfection were used to knock down and overexpress gene expression in CRC cell lines. Immunoprecipitation (IP), mass spectrometry, and co-IP analyses were used to determine protein interactions and the assembly of the SCF complex. Cell proliferation, migration, and tumor xenograft assays were performed to examine the effects of SCF members on CRC cell growth in vitro and in vivo. RESULTS: Hypoxia activated the docking of hypoxia-inducible factor 1α (HIF1α) onto the CUL1 promoter and induced CUL1 expression in CRC cells. CUL1 coupled with RBX1, SKP1, and FBXL1 to assemble the SCFFBXL1 complex in CRC biopsies and cells. The SCFFBXL1 E3 ligase specifically ubiquitinated and degraded the MEN1 tumor suppressor. Knockdown of HIF1α or SCFFBXL1 members, or blockage of SCFFBXL1 by two inhibitors (DT204 and SZLP1-41) caused the accumulation of MEN1 protein and led to a significant decrease in cell proliferation and migration in vitro and tumor growth in vivo. CONCLUSION: The SCFFBXL1 E3 ligase is required for the ubiquitination of MEN1, and disruption of this complex may represent a new therapeutic strategy for the treatment of CRC.

microRNA-377-3p inhibits osteosarcoma progression by targeting CUL1 and regulating Wnt/B-catenin signaling pathway

Objective Emerging studies highlight the crucial effects of microRNAs on cancer initiation and malignant progression of various tumors. This study focused on the biological effect of miR-377-3p on CUL1 and epithelial–mesenchymal transition (EMT) and Wnt/β-catenin pathways in osteosarcoma (OS). Methods We performed quantitative real-time polymerase chain reaction (qRT-PCR) to analyze miR-377-3p and CUL1 expression levels in OS tissues and MG-63 cells. Then, cell counting kit (CCK)-8 and Transwell assay were used to examine the functions of miR-377-3p in OS cell growth and metastasis abilities. Meanwhile, luciferase reporter assay was used to validate CUL1 as direct target of miR-377-3p. qRT-PCR and Western blot were then carried out to detect the impact of miR-377-3p on EMT and Wnt/β-catenin pathways. Tumor xenograft models were established to further examine the effects of miR-377-3p on OS tumorigenesis in vivo. Results miR-377-3p downregulation was frequently identified in OS tissues and cells, which was associated with worse prognosis of OS patients. Functional experiments showed miR-377-3p restoration could dramatically repress OS cell growth and migration by regulation of EMT and Wnt/β-catenin pathways. Moreover, luciferase reporter assay revealed that CUL1 acted as a functional target of miR-377-3p. Additionally, the elevated CUL1 expressions in OS tissues also indicated poor prognosis of OS patients. Furthermore, the OS tumor growth was also obviously inhibited by miR-377-3p overexpression in vivo. Conclusions Collectively, all the above findings revealed that miR-377-3p exerted anti-OS functions via CUL1 and EMT and Wnt/β-catenin pathways. These results may contribute to the development of clinical OS treatment (AU)

Cullin 1 (CUL1) Promotes Primary Ciliogenesis through the Induction of Ubiquitin-Proteasome-Dependent Dvl2 Degradation.

Primary cilia are nonmotile cellular signal-sensing antenna-like structures composed of microtubule-based structures that distinguish them from motile cilia in structure and function. Primary ciliogenesis is regulated by various cellular signals, such as Wnt, hedgehog (Hh), and platelet-derived growth factor (PDGF). The abnormal regulation of ciliogenesis is closely related to developing various human diseases, including ciliopathies and cancer. This study identified a novel primary ciliogenesis factor Cullin 1 (CUL1), a core component of Skp1-Cullin-F-box (SCF) E3 ubiquitin ligase complex, which regulates the proteolysis of dishevelled 2 (Dvl2) through the ubiquitin-proteasome system. Through immunoprecipitation-tandem mass spectrometry analysis, 176 Dvl2 interacting candidates were identified, of which CUL1 is a novel Dvl2 modulator that induces Dvl2 ubiquitination-dependent degradation. Neddylation-dependent CUL1 activity at the centrosomes was essential for centrosomal Dvl2 degradation and primary ciliogenesis. Therefore, this study provides a new mechanism of Dvl2 degradation by CUL1, which ultimately leads to primary ciliogenesis, and suggest a novel target for primary cilia-related human diseases.

microRNA-377-3p inhibits osteosarcoma progression by targeting CUL1 and regulating Wnt/ß-catenin signaling pathway.

OBJECTIVE: Emerging studies highlight the crucial effects of microRNAs on cancer initiation and malignant progression of various tumors. This study focused on the biological effect of miR-377-3p on CUL1 and epithelial-mesenchymal transition (EMT) and Wnt/ß-catenin pathways in osteosarcoma (OS). METHODS: We performed quantitative real-time polymerase chain reaction (qRT-PCR) to analyze miR-377-3p and CUL1 expression levels in OS tissues and MG-63 cells. Then, cell counting kit (CCK)-8 and Transwell assay were used to examine the functions of miR-377-3p in OS cell growth and metastasis abilities. Meanwhile, luciferase reporter assay was used to validate CUL1 as direct target of miR-377-3p. qRT-PCR and Western blot were then carried out to detect the impact of miR-377-3p on EMT and Wnt/ß-catenin pathways. Tumor xenograft models were established to further examine the effects of miR-377-3p on OS tumorigenesis in vivo. RESULTS: miR-377-3p downregulation was frequently identified in OS tissues and cells, which was associated with worse prognosis of OS patients. Functional experiments showed miR-377-3p restoration could dramatically repress OS cell growth and migration by regulation of EMT and Wnt/ß-catenin pathways. Moreover, luciferase reporter assay revealed that CUL1 acted as a functional target of miR-377-3p. Additionally, the elevated CUL1 expressions in OS tissues also indicated poor prognosis of OS patients. Furthermore, the OS tumor growth was also obviously inhibited by miR-377-3p overexpression in vivo. CONCLUSIONS: Collectively, all the above findings revealed that miR-377-3p exerted anti-OS functions via CUL1 and EMT and Wnt/ß-catenin pathways. These results may contribute to the development of clinical OS treatment.

A Comprehensive Assessment of Genetic and Epigenetic Alterations Identifies Frequent Variations Impacting Six Prototypic SCF Complex Members.

The SKP1, CUL1, F-box protein (SCF) complex represents a family of 69 E3 ubiquitin ligases that poly-ubiquitinate protein substrates marking them for proteolytic degradation via the 26S proteasome. Established SCF complex targets include transcription factors, oncoproteins and tumor suppressors that modulate cell cycle activity and mitotic fidelity. Accordingly, genetic and epigenetic alterations involving SCF complex member genes are expected to adversely impact target regulation and contribute to disease etiology. To gain novel insight into cancer pathogenesis, we determined the prevalence of genetic and epigenetic alterations in six prototypic SCF complex member genes (SKP1, CUL1, RBX1, SKP2, FBXW7 and FBXO5) from patient datasets extracted from The Cancer Genome Atlas (TCGA). Collectively, ~45% of observed SCF complex member mutations are predicted to impact complex structure and/or function in 10 solid tumor types. In addition, the distribution of encoded alterations suggest SCF complex members may exhibit either tumor suppressor or oncogenic mutational profiles in a cancer type dependent manner. Further bioinformatic analyses reveal the potential functional implications of encoded alterations arising from missense mutations by examining predicted deleterious mutations with available crystal structures. The SCF complex also exhibits frequent copy number alterations in a variety of cancer types that generally correspond with mRNA expression levels. Finally, we note that SCF complex member genes are differentially methylated across cancer types, which may effectively phenocopy gene copy number alterations. Collectively, these data show that SCF complex member genes are frequently altered at the genetic and epigenetic levels in many cancer types, which will adversely impact the normal targeting and timely destruction of protein substrates, which may contribute to the development and progression of an extensive array of cancer types.

Knockout Mouse Models Provide Insight into the Biological Functions of CRL1 Components.

The CRL1 complex, also known as the SCF complex, is a ubiquitin ligase that in mammals consists of an adaptor protein (SKP1), a scaffold protein (CUL1), a RING finger protein (RBX1, also known as ROC1), and one of about 70 F-box proteins. Given that the F-box proteins determine the substrate specificity of the CRL1 complex, the variety of these proteins allows the generation of a large number of ubiquitin ligases that promote the degradation or regulate the function of many substrate proteins and thereby control numerous key cellular processes. The physiological and pathological functions of these many CRL1 ubiquitin ligases have been studied by the generation and characterization of knockout mouse models that lack specific CRL1 components. In this chapter, we provide a comprehensive overview of these mouse models and discuss the role of each CRL1 component in mouse physiology and pathology.

CUL1 Knockdown Attenuates the Adhesion, Invasion, and Migration of Triple-Negative Breast Cancer Cells via Inhibition of Epithelial-Mesenchymal Transition.

Cullin-1 (CUL1) is an important factor for tumor growth and a potential therapeutic target for breast cancer therapy, but the molecular mechanism in triple-negative breast cancer (TNBC) is unknown. In the present study, CUL1 shRNA was transfected into BT549 and MDA-MB-231 breast cancer cells. Cell morphology, adhesion, invasion, and migration assays were carried out in the CUL1 knockdown cells. Additionally, protein expression levels of epithelial-mesenchymal transition (EMT)-related factors, Akt phosphorylation at S473 (pAkt), glycogen synthase kinase-3ß phosphorylation at ser9 (pGSK3ß), cytoplasmic and nuclear ß-catenin, and epidermal growth factor receptor phosphorylation at Tyr1068 (pEGFR) were detected by Western blot analysis. CUL1 knockdown significantly suppressed the adhesion, invasion and migration capabilities of the cells, and decreased the expression of Snail1/2, ZEB1/2, Twist1/2, Vimentin, and increased the expression of Cytokeratin 18 (CK18). Moreover, CUL1 knockdown significantly downregulated the phosphorylated levels of Akt, GSK3ß, and EGFR, inhibiting the translocation of ß-catenin from the cytoplasm to the nucleus. The results indicate that CUL1 knockdown prohibited the metastasis behaviors of breast cancer cells through downregulation (dephosphorylation) of the EMT signaling pathways of EGFR and Akt/GSK3ß/ß-catenin in breast cancer. These results strongly suggested that reinforcement of the EMT might be a key for CUL1 to accelerate TNBC metastasis.

Proteostasis in the Hedgehog signaling pathway.

The Hedgehog (Hh) signaling pathway is crucial for the development of vertebrate and invertebrate animals alike. Hh ligand binds its receptor Patched (Ptc), allowing the activation of the obligate signal transducer Smoothened (Smo). The levels and localizations of both Ptc and Smo are regulated by ubiquitination, and Smo is under additional regulation by phosphorylation and SUMOylation. Downstream of Smo, the Ci/Gli family of transcription factors regulates the transcriptional responses to Hh. Phosphorylation, ubiquitination and SUMOylation are important for the stability and localization of Ci/Gli proteins and Hh signaling output. Finally, Suppressor of Fused directly regulates Ci/Gli proteins and itself is under proteolytic regulation that is critical for normal Hh signaling.

SCFFbxw7 ubiquitylates KLF7 for degradation in a manner dependent on GSK-3-mediated phosphorylation.

The biological relation between ubiquitin ligases and their substrates has been largely unclear. We previously developed a method-differential proteomics-based identification of ubiquitylation substrates (DiPIUS)-for the comprehensive identification of substrates for a given ubiquitin ligase. We have now applied DiPIUS to the F-box protein Fbxw7 in three cell lines (mHepa, Neuro2A and C2C12) and thereby identified Krüppel-like factor 7 (KLF7) as a candidate substrate of the SCFFbxw7 ubiquitin ligase complex. KLF7 was shown to interact with Fbxw7 and to undergo Fbxw7-mediated polyubiquitylation. The stability of KLF7 was increased by depletion of Fbxw7, mutation of a putative Cdc4 phosphodegron (CPD) of KLF7 or exposure to inhibitors of glycogen synthase kinase-3 (GSK-3). Over-expression of Fbxw7 in Neuro2A cells down-regulated expression of the p21Cip1 gene, which is a transcriptional target of KLF7 in neuronal differentiation and maintenance. Despite the presence of an almost identical CPD sequence in KLF6, the closest paralog of KLF7, mutation of this sequence affected neither the interaction of KLF6 with Fbxw7 nor its half-life. Our results suggest that KLF7, but not KLF6, is a bona fide substrate of SCFFbxw7 , and that control of KLF7 abundance by SCFFbxw7 might contribute to the regulation of neuronal differentiation and maintenance.

CENP-W inhibits CDC25A degradation by destabilizing the SCFß-TrCP-1 complex at G2/M.

Skp, Cullin, F-box (SCF)ß-TrCP-1 ubiquitin ligases play a central role in cell cycle regulation and tumorigenesis via proteolytic cleavage of many essential cell cycle regulators. In this study, we propose that centromere protein (CENP)-W, a newly identified kinetochore component, is a novel negative regulator of the SCFß-TrCP-1 complex. CENP-W interacts with Cullin (CUL)-1 and ß-Transducin repeat-containing protein (ß-TrCP)-1 through highly overlapped binding sites with S-phase kinase-associated protein (SKP)-1. CENP-W is incorporated into the SCFß-TrCP-1 complex to promote complex disassembly. Unlike other known regulators that increase SCFß-TrCP-1 ubiquitin ligase activity by promoting complex reassociation, CENP-W-mediated complex disorganization induced ß-TrCP1 degradation and consequently decreased its activity. The association between CENP-W and the SCFß-TrCP-1 complex was prominent during the G2/M transition in the nucleus. Especially, CENP-W knockdown decreased the cell division cycle-25A protein level, leading to a delay in mitotic progression. We propose that CENP-W participates in cell cycle regulation by modulating SCFß-TrCP-1 ubiquitin ligase activity.-Cheon, Y., Lee, S. CENP-W inhibits CDC25A degradation by destabilizing the SCFß-TrCP-1 complex at G2/M.

Increasing the Unneddylated Cullin1 Portion Rescues the csn Phenotypes by Stabilizing Adaptor Modules To Drive SCF Assembly.

The dynamic SCF (Skp1-cullin1-F-box protein) assembly is controlled by cycles of cullin neddylation/deneddylation based on the deneddylation activity of the COP9 signalosome (CSN) and global sequestration of cullins by CAND1. However, acceptance of this prediction was hampered by the results of recent studies, and the regulatory mechanism and key players remain to be identified. We found that maintaining a proper Cul1Nedd8/Cul1 ratio is crucial to ensure SCF functions. Reducing the high Cul1Nedd8/Cul1 ratios in csn mutants through ectopic expression of the nonneddylatable Cul1K722R proteins or introducing the endogenous cul1K722R point mutation significantly rescues their defective phenotypes. In vivo protein degradation assays revealed that the large portion of the unneddylated Cul1 contributes to F-box protein stabilization. Moreover, the unneddylated Cul1 tends to associate with adaptor modules, and disruption of Cul1-Skp-1 binding fails to restore the csn phenotypes. Taking the data together, we propose that unneddylated Cul1 is another central player involved in maintenance of the adaptor module pool through the formation of Cul1-Skp-1-F-box complexes and promotion of rapid SCF assembly.

Expression of CUL1 correlates with tumour-grade and recurrence in urothelial carcinoma.

BACKGROUND: Urothelial carcinoma (UC) is a major health problem in the general population. We aimed to evaluate the function of Cullin-1 (CUL1) and unravel its underlying molecular mechanism to develop novel treatment options equivalent to UC. METHODS: To evaluate the function of CUL1, a group of 132 pairs of UC patients were recruited for this study. UC tissues and their adjacent noncancerous tissues (NCTs) were collected between 2008 and 2009. We used immunohistochemistry to analyse the correlation between CUL1 expression and clinicopathologic variables and patient survival. RESULTS: CUL1 was dramatically overexpressed in high-grade UC tissues compared with low-grade UC tissues. CUL1 up-regulation in recurrence cases in comparison with the non-recurrence cases. CUL1 expression upregulated in human UC tissues versus NCTs. CUL1 protein expression associated with androgen receptor. CONCLUSIONS: Our results demonstrate that increased CUL1 expression is significantly correlated with poor prognosis of patients with UC. CUL1 might be an important marker and a therapeutic target for UC.