Research IndicatorsGraph generated 15 March 2017 using data from PubMed using criteria.
Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic. Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex
Specific Cancers (2)
Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.
Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).
OMIM, Johns Hopkin University
Referenced article focusing on the relationship between phenotype and genotype.
International Cancer Genome Consortium.
Summary of gene and mutations by cancer type from ICGC
Cancer Genome Anatomy Project, NCI
COSMIC, Sanger Institute
Somatic mutation information and related details
GEO Profiles, NCBI
Search the gene expression profiles from curated DataSets in the Gene Expression Omnibus (GEO) repository.
Latest Publications: CUL1 (cancer-related)
Wu WJ, Shi J, Hu G, et al.Wnt/β-catenin signaling inhibits FBXW7 expression by upregulation of microRNA-770 in hepatocellular carcinoma.
Tumour Biol. 2016; 37(5):6045-51 [PubMed
] Related Publications
FBXW7 (F-box and WD repeat domain-containing 7) is the F-box protein component of a Skp1-Cul1-F-box protein-type (SCF-type) ubiquitin ligase. Previous studies have shown that FBXW7 serves as a tumor suppressor and is frequently downregulated in many types of human neoplasms. However, the molecular mechanisms for its downregulation remain poorly understood. Hyperactivation of Wnt/β-catenin signaling pathway is viewed as crucial for tumorigenesis, including hepatocellular carcinoma (HCC). In the present study, we show that protein levels, but not message RNA, of FBXW7 were suppressed by Wnt3a treatment or transfection of a constitutively activated β-catenin in HCC cells. Besides, microRNA-770 was identified as an important downstream target of Wnt/β-catenin signaling, to inhibit FBXW7 expression through targeting its 3'-untranslated region. Thus, our results suggest a previously unknown Wnt/β catenin-miR-770-FBXW7 molecular network in the HCC development.
The cullin proteins are a family of scaffolding proteins that associate with RING proteins and ubiquitin E3 ligases and mediate substrate-receptor bindings. Thus, cullin proteins regulate the specificity of ubiquitin targeting in the regulation of proteins involved in various cellular processes, including proliferation, differentiation, and apoptosis. There are seven cullin proteins that have been identified in eukaryotes: CUL1, CUL2, CUL3, CUL4A, CUL4B, CUL5, and CUL7/p53-associated parkin-like cytoplasmic protein. All of these proteins contain a conserved cullin homology domain that binds to RING box proteins. Cullin-RING ubiquitin ligase complexes are activated upon post-translational modification by neural precursor cell-expressed, developmentally downregulated protein 8. The aberrant expression of several cullin proteins has been implicated in many cancers though the significance in gastric cancer has been less well investigated. This review provides the first systematic discussion of the associations between all members of the cullin protein family and gastric cancer. Functional and regulatory mechanisms of cullin proteins in gastric carcinoma progression are also summarized along with a discussion concerning future research areas. Accumulating evidence suggests a critical role of cullin proteins in tumorigenesis, and a better understanding of the function of these individual cullin proteins and their targets will help identify potential biomarkers and therapeutic targets.
Mäki-Nevala S, Sarhadi VK, Knuuttila A, et al.Driver Gene and Novel Mutations in Asbestos-Exposed Lung Adenocarcinoma and Malignant Mesothelioma Detected by Exome Sequencing.
Lung. 2016; 194(1):125-35 [PubMed
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BACKGROUND: Asbestos is a carcinogen linked to malignant mesothelioma (MM) and lung cancer. Some gene aberrations related to asbestos exposure are recognized, but many associated mutations remain obscure. We performed exome sequencing to determine the association of previously known mutations (driver gene mutations) with asbestos and to identify novel mutations related to asbestos exposure in lung adenocarcinoma (LAC) and MM.
METHODS: Exome sequencing was performed on DNA from 47 tumor tissues of MM (21) and LAC (26) patients, 27 of whom had been asbestos-exposed (18 MM, 9 LAC). In addition, 9 normal lung/blood samples of LAC were sequenced. Novel mutations identified from exome data were validated by amplicon-based deep sequencing. Driver gene mutations in BRAF, EGFR, ERBB2, HRAS, KRAS, MET, NRAS, PIK3CA, STK11, and ephrin receptor genes (EPHA1-8, 10 and EPHB1-4, 6) were studied for both LAC and MM, and in BAP1, CUL1, CDKN2A, and NF2 for MM.
RESULTS: In asbestos-exposed MM patients, previously non-described NF2 frameshift mutation (one) and BAP1 mutations (four) were detected. Exome data mining revealed some genes potentially associated with asbestos exposure, such as MRPL1 and SDK1. BAP1 and COPG1 mutations were seen exclusively in MM. Pathogenic KRAS mutations were common in LAC patients (42 %), both in non-exposed (n = 5) and exposed patients (n = 6). Pathogenic BRAF mutations were found in two LACs.
CONCLUSION: BAP1 mutations occurred in asbestos-exposed MM. MRPL1, SDK1, SEMA5B, and INPP4A could possibly serve as candidate genes for alterations associated with asbestos exposure. KRAS mutations in LAC were not associated with asbestos exposure.
MicroRNAs (miRNAs) are small endogenous non-coding RNAs, which play critical roles in cancer development by suppressing gene expression at the post-transcriptional level. In general, oncogenic miRNAs are upregulated in cancer, while miRNAs that act as tumor suppressors are downregulated, leading to decreased expression of tumor suppressors and upregulated oncogene expression, respectively. F-box proteins function as the substrate-recognition components of the SKP1-CUL1-F-box (SCF)-ubiquitin ligase complex for the degradation of their protein targets by the ubiquitin-proteasome system. Therefore F-box proteins and miRNAs both negatively regulate target gene expression post-transcriptionally. Since each miRNA is capable of fine-tuning the expression of multiple target genes, multiple F-box proteins may be suppressed by the same miRNA. Meanwhile, one F-box proteins could be regulated by several miRNAs in different cancer types. In this review, we will focus on miRNA-mediated downregulation of various F-box proteins, the resulting stabilization of F-box protein substrates and the impact of these processes on human malignancies. We provide insight into how the miRNA: F-box protein axis may regulate cancer progression and metastasis. We also consider the broader role of F-box proteins in the regulation of pathways that are independent of the ubiquitin ligase complex and how that impacts on oncogenesis. The area of miRNAs and the F-box proteins that they regulate in cancer is an emerging field and will inform new strategies in cancer treatment.
Randle SJ, Laman HF-box protein interactions with the hallmark pathways in cancer.
Semin Cancer Biol. 2016; 36:3-17 [PubMed
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F-box proteins (FBP) are the substrate specifying subunit of Skp1-Cul1-FBP (SCF)-type E3 ubiquitin ligases and are responsible for directing the ubiquitination of numerous proteins essential for cellular function. Due to their ability to regulate the expression and activity of oncogenes and tumour suppressor genes, FBPs themselves play important roles in cancer development and progression. In this review, we provide a comprehensive overview of FBPs and their targets in relation to their interaction with the hallmarks of cancer cell biology, including the regulation of proliferation, epigenetics, migration and invasion, metabolism, angiogenesis, cell death and DNA damage responses. Each cancer hallmark is revealed to have multiple FBPs which converge on common signalling hubs or response pathways. We also highlight the complex regulatory interplay between SCF-type ligases and other ubiquitin ligases. We suggest six highly interconnected FBPs affecting multiple cancer hallmarks, which may prove sensible candidates for therapeutic intervention.
Uddin S, Bhat AA, Krishnankutty R, et al.Involvement of F-BOX proteins in progression and development of human malignancies.
Semin Cancer Biol. 2016; 36:18-32 [PubMed
] Related Publications
The Ubiquitin Proteasome System (UPS) is a core regulator with various protein components (ubiquitin-activating E1 enzymes, ubiquitin-conjugating E2 enzymes, ubiquitin-protein E3 ligases, and the 26S proteasome) which work together in a coordinated fashion to ensure the appropriate and efficient proteolysis of target substrates. E3 ubiquitin ligases are essential components of the UPS machinery, working with E1 and E2 enzymes to bind substrates and assist the transport of ubiquitin molecules onto the target protein. As the UPS controls the degradation of several oncogenes and tumor suppressors, dysregulation of this pathway leads to several human malignancies. A major category of E3 Ub ligases, the SCF (Skp-Cullin-F-box) complex, is composed of four principal components: Skp1, Cul1/Cdc53, Roc1/Rbx1/Hrt1, and an F-box protein (FBP). FBPs are the substrate recognition components of SCF complexes and function as adaptors that bring substrates into physical proximity with the rest of the SCF. Besides acting as a component of SCF complexes, FBPs are involved in DNA replication, transcription, cell differentiation and cell death. This review will highlight the recent literature on three well characterized FBPs SKP2, Fbw7, and beta-TRCP. In particular, we will focus on the involvement of these deregulated FBPs in the progression and development of various human cancers. We will also highlight some novel substrates recently identified for these FBPs.
Diniz MG, Silva Jde F, de Souza FT, et al.Association between cell cycle gene transcription and tumor size in oral squamous cell carcinoma.
Tumour Biol. 2015; 36(12):9717-22 [PubMed
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Higher tumor size correlates with poor prognosis and is an independent predictive survival factor in oral squamous cell carcinoma (OSCC) patients. However, the molecular events underlining OSCC tumor evolution are poorly understood. We aimed to investigate if large OSCC tumors show different cell cycle gene transcriptional signature compared to small tumors. Seventeen fresh OSCC tumor samples with different tumor sizes (T) were included in the study. Tumors were from the tongue or from the floor of the mouth, and only three patients were nonsmokers. Samples were categorized according to clinical tumor size in tumors ≤2 cm (T1, n = 5) or tumors >2 cm (T2, n = 9; T3, n = 2; T4, n = 1). The group of tumors ≤2 cm was considered the reference group, while the larger tumors were considered the test group. We assessed the expression of 84 cell cycle genes by qRT-PCR array and normalized it to the expression of two housekeeping genes. Results were analyzed according to the formula 2(^-DeltaCt). A five-fold change cutoff was used, and p values <0.05 were considered statistically significant. Ki-67 immunohistochemistry was performed to estimate cell proliferation index. Twenty-nine genes were downregulated in the test group (larger tumors) compared to the reference group (smaller tumors). Among these genes, 13 reached statistical significance: ANAPC4, CUL1, SUMO1, KPNA2, MAD2L2, CCNG2, E2F4, NBN, CUL2, PCNA, TFDP1, KNTC1, and ATR. Ki-67 labeling index was similar in both tumor groups. Our findings suggest that the transcriptional activity of specific cell cycle genes varies according to the size of OSCC tumor, which probably reflects tumor molecular evolution and adaptation to the microenvironment.
Loss of function/dysregulation of inhibitor of growth 4 (ING4) and hyperactivation of NF-κB are frequent events in many types of human malignancies. However, the molecular mechanisms underlying these remarkable aberrations are not understood. Here, we report that ING4 is physically associated with JFK. We demonstrated that JFK targets ING4 for ubiquitination and degradation through assembly of an Skp1-Cul1-F-box (SCF) complex. We showed that JFK-mediated ING4 destabilization leads to the hyperactivation of the canonical NF-κB pathway and promotes angiogenesis and metastasis of breast cancer. Significantly, the expression of JFK is markedly up-regulated in breast cancer, and the level of JFK is negatively correlated with that of ING4 and positively correlated with an aggressive clinical behavior of breast carcinomas. Our study identified SCF(JFK) as a bona fide E3 ligase for ING4 and unraveled the JFK-ING4-NF-κB axis as an important player in the development and progression of breast cancer, supporting the pursuit of JFK as a potential target for breast cancer intervention.
Wang W, Chen Y, Deng J, et al.Cullin1 is a novel prognostic marker and regulates the cell proliferation and metastasis in colorectal cancer.
J Cancer Res Clin Oncol. 2015; 141(9):1603-12 [PubMed
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PURPOSE: To investigate the precise function of Cullin1 (CUL1) in colorectal cancer (CRC).
METHODS: Immunohistochemistry was performed to test the expression of CUL1 on a CRC tissue microarray containing the tumor and corresponding normal tissues. Simultaneously, the correlation of CUL1 expression with clinicopathological parameters and survival was evaluated. CUL1 was over-expressed or knocked down in HCT116 and SW480 cells, then the cell proliferation, migration and invasion assays in vitro and in vivo were performed.
RESULTS: In this study, we found that CUL1 expression was significantly up-regulated in CRC compared with normal colon tissues. High CUL1 expression was positively associated with lymph node metastasis (P = 0.007) and tumor diameter (P = 0.052). Multivariate Cox regression analysis revealed that high CUL1 expression was an independent unfavorable prognostic factor for CRC patients (HR = 13.9, 95% confidence interval = 5.89-32.6, P < 0.001). Moreover, we found that CUL1 over-expression induced CRC cell proliferation and the growth of xenografts in nude mice via the changing of cell-cycle proteins. In addition, increased CUL1 expression in CRC cells significantly promoted cell migration and invasion abilities in vitro and peritoneal metastasis in vivo through inducing high expression of MMPs.
CONCLUSION: Our findings imply that CUL1 may serve as promising prognostic markers in CRC patients.
The microRNA miR-21 is overexpressed in most human cancers and accumulating evidence indicates that it functions as an oncogene. Since miRNAs suppress the expression of their target genes, we hypothesized that some miR-21 targets may act as tumor suppressors, and thus their expression would be anticipated to be reduced by the high miR-21 levels observed in various human cancers. By microarray analysis and quantitative PCR we identified and validated FBXO11 (a member of the F-box subfamily lacking a distinct unifying domain) as a miR-21 target gene. FBXO11 is a component of the SKP1-CUL1-F-box ubiquitin ligase complex that targets proteins for ubiquitination and proteosomal degradation. By loss of function and gain of function studies, we show that FBXO11 acts as a tumor suppressor, promotes apoptosis and mediates the degradation of the oncogenic protein BCL6. The critical role that FBXO11 plays in miR-21-mediated tumorigenesis was demonstrated by a rescue experiment, in which silencing FBXO11 in miR-21KD cancer cells restored their high tumorigenicity. Expression of miR-21 and FBXO11 are inversely correlated in tumor tissue, and their expression correlates with patient survival and tumor grade. High FBXO11 expression correlates with better patient survival and lower tumor grade consistent with its tumor suppressor activity. In contrast high miR-21 expression, which correlates with poor patient survival and higher tumor grade, is consistent with its oncogenic activity. Our results identify FBXO11 as a novel miR-21 target gene, and demonstrate that the oncogenic miRNA miR-21 decreases the expression of FBXO11, which normally acts as a tumor suppressor, and thereby promotes tumorigenesis.
Guo G, Chmielecki J, Goparaju C, et al.Whole-exome sequencing reveals frequent genetic alterations in BAP1, NF2, CDKN2A, and CUL1 in malignant pleural mesothelioma.
Cancer Res. 2015; 75(2):264-9 [PubMed
] Related Publications
Malignant pleural mesothelioma (MPM) is an aggressive neoplasm associated with asbestos exposure. Although previous studies based on candidate gene approaches have identified important common somatic mutations in MPM, these studies have focused on small sets of genes and have provided a limited view of the genetic alterations underlying this disease. Here, we performed whole-exome sequencing on DNA from 22 MPMs and matched blood samples, and identified 517 somatic mutations across 490 mutated genes. Integrative analysis of mutations and somatic copy-number alterations revealed frequent genetic alterations in BAP1, NF2, CDKN2A, and CUL1. Our study presents the first unbiased view of the genomic basis of MPM.
Baumann U, Fernández-Sáiz V, Rudelius M, et al.Disruption of the PRKCD-FBXO25-HAX-1 axis attenuates the apoptotic response and drives lymphomagenesis.
Nat Med. 2014; 20(12):1401-9 [PubMed
] Related Publications
We searched for genetic alterations in human B cell lymphoma that affect the ubiquitin-proteasome system. This approach identified FBXO25 within a minimal common region of frequent deletion in mantle cell lymphoma (MCL). FBXO25 encodes an orphan F-box protein that determines the substrate specificity of the SCF (SKP1-CUL1-F-box)(FBXO25) ubiquitin ligase complex. An unbiased screen uncovered the prosurvival protein HCLS1-associated protein X-1 (HAX-1) as the bona fide substrate of FBXO25 that is targeted after apoptotic stresses. Protein kinase Cδ (PRKCD) initiates this process by phosphorylating FBXO25 and HAX-1, thereby spatially directing nuclear FBXO25 to mitochondrial HAX-1. Our analyses in primary human MCL identify monoallelic loss of FBXO25 and stabilizing HAX1 phosphodegron mutations. Accordingly, FBXO25 re-expression in FBXO25-deleted MCL cells promotes cell death, whereas expression of the HAX-1 phosphodegron mutant inhibits apoptosis. In addition, knockdown of FBXO25 significantly accelerated lymphoma development in Eμ-Myc mice and in a human MCL xenotransplant model. Together we identify a PRKCD-dependent proapoptotic mechanism controlling HAX-1 stability, and we propose that FBXO25 functions as a haploinsufficient tumor suppressor and that HAX1 is a proto-oncogene in MCL.
Fan YC, Zhu YS, Mei PJ, et al.Cullin1 regulates proliferation, migration and invasion of glioma cells.
Med Oncol. 2014; 31(10):227 [PubMed
] Related Publications
This study was designed to explore the role of Cullin1 (Cul1) in the pathogenesis of human glioma and to investigate the role of Cul1 in the growth, migration and invasion of glioma cells. Expression of Cul1 in 191 glioma tissues, 8 normal brain tissues and 8 tumor adjacent normal brain tissues was analyzed by tissue microarray and immunohistochemistry. Cul1 expression in human glioblastoma cells was knocked down by specific siRNA to study the effect of down-regulation of Cul1 on proliferation, invasion and migration of glioma cells. Our results showed that Cul1 expression increased significantly in tissues from the benign tumor and malignant tumor in comparison with those from the tumor-adjacent normal brain (P<0.05 for both). We did not find any correlation between Cul1 expression and clinicopathological parameters. In addition, we found that knockdown of Cul1 by RNA interference markedly inhibited cell proliferation and caused cessation of cell cycle. This reduced cell proliferation was due to G1 phase arrest as cyclinA, cyclinD1 and cyclinE were diminished, whereas p21 and p27 were up-regulated. We further demonstrated that silencing of Cul1 in glioma cells inhibited the cell migration and invasion abilities, and down-regulation of MMP-2 and MMP-9 expression greatly contributed to the reduced cell invasion and migration abilities. Our data indicated that Cul1 expression significantly increased in human glioma, and it may be involved in proliferation, migration and invasion of glioma cells.
Zhou Y, Hu HY, Meng W, et al.MEK inhibitor effective against proliferation in breast cancer cell.
Tumour Biol. 2014; 35(9):9269-79 [PubMed
] Related Publications
The targeted small-molecule drug AZD6244 is an allosteric, ATP-noncompetitive inhibitor of MEK1/2 that has shown activity against several malignant tumors. Here, we report that AZD6244 repressed cell growth and induced apoptosis and G1-phase arrest in the breast cancer cell lines MDA-MB-231 and HCC1937. Using microRNA (miRNA) arrays and quantitative RT-PCR, we found that miR-203 was up-regulated after AZD6244 treatment. In accordance with bioinformatics and luciferase activity analyses, CUL1 was found to be the direct target of miR-203. Furthermore, miR-203 inhibition and CUL1 overexpression reversed the cytotoxicity of AZD6244 on the MDA-MB-231 and HCC1937 cells. Collectively, our data indicate that miR-203 mediates the AZD6244-induced cytotoxicity of breast cancer cells and that the MEK/ERK/miR-203/CUL1 signaling pathway may participate in this process.
Although it has been suggested that kinesin family member 14 (KIF14) has oncogenic potential in various cancers, including hepatocellular carcinoma (HCC), the molecular mechanism of this potential remains unknown. We aimed to elucidate the role of KIF14 in hepatocarcinogenesis by knocking down KIF14 in HCC cells that overexpressed KIF14. After KIF14 knockdown, changes in tumor cell growth, cell cycle and cytokinesis were examined. We also examined cell cycle regulatory molecules and upstream Skp1/Cul1/F-box (SCF) complex molecules. Knockdown of KIF14 resulted in suppression of cell proliferation and failure of cytokinesis, whereas KIF14 overexpression increased cell proliferation. In KIF14-silenced cells, the levels of cyclins E1, D1 and B1 were profoundly decreased compared with control cells. Of the cyclin-dependent kinase inhibitors, the p27(Kip1) protein level specifically increased after KIF14 knockdown. The increase in p27(Kip1) was not due to elevation of its mRNA level, but was due to inhibition of the proteasome-dependent degradation pathway. To explore the pathway upstream of this event, we measured the levels of SCF complex molecules, including Skp1, Skp2, Cul1, Roc1 and Cks1. The levels of Skp2 and its cofactor Cks1 decreased in the KIF14 knockdown cells where p27(Kip1) accumulated. Overexpression of Skp2 in the KIF14 knockdown cells attenuated the failure of cytokinesis. On the basis of these results, we postulate that KIF14 knockdown downregulates the expression of Skp2 and Cks1, which target p27(Kip1) for degradation by the 26S proteasome, leading to accumulation of p27(Kip1). The downregulation of Skp2 and Cks1 also resulted in cytokinesis failure, which may inhibit tumor growth. To the best of our knowledge, this is the first report that has identified the molecular target and oncogenic effect of KIF14 in HCC.
The pathogenesis of splenic marginal zone lymphoma (SMZL) remains largely unknown. Recent high-throughput sequencing studies have identified recurrent mutations in key pathways, most notably NOTCH2 mutations in >25% of patients. These studies are based on small, heterogeneous discovery cohorts, and therefore only captured a fraction of the lesions present in the SMZL genome. To identify further novel pathogenic mutations within related biochemical pathways, we applied whole exome sequencing (WES) and copy number (CN) analysis to a biologically and clinically homogeneous cohort of seven SMZL patients with 7q abnormalities and IGHV1-2*04 gene usage. We identified 173 somatic non-silent variants, affecting 160 distinct genes. In additional to providing independent validation of the presence of mutation in several previously reported genes (NOTCH2, TNFAIP3, MAP3K14, MLL2 and SPEN), our study defined eight additional recurrently mutated genes in SMZL; these genes are CREBBP, CBFA2T3, AMOTL1, FAT4, FBXO11, PLA2G4D, TRRAP and USH2A. By integrating our WES and CN data we identified three mutated putative candidate genes targeted by 7q deletions (CUL1, EZH2 and FLNC), with FLNC positioned within the well-characterized 7q minimally deleted region. Taken together, this work expands the reported directory of recurrently mutated cancer genes in this disease, thereby expanding our understanding of SMZL pathogenesis. Ultimately, this work will help to establish a stratified approach to care including the possibility of targeted therapy.
Ewing sarcoma is the second most frequent pediatric bone tumor. In most of the patients, a chromosomal translocation leads to the expression of the EWS-FLI1 chimeric transcription factor that is the major oncogene in this pathology. Relative genetic simplicity of Ewing sarcoma makes it particularly attractive for studying cancer in a systemic manner. Silencing EWS-FLI1 induces cell cycle alteration and ultimately leads to apoptosis, but the exact molecular mechanisms underlying this phenotype are unclear. In this study, a network linking EWS-FLI1 to cell cycle and apoptosis phenotypes was constructed through an original method of network reconstruction. Transcriptome time-series after EWS-FLI1 silencing were used to identify core modulated genes by an original scoring method based on fitting expression profile dynamics curves. Literature data mining was then used to connect these modulated genes into a network. The validity of a subpart of this network was assessed by siRNA/RT-QPCR experiments on four additional Ewing cell lines and confirmed most of the links. Based on the network and the transcriptome data, CUL1 was identified as a new potential target of EWS-FLI1. Altogether, using an original methodology of data integration, we provide the first version of EWS-FLI1 network model of cell cycle and apoptosis regulation.
Cepeda D, Ng HF, Sharifi HR, et al.CDK-mediated activation of the SCF(FBXO) (28) ubiquitin ligase promotes MYC-driven transcription and tumourigenesis and predicts poor survival in breast cancer.
EMBO Mol Med. 2013; 5(7):1067-86 [PubMed
] Free Access to Full Article Related Publications
SCF (Skp1/Cul1/F-box) ubiquitin ligases act as master regulators of cellular homeostasis by targeting key proteins for ubiquitylation. Here, we identified a hitherto uncharacterized F-box protein, FBXO28 that controls MYC-dependent transcription by non-proteolytic ubiquitylation. SCF(FBXO28) activity and stability are regulated during the cell cycle by CDK1/2-mediated phosphorylation of FBXO28, which is required for its efficient ubiquitylation of MYC and downsteam enhancement of the MYC pathway. Depletion of FBXO28 or overexpression of an F-box mutant unable to support MYC ubiquitylation results in an impairment of MYC-driven transcription, transformation and tumourigenesis. Finally, in human breast cancer, high FBXO28 expression and phosphorylation are strong and independent predictors of poor outcome. In conclusion, our data suggest that SCF(FBXO28) plays an important role in transmitting CDK activity to MYC function during the cell cycle, emphasizing the CDK-FBXO28-MYC axis as a potential molecular drug target in MYC-driven cancers, including breast cancer.
Lockwood WW, Chandel SK, Stewart GL, et al.The novel ubiquitin ligase complex, SCF(Fbxw4), interacts with the COP9 signalosome in an F-box dependent manner, is mutated, lost and under-expressed in human cancers.
PLoS One. 2013; 8(5):e63610 [PubMed
] Free Access to Full Article Related Publications
Identification of novel proteins that can potentially contribute to carcinogenesis is a requisite venture. Herein, we report the first biochemical characterization of the novel F-box and WD40 containing protein, FBXW4. We have identified interacting protein partners and demonstrated that FBXW4 is part of a ubiquitin ligase complex. Furthermore, the Fbxw4 locus is a common site of proviral insertion in a variety of retroviral insertional mutagenesis murine cancer models and Fbxw4 mRNA is highly expressed in the involuting murine mammary gland. To begin to characterize the biochemical function of Fbxw4, we used proteomic analysis to demonstrate that Fbxw4 interacts with Skp1 (SKP1), Cullin1 (CUL1), Ring-box1 (RBX1) and all components of the COP9 signalosome. All of these interactions are dependent on an intact F-box domain of Fbxw4. Furthermore, Fbxw4 is capable of interacting with ubiquitinated proteins within cells in an F-box dependent manner. Finally, we demonstrate that FBXW4 is mutated, lost and under-expressed in a variety of human cancer cell lines and clinical patient samples. Importantly, expression of FBXW4 correlates with survival of patients with non-small cell lung cancer. Taken together, we suggest that FBXW4 may be a novel tumor suppressor that regulates important cellular processes.
Many biological processes such as cell proliferation, differentiation, and cell death depend precisely on the timely synthesis and degradation of key regulatory proteins. While protein synthesis can be regulated at multiple levels, protein degradation is mainly controlled by the ubiquitin-proteasome system (UPS), which consists of two distinct steps: (1) ubiquitylation of targeted protein by E1 ubiquitin-activating enzyme, E2 ubiquitin-conjugating enzyme and E3 ubiquitin ligase, and (2) subsequent degradation by the 26S proteasome. Among all E3 ubiquitin ligases, the SCF (SKP1-CUL1-F-box protein) E3 ligases are the largest family and are responsible for the turnover of many key regulatory proteins. Aberrant regulation of SCF E3 ligases is associated with various human diseases, such as cancers, including skin cancer. In this review, we provide a comprehensive overview of all currently published data to define a promoting role of SCF E3 ligases in the development of skin cancer. The future directions in this area of research are also discussed with an ultimate goal to develop small molecule inhibitors of SCF E3 ligases as a novel approach for the treatment of human skin cancer. Furthermore, altered components or substrates of SCF E3 ligases may also be developed as the biomarkers for early diagnosis or predicting prognosis.
BRCA1 mutations account for a significant proportion of familial breast and ovarian cancers. In addition, reduced BRCA1 protein is associated with sporadic cancer cases in these tissues. At the cellular level, BRCA1 plays a critical role in multiple cellular functions such as DNA repair and cell cycle checkpoint control. Its protein level is regulated in a cell cycle-dependent manner. However, regulation of BRCA1 protein stability is not fully understood. Our earlier study showed that the amino terminus of BRCA1 harbors a degron sequence that is sufficient and necessary for conferring BRCA1 degradation. In the current study, we used mass spectrometry to identify Skp1 that regulates BRCA1 protein stability. Small interfering RNA screening that targets all human F-box proteins uncovered FBXO44 as an important protein that influences BRCA1 protein level. The Skp1-Cul1-F-box-protein44 (SCF(FBXO44)) complex ubiquitinates full-length BRCA1 in vitro. Furthermore, the N terminus of BRCA1 mediates the interaction between BRCA1 and FBXO44. Overexpression of SCF(FBXO44) reduces BRCA1 protein level. Taken together, our work strongly suggests that SCF(FBXO44) is an E3 ubiquitin ligase responsible for BRCA1 degradation. In addition, FBXO44 expression pattern in breast carcinomas suggests that SCF(FBXO44)-mediated BRCA1 degradation might contribute to sporadic breast tumor development.
Centrosomes play a crucial role in the maintenance of genome stability by orchestrating bipolar mitotic spindle formation. The centrosome normally duplicates precisely once before mitosis in a process that is extensively regulated by protein degradation including SKP1-Cullin 1 (CUL1)-F-box (SCF) E3 ubiquitin ligase activity. The core SCF component CUL1 has recently been found to be required to suppress the formation of supernumerary centrosomes and centrioles, the core-forming units of centrosomes. Here, we identify the CUL1-interacting protein cullin-associated and neddylation-dissociated 1 (CAND1) as a novel centrosomal protein with a role in centriole duplication control. CAND1 was found to synergize with Polo-like kinase 4 (PLK4), a master regulator of centriole biogenesis, in the induction of centriole overduplication. We provide evidence that CAND1 functions in this process by increasing PLK4 protein stability. Furthermore, mutants of CUL1 that lack the ability to interact with CAND1 and are unable to assemble functional E3 ubiquitin ligase complexes were impaired in their ability to restrain aberrant daughter centriole synthesis. To corroborate a role of CAND1 in human carcinogenesis, we analyzed a series of prostate adenocarcinomas and found altered expression of CAND1 on the mRNA or protein level in 52.9% and 40.8%, respectively, of the tumor samples analyzed. These results highlight the role of altered SCF components in cancer in general and encourage further studies to explore the SCF-CAND1 axis for the development of novel predictive biomarkers and therapeutic approaches in prostate cancer.
Mora-Santos M, Castilla C, Herrero-Ruiz J, et al.A single mutation in Securin induces chromosomal instability and enhances cell invasion.
Eur J Cancer. 2013; 49(2):500-10 [PubMed
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Pituitary tumour transforming gene (pttg1) encodes Securin, a protein involved in the inhibition of sister chromatid separation binding to Separase until the onset of anaphase. Separase is a cysteine-protease that degrades cohesin to segregate the sister chromatids to opposite poles of the cell. The amount of Securin is strongly regulated because it should allow Separase activation when it is degraded by the anaphase promoting complex/cyclosome, should arrest the cell cycle after DNA damage, when it is degraded through SKP1-CUL1-βTrCP ubiquitin ligase, and its overexpression induces tumour formation and correlates with metastasis in multiple tumours. Securin is a phosphoprotein that contains 32 potentially phosphorylatable residues. We mutated and analysed most of them, and found a single mutant, hSecT60A, that showed enhanced oncogenic properties. Our fluorescence activated cell sorting analysis, fluorescence in situ hybridisation assays, tumour cell migration and invasion experiments and gene expression by microarrays analysis clearly involved hSecT60A in chromosomal instability and cell invasion. These results show, for the first time, that a single mutation in pttg1 is sufficient to trigger the oncogenic properties of Securin. The finding of this point mutation in patients might be used as an effective strategy for early detection of cancer.
Zhang L, Zhou F, Li Y, et al.Fas-associated factor 1 is a scaffold protein that promotes β-transducin repeat-containing protein (β-TrCP)-mediated β-catenin ubiquitination and degradation.
J Biol Chem. 2012; 287(36):30701-10 [PubMed
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FAS-associated factor 1 (FAF1) antagonizes Wnt signaling by stimulating β-catenin degradation. However, the molecular mechanism underlying this effect is unknown. Here, we demonstrate that the E3 ubiquitin ligase β-transducin repeat-containing protein (β-TrCP) is required for FAF1 to suppress Wnt signaling and that FAF1 specifically associates with the SCF (Skp1-Cul1-F-box protein)-β-TrCP complex. Depletion of β-TrCP reduced FAF1-mediated β-catenin polyubiquitination and impaired FAF1 in antagonizing Wnt/β-catenin signaling. FAF1 was shown to act as a scaffold for β-catenin and β-TrCP and thereby to potentiate β-TrCP-mediated β-catenin ubiquitination and degradation. Data mining revealed that FAF1 expression is statistically down-regulated in human breast carcinoma compared with normal breast tissue. Consistent with this, FAF1 expression is higher in epithelial-like MCF7 than mesenchymal-like MDA-MB-231 human breast cancer cells. Depletion of FAF1 in MCF7 cells resulted in increased β-catenin accumulation and signaling. Importantly, FAF1 knockdown promoted a decrease in epithelial E-cadherin and an increase in mesenchymal vimentin expression, indicative for an epithelial to mesenchymal transition. Moreover, ectopic FAF1 expression reduces breast cancer cell migration in vitro and invasion/metastasis in vivo. Thus, our studies strengthen a tumor-suppressive function for FAF1.
Surjit M, Varshney B, Lal SKThe ORF2 glycoprotein of hepatitis E virus inhibits cellular NF-κB activity by blocking ubiquitination mediated proteasomal degradation of IκBα in human hepatoma cells.
BMC Biochem. 2012; 13:7 [PubMed
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BACKGROUND: Nuclear factor kappa B (NF-κB) is a key transcription factor that plays a crucial role in host survival during infection by pathogens. Therefore, it has been a priority of many pathogens to manipulate the cellular NF-κB activity in order to create a favorable environment for their survival inside the host.
RESULTS: We observed that heterologous expression of the open reading frame 2 (ORF2) protein in human hepatoma cells led to stabilization of the cellular I kappa B alpha (IκBα) pool, with a concomitant reduction in the nuclear localization of the p65 subunit of NF-κB and inhibition of NF-κB activity. Although basal or TPA induced phosphorylation of IκBα was not altered, its ubiquitination was markedly reduced in ORF2 expressing cells. Further analysis revealed that ORF2 protein could directly associate with the F-box protein, beta transducin repeat containing protein (βTRCP) and ORF2 over expression resulted in reduced association of IκBα with the SKP1 and CUL1 components of the SCFβTRCP complex. Chromatin immunoprecipitation (ChIP) assay of the proximal promoter regions of MHC-I heavy chain and IL-8 genes using p65 antibody and LPS stimulated ORF2 expressing cell extract revealed decreased association of p65 with the above regions, indicating that ORF2 inhibited p65 binding at endogenous promoters.
CONCLUSIONS: In this report we suggest a mechanism by which ORF2 protein of HEV may inhibit host cell NF-κB activity during the course of a viral infection.
Zhu H, Wang Z, Xu Q, et al.Inhibition of STAT1 sensitizes renal cell carcinoma cells to radiotherapy and chemotherapy.
Cancer Biol Ther. 2012; 13(6):401-7 [PubMed
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Renal cell carcinoma is resistant to chemotherapy and radiotherapy. STAT1 is overexpressed in human RCC tissue. Downregulation of STAT1 expression could significantly increase the radiosensitivity in RCC cell lines. To further investigate the function of STAT1 in RCC resistance to chemoradiotherapy, a stable STAT1 knockdown cell line was established. Knockdown of STAT1 led to significant growth suppression in vitro and in vivo. Inhibition of STAT1 sensitized 786-O cells to radiotherapy and Taxol treatment. Cells with low STAT1 expression accumulated more strongly in the G 2/M phase after treatment with chemotherapy and radiotherapy. The Human Cell Cycle and DNA Damage Signaling Pathway Real-time PCR arrays were performed and 3 genes upregulated and 16 genes downregulated after STAT1 knockdown were selected. Functional gene grouping showed that genes involved in the M phase, S phase and DNA replication did not differ between the two cell lines. G 1 phase related genes ANAPC2, CCNE1, CUL1 were downregulated, and G 2/M checkpoint genes p21, GADD45A and Rb were strongly reduced by STAT1 knockdown. DNA damage-related genes GADD45A, MAP2K6, were significantly downregulated. The results prove that overexpression of STAT1 in human RCC is associated with the chemoradioresistance. Targeting of STAT1 might be a potential strategy to sensitize RCC to chemotherapy and radiotherapy.
BCL6 is the product of a proto-oncogene implicated in the pathogenesis of human B-cell lymphomas. By binding specific DNA sequences, BCL6 controls the transcription of a variety of genes involved in B-cell development, differentiation and activation. BCL6 is overexpressed in the majority of patients with aggressive diffuse large B-cell lymphoma (DLBCL), the most common lymphoma in adulthood, and transgenic mice constitutively expressing BCL6 in B cells develop DLBCLs similar to the human disease. In many DLBCL patients, BCL6 overexpression is achieved through translocation (~40%) or hypermutation of its promoter (~15%). However, many other DLBCLs overexpress BCL6 through an unknown mechanism. Here we show that BCL6 is targeted for ubiquitylation and proteasomal degradation by a SKP1–CUL1–F-box protein (SCF) ubiquitin ligase complex that contains the orphan F-box protein FBXO11 (refs 5, 6). The gene encoding FBXO11 was found to be deleted or mutated in multiple DLBCL cell lines, and this inactivation of FBXO11 correlated with increased levels and stability of BCL6. Similarly, FBXO11 was either deleted or mutated in primary DLBCLs. Notably, tumour-derived FBXO11 mutants displayed an impaired ability to induce BCL6 degradation. Reconstitution of FBXO11 expression in FBXO11-deleted DLBCL cells promoted BCL6 ubiquitylation and degradation, inhibited cell proliferation, and induced cell death. FBXO11-deleted DLBCL cells generated tumours in immunodeficient mice, and the tumorigenicity was suppressed by FBXO11 reconstitution. We reveal a molecular mechanism controlling BCL6 stability and propose that mutations and deletions in FBXO11 contribute to lymphomagenesis through BCL6 stabilization. The deletions/mutations found in DLBCLs are largely monoallelic, indicating that FBXO11 is a haplo-insufficient tumour suppressor gene.
Bai J, Zhou Y, Chen G, et al.Overexpression of Cullin1 is associated with poor prognosis of patients with gastric cancer.
Hum Pathol. 2011; 42(3):375-83 [PubMed
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Cullin1 (Cul1) is a scaffold protein of the ubiquitin E3 ligase Skp1/Cullin1/Rbx1/F-box protein complex, which ubiquitinates a broad range of proteins involved in cell-cycle progression, signal transduction, and transcription. To investigate the role of Cullin1 in the development of gastric cancer, we examined the expression of Cullin1 in primary gastric cancer tissues and analyzed the correlation between Cullin1 expression and clinicopathologic variables and patients survival. We constructed a tissue microarray that includes 792 primary gastric cancer tissues and evaluated the Cullin1 expression by immunohistochemistry in the tumor biopsies. We also studied the role of Cullin1 in gastric cancer cell proliferation and adhesion by performing sulforhodamine B cell proliferation assay and cell attachment assay. The Cullin1 overexpression was significantly correlated with gastric cancer TNM stage (P = .011), depth of invasion (P = .035, comparing T1-T3 versus T4), and lymph node metastasis (P = .036). Furthermore, we showed a strong correlation between high Cullin1 expression and worse overall and 3-year survival rates in gastric cancer patients (P = .042 and P = .026, respectively). Cox regression analysis revealed that Cullin1 expression was an independent prognostic factor to predict 3-year patient outcome in gastric cancer (P = .028). Finally, we found that Cullin1 knockdown inhibits cell growth by up-regulating p27 expression and decreases cell adhesion ability by suppressing the expression of Src family kinases and focal adhesion kinase. Our data indicated that Cullin1 may be an important marker for human gastric cancer lymph node metastasis and prognosis.
Chen G, Li GIncreased Cul1 expression promotes melanoma cell proliferation through regulating p27 expression.
Int J Oncol. 2010; 37(5):1339-44 [PubMed
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Cullin1 (Cul1) serves as a rigid scaffold in SCF (Skp1/Cullin/Rbx1/F-box protein) complex, the largest family of ubiquitin-protein E3 ligases, and aberrant expression of Cul1 is involved in dysfunction of SCF E3 ligases. Previously, we found that Cul1 expression is increased in early stages of melanoma. In the present study, we further investigated the role of Cul1 in melanoma development. Our results showed that knockdown of Cul1 inhibits melanoma cell growth while overexpression of Cul1 enhances cell proliferation through the control of cell cycle progression. We also found that Cul1 regulates melanoma cell growth and cell cycle progression through degradation of p27 by functional SCFSkp2 complex. This study elucidates the role of Cul1 in melanoma cell proliferation and improves our understanding of increased expression of Cul1 in early stages of melanoma.
DNA methylation and histone modifications play an important role in transcription regulation. In cancer cells, many promoters become aberrantly methylated through the activity of the de novo DNA methyltransferases DNMT3a and DNMT3b and acquire repressive chromatin marks. NEDD8 is a ubiquitin-like protein modifier that is conjugated to target proteins, such as cullins, to regulate their activity, and cullin 4A (CUL4A) in its NEDD8-modified form is essential for repressive chromatin formation. We found that DNMT3b associates with NEDD8-modified proteins. Whereas DNMT3b interacts directly in vitro with NEDD8, conjugation of NEDD8 to target proteins enhances this interaction in vivo. DNMT3b immunoprecipitated two major bands of endogenously NEDDylated proteins at the size of NEDDylated cullins, and indeed DNMT3b interacted with CUL1, CUL2, CUL3, CUL4A, and CUL5. Moreover, DNMT3b preferentially immunoprecipitated the NEDDylated form of endogenous CUL4A. NEDD8 enhanced DNMT3b-dependent DNA methylation. Chromatin immunoprecipitation assays suggest that DNMT3b recruits CUL4A and NEDD8 to chromatin, whereas deletion of Dnmt3b reduces the association of CUL4A and NEDD8 at a repressed promoter in a cancer cell line.