Gene Summary

Gene:COPS5; COP9 signalosome subunit 5
Aliases: CSN5, JAB1, SGN5, MOV-34
Summary:The protein encoded by this gene is one of the eight subunits of COP9 signalosome, a highly conserved protein complex that functions as an important regulator in multiple signaling pathways. The structure and function of COP9 signalosome is similar to that of the 19S regulatory particle of 26S proteasome. COP9 signalosome has been shown to interact with SCF-type E3 ubiquitin ligases and act as a positive regulator of E3 ubiquitin ligases. This protein is reported to be involved in the degradation of cyclin-dependent kinase inhibitor CDKN1B/p27Kip1. It is also known to be an coactivator that increases the specificity of JUN/AP1 transcription factors. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:COP9 signalosome complex subunit 5
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

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).

Latest Publications: COPS5 (cancer-related)

Lee CC, Yang WH, Li CH, et al.
Ligand independent aryl hydrocarbon receptor inhibits lung cancer cell invasion by degradation of Smad4.
Cancer Lett. 2016; 376(2):211-7 [PubMed] Related Publications
The aryl hydrocarbon receptor (AhR) is a ligand-dependent-activated transcriptional factor that regulates the metabolism of xenobiotic and endogenous compounds. Although AhR plays a crucial role in air toxicant-induced carcinogenesis, AhR expression was shown to negatively regulate tumorigenesis. Therefore, in the present study, we investigated the effect of AhR without ligand treatment on cancer invasion in lung cancer cell lines. Lung cancer cells expressing lower levels of AhR showed higher invasion ability (H1299 cells) compared with cells expressing higher levels of AhR (A549 cells). Overexpression of AhR in H1299 cells inhibited the invasion ability. We found that vimentin expression was inhibited in AhR-overexpressing H1299 cells. Additionally, the expression of EMT-related transcriptional factors Snail and ID-1 decreased. Interestingly, we found that Smad4 degradation was induced in AhR-overexpressing H1299 cells. Our data showed that AhR could interact with Jun-activation domain binding protein (Jab1) and Smad4, which may cause degradation of Smad4 by the proteasome. Our data suggest that AhR affects the transforming growth factor-β signaling pathway by inducing Smad4 degradation by the proteasome and suppressing tumor metastasis via epithelial to mesenchymal transition reduction in lung cancer cells.

Choi HY, Park N, Na JB, et al.
Direct binding of Copine3 with Jab1 activates downstream ErbB2 signaling and motility in SKBr3 breast cancer cells.
Oncol Rep. 2016; 35(2):1147-52 [PubMed] Related Publications
Copine3, a known calcium-dependent membrane binding protein, contains two tandem C2 domains and an A domain. This protein has been shown to interact with receptor tyrosine kinase 2 (ErbB2), but little is known concerning the physiological function of Copine3. To better understand its cellular function, we carried out a yeast two-hybrid screen to find Copine3 binding partners. Among the identified proteins, Jun activation domain-binding protein 1 (Jab1) appears to directly interact with Copine3. This physical interaction between Copine3 and Jab1 as well as the specific binding regions of both proteins were confirmed in vitro and in vivo. Our results also demonstrate that binding of Copine3 to ErbB2 is increased when Jab1 is overexpressed in SKBr3 breast cancer cells. Furthermore, two ErbB2 downstream signaling proteins [phosphatidylinositol 3 (PI3) kinase and protein kinase B (AKT)] were also activated by Jab1 overexpression in these cells. These data suggest that binding of Copine3 and Jab1 regulates, at least to some extent, the ErbB2 signaling pathway. Moreover, overexpression of both Copine3 and Jab1 in SKBr3 cells effectively increased cellular migration. Collectively, our findings indicating that Jab1 enhances the ErbB2 binding ability of Copine3, further activating the ErbB2 signaling pathways involved in breast cancer cell pathogenesis.

Sang MM, Du WQ, Zhang RY, et al.
Suppression of CSN5 promotes the apoptosis of gastric cancer cells through regulating p53-related apoptotic pathways.
Bioorg Med Chem Lett. 2015; 25(15):2897-901 [PubMed] Related Publications
As one of the COP9 signalosome complex, CSN5 (also known as Jab1) has been confirmed overexpression in many human cancers and affected multiple pathways associating with cell proliferation and apoptosis. Correlation of CSN5 overexpression with poor prognosis for cancer provides evidence that it is involved in the tumorigenesis. However, little is known about the functional role and the underlying mechanism of CSN5 in gastric cancer progression. In the current study, the effect of CSN5 siRNA (small-interfering RNA) on the proliferation and apoptosis of human gastric cancer cells (AGS and MKN45) were examined. Our results showed that knockdown of CSN5 could inhibit proliferation and promote apoptosis of gastric cancer cells. Additionally, suppression of CSN5 expression contributed to the increased expression levels of p53 and Bax. In conclusion, CSN5 overexpression is significantly correlated with gastric cancer progression, and CSN5 could be a novel target in gastric cancer therapy.

Zhong G, Li H, Shan T, Zhang N
CSN5 silencing inhibits invasion and arrests cell cycle progression in human colorectal cancer SW480 and LS174T cells in vitro.
Int J Clin Exp Pathol. 2015; 8(3):2809-15 [PubMed] Free Access to Full Article Related Publications
CSN5 has been implicated as a candidate oncogene in human cancers by genetic linkage with activation of the poor-prognosis, wound response gene expression signature. The present study aimed to investigate the effect of silencing CSN5 on invasion and cell cycle progression of human colorectal cancer cells, and to determine the potential molecular mechanisms that are involved. The CSN5 specific small interfering RNA (shRNA) plasmid vector was constructed and then transfected into colorectal cancer cells. The expression of CSN5 mRNA and protein was detected by quantitative polymerase chain reaction and western blot analysis, respectively. Cell adhesion and invasion were analyzed using MTS and Transwell assays, respectively, and cell cycle progression was analyzed using flow cytometry. Adhesion, invasion, and cell cycle distribution were assessed following knockdown of CSN5 by RNA interference (RNAi). Furthermore, knockdown of CSN5 significantly inhibited cell adhesion and reduced the number of invasive cells, while increasing the percentage of cells in the G0/G1 phase (P<0.05). Western blot and real-time PCR analysis were used to identify differentially expressed invasion and cell cycle associated proteins in cells with silenced CSN5. The expression levels of CSN5 in colorectal cancer cells transfected with siRNA were decreased, leading to a significant inhibition of colorectal cancer cell adhesion and invasion. Western blot analysis revealed that silencing of CSN5 may inhibit CD44, matrix metalloproteinase (MMP) 2 and MMP 9 protein expression, significantly promoted cell cycle-related genes P53 and P27 expression. In addition, CSN5 silencing may induce activation PI3K/AKT signal regulated cell invasion. Moreover, CSN5 silencing inhibited the secretion of TGF-β, IL-1β and IL-6 and the transcriptional activity of transcription factor NF-κB and Twist in human colorectal cancer cells. Taken together, down regulation of CSN5 may inhibit invasion and arrests cell cycle progression in colorectal cancer via PI3K/AKT/NF-κB signal pathway, which indicates that there is a potential of targeting CSN5 as a novel gene therapy approach for the treatment of colorectal cancer.

Wang H, Qian Z, Zhao H, et al.
CSN5 silencing reverses sorafenib resistance of human hepatocellular carcinoma HepG2 cells.
Mol Med Rep. 2015; 12(3):3902-8 [PubMed] Related Publications
Hepatocellular carcinoma (HCC) is one of the most common tumor types, and is the third leading cause of cancer mortalities worldwide. A large number of patients with HCC are diagnosed at a late stage when the curative treatment of surgical resection and liver transplantation are no longer applicable. Sorafenib has been proved to improve overall survival in advanced HCC; however, drug resistance is common. The present study reported that the CSN5 is correlated with sorafenib resistance of the HCC cell line HepG2/S. Following silencing of CSN5, resistance to sorafenib was reversed, and multi-drug‑resistance proteins, including as adenosine triphosphate binding cassette (ABC)B1, ABCC2 and ABCG2 as well as CDK6, cyclin D1 and B‑cell lymphoma 2 were downregulated. In addition, it was demonstrated that the integrin beta-1, transforming growth factor‑β1 and nuclear factor‑κB pathways were modified by CSN5.

Okoh VO, Garba NA, Penney RB, et al.
Redox signalling to nuclear regulatory proteins by reactive oxygen species contributes to oestrogen-induced growth of breast cancer cells.
Br J Cancer. 2015; 112(10):1687-702 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: 17β-Oestradiol (E2)-induced reactive oxygen species (ROS) have been implicated in regulating the growth of breast cancer cells. However, the underlying mechanism of this is not clear. Here we show how ROS through a novel redox signalling pathway involving nuclear respiratory factor-1 (NRF-1) and p27 contribute to E2-induced growth of MCF-7 breast cancer cells.
METHODS: Chromatin immunoprecipitation, qPCR, mass spectrometry, redox western blot, colony formation, cell proliferation, ROS assay, and immunofluorescence microscopy were used to study the role of NRF-1.
RESULTS: The major novel finding of this study is the demonstration of oxidative modification of phosphatases PTEN and CDC25A by E2-generated ROS along with the subsequent activation of AKT and ERK pathways that culminated in the activation of NRF-1 leading to the upregulation of cell cycle genes. 17β-Oestradiol-induced ROS by influencing nuclear proteins p27 and Jab1 also contributed to the growth of MCF-7 cells.
CONCLUSIONS: Taken together, our results present evidence in the support of E2-induced ROS-mediated AKT signalling leading to the activation of NRF-1-regulated cell cycle genes as well as the impairment of p27 activity, which is presumably necessary for the growth of MCF-7 cells. These observations are important because they provide a new paradigm by which oestrogen may contribute to the growth of breast cancer.

Zhang ZY, Xu RQ, Guo TJ, et al.
Identification of differently expressed genes in leukemia using multiple microarray datasets.
Genet Mol Res. 2014; 13(4):10482-9 [PubMed] Related Publications
The purpose of this study was to identify differentially expressed genes and analyze biological processes related to leukemia. A meta-analysis was performed using the Rank Product package of Gene Expression Omnibus datasets for leukemia. Next, Gene Ontology-enrichment analysis and pathway analysis were performed using the Gene Ontology website and Kyoto Encyclopedia of Genes and Genomes. A protein-protein interaction network was constructed using the Cytoscape software. Using the Rank Product package for leukemia, we identified a total of 1294 differentially expressed genes, 357 of which were not involved in individual differentially expressed genes. Gene Ontology-enrichment analyses showed that these 357 genes were enriched in biological processes such as mRNA metabolism, RNA splicing, and mRNA processing. Pathway-enrichment analysis showed that the genes were involved in the intestinal immune network for IgA production, endocytosis, and the mitogen-activated protein kinase signaling pathway. The protein-protein interaction network indicated that HRAS, CD44, STAT1, SMAD2, and COPS5 were important in many interactions. Our study revealed genes that were consistently differentially expressed in leukemia, as well as the biological pathways and protein-protein interaction network associated with these genes.

Jumpertz S, Hennes T, Asare Y, et al.
The β-catenin E3 ubiquitin ligase SIAH-1 is regulated by CSN5/JAB1 in CRC cells.
Cell Signal. 2014; 26(9):2051-9 [PubMed] Related Publications
COP9 signalosome subunit 5 (CSN5) plays a decisive role in cellular processes such as cell cycle regulation and apoptosis via promoting protein degradation, gene transcription, and nuclear export. CSN5 regulates cullin-RING-E3 ligase (CRL) activity through its deNEDDylase function. It is overexpressed in several tumor entities, but its role in colorectal cancer (CRC) is poorly understood. Wnt/β-catenin signaling is aberrant in most CRC cells, resulting in increased levels of oncogenic β-catenin and thus tumor progression. Under physiological conditions, β-catenin levels are tightly regulated by continuous proteasomal degradation. We recently showed that knockdown of CSN5 in model and CRC cells results in decreased (phospho)-β-catenin levels. Reduced β-catenin levels were associated with an attenuated proliferation rate of different CRC cell types after CSN5 knockdown. The canonical Wnt pathway involves degradation of β-catenin by a β-TrCP1-containing E3 ligase, but is mostly non-functional in CRC cells. We thus hypothesized that alternative β-catenin degradation mediated by SIAH-1 (seven in absentia homolog-1), is responsible for the effect of CSN5 on β-catenin signaling in CRC cells. We found that SIAH-1 plays an essential role in β-catenin degradation in HCT116 CRC cells and that CSN5 affects β-catenin target gene expression in these cells. Of note, CSN5 affected SIAH-1 mRNA and SIAH-1 protein levels. Moreover, β-catenin and SIAH-1 form protein complexes with CSN5 in HCT116 cells. Lastly, we demonstrate that CSN5 promotes SIAH-1 degradation in HCT116 and SW480 cells and that this is associated with its deNEDDylase activity. In conclusion, we have identified a CSN5/β-catenin/SIAH-1 interaction network that might control β-catenin degradation in CRC cells.

Bhansali M, Shemshedini L
COP9 subunits 4 and 5 target soluble guanylyl cyclase α1 and p53 in prostate cancer cells.
Mol Endocrinol. 2014; 28(6):834-45 [PubMed] Free Access to Full Article Related Publications
Our laboratory previously has identified soluble guanylyl cyclase α1 (sGCα1) as a direct target of androgen receptor and essential for prostate cancer cell growth via a pathway independent of nitric oxide (NO) signaling. We identified the COP9 signalosome subunit 4 (CSN4) as a novel interacting partner for sGCα1. Importantly, the CSN4-sGCα1 interaction inhibits sGCα1 proteasomal degradation. Consistent with this, disruption of CSN4 led to a significant decrease in prostate cancer cell proliferation, which was significantly but not completely rescued by sGCα1 overexpression, opening the possibility of an additional target of CSN4. Interestingly, immunoprecipitation experiments showed that p53 is found in the CSN4-sGCα1 cytoplasmic protein complex. However, in contrast to sGCα1, p53 protein stability was compromised by CSN4, leading to prostate cancer cell survival and proliferation. Interestingly, we observed that CSN4 was overexpressed in prostate tumors, and its protein level correlates directly with sGCα1 and inversely with p53 proteins, mimicking what was observed in prostate cancer cells. Our data further showed that CSN4 silencing decreased CSN5 protein levels and suggest that the CSN4 effects on sGCα1 and p53 proteins are mediated by CSN5. Lastly, our study showed that caseine kinase-2 (CK2) was involved in regulating p53 and sGCα1 protein stability as determined by both disruption of CK2 expression and inhibition of its kinase activity. Collectively, our study has identified a novel endogenous CSN4-CSN5-CK2 complex with sGCα1and p53 that oppositely controls the stability of these 2 proteins and provides prostate cancer cells an important mechanism for survival and proliferation.

Nagarajan A, Dogra SK, Liu AY, et al.
PEA15 regulates the DNA damage-induced cell cycle checkpoint and oncogene-directed transformation.
Mol Cell Biol. 2014; 34(12):2264-82 [PubMed] Free Access to Full Article Related Publications
Regulation of the DNA damage response and cell cycle progression is critical for maintaining genome integrity. Here, we report that in response to DNA damage, COPS5 deubiquitinates and stabilizes PEA15 in an ATM kinase-dependent manner. PEA15 expression oscillates throughout the cell cycle, and the loss of PEA15 accelerates cell cycle progression by activating CDK6 expression via the c-JUN transcription factor. Cells lacking PEA15 exhibit a DNA damage-induced G2/M checkpoint defect due to increased CDC25C activity and, consequentially, higher cyclin-dependent kinase 1 (CDK1)/cyclin B activity, and accordingly they have an increased rate of spontaneous mutagenesis. We find that oncogenic RAS inhibits PEA15 expression and that ectopic PEA15 expression blocks RAS-mediated transformation, which can be partially rescued by ectopic expression of CDK6. Finally, we show that PEA15 expression is downregulated in colon, breast, and lung cancer samples. Collectively, our results demonstrate that tumor suppressor PEA15 is a regulator of genome integrity and is an integral component of the DNA damage response pathway that regulates cell cycle progression, the DNA-damage-induced G2/M checkpoint, and cellular transformation.

Liu N, Liu X, Zhou N, et al.
Gene expression profiling and bioinformatics analysis of gastric carcinoma.
Exp Mol Pathol. 2014; 96(3):361-6 [PubMed] Related Publications
Gastric cancer remains one of the major health problems worldwide, and it is one of the most common cancers and the leading cause of cancer-related deaths in China. This study was to analyze the expression profiles of genes in gastric carcinoma, and predict potential regulating factors. The gene expression profile data GSE13911 was downloaded from Gene Expression Omnibus and the differentially expressed genes (DEGs) were identified by t-test. Gene modules were constructed using hierarchical clustering in R based on average linkage and Pearson's correlation coefficient and functional analysis for these genes were performed with DAVID. Genes in each module with Pearson's correlation coefficient >0.3 were obtained to construct co-expression network. Protein-protein interactions (PPIs) were identified by comparing protein-protein interaction (PPI) network with co-expression networks. In addition, the potential regulatory microRNAs and the transcription factors for each module were screened out. In this study, six modules associated with protein degradation, cell cycle, protein trafficking and immunoreaction were identified. COPS5 (COP9 Subunit 5) was the core protein in the largest PPI network of module 1. The transcription factors MYC and MAZ (Myc-associated zinc-finger protein) were enriched in module 1. A total of 9 microRNA-target bi-clusters were identified and module 1 enriched 20 genes targeting to miR-17-92 gene cluster(miR-17/20ab)and miR-106b-25 gene cluster (miR-106b/93). In conclusion, we constructed 6 gene modules and screened out some genes, transcriptional factors and microRNAs that may be used as potential molecular biomarkers for gastric carcinoma.

Wu XQ, Huang C, He X, et al.
Feedback regulation of telomerase reverse transcriptase: new insight into the evolving field of telomerase in cancer.
Cell Signal. 2013; 25(12):2462-8 [PubMed] Related Publications
Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase, especially the rate-limiting determinant of telomerase activity. So far, TERT has been reported to be over-expressed in more than 90% of cancers, thereby playing a critical role in sustained proliferation and survival potentials of various cancer cells. Over the past decade, a comprehensive network of transcription factors has been shown to be involved in the regulation of TERT. Furthermore, accumulating evidence has suggested that TERT could modulate the expression of numerous genes involved in diverse group of cellular processes, including cell cycle regulation and cellular signaling. Therefore, it indicates that TERT is both an effector and a regulator in carcinoma. However, the mechanisms of the interaction between TERT and its target genes are still not fully understood. Thus, it is necessary to consolidate and summarize recent developments of the cross-talk between TERT and related genes in cancer cells or other cells with cancer cell characteristics, and elucidate these relevant mechanisms. In this review, we focus on various signaling pathways and genes that participate in the feedback regulation of TERT and the underlying feedback loop mechanism of TERT, further providing new insights into non-telomeric functions of telomerase and potentially to be used as a novel therapeutic target for cancer.

Nishimoto A, Kugimiya N, Hosoyama T, et al.
JAB1 regulates unphosphorylated STAT3 DNA-binding activity through protein-protein interaction in human colon cancer cells.
Biochem Biophys Res Commun. 2013; 438(3):513-8 [PubMed] Related Publications
Recent studies have revealed that unphosphorylated STAT3 forms a dimer, translocates to the nucleus, binds to the STAT3 binding site, and activates the transcription of STAT3 target genes, thereby playing an important role in oncogenesis in addition to phosphorylated STAT3. Among signaling steps of unphosphorylated STAT3, nuclear translocation and target DNA-binding are the critical steps for its activation. Therefore, elucidating the regulatory mechanism of these signaling steps of unphosphorylated STAT3 is a potential step in the discovery of a novel cancer drug. However, the mechanism of unphosphorylated STAT3 binding to the promoter of target genes remains unclear. In this study, we focused on Jun activation domain-binding protein 1 (JAB1) as a candidate protein that regulates unphosphorylated STAT3 DNA-binding activity. Initially, we observed that both unphosphorylated STAT3 and JAB1 existed in the nucleus of human colon cancer cell line COLO205 at the basal state (no cytokine stimulation). On the other hand, phosphorylated STAT3 did not exist in the nucleus of COLO205 cells at the basal state. Immunoprecipitation using nuclear extract of COLO205 cells revealed that JAB1 interacted with unphosphorylated STAT3. To investigate the effect of JAB1 on unphosphorylated STAT3 activity, RNAi studies were performed. Although JAB1 knockdown tended to increase nuclear STAT3 expression, it significantly decreased unphosphorylated STAT3 DNA-binding activity. Subsequently, JAB1 knockdown significantly decreased the expression levels of MDR1, NANOG, and VEGF, which are STAT3 target genes. Furthermore, the expression level of nuclear JAB1, but not nuclear STAT3, correlated with unphosphorylated STAT3 DNA-binding activity between COLO205 and LoVo cells. Taken together, these results suggest that nuclear JAB1 positively regulates unphosphorylated STAT3 DNA-binding activity through protein-protein interaction in human colon cancer cell line COLO205.

Tsujimoto I, Yoshida A, Yoneda-Kato N, Kato JY
Depletion of CSN5 inhibits Ras-mediated tumorigenesis by inducing premature senescence in p53-null cells.
FEBS Lett. 2012; 586(24):4326-31 [PubMed] Related Publications
The mammalian COP9 signalosome (CSN) complex is involved in cell transformation, but its molecular mechanism remains undetermined. Here we show that disruption of the fifth component (CSN5) prevented the formation of tumors by p53-null cells transformed with an active form of Ras in subcutaneously injected mice. Depletion of CSN5 suppressed cell proliferation, and induced premature senescence characterized by upregulation of senescence-associated-β-galactosidase activity and increased expression of CDK inhibitors. CSN5-depleted cells exhibited enhanced activation of the PI3 kinase-Akt pathway, and chemical inhibition of this pathway reduced the level of senescence. Thus, CSN5 is suggested to be a novel target in cancer therapy and for drugs against tumor cells harboring mutated p53.

Wei S, Chu PC, Chuang HC, et al.
Targeting the oncogenic E3 ligase Skp2 in prostate and breast cancer cells with a novel energy restriction-mimetic agent.
PLoS One. 2012; 7(10):e47298 [PubMed] Free Access to Full Article Related Publications
Substantial evidence supports the oncogenic role of the E3 ubiquitin ligase S-phase kinase-associated protein 2 (Skp2) in many types of cancers through its ability to target a broad range of signaling effectors for ubiquitination. Thus, this oncogenic E3 ligase represents an important target for cancer drug discovery. In this study, we report a novel mechanism by which CG-12, a novel energy restriction-mimetic agent (ERMA), down-regulates the expression of Skp2 in prostate cancer cells. Pursuant to our previous finding that upregulation of β-transducin repeat-containing protein (β-TrCP) expression represents a cellular response in cancer cells to ERMAs, including CG-12 and 2-deoxyglucose, we demonstrated that this β-TrCP accumulation resulted from decreased Skp2 expression. Evidence indicates that Skp2 targets β-TrCP for degradation via the cyclin-dependent kinase 2-facilitated recognition of the proline-directed phosphorylation motif (412)SP. This Skp2 downregulation was attributable to Sirt1-dependent suppression of COP9 signalosome (Csn)5 expression in response to CG-12, leading to increased cullin 1 neddylation in the Skp1-cullin1-F-box protein complex and consequent Skp2 destabilization. Moreover, we determined that Skp2 and β-TrCP are mutually regulated, providing a feedback mechanism that amplifies the suppressive effect of ERMAs on Skp2. Specifically, cellular accumulation of β-TrCP reduced the expression of Sp1, a β-TrCP substrate, which, in turn, reduced Skp2 gene expression. This Skp2-β-TrCP-Sp1 feedback loop represents a novel crosstalk mechanism between these two important F-box proteins in cancer cells with aberrant Skp2 expression under energy restriction, which provides a proof-of-concept that the oncogenic Csn5/Skp2 signaling axis represents a "druggable" target for this novel ERMA.

Hu MD, Xu JC, Fan Y, et al.
Hypoxia-inducible factor 1 promoter-induced JAB1 overexpression enhances chemotherapeutic sensitivity of lung cancer cell line A549 in an anoxic environment.
Asian Pac J Cancer Prev. 2012; 13(5):2115-20 [PubMed] Related Publications
The presence of lung cancer cells in anoxic zones is a key cause od chemotherapeutic resistance. Thus, it is necessary to enhance the sensitivity of such lung cancer cells. However, loss of efficient gene therapeutic targeting and inefficient objective gene expression in the anoxic zone in lung cancer are dilemmas. In the present study, a eukaryotic expression plasmid pUC57-HRE-JAB1 driven by a hypoxia response elements promoter was constructed and introduced into lung cancer cell line A549. The cells were then exposed to a chemotherapeutic drug cis-diamminedichloroplatinum (C-DDP). qRT-PCR and western blotting were used to determine the mRNA and protein level and flow cytometry to examine the cell cycle and apoptosis of A549 transfected pUC57-HRE-JAB1. The results showed that JAB1 gene in the A549 was overexpressed after the transfection, cell proliferation being arrested in G1 phase and the apoptosis ratio significantly increased. Importantly, introduction of pUC57-HRE-JAB1 significantly increased the chemotherapeutic sensitivity of A549 in an anoxic environment. In conclusion, JAB1 overexpression might provide a novel strategy to overcome chemotherapeutic resistance in lung cancer.

Pan Y, Claret FX
Targeting Jab1/CSN5 in nasopharyngeal carcinoma.
Cancer Lett. 2012; 326(2):155-60 [PubMed] Free Access to Full Article Related Publications
Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus-associated head and neck cancer that is most common in eastern Asia. Epstein-Barr virus infection, environmental factors, and genetic susceptibility play important roles in NPC pathogenesis. Jab1/CSN5 is a multifunctional protein that participates in affecting integrin signaling, controlling cell proliferation and apoptosis, and regulating genomic instability and DNA repair. Correlation of Jab1/CSN5 overexpression with poor prognosis for NPC provides evidence that it is involved in the tumorigenic process. In this review, we highlight recent advances in studies of the oncogenic role of Jab1/CSN5 in NPC and its potential as a therapeutic target for this cancer.

Schütz AK, Hennes T, Jumpertz S, et al.
Role of CSN5/JAB1 in Wnt/β-catenin activation in colorectal cancer cells.
FEBS Lett. 2012; 586(11):1645-51 [PubMed] Related Publications
CSN5/JAB1 is a critical subunit of the COP9 signalosome (CSN) and is overexpressed in many human cancers, but little is known about the role of CSN5 in colorectal cancer (CRC). To explore the functional role of CSN5 in colorectal tumorigenesis, we applied siRNA technology to silence CSN5 in HeLa, SW480, HCT116, HT29, and CaCo2 cells. CSN5 knock-down led to reduced β-catenin and phospho-bcatenin levels and this was paralleled by reduced CRC cell proliferation and reduced apoptosis rates, whereas the short-term β-catenin protein stability was enhanced by CSN5 knock-down in SW480 cells. Together, these data implicate the CSN in the pathogenesis of CRC via regulation of the Wnt/β-catenin pathway

Yang KT, Wang MC, Chen JY, et al.
Bcr-Abl oncogene stimulates Jab1 expression via cooperative interaction of β-catenin and STAT1 in chronic myeloid leukemia cells.
J Cell Physiol. 2011; 226(11):2849-56 [PubMed] Related Publications
Jab1, a co-activator of AP-1 transcription factor and the fifth subunit of the COP9 signalosome, mediates degradation of the tumor suppressor p53 and p27(Kip1) and functions as a tumor promoter in different types of human cancer. In this study, we show that inhibition of Bcr-Abl oncogene by imatinib induces down-regulation of Jab1 in Bcr-Abl-positive K562, Ku812, and MEG01 leukemia cells suggesting Bcr-Abl may regulate Jab1 expression. Promoter deletion and mutation analysis indicate the Tcf-4/β-catenin and STAT1 binding sites located between the -405/-223 region of the human Jab1 promoter are important for the activation of Jab1 by Bcr-Abl. Double mutation of these two sites reverses the inhibitory effect of imatinib. Chromatin immunoprecipitation assay verifies the binding of β-catenin and STAT1 to human Jab1 promoter. Ectopic expression of dominant-negative Tcf-4 mutant significantly attenuates Jab1 expression while over-expression of β-catenin and STAT1 cooperatively up-regulates Jab1 promoter activity and mRNA expression. Our results also demonstrate that the AKT signaling pathway is involved in the regulation of Jab1 by Bcr-Abl because the AKT inhibitor LY294002 but not the ERK inhibitor PD98059 reduces Jab1 promoter activity and mRNA expression. Taken together, our results suggest that Bcr-Abl stimulates Jab1 expression via the cooperative interaction of β-catenin and STAT1 in leukemia cells.

Lee MH, Zhao R, Phan L, Yeung SC
Roles of COP9 signalosome in cancer.
Cell Cycle. 2011; 10(18):3057-66 [PubMed] Free Access to Full Article Related Publications
The constitutive photomorphogenesis 9 signalosome (COP9 or CSN) is an evolutionarily conserved multiprotein complex found in plants and animals. Because of the homology between the COP9 signalosome and the 19S lid complex of the proteosome, COP9 has been postulated to play a role in regulating the degradation of polyubiquitinated proteins. Many tumor suppressor and oncogene products are regulated by ubiquitination- and proteosome-mediated protein degradation. Therefore, it is conceivable that COP9 plays a significant role in cancer, regulating processes relevant to carcinogenesis and cancer progression (e.g., cell cycle control, signal transduction and apoptosis). In mammalian cells, it consists of eight subunits (CSN1 to CSN8). The relevance and importance of some subunits of COP9 to cancer are emerging. However, the mechanistic regulation of each subunit in cancer remains unclear. Among the CSN subunits, CSN5 and CSN6 are the only two that each contain an MPN (Mpr1p and Pad1p N-terminal) domain. The deneddylation activity of an MPN domain toward cullin-RING ubiquitin ligases (CRL) may coordinate CRL-mediated ubiquitination activity. More recent evidence shows that CSN5 and CSN6 are implicated in ubiquitin-mediated proteolysis of important mediators in carcinogenesis and cancer progression. Here, we discuss the mechanisms by which some CSN subunits are involved in cancer to provide a much needed perspective regarding COP9 in cancer research, hoping that these insights will lay the groundwork for cancer intervention.

Merk M, Zierow S, Leng L, et al.
The D-dopachrome tautomerase (DDT) gene product is a cytokine and functional homolog of macrophage migration inhibitory factor (MIF).
Proc Natl Acad Sci U S A. 2011; 108(34):E577-85 [PubMed] Free Access to Full Article Related Publications
Macrophage migration inhibitory factor (MIF) is a pivotal regulator of the immune response. Neutralization or genetic deletion of MIF does not completely abrogate activation responses, however, and deletion of the MIF receptor, CD74, produces a more pronounced phenotype than MIF deficiency. We hypothesized that these observations may be explained by a second MIF-like ligand, and we considered a probable candidate to be the protein encoded by the homologous, D-dopachrome tautomerase (D-DT) gene. We show that recombinant D-DT protein binds CD74 with high affinity, leading to activation of ERK1/2 MAP kinase and downstream proinflammatory pathways. Circulating D-DT levels correlate with disease severity in sepsis or malignancy, and the specific immunoneutralization of D-DT protects mice from lethal endotoxemia by reducing the expression of downstream effector cytokines. These data indicate that D-DT is a MIF-like cytokine with an overlapping spectrum of activities that are important for our understanding of MIF-dependent physiology and pathology.

Shackleford TJ, Zhang Q, Tian L, et al.
Stat3 and CCAAT/enhancer binding protein beta (C/EBP-beta) regulate Jab1/CSN5 expression in mammary carcinoma cells.
Breast Cancer Res. 2011; 13(3):R65 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: The c-Jun coactivator, Jun activation-domain binding protein 1 (Jab1) also known as the fifth component of the COP9 signalosome complex (CSN5), is a novel candidate oncogene whose aberrant expression contributes to the progression of breast carcinoma and other human cancers. The mechanism of Jab1 gene expression and its deregulation in cancer cells remains to be identified. We therefore investigated the transcriptional regulatory mechanisms of Jab1 expression in human breast carcinoma cells.
METHODS: To identify potential regulators of Jab1 transcription, we cloned the 5' upstream region of the human Jab1 gene and mapped its transcriptional start site. We identified binding sequences for the CCAAT/enhancer binding protein (C/EBP) and GATA, as well as a signal transducer and activator of transcription-3 (Stat3) consensus sequence overlapping the C/EBP site, using 5'- deletion analysis and a gene reporter assay. Mutational analysis of these binding sites was performed to confirm their roles in promoting Jab1 transcription in breast cancer cells. We further confirmed these binding sites using electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP) assays. We also analyzed whether the siRNA-mediated inactivation of Stat3 and Src could reduce Jab1-promoter activity and whether interleukine-6 (IL-6) could mediate increased Jab1 expression through Stat3 signaling.
RESULTS: We identified binding sequences for C/EBP, GATA, as well as a Stat3 consensus sequence overlapping the C/EBP site in the promoter region of Jab1. C/EBP-beta2 is a potential transcriptional activator of Jab1 and mutation of the C/EBP/Stat3 binding site significantly reduced Jab1-promoter activity. In addition, inhibiting Stat3 significantly reduced Jab1-promoter activation. EMSA and ChIP assays confirmed that C/EBP, GATA1 and Stat3 bind to Jab1 promoter in breast carcinoma cells. We also found that Src, an activator of Stat3, is involved in Jab1-promoter activation. siRNA knockdown of Src reduced the Jab1-promoter activity, similar to the results seen when Stat3 was inhibited in breast carcinoma cells. Interestingly, reactivation of Stat3 in normal mammary epithelial cells (MCF-10A, MCF-10F) is sufficient to reactivate Jab1 expression. Treatment with the cytokine IL-6 resulted in increased Jab1 expression that was blocked by inhibition of Stat3.
CONCLUSIONS: These findings reveal a novel mechanism of Jab1 gene regulation and provide functional and mechanistic links between the Src/Stat3 and IL-6/Stat3 signaling axes that are involved in the activation of Jab1 transcription and regulation of this novel oncogenic protein.

Lee YH, Judge AD, Seo D, et al.
Molecular targeting of CSN5 in human hepatocellular carcinoma: a mechanism of therapeutic response.
Oncogene. 2011; 30(40):4175-84 [PubMed] Free Access to Full Article Related Publications
Development of targeted therapy for hepatocellular carcinoma (HCC) remains a major challenge. We have recently identified an elevated expression of the fifth subunit of COP9 signalosome (CSN5) in early HCC as compared with dysplastic stage. In the present study, we explored the possibility of CSN5 being a potential therapeutic target for HCC. Our results show that CSN5 knockdown by small-interfering (si) RNA caused a strong induction of apoptosis and inhibition of cell-cycle progression in HCC cells in vitro. The down-regulation of CSN5 was sufficient to interfere with CSN function as evidenced by the accumulation of neddylated Cullin 1 and changes in the protein levels of CSN-controlled substrates SKP2, p53, p27 and nuclear factor-κB, albeit to a different degree depending on the HCC cell line, which could account for the CSN5 knockdown phenotype. The transcriptomic analysis of CSN5 knockdown signature showed that the anti-proliferative effect was driven by a common subset of molecular alterations including down-regulation of cyclin-dependent kinase 6 (CDK6) and integrin β1 (ITGB1), which were functionally interconnected with key oncogenic regulators MYC and TGFβ1 involved in the control of proliferation, apoptotic cell death and HCC progression. Consistent with microarray analysis, western blotting revealed that CSN5 depletion increased phosphorylation of Smad 2/3, key mediators of TGFβ1 signaling, decreased the protein levels of ITGB1, CDK6 and cyclin D1 and caused reduced expression of anti-apoptotic Bcl-2, while elevating the levels of pro-apoptotic Bak. A chemically modified variant of CSN5 siRNA was then selected for in vivo application based on the growth inhibitory effect and minimal induction of unwanted immune response. Systemic delivery of the CSN5 3/8 variant by stable-nucleic-acid-lipid particles significantly suppressed the tumor growth in Huh7-luc+ orthotopic xenograft model. Taken together, these results indicate that CSN5 has a pivotal role in HCC pathogenesis and maybe an attractive molecular target for systemic HCC therapy.

Shi Y, Chen J, Li Z, et al.
C10ORF97 is a novel tumor-suppressor gene of non-small-cell lung cancer and a functional variant of this gene increases the risk of non-small-cell lung cancer.
Oncogene. 2011; 30(39):4107-17 [PubMed] Related Publications
In an earlier study we showed that C10ORF97 (chromosome-10, open reading frame-97) was expressed in almost all of the tissues and cell lines tested, and that it inhibited the growth of seven tumor cell lines, including two lung carcinoma cell lines (A549 and PG). Here, we show that C10ORF97 is downregulated in non-small-cell lung cancer (NSCLC) tissue compared with normal lung tissue. Overexpression of C10ORF97 significantly suppressed human lung carcinoma A549 cell growth (proliferation and anchorage-independent growth in soft agar) and motility (migration and adhesion). This tumor-suppressive function of C10ORF97 was also verified in vivo. We further found that C10ORF97 caused G(1) arrest of A549 cells and modulated the expression level of several cell-cycle regulators (such as CDK2, cyclin-E and p27). These effects of C10ORF97 were mediated by physical association between C10ORF97 and Jun-activating domain-binding protein-1 (JAB1), and blocking of JAB1-mediated translocation of p27 from the nucleus to the cytoplasm. Together, these results indicated that C10ORF97 functions as a novel tumor suppressor by modulating several key G(1)/S-regulatory proteins by interacting with JAB1. These findings led us to hypothesize that a single-nucleotide polymorphism (SNP) in the C10ORF97 gene that affects its expression might be associated with susceptibility to NSCLC. SNP216 C>T (rs2297882) in the C10ORF97 Kozak sequence was identified, and allele T of SNP216 suppressed C10ORF97 expression in vitro and in vivo. Furthermore, the TT genotype of SNP216 was associated with an increased risk of NSCLC (adjusted odds ratio=1.73 (95% confidence interval: 1.33-2.25), P=4.6 × 10(-5)). These data indicated that C10ORF97 is a tumor suppressor of NSCLC progression and C10ORF97-SNP216 may serve as a predictor of NSCLC.

Chen MC, Chen CH, Chuang HC, et al.
Novel mechanism by which histone deacetylase inhibitors facilitate topoisomerase IIα degradation in hepatocellular carcinoma cells.
Hepatology. 2011; 53(1):148-59 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Histone deacetylase (HDAC) inhibitors exhibit a unique ability to degrade topoisomerase (topo)IIα in hepatocellular carcinoma (HCC) cells, which contrasts with the effect of topoII-targeted drugs on topoIIβ degradation. This selective degradation might foster novel strategies for HCC treatment in light of the correlation of topoIIα overexpression with the aggressive tumor phenotype and chemoresistance. Here we report a novel pathway by which HDAC inhibitors mediate topoIIα proteolysis in HCC cells. Our data indicate that HDAC inhibitors transcriptionally activated casein kinase (CK)2α expression through increased association of acetylated histone H3 with the CK2α gene promoter. In turn, CK2 facilitated the binding of topoIIα to COP9 signalosome subunit (Csn)5 by way of topoIIα phosphorylation. Furthermore, we identified Fbw7, a Csn5-interacting F-box protein, as the E3 ligase that targeted topoIIα for degradation. Moreover, knockdown of CK2α, Csn5, or Fbw7 reversed HDAC inhibitor-induced topoIIα degradation. Mutational analysis indicates that the (1361) SPKLSNKE(1368) motif plays a crucial role in regulating topoIIα protein stability. This motif contains the consensus recognition sites for CK2 (SXXE), glycogen synthase kinase (GSK)3β (SXXXS), and Fbw7 (SPXXS). This study also reports the novel finding that topoIIα may be a target of GSK3β phosphorylation. Evidence suggests that CK2 serves as a priming kinase, through phosphorylation at Ser1365, for GSK3β-mediated phosphorylation at Ser1361. This double phosphorylation facilitated the recruitment of Fbw7 to the phospho-degron (1361) pSPKLpS(1365) of topoIIα, leading to its ubiquitin-dependent degradation.
CONCLUSION: This study shows a novel pathway by which HDAC inhibitors facilitate the selective degradation of topoIIα, which underlies the complexity of the functional role of HDAC in regulating tumorigenesis and aggressive phenotype in HCC cells.

Shiraso S, Katayose Y, Yamamoto K, et al.
Overexpression of adenovirus-mediated p27kip1 lacking the Jab1-binding region enhances cytotoxicity and inhibits xenografted human cholangiocarcinoma growth.
Anticancer Res. 2009; 29(6):2015-24 [PubMed] Related Publications
The cyclin-dependent kinase inhibitor (CDK1) p27(kip1) is a negative regulator of cell cycling and has antitumor effects. In our previous study, the recombinant adenovirus expressing wild-type p27(kip1) (Adp27-wt) induced cell cycle arrest and apoptosis, and proved that p27 is a tumor suppressor gene like p53. Another adenovirus vector expressing mutant p27(kip1) (Adp27-mt), which inhibited degradation by the ubiquitin-proteasome system, showed increased protein stability and caused a stronger induction of apoptosis. Recently, the p27(kip1) protein binding with Jab1 (Jun activating binding protein 1) was found to translocate from the nucleus into the cytosol, and then become degraded by the 26S proteasome system. The inhibition of nuclear-cytoplasmic translocation increases the protein stability of p27(kip1) and p27(kip1) with a deletion of the Jab1-binding region (p27-jab-d) is not translocated and not degraded. Therefore, a new recombinant adenovirus (Adp27-jab-d) expressing p27-jab-d was made which was able to induce greater cytotoxicity. Adp27-jab-d inhibited the growth of human cholangiocarcinoma cell line (TFK-1) cells in vitro at 3.3 times (IC(50)) lower concentration than Adp27-wt. Moreover, in a xenografted severe combined immuno-deficient (SCID) mouse model injected with TFK-1 cells in the subcutaneous tissue, treatment by intratumor injection of Adp27-jab-d once a day for 3 days after the tumor was established, inhibited tumor growth more strongly than Adp27-wt or Adp27-mt and even induced tumor regression. However, the flow cytometric TUNEL assay showed little enhancement of apoptosis. Adp27-jab-d was thought to induce not only apoptosis but also necrosis, which was due to a specific effect of the Adp27-jab-d. Thus, by enhancing the cytotoxicity through inhibiting the translocaton of p27(kip1), p27(kip1) lacking the Jab1-binding region might be useful for cancer therapy. The control protein localization might also be a new target not only for cancer treatment, but also other diseases.

Ahn J, Hong SA, Lee SE, et al.
Cytoplasmic localization of Jab1 and p27 Kip1 might be associated with invasiveness of papillary thyroid carcinoma.
Endocr J. 2009; 56(5):707-13 [PubMed] Related Publications
p27(kip1) is a well known negative regulator of cell cycle progression. Jab1 directly binds to p27(kip1) and induces nuclear export and subsequent degradation. Recent studies have shown that overexpression of Jab1 and reduced expression of p27(kip1) are associated with advanced tumor stage and poor prognosis in several human cancers. Here, we evaluated 50 papillary thyroid carcinomas (PTC) and adjacent normal thyroid tissue samples by immunohistochemistry for Jab1 and p27(kip1) to elucidate expression levels and subcellular localization. Expression of Jab1 was markedly increased and that of p27(kip1) was reduced in the tumors compared with paired normal samples. Jab1 expression was inversely related to p27(kip1) expression. Jab1 was especially overexpressed within the invasive region compared to center of the tumors. Among clinicopathologic parameters, only tumor size was related with Jab1 (positively) and p27(kip1) expression (negatively) in the invasive region of the tumors. Both Jab1 and p27(kip1) were found predominantly in the cytoplasm of the tumor cells from the invasive regions compared to center of the tumors. The Ki-67 proliferative index was higher in the invasive region than in center of the tumors. A much stronger correlation with the Ki-67 index was noted when both Jab1 and p27(kip1) were simultaneously localized in the cytoplasm than when either Jab1 or p27(kip1) was localized in the cytoplasm alone. These data suggest that in addition to overexpression of Jab1 and reduced expression of p27(kip1), cytoplasmic localization of Jab1 and p27(kip1) are associated with increased cancer cell proliferation and might be related to the invasiveness of PTC.

Yabuuchi S, Katayose Y, Oda A, et al.
ZD1839 (IRESSA) stabilizes p27Kip1 and enhances radiosensitivity in cholangiocarcinoma cell lines.
Anticancer Res. 2009; 29(4):1169-80 [PubMed] Related Publications
The prognosis of cholangiocarcinoma patients is extremely poor despite the aggressive multidisciplinary cancer therapies that have been used clinically (1). Recently, molecular target therapy has attracted attention. Epidermal growth factor receptor (EGFR) tyrosine kinase (TK) is a promising target for anticancer therapy. ZD1839 (IRESSA) is an orally active, selective inhibitor of EGFR-TK. This study examined the effects of ZD1839 in TFK-1 and HuCCT1, the human cholangiocarcinoma cell lines that express EGFR. Somatic mutations in the TK domain of the EGFR gene are associated with the sensitivity of lung cancers to ZD1839 (2). In the analysis of the EGFR sequence, no mutations were found in TFK-1 and HuCCT1. The TFK-1 and HuCCT1 cells showed almost the same sensitivity to ZD1839. It is shown that ZD1839 induced apoptotic cell death of TFK-1 cells as indicated by apoptotic morphological changes and an enhancement of TUNEL-positive cells. ZD1839 produced a dose-dependent inhibition of cellular proliferation in TFK-1. Cell cycle analysis demonstrated that ZD1839 induces G1 arrest. Moreover, concurrent evaluation of the expression of p27(Kip1) protein and Jun activating domain-binding protein 1 (Jab1) with ZD1839 by Western blotting analysis was performed. It was found that ZD1839 activity causes an increase of p27(Kip1) stability that correlates with Jab1 down-regulation. Thus, ZD1839 affects key cellular pathways, controlling cell proliferation and apoptosis. Furthermore, the treatment of TFK-1 with ZD1839 reduced the cell survival after radiation exposure. ZD1839 in combination with radiation produced a dose-dependent and synergic inhibitory effect on cellular proliferation. In conclusion, these results suggest that ZD1839 may have clinical activity against cholangiocarcinoma.

Kaposi-Novak P, Libbrecht L, Woo HG, et al.
Central role of c-Myc during malignant conversion in human hepatocarcinogenesis.
Cancer Res. 2009; 69(7):2775-82 [PubMed] Free Access to Full Article Related Publications
Hepatocarcinogenesis is a multistage process in which precursor lesions progress into early hepatocellular carcinomas (eHCC) by sequential accumulation of multiple genetic and epigenetic alterations. To decode the molecular events during early stages of liver carcinogenesis, we performed gene expression profiling on cirrhotic (regenerative) and dysplastic nodules (DN), as well as eHCC. Although considerable heterogeneity was observed at the regenerative and dysplastic stages, overall, 460 differentially expressed genes were detected between DN and eHCC. Functional analysis of the significant gene set identified the MYC oncogene as a plausible driver gene for malignant conversion of the DNs. In addition, gene set enrichment analysis revealed global activation of the MYC up-regulated gene set in eHCC versus dysplasia. Presence of the MYC signature significantly correlated with increased expression of CSN5, as well as with higher overall transcription rate of genes located in the 8q chromosome region. Furthermore, a classifier constructed from MYC target genes could robustly discriminate eHCC from high-grade and low-grade DNs. In conclusion, our study identified unique expression patterns associated with the transition of high-grade DNs into eHCC and showed that activation of the MYC transcription signature is strongly associated with the malignant conversion of preneoplastic liver lesions.

Mori M, Yoneda-Kato N, Yoshida A, Kato JY
Stable form of JAB1 enhances proliferation and maintenance of hematopoietic progenitors.
J Biol Chem. 2008; 283(43):29011-21 [PubMed] Free Access to Full Article Related Publications
Overexpression of JAB1 is observed in a variety of human cancers, but how JAB1 is involved in tumor development remained to be investigated. Here we analyzed mice with modified Jab1 expression. Mice ectopically expressing a more stable form of JAB1 protein under the control of a constitutive promoter were rescued from the embryonic lethality caused by the Jab1(-/-) allele and developed a myeloproliferative disorder in a gene dosage-dependent manner. Hematopoietic cells from the bone marrow of Jab1 transgenic mice had a significantly larger stem cell population and exhibited higher and transplantable proliferative potential. In contrast, Jab1(+/-) mice, which express approximately 70% as much JAB1 protein as their wild-type littermates, showed inefficient hematopoiesis. Expression of the tumor suppressor p16(INK4a) was inversely correlated with that of JAB1, and the oncoprotein SMYD3, a newly identified JAB1 interactor, suppressed transcription of p16 in cooperation with JAB1. Thus, the expression and function of JAB1 are critical for the proliferation and maintenance of hematopoietic progenitors.

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