Gene Summary

Gene:CBX7; chromobox homolog 7
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:chromobox protein homolog 7
Source:NCBIAccessed: 21 August, 2015


What does this gene/protein do?
Show (11)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 21 August 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Brain Tumours
  • Sequence Homology, Nucleic Acid
  • Cell Proliferation
  • MicroRNAs
  • Western Blotting
  • p53 Protein
  • Stomach Cancer
  • Cancer Gene Expression Regulation
  • Nuclear Proteins
  • Bladder Cancer
  • Thyroid Cancer
  • Tumor Suppressor Protein p14ARF
  • Immunohistochemistry
  • Polycomb Repressive Complex 1
  • Retinoic Acid
  • Cell Aging
  • beta Catenin
  • Loss of Heterozygosity
  • Tissue Array Analysis
  • Glioblastoma
  • Prostate Cancer
  • Messenger RNA
  • Chromosome 22
  • Ubiquitin-Protein Ligases
  • Repressor Proteins
  • Promoter Regions
  • RNA Interference
  • Young Adult
  • Tumor Markers
  • Up-Regulation
  • Down-Regulation
  • Transforming Growth Factor beta
  • Cancer Stem Cells
  • HEK293 Cells
  • Proto-Oncogene Proteins
  • Gene Expression Profiling
  • Tumor Suppressor Proteins
  • Staging
  • CDKN2A Protein
  • Polycomb-Group Proteins
Tag cloud generated 21 August, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

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: CBX7 (cancer-related)

Kim HY, Park JH, Won HY, et al.
CBX7 inhibits breast tumorigenicity through DKK-1-mediated suppression of the Wnt/β-catenin pathway.
FASEB J. 2015; 29(1):300-13 [PubMed] Related Publications
Polycomb protein chromobox homolog 7 (CBX7) is involved in several biologic processes including stem cell regulation and cancer development, but its roles in breast cancer remain unknown. Here, we demonstrate that CBX7 negatively regulates breast tumor initiation. CD44(+)/CD24(-)/ESA(+) breast stem-like cells showed diminished CBX7 expression. Furthermore, small hairpin RNA-mediated CBX7 knockdown in breast epithelial and cancer cells increased the CD44(+)/CD24(-)/ESA(+) cell population and reinforced in vitro self-renewal and in vivo tumor-initiating ability. Similarly, CBX7 overexpression repressed these effects. We also found that CBX7 inhibits the Wnt/β-catenin/T cell factor pathway by enhancing the expression of Dickkopf-1 (DKK-1), a Wnt antagonist. In particular, CBX7 increased DKK-1 transcription by cooperating with p300 acetyltransferase and subsequently enhancing the histone acetylation of the DKK-1 promoter. Furthermore, pharmacologic inhibition of DKK-1 in CBX7-overexpressing cells showed recovery of Wnt signaling and consequent rescue of the CD44(+)/CD24(-)/ESA(+) cell population. Taken together, these findings indicate that CBX7-mediated epigenetic induction of DKK-1 is crucial for the inhibition of breast tumorigenicity, suggesting that CBX7 could be a potential tumor suppressor in human breast cancer.

Pallante P, Sepe R, Federico A, et al.
CBX7 modulates the expression of genes critical for cancer progression.
PLoS One. 2014; 9(5):e98295 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: We have previously shown that the expression of CBX7 is drastically decreased in several human carcinomas and that its expression progressively decreases with the appearance of a highly malignant phenotype. The aim of our study has been to investigate the mechanism by which the loss of CBX7 expression may contribute to the emergence of a more malignant phenotype.
METHODS: We analyzed the gene expression profile of a thyroid carcinoma cell line after the restoration of CBX7 and, then, analyzed the transcriptional regulation of identified genes. Finally, we evaluated the expression of CBX7 and regulated genes in a panel of thyroid and lung carcinomas.
RESULTS: We found that CBX7 negatively or positively regulates the expression of several genes (such as SPP1, SPINK1, STEAP1, and FOS, FOSB, EGR1, respectively) associated to cancer progression, by interacting with their promoter regions and modulating their transcriptional activity. Quantitative RT-PCR analyses in human thyroid and lung carcinoma tissues revealed a negative correlation between CBX7 and its down-regulated genes, while a positive correlation was observed with up-regulated genes.
CONCLUSION: In conclusion, the loss of CBX7 expression might play a critical role in advanced stages of carcinogenesis by deregulating the expression of specific effector genes.

Shinjo K, Yamashita Y, Yamamoto E, et al.
Expression of chromobox homolog 7 (CBX7) is associated with poor prognosis in ovarian clear cell adenocarcinoma via TRAIL-induced apoptotic pathway regulation.
Int J Cancer. 2014; 135(2):308-18 [PubMed] Related Publications
Ovarian cancer is the most lethal gynecologic malignancy, and clear cell adenocarcinoma of the ovary (OCCA), in particular, has a relatively poor prognosis among the ovarian cancer subtypes because of its high chemoresistance. Chromobox (CBX) 7 is a polycomb repressive complex 1 component that prolongs the lifespan of normal human cells by downregulating the INK4a/ARF expression which promotes cell-cycle progression. However, recent reports studying the relationship between CBX7 expression and patient survival have differed regarding the tumor cell origins, and the precise role of CBX7 in human carcinomas remains obscure. In this study, we analyzed CBX7 expression by immunohistochemistry in 81 OCCA patients and evaluated its association with their clinical outcomes. Both the overall and progression-free survival rates of the CBX7-positive patients were significantly shorter than those of the CBX7-negative patients (p < 0.05). CBX7 knockdown experiments using two OCCA cell lines, TOV21G and KOC-7C, revealed that cell viability was significantly reduced compared to the control cells (p < 0.001). Expression microarray analysis revealed that apoptosis-related genes, particularly tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), were significantly upregulated in CBX7 knockdown cells (p < 0.01). We further confirmed that CBX7 knockdown resulted in TRAIL-induced apoptosis in the OCCA cells. Thus, in this study, we showed for the first time that CBX7 was associated with a decreased OCCA prognosis. We also successfully demonstrated that the TRAIL pathway is a novel target for CBX7 expression modulation in these cells, and therapeutic agents utilizing the TRAIL pathway may be particularly effective for targeted OCCA therapy.

Li G, Warden C, Zou Z, et al.
Altered expression of polycomb group genes in glioblastoma multiforme.
PLoS One. 2013; 8(11):e80970 [PubMed] Free Access to Full Article Related Publications
The Polycomb group (PcG) proteins play a critical role in histone mediated epigenetics which has been implicated in the malignant evolution of glioblastoma multiforme (GBM). By systematically interrogating The Cancer Genome Atlas (TCGA), we discovered widespread aberrant expression of the PcG members in GBM samples compared to normal brain. The most striking differences were upregulation of EZH2, PHF19, CBX8 and PHC2 and downregulation of CBX7, CBX6, EZH1 and RYBP. Interestingly, changes in EZH2, PHF19, CBX7, CBX6 and EZH1 occurred progressively as astrocytoma grade increased. We validated the aberrant expression of CBX6, CBX7, CBX8 and EZH2 in GBM cell lines by Western blotting and qRT-PCR, and further the aberrant expression of CBX6 in GBM tissue samples by immunohistochemical staining. To determine if there was functional significance to the diminished CBX6 levels in GBM, CBX6 was overexpressed in GBM cells resulting in decreased proliferative capacity. In conclusion, aberrant expression of PcG proteins in GBMs may play a role in the development or maintenance of the malignancy.

Gargiulo G, Cesaroni M, Serresi M, et al.
In vivo RNAi screen for BMI1 targets identifies TGF-β/BMP-ER stress pathways as key regulators of neural- and malignant glioma-stem cell homeostasis.
Cancer Cell. 2013; 23(5):660-76 [PubMed] Related Publications
In mouse and human neural progenitor and glioblastoma "stem-like" cells, we identified key targets of the Polycomb-group protein BMI1 by combining ChIP-seq with in vivo RNAi screening. We discovered that Bmi1 is important in the cellular response to the transforming growth factor-β/bone morphogenetic protein (TGF-β/BMP) and endoplasmic reticulum (ER) stress pathways, in part converging on the Atf3 transcriptional repressor. We show that Atf3 is a tumor-suppressor gene inactivated in human glioblastoma multiforme together with Cbx7 and a few other candidates. Acting downstream of the ER stress and BMP pathways, ATF3 binds to cell-type-specific accessible chromatin preloaded with AP1 and participates in the inhibition of critical oncogenic networks. Our data support the feasibility of combining ChIP-seq and RNAi screens in solid tumors and highlight multiple p16(INK4a)/p19(ARF)-independent functions for Bmi1 in development and cancer.

Quint K, Tonigold M, Di Fazio P, et al.
Pancreatic cancer cells surviving gemcitabine treatment express markers of stem cell differentiation and epithelial-mesenchymal transition.
Int J Oncol. 2012; 41(6):2093-102 [PubMed] Related Publications
Objective response rates to standard chemotherapeutic regimens remain low in pancreatic cancer. Subpopulations of cells have been identified in various solid tumors which express stem cell-associated markers and are associated with increased resistance against radiochemotherapy. We investigated the expression of stem cell genes and markers of epithelial-mesenchymal transition in pancreatic cancer cells that survived high concentrations of gemcitabine treatment. Capan-1 and Panc-1 cells were continuously incubated with 1 and 10 µM gemcitabine. Surviving cells were collected after 1, 3 and 6 days. Expression of PDX-1, SHH, CD24, CD44, CD133, EpCAM, CBX7, OCT4, SNAIL, SLUG, TWIST, Ki-67, E-cadherin, β-catenin and vimentin were quantified by qPCR or immunocytochemistry. Migration was assessed by wound‑healing assay. SHH was knocked down using RNA interference. Five primary pancreatic cancer cell lines were used to validate the qPCR results. All investigated genes were upregulated after 6 days of gemcitabine incubation. Highest relative expression levels were observed for OCT4 (13.4-fold), CD24 (47.3-fold) and EpCAM (15.9-fold) in Capan-1 and PDX-1 (13.3‑fold), SHH (24.1-fold), CD44 (17.4-fold), CD133 (20.2-fold) and SLUG (15.2-fold) in Panc-1 cells. Distinct upregulation patterns were observed in the primary cells. Migration was increased in Panc-1 cells and changes in the expression of E-cadherin and β-catenin were typical of epithelial-mesenchymal transition in both cell lines. SHH knockdown reduced IC(50) from 30.1 to 27.6 nM in Capan-1 while it strongly inhibited proli-feration in Panc-1 cells. Cells surviving high-dose gemcitabine treatment express increased levels of stem cell genes, show characteristics associated with epithelial-mesenchymal transition and retain their proliferative capacity.

Forzati F, Federico A, Pallante P, et al.
Tumor suppressor activity of CBX7 in lung carcinogenesis.
Cell Cycle. 2012; 11(10):1888-91 [PubMed] Related Publications
The generation of knockout mice for the Cbx7 gene validates the tumor suppressor role of CBX7, whose expression is lost in several human malignancies. Indeed, these mice developed liver and lung adenomas and carcinomas. Cyclin E overexpression due to the lack of Cbx7 negative regulation of its expression likely accounts for the phenotype of the Cbx7-KO mice. A similar mechanism is likely involved in human lung carcinogenesis, since cyclin E upregulation associated with the loss of CBX7 expression has been observed in most of the human lung carcinomas analyzed.

Forzati F, Federico A, Pallante P, et al.
CBX7 is a tumor suppressor in mice and humans.
J Clin Invest. 2012; 122(2):612-23 [PubMed] Free Access to Full Article Related Publications
The CBX7 gene encodes a polycomb group protein that is known to be downregulated in many types of human cancers, although the role of this protein in carcinogenesis remains unclear. To shed light on this issue, we generated mice null for Cbx7. Mouse embryonic fibroblasts derived from these mice had a higher growth rate and reduced susceptibility to senescence compared with their WT counterparts. This was associated with upregulated expression of multiple cell cycle components, including cyclin E, which is known to play a key role in lung carcinogenesis in humans. Adult Cbx7-KO mice developed liver and lung adenomas and carcinomas. In in vivo and in vitro experiments, we demonstrated that CBX7 bound to the CCNE1 promoter in a complex that included HDAC2 and negatively regulated CCNE1 expression. Finally, we found that the lack of CBX7 protein expression in human lung carcinomas correlated with CCNE1 overexpression. These data suggest that CBX7 is a tumor suppressor and that its loss plays a key role in the pathogenesis of cancer.

Hannafon BN, Sebastiani P, de las Morenas A, et al.
Expression of microRNA and their gene targets are dysregulated in preinvasive breast cancer.
Breast Cancer Res. 2011; 13(2):R24 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: microRNA (miRNA) are short, noncoding RNA that negatively regulate gene expression and may play a causal role in invasive breast cancer. Since many genetic aberrations of invasive disease are detectable in early stages, we hypothesized that miRNA expression dysregulation and the predicted changes in gene expression might also be found in early breast neoplasias.
METHODS: Expression profiling of 365 miRNA by real-time quantitative polymerase chain reaction assay was combined with laser capture microdissection to obtain an epithelium-specific miRNA expression signature of normal breast epithelium from reduction mammoplasty (RM) (n = 9) and of paired samples of histologically normal epithelium (HN) and ductal carcinoma in situ (DCIS) (n = 16). To determine how miRNA may control the expression of codysregulated mRNA, we also performed gene expression microarray analysis in the same paired HN and DCIS samples and integrated this with miRNA target prediction. We further validated several target pairs by modulating the expression levels of miRNA in MCF7 cells and measured the expression of target mRNA and proteins.
RESULTS: Thirty-five miRNA were aberrantly expressed between RM, HN and DCIS. Twenty-nine miRNA and 420 mRNA were aberrantly expressed between HN and DCIS. Combining these two data sets with miRNA target prediction, we identified two established target pairs (miR-195:CCND1 and miR-21:NFIB) and tested several novel miRNA:mRNA target pairs. Overexpression of the putative tumor suppressor miR-125b, which is underexpressed in DCIS, repressed the expression of MEMO1, which is required for ErbB2-driven cell motility (also a target of miR-125b), and NRIP1/RIP140, which modulates the transcriptional activity of the estrogen receptor. Knockdown of the putative oncogenic miRNA miR-182 and miR-183, both highly overexpressed in DCIS, increased the expression of chromobox homolog 7 (CBX7) (which regulates E-cadherin expression), DOK4, NMT2 and EGR1. Augmentation of CBX7 by knockdown of miR-182 expression, in turn, positively regulated the expression of E-cadherin, a key protein involved in maintaining normal epithelial cell morphology, which is commonly lost during neoplastic progression.
CONCLUSIONS: These data provide the first miRNA expression profile of normal breast epithelium and of preinvasive breast carcinoma. Further, we demonstrate that altered miRNA expression can modulate gene expression changes that characterize these early cancers. We conclude that miRNA dysregulation likely plays a substantial role in early breast cancer development.

Li Q, Wang X, Lu Z, et al.
Polycomb CBX7 directly controls trimethylation of histone H3 at lysine 9 at the p16 locus.
PLoS One. 2010; 5(10):e13732 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: H3K9 trimethylation (H3K9me3) and binding of PcG repressor complex-1 (PRC1) may play crucial roles in the epigenetic silencing of the p16 gene. However, the mechanism of the initiation of this trimethylation is unknown.
METHODOLOGY/PRINCIPAL FINDINGS: In the present study, we found that upregulating the expression of PRC1 component Cbx7 in gastric cancer cell lines MGC803 and BGC823 led to significantly suppress the expression of genes within the p16-Arf-p15 locus. H3K9me3 formation was observed at the p16 promoter and Regulatory Domain (RD). CBX7 and SUV39H2 binding to these regions were also detectable in the CBX7-stably upregulated cells. CBX7-SUV39H2 complexes were observed within nucleus in bimolecular fluorescence complementation assay (BiFC). Mutations of the chromodomain or deletion of Pc-box abolished the CBX7-binding and H3K9me3 formation, and thus partially repressed the function of CBX7. SiRNA-knockdown of Suv39h2 blocked the repressive effect of CBX7 on p16 transcription. Moreover, we found that expression of CBX7 in gastric carcinoma tissues with p16 methylation was significantly lower than that in their corresponding normal tissues, which showed a negative correlation with transcription of p16 in gastric mucosa.
CONCLUSION/SIGNIFICANCE: These results demonstrated for the first time, to our knowledge, that CBX7 could initiate H3K9me3 formation at the p16 promoter.

Zhang XW, Zhang L, Qin W, et al.
Oncogenic role of the chromobox protein CBX7 in gastric cancer.
J Exp Clin Cancer Res. 2010; 29:114 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Chromobox 7 (CBX7) is a Polycomb family protein that extends the lifespan of normal human cells via downregulating the expression of INK4a/ARF tumor suppressor locus. It was found that CBX7 expression was upregulated in lymphoma, but downregulated in some other human malignancies. The role of CBX7 in most types of cancer is still not clear. The purpose of this study is to investigate the role of CBX7 in gastric cancer.
METHODS: The expression of CBX7 and its potential target protein p16(INK4a) in gastric cancer cell lines and gastric tumors was assayed by Western blot analysis and immunohistochemistry(IHC). The correlations between CBX7 expression and p16(INK4a), clinicopathological characteristics, and prognosis were analyzed. Gastric cancer cell line SGC-7901 was transfected with CBX7 siRNA expressing plasmids, and the expression of various proteins was analyzed by Western blot analysis. Cellular senescence, anchorage independent growth, and cell migration assays were performed to determine the functional role of CBX7 in gastric cancer cells.
RESULTS: CBX7 was found to be overexpressed in gastric cancer cell lines and gastric tumors. Overexpression of CBX7 in gastric cancer tissues correlated with patients' age, clinical stage and lymph node metastasis. Knockdown of CBX7 expression in gastric cancer cells led to increased cellular senescence, decreased cellular proliferation and migration ability, accompanied by upregulation of p16(INK4a).
CONCLUSIONS: CBX7 acts as an oncogene in the carcinogenesis and progression of gastric cancer, and it may regulate tumorigenesis, cell migration and cancer metastasis partially via p16(INK4a) regulatory pathway.

Pallante P, Terracciano L, Carafa V, et al.
The loss of the CBX7 gene expression represents an adverse prognostic marker for survival of colon carcinoma patients.
Eur J Cancer. 2010; 46(12):2304-13 [PubMed] Related Publications
We have previously shown that CBX7 expression is associated with a more malignant phenotype in thyroid cancer. On this basis, we decided to investigate its possible prognostic value in colorectal cancer (CRC). CBX7 expression has been analysed by immunohistochemistry in tissue microarray (TMA) specimens obtained from a large series of sporadic CRC resections (n=1420). The CBX7 expression data have been correlated with several clinico-pathological parameters. CBX7 expression is reduced or absent in a significant number of CRC samples in comparison to the normal colonic mucosa and the loss of CBX7 expression correlates with a poor outcome of CRC (p<0.001). The block of CBX7 expression seems to occur at a transcriptional level since quantitative RT-PCR analysis showed a reduced CBX7-specific mRNA levels in CRC samples versus normal counterpart tissue (up to more than 50-fold). Finally, the restoration of CBX7 expression in two CRC cell lines reduces their proliferation rate suggesting a role of the loss of CBX7 expression in the progression step of colon carcinogenesis. Therefore, the data reported here indicate that the evaluation of CBX7 expression may represent a valid tool in the prognosis of colon cancer since a reduced survival of CRC patients is associated with the loss of CBX7 expression.

Yap KL, Li S, Muñoz-Cabello AM, et al.
Molecular interplay of the noncoding RNA ANRIL and methylated histone H3 lysine 27 by polycomb CBX7 in transcriptional silencing of INK4a.
Mol Cell. 2010; 38(5):662-74 [PubMed] Free Access to Full Article Related Publications
Expression of the INK4b/ARF/INK4a tumor suppressor locus in normal and cancerous cell growth is controlled by methylation of histone H3 at lysine 27 (H3K27me) as directed by the Polycomb group proteins. The antisense noncoding RNA ANRIL of the INK4b/ARF/INK4a locus is also important for expression of the protein-coding genes in cis, but its mechanism has remained elusive. Here we report that chromobox 7 (CBX7) within the polycomb repressive complex 1 binds to ANRIL, and both CBX7 and ANRIL are found at elevated levels in prostate cancer tissues. In concert with H3K27me recognition, binding to RNA contributes to CBX7 function, and disruption of either interaction impacts the ability of CBX7 to repress the INK4b/ARF/INK4a locus and control senescence. Structure-guided analysis reveals the molecular interplay between noncoding RNA and H3K27me as mediated by the conserved chromodomain. Our study suggests a mechanism by which noncoding RNA participates directly in epigenetic transcriptional repression.

Karamitopoulou E, Pallante P, Zlobec I, et al.
Loss of the CBX7 protein expression correlates with a more aggressive phenotype in pancreatic cancer.
Eur J Cancer. 2010; 46(8):1438-44 [PubMed] Related Publications
Polycomb group (PcG) proteins function as multiprotein complexes and are part of a gene regulatory mechanism that determines cell fate during normal and pathogenic development. Several studies have implicated the deregulation of different PcG proteins in neoplastic progression. Pancreatic ductal adenocarcinoma is an aggressive neoplasm that follows a multistep model of progression through precursor lesions called pancreatic intraepithelial neoplasia (PanIN). Aim of this study was to investigate the role of PcG protein CBX7 in pancreatic carcinogenesis and to evaluate its possible diagnostic and prognostic significance. We analysed by immunohistochemistry the expression of CBX7 in 210 ductal pancreatic adenocarcinomas from resection specimens, combined on a tissue microarray (TMA) including additional 40 PanIN cases and 40 normal controls. The results were evaluated by using receiver operating characteristic (ROC) curve analysis for the selection of cut-off scores and correlated to the clinicopathological parameters of the tumours and the outcome of the patients. Expression of E-cadherin, a protein positively regulated by CBX7, was also assessed. A significantly differential, and progressively decreasing CBX7 protein expression was found between normal pancreatic tissue, PanINs and invasive ductal adenocarcinoma. Loss of CBX7 expression was associated with increasing malignancy grade in pancreatic adenocarcinoma, whereas the maintenance of CBX7 expression showed a trend toward a longer survival. Moreover, loss of E-cadherin expression was associated with loss of CBX7 and with a trend towards worse patient survival. These results suggest that CBX7 plays a role in pancreatic carcinogenesis and that its loss of expression correlates to a more aggressive phenotype.

Jiang Z, Guo J, Xiao B, et al.
Increased expression of miR-421 in human gastric carcinoma and its clinical association.
J Gastroenterol. 2010; 45(1):17-23 [PubMed] Related Publications
BACKGROUND: Gastric cancer is a worldwide cancer with poor prognosis. Identification of diagnostic biomarkers and effective therapeutic targets is important in the treatment and diagnosis of gastric cancer. Recently, researchers have found that microRNAs play several important roles in carcinogenesis. The purpose of this study was to investigate the relationships between miR-421 expression patterns in human gastric cancer tissues with clinicopathological features.
METHODS: Sixty gastric carcinoma and 18 non-tumor tissues were collected from the Secondary Hospital of Ningbo, China. For quantitative detection of the expression level of miR-421, total RNA was extracted and then reverse transcription-polymerase chain reaction was performed. The relationship between miR-421 expression in gastric cancer and clinicopathological features was analyzed. After miR-421 inhibitor was transfected into gastric cancer cells, cell growth was measured by MTT assay. Finally, the expression of its target genes was detected by Western blotting.
RESULTS: The miR-421 was over-expressed in 73.33% (44/60) of the gastric cancer samples examined. Over-expression of miR-421 in gastric cancer tissues was not found associated with clinicopathological features. The positive detection rate of miR-421 was higher than that of serum carcino-embryonic antigen (chi(2) = 39.811, P < 0.001). Inhibition of miR-421 expression decreased the growth of both MGC-803 and SGC-7901 gastric cancer cells in vitro, with up-regulating the expression of its cancer-related target genes, CBX7 and RBMXL1.
CONCLUSIONS: miR-421 may involve in the early stage of stomach carcinogenesis and could be used as an efficient diagnostic biomarker.

Federico A, Pallante P, Bianco M, et al.
Chromobox protein homologue 7 protein, with decreased expression in human carcinomas, positively regulates E-cadherin expression by interacting with the histone deacetylase 2 protein.
Cancer Res. 2009; 69(17):7079-87 [PubMed] Related Publications
Chromobox protein homologue 7 (CBX7) is a chromobox family protein encoding a novel polycomb protein, the expression of which shows a progressive reduction, well related with the malignant grade of the thyroid neoplasias. Indeed, CBX7 protein levels decreased in an increasing percentage of cases going from benign adenomas to papillary, follicular, and anaplastic thyroid carcinomas. To elucidate the function of CBX7 in carcinogenesis, we searched for CBX7 interacting proteins by a proteomic analysis. By this approach, we identified several proteins. Among these proteins, we selected histone deacetylase 2 (HDAC2), which is well known to play a key role in neoplastic cell transformation and down-regulation of E-cadherin expression, the loss of which is a critical event in the epithelial-to-mesenchymal transition. We confirmed by coimmunoprecipitation that CBX7 physically interacts with the HDAC2 protein and is able to inhibit its activity. Then, we showed that both these proteins bind the E-cadherin promoter and that CBX7 up-regulates E-cadherin expression. Consistent with these data, we found a positive statistical correlation between CBX7 and E-cadherin expression in human thyroid carcinomas. Finally, we showed that the expression of CBX7 increases the acetylation status of the histones H3 and H4 on the E-cadherin promoter. Therefore, the ability of CBX7 to positively regulate E-cadherin expression by interacting with HDAC2 and inhibiting its activity on the E-cadherin promoter would account for the correlation between the loss of CBX7 expression and a highly malignant phenotype.

Mohammad HP, Cai Y, McGarvey KM, et al.
Polycomb CBX7 promotes initiation of heritable repression of genes frequently silenced with cancer-specific DNA hypermethylation.
Cancer Res. 2009; 69(15):6322-30 [PubMed] Free Access to Full Article Related Publications
Epigenetic silencing of genes in association with aberrant promoter DNA hypermethylation has emerged as a significant mechanism in the development of human cancers. Such genes are also often targets of the polycomb group repressive complexes in embryonic cells. The polycomb repressive complex 2 (PRC2) has been best studied in this regard. We now examine a link between PRC1 and cancer-specific gene silencing. Here, we show a novel and direct association between a constituent of the PRC1 complex, CBX7, with gene repression and promoter DNA hypermethylation of genes frequently silenced in cancer. CBX7 is able to complex with DNA methyltransferase (DNMT) enzymes, leading us to explore a role for CBX7 in maintenance and initiation of gene silencing. Knockdown of CBX7 was unable to relieve suppression of deeply silenced genes in cancer cells; however, in embryonal carcinoma (EC) cells, CBX7 can initiate stable repression of genes that are frequently silenced in adult cancers. Furthermore, we are able to observe assembly of DNMTs at CBX7 target gene promoters. Sustained expression of CBX7 in EC cells confers a growth advantage and resistance to retinoic acid-induced differentiation. In this setting, especially, there is increased promoter DNA hypermethylation for many genes by analysis of specific genes, as well as through epigenomic studies. Our results allow us to propose a potential mechanism through assembly of novel repressive complexes, by which the polycomb component of PRC1 can promote the initiation of epigenetic changes involving abnormal DNA hypermethylation of genes frequently silenced in adult cancers.

Hinz S, Kempkensteffen C, Christoph F, et al.
Expression parameters of the polycomb group proteins BMI1, SUZ12, RING1 and CBX7 in urothelial carcinoma of the bladder and their prognostic relevance.
Tumour Biol. 2008; 29(5):323-9 [PubMed] Related Publications
BACKGROUND: The polycomb group (PCG) proteins are epigenetic transcriptional repressors involved in the control of cellular proliferation and oncogenesis. This study aimed at examining whether mRNA tumor levels of the PCG family members BMI1, SUZ12, RING1, and CBX7 relate to histopathological parameters in urothelial carcinomas of the bladder and whether they may provide prognostic information following tumor resection.
METHODS: The relative gene expression of BMI1, SUZ12, RING1, and CBX7 was analyzed by real-time RT-PCR in tumor tissue obtained from 93 patients with urothelial carcinoma of the bladder undergoing surgical treatment. Expression data was correlated with pathological variables and outcome.
RESULTS: PCG family members BMI1, SUZ12, RING1, and CBX7 are commonly expressed in urothelial carcinomas of the bladder. The relative CBX7 mRNA expression levels gradually decreased from superficial (pTa) to invasive (pT1) and finally to muscle-invasive (> or =pT2) tumors (p = 0.008). Furthermore, CBX7 expression was statistically significantly correlated with tumor grade (p = 0.04). No correlation of mRNA levels with histopathological tumor features or tumor recurrence was observed for the other PCG components investigated.
CONCLUSION: Expression levels of CBX7 inversely correlate with the progression of tumor stage and grade in urothelial carcinomas of the bladder, suggesting that downregulation of CBX7 indicates aggressive urothelial carcinoma phenotype.

Pallante P, Federico A, Berlingieri MT, et al.
Loss of the CBX7 gene expression correlates with a highly malignant phenotype in thyroid cancer.
Cancer Res. 2008; 68(16):6770-8 [PubMed] Related Publications
Using gene expression profiling, we found that the CBX7 gene was drastically down-regulated in six thyroid carcinoma cell lines versus control cells. The aims of this study were to determine whether CBX7 is related to the thyroid cancer phenotype and to try to identify new tools for the diagnosis and prognosis of thyroid cancer. We thus evaluated CBX7 expression in various snap-frozen and paraffin-embedded thyroid carcinoma tissues of different degrees of malignancy by quantitative reverse transcription-PCR and immunohistochemistry, respectively. CBX7 expression progressively decreased with malignancy grade and neoplasia stage. Indeed, it decreased in an increasing percentage of cases going from benign adenomas to papillary (PTC), follicular, and anaplastic (ATC) thyroid carcinomas. This finding coincides with results obtained in rat and mouse models of thyroid carcinogenesis. CBX7 loss of heterozygosity occurred in 36.8% of PTC and in 68.7% of ATC. Restoration of CBX7 expression in thyroid cancer cells reduced growth rate, with a retention in the G(1) phase of the cell cycle, suggesting that CBX7 can contribute to the proliferation of the transformed thyroid cells. In conclusion, loss of CBX7 expression correlates with a highly malignant phenotype in thyroid cancer patients.

Bernard D, Martinez-Leal JF, Rizzo S, et al.
CBX7 controls the growth of normal and tumor-derived prostate cells by repressing the Ink4a/Arf locus.
Oncogene. 2005; 24(36):5543-51 [PubMed] Related Publications
Control of cell proliferation by Polycomb group proteins (PcG) is an important facet of cellular homeostasis and its disruption can promote tumorigenesis. We recently described CBX7 as a novel PcG protein controlling the growth of normal cells. In an attempt to identify a putative role of CBX7 in tumorigenesis, we analysed CBX7 expression in a panel of cancer cell lines and primary tissues. CBX7 was highly expressed in three different prostate cancer cell lines and present at elevated levels in normal prostate. Ablation of CBX7 expression using short hairpin RNAs (shRNA) resulted in upregulation of p16Ink4a and p14Arf in both LNCaP and PC-3 prostate cell lines. CBX7 knockdown caused an impairment of cell growth that was dependent on the status of the p14Arf/p53 and p16Ink4a/Rb pathways in both normal and cancer prostate cells. CBX7 overexpression in LNCaP cells resulted in a slight growth advantage in both androgen-dependent and -independent conditions. Moreover, CBX7 expression cooperated with c-Myc in rendering LNCaP cells insensitive to growth arrest by androgen receptor inhibition. Together, these data suggest that CBX7 represses p16Ink4a and p14Arf expression in normal and tumor-derived prostate cells, affecting their growth depending on the status of the p16Ink4a/Rb and the p14Arf/p53 pathways.

Suarez-Merino B, Hubank M, Revesz T, et al.
Microarray analysis of pediatric ependymoma identifies a cluster of 112 candidate genes including four transcripts at 22q12.1-q13.3.
Neuro Oncol. 2005; 7(1):20-31 [PubMed] Free Access to Full Article Related Publications
Ependymomas are glial cell-derived tumors characterized by varying degrees of chromosomal abnormalities and variability in clinical behavior. Cytogenetic analysis of pediatric ependymoma has failed to identify consistent patterns of abnormalities, with the exception of monosomy of 22 or structural abnormalities of 22q. In this study, a total of 19 pediatric ependymoma samples were used in a series of expression profiling, quantitative real-time PCR (Q-PCR), and loss of heterozygosity experiments to identify candidate genes involved in the development of this type of pediatric malignancy. Of the 12,627 genes analyzed, a subset of 112 genes emerged as being abnormally expressed when compared to three normal brain controls. Genes with increased expression included the oncogene WNT5A; the p53 homologue p63; and several cell cycle, cell adhesion, and proliferation genes. Underexpressed genes comprised the NF2 interacting gene SCHIP-1 and the adenomatous polyposis coli (APC)-associated gene EB1 among others. We validated the abnormal expression of six of these genes by Q-PCR. The subset of differentially expressed genes also included four underexpressed transcripts mapping to 22q12.313.3. By Q-PCR we show that one of these genes, 7 CBX7(22q13.1), was deleted in 55% of cases. Other genes mapping to cytogenetic hot spots included two overexpressed and three underexpressed genes mapping to 1q31-41 and 6q21-q24.3, respectively. These genes represent candidate genes involved in ependymoma tumorigenesis. To the authors' knowledge, this is the first time microarray analysis and Q-PCR have been linked to identify heterozygous/homozygous deletions.

Gil J, Bernard D, Peters G
Role of polycomb group proteins in stem cell self-renewal and cancer.
DNA Cell Biol. 2005; 24(2):117-25 [PubMed] Related Publications
Polycomb group proteins (PcG) form part of a gene regulatory mechanism that determines cell fate during normal and pathogenic development. The mechanism relies on epigenetic modifications on specific histone tails that are inherited through cell divisions, thus behaving de facto as a cellular memory. This cellular memory governs key events in organismal development as well as contributing to the control of normal cell growth and differentiation. Consequently, the dysregulation of PcG genes, such as Bmi1, Pc2, Cbx7, and EZH2 has been linked with the aberrant proliferation of cancer cells. Furthermore, at least three PcG genes, Bmi1, Rae28, and Mel18, appear to regulate self-renewal of specific stem cell types suggesting a link between the maintenance of cellular homeostasis and tumorigenesis. In this review, we will briefly summarize current views on PcG function and the evidence linking specific PcG proteins with the behavior of stem cells and cancer cells.

Gil J, Bernard D, Martínez D, Beach D
Polycomb CBX7 has a unifying role in cellular lifespan.
Nat Cell Biol. 2004; 6(1):67-72 [PubMed] Related Publications
In contrast to cancer cells and embryonic stem cells, the lifespan of primary human cells is finite. After a defined number of population doublings, cells enter in an irreversible growth-arrested state termed replicative senescence. Mutations of genes involved in immortalization can contribute to cancer. In a genetic screen for cDNAs bypassing replicative senescence of normal human prostate epithelial cells (HPrEC), we identified CBX7, a gene that encodes a Polycomb protein, as shown by sequence homology, its interaction with Ring1 and its localization to nuclear Polycomb bodies. CBX7 extends the lifespan of a wide range of normal human cells and immortalizes mouse fibroblasts by downregulating expression of the Ink4a/Arf locus. CBX7 does not inter-function or colocalize with Bmi1, and both can exert their actions independently of each other as shown by reverse genetics. CBX7 expression is downregulated during replicative senescence and its ablation by short-hairpin RNA (shRNA) treatment inhibited growth of normal cells though induction of the Ink4a/Arf locus. Taken together, these data show that CBX7 controls cellular lifespan through regulation of both the p16(Ink4a)/Rb and the Arf/p53 pathways.

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Cite this page: Cotterill SJ. CBX7, Cancer Genetics Web: http://www.cancer-genetics.org/CBX7.htm Accessed:

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