PCGF2

Gene Summary

Gene:PCGF2; polycomb group ring finger 2
Aliases: MEL-18, RNF110, ZNF144
Location:17q12
Summary:The protein encoded by this gene contains a RING finger motif and is similar to the polycomb group (PcG) gene products. PcG gene products form complexes via protein-protein interaction and maintain the transcription repression of genes involved in embryogenesis, cell cycles, and tumorigenesis. This protein was shown to act as a negative regulator of transcription and has tumor suppressor activity. The expression of this gene was detected in various tumor cells, but is limited in neural organs in normal tissues. Knockout studies in mice suggested that this protein may negatively regulate the expression of different cytokines, chemokines, and chemokine receptors, and thus plays an important role in lymphocyte differentiation and migration, as well as in immune responses. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:polycomb group RING finger protein 2
Source:NCBIAccessed: 11 March, 2017

Ontology:

What does this gene/protein do?
Show (19)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 March 2017 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.

  • Polycomb-Group Proteins
  • Tumor Suppressor Gene
  • Cancer Gene Expression Regulation
  • Gene Expression Profiling
  • Reproducibility of Results
  • Chromosome 17
  • Epigenetics
  • Proto-Oncogene Proteins
  • Messenger RNA
  • DNA-Binding Proteins
  • Tumor Suppressor Protein p14ARF
  • Survival Rate
  • Down-Regulation
  • Neoplastic Cell Transformation
  • Polycomb Repressive Complex 1
  • Oncogene Fusion Proteins
  • Immunohistochemistry
  • Signal Transduction
  • Cell Cycle
  • Wnt Signaling Pathway
  • Biomarkers, Tumor
  • Disease Progression
  • Breast Cancer
  • DNA Sequence Analysis
  • Nuclear Proteins
  • RTPCR
  • Western Blotting
  • Zinc Fingers
  • Zinc Finger E-box-Binding Homeobox 1
  • Immunoenzyme Techniques
  • RNA Interference
  • Young Adult
  • Polymerase Chain Reaction
  • Repressor Proteins
  • Polycomb Repressive Complex 2
  • Ubiquitin-Protein Ligases
  • Prostate Cancer
  • Transcription Factors
  • Gene Expression
  • Transfection
Tag cloud generated 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (2)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: PCGF2 (cancer-related)

Jo S, Lee YL, Kim S, et al.
PCGF2 negatively regulates arsenic trioxide-induced PML-RARA protein degradation via UBE2I inhibition in NB4 cells.
Biochim Biophys Acta. 2016; 1863(7 Pt A):1499-509 [PubMed] Related Publications
Arsenic trioxide (ATO) is a therapeutic agent for acute promyelocytic leukemia (APL) which induces PML-RARA protein degradation via enhanced UBE2I-mediated sumoylation. PCGF2, a Polycomb group protein, has been suggested as an anti-SUMO E3 protein by inhibiting the sumoylation of UBE2I substrates, HSF2 and RANGAP1, via direct interaction. Thus, we hypothesized that PCGF2 might play a role in ATO-induced PML-RARA degradation by interacting with UBE2I. PCGF2 protein was down-regulated upon ATO treatment in human APL cell line, NB4. Knockdown of PCGF2 in NB4 cells, in the absence of ATO treatment, was sufficient to induce sumoylation-, ubiquitylation- and PML nuclear body-mediated degradation of PML-RARA protein. Moreover, overexpression of PCGF2 protected ATO-mediated degradation of ectopic and endogenous PML-RARA in 293T and NB4 cells, respectively. In 293T cells, UBE2I-mediated PML-RARA degradation was reduced upon PCGF2 co-expression. In addition, UBE2I-mediated sumoylation of PML-RARA was reduced upon PCGF2 co-expression and PCGF2-UBE2I interaction was confirmed by co-immunoprecipitation. Likewise, endogenous PCGF2-UBE2I interaction was detected by co-immunoprecipitation and immunofluorescence assays in NB4 cells. Intriguingly, upon ATO-treatment, such interaction was disrupted and UBE2I was co-immunoprecipitated or co-localized with its SUMO substrate, PML-RARA. Taken together, our results suggested a novel role of PCGF2 in ATO-mediated degradation of PML-RARA that PCGF2 might act as a negative regulator of UBE2I via direct interaction.

Wein F, Otto T, Lambertz P, et al.
Potential role of hypoxia in early stages of Hodgkin lymphoma pathogenesis.
Haematologica. 2015; 100(10):1320-6 [PubMed] Free Access to Full Article Related Publications
A unique feature of the germinal center B cell-derived Hodgkin and Reed/Sternberg cells of classical Hodgkin lymphoma is their lost B cell phenotype and the aberrant expression of factors of other hematopoietic cell types, including ID2 and NOTCH1. As cellular dedifferentiation and upregulation of ID2 and NOTCH1 are typical consequences of a hypoxic response, we wondered whether hypoxia may impose an HRS cell-like phenotype in B cells. Culturing normal B cells or cell lines of germinal center-type diffuse large B-cell lymphoma under hypoxic conditions caused partial downregulation of several B cell markers, ID2 upregulation, and increased NOTCH1 activity. The hypoxic cells acquired further features of Hodgkin and Reed/Sternberg cells, including increased JUN expression, and enhanced NFκB activity. The Hodgkin and Reed/Sternberg cell-expressed epigenetic regulators KDM4C and PCGF2, as well as the phosphatase DUSP1 were partially induced in hypoxic B cells. Inhibition of DUSP1 was toxic for classical Hodgkin lymphoma cell lines. Thus, hypoxia induces key Hodgkin and Reed/Sternberg cell characteristics in mature B cells. We speculate that hypoxic conditions in the germinal center may impose phenotypic changes in germinal center B cells, promoting their survival and initiating their differentiation towards a Hodgkin and Reed/Sternberg cell-like phenotype. These may then be stabilized by transforming events in the Hodgkin and Reed/Sternberg precursor cells.

Coradini D, Boracchi P, Oriana S, et al.
Differential expression of genes involved in the epigenetic regulation of cell identity in normal human mammary cell commitment and differentiation.
Chin J Cancer. 2014; 33(10):501-10 [PubMed] Free Access to Full Article Related Publications
The establishment and maintenance of mammary epithelial cell identity depends on the activity of a group of proteins, collectively called maintenance proteins, that act as epigenetic regulators of gene transcription through DNA methylation, histone modification, and chromatin remodeling. Increasing evidence indicates that dysregulation of these crucial proteins may disrupt epithelial cell integrity and trigger breast tumor initiation. Therefore, we explored in silico the expression pattern of a panel of 369 genes known to be involved in the establishment and maintenance of epithelial cell identity and mammary gland remodeling in cell subpopulations isolated from normal human mammary tissue and selectively enriched in their content of bipotent progenitors, committed luminal progenitors, and differentiated myoepithelial or differentiated luminal cells. The results indicated that, compared to bipotent cells, differentiated myoepithelial and luminal subpopulations were both characterized by the differential expression of 4 genes involved in cell identity maintenance: CBX6 and PCGF2, encoding proteins belonging to the Polycomb group, and SMARCD3 and SMARCE1, encoding proteins belonging to the Trithorax group. In addition to these common genes, the myoepithelial phenotype was associated with the differential expression of HDAC1, which encodes histone deacetylase 1, whereas the luminal phenotype was associated with the differential expression of SMARCA4 and HAT1, which encode a Trithorax protein and histone acetylase 1, respectively. The luminal compartment was further characterized by the overexpression of ALDH1A3 and GATA3, and the down-regulation of NOTCH4 and CCNB1, with the latter suggesting a block in cell cycle progression at the G2 phase. In contrast, myoepithelial differentiation was associated with the overexpression of MYC and the down-regulation of CCNE1, with the latter suggesting a block in cell cycle progression at the G1 phase.

Abd Al Kader L, Oka T, Takata K, et al.
In aggressive variants of non-Hodgkin lymphomas, Ezh2 is strongly expressed and polycomb repressive complex PRC1.4 dominates over PRC1.2.
Virchows Arch. 2013; 463(5):697-711 [PubMed] Related Publications
Polycomb group (PcG) proteins are important for the regulation of hematopoiesis by regulating chromatin compaction and silencing genes related to differentiation and cell cycle. Overexpression of enhancer of zeste homologue 2 (Ezh2) and Bmi-1/PCGF4 has been implicated in solid organ cancers, while Mel-18/PCGF2 has been reported as a tumor suppressor. Detailed expression profiles of PcG proteins and their diagnostic significance in malignant lymphomas are still unknown. In this study, we analyzed the expression levels of Ezh2, Bmi-1, Mel-18, and Ki67 in 197 Hodgkin's and non-Hodgkin's lymphoma patient samples and in lymphoma cell lines using immunohistochemistry, fluorescent immunocytochemistry, and Western blotting. Immunohistochemical staining showed that Ezh2 expression was significantly increased in aggressive compared to indolent subtypes of B cell neoplasms (P = 0.000-0.030), while no significant differences in Bmi-1 expression were found between these subtypes. Compared to the normal counterpart, T cell lymphomas showed significant overexpression of Bmi-1 (P = 0.011) and Ezh2 (P = 0.000). The Ki67 labeling index showed a positive correlation with Ezh2 expression in B cell lymphomas (correlation coefficient (Co) = 0.983, P = 0.000) and T/NK cell lymphomas (Co = 0.629, P = 0.000). Fluorescent immunohistochemical staining showed coexpression of Ezh2 and Ki67 in the same tumor cells, indicating that Ezh2 expression correlates with cell proliferation. Both B and T/NK cell neoplasms showed low expression of Mel-18 and high expression of both Bmi-1 and Ezh2. In conclusion, in aggressive lymphoma variants, Ezh2 is strongly expressed and polycomb repressive complex PRC1.4 dominates over PRC1.2. Coexpression of Bmi-1 and Ezh2 is a characteristic of aggressive lymphomas. Ezh2 correlates with the proliferation and aggressive nature of non-Hodgkin's lymphomas.

Lee JY, Park MK, Park JH, et al.
Loss of the polycomb protein Mel-18 enhances the epithelial-mesenchymal transition by ZEB1 and ZEB2 expression through the downregulation of miR-205 in breast cancer.
Oncogene. 2014; 33(10):1325-35 [PubMed] Related Publications
The epithelial-mesenchymal transition (EMT) is the pivotal mechanism underlying the initiation of cancer invasion and metastasis. Although Mel-18 has been implicated in several biological processes in cancer, its function in the EMT of human cancers has not yet been studied. Here, we demonstrate that Mel-18 negatively regulates the EMT by epigenetically modulating miR-205. We identified miR-205 as a novel target of Mel-18 using a microRNA microarray analysis and found that Mel-18 increased miR-205 transcription by the inhibition of DNA methyltransferase-mediated DNA methylation of the miR-205 promoter, thereby downregulating its target genes, ZEB1 and ZEB2. Furthermore, the loss of Mel-18 promoted ZEB1- and ZEB2-mediated downregulation of E-cadherin transcription and also enhanced the expression of mesenchymal markers, leading to increased migration and invasion in MCF-7 cells. In MDA-MB-231 cells, Mel-18 overexpression restored E-cadherin expression, resulting in reduced migration and invasion. These effects were reversed by miR-205 overexpression or inhibition. A tumor xenograft with Mel-18 knockdown MCF-7 cells consistently showed increased ZEB1 and ZEB2 expression and decreased E-cadherin expression. Taken together, these results suggest that Mel-18 functions as a tumor suppressor by its novel negative control of the EMT, achieved through regulating the expression of miR-205 and its target genes, ZEB1 and ZEB2.

Schulte I, Batty EM, Pole JC, et al.
Structural analysis of the genome of breast cancer cell line ZR-75-30 identifies twelve expressed fusion genes.
BMC Genomics. 2012; 13:719 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: It has recently emerged that common epithelial cancers such as breast cancers have fusion genes like those in leukaemias. In a representative breast cancer cell line, ZR-75-30, we searched for fusion genes, by analysing genome rearrangements.
RESULTS: We first analysed rearrangements of the ZR-75-30 genome, to around 10kb resolution, by molecular cytogenetic approaches, combining array painting and array CGH. We then compared this map with genomic junctions determined by paired-end sequencing. Most of the breakpoints found by array painting and array CGH were identified in the paired end sequencing-55% of the unamplified breakpoints and 97% of the amplified breakpoints (as these are represented by more sequence reads). From this analysis we identified 9 expressed fusion genes: APPBP2-PHF20L1, BCAS3-HOXB9, COL14A1-SKAP1, TAOK1-PCGF2, TIAM1-NRIP1, TIMM23-ARHGAP32, TRPS1-LASP1, USP32-CCDC49 and ZMYM4-OPRD1. We also determined the genomic junctions of a further three expressed fusion genes that had been described by others, BCAS3-ERBB2, DDX5-DEPDC6/DEPTOR and PLEC1-ENPP2. Of this total of 12 expressed fusion genes, 9 were in the coamplification. Due to the sensitivity of the technologies used, we estimate these 12 fusion genes to be around two-thirds of the true total. Many of the fusions seem likely to be driver mutations. For example, PHF20L1, BCAS3, TAOK1, PCGF2, and TRPS1 are fused in other breast cancers. HOXB9 and PHF20L1 are members of gene families that are fused in other neoplasms. Several of the other genes are relevant to cancer-in addition to ERBB2, SKAP1 is an adaptor for Src, DEPTOR regulates the mTOR pathway and NRIP1 is an estrogen-receptor coregulator.
CONCLUSIONS: This is the first structural analysis of a breast cancer genome that combines classical molecular cytogenetic approaches with sequencing. Paired-end sequencing was able to detect almost all breakpoints, where there was adequate read depth. It supports the view that gene breakage and gene fusion are important classes of mutation in breast cancer, with a typical breast cancer expressing many fusion genes.

Won HY, Lee JY, Shin DH, et al.
Loss of Mel-18 enhances breast cancer stem cell activity and tumorigenicity through activating Notch signaling mediated by the Wnt/TCF pathway.
FASEB J. 2012; 26(12):5002-13 [PubMed] Related Publications
Mel-18 has been proposed as a negative regulator of Bmi-1, a cancer stem cell (CSC) marker, but it is still unclear whether Mel-18 is involved in CSC regulation. Here, we examined the effect of Mel-18 on the stemness of human breast CSCs. In Mel-18 small hairpin RNA (shRNA)-transduced MCF-7 cells, side population (SP) cells and breast CSC surface marker (CD44(+)/CD24(-)/ESA(+))-expressing cells, which imply a CSC population, were enriched. Moreover, the self-renewal of CSCs was enhanced by Mel-18 knockdown, as measured by the ability for tumorsphere formation in vitro and tumor-initiating capacity in vivo. Similarly, Mel-18 overexpression inhibited the number and self-renewal activity of breast CSCs in SK-BR-3 cells. Furthermore, our data showed that Mel-18 blockade up-regulated the expression of the Wnt/TCF target Jagged-1, a Notch ligand, and consequently activated the Notch pathway. Pharmacologic inhibition of the Notch and Wnt pathways abrogated Mel-18 knockdown-mediated tumorsphere formation ability. Taken together, our findings suggest that Mel-18 is a novel negative regulator of breast CSCs that inhibits the stem cell population and in vitro and in vivo self-renewal through the inactivation of Wnt-mediated Notch signaling.

Jo S, Lee H, Kim S, et al.
Inhibition of PCGF2 enhances granulocytic differentiation of acute promyelocytic leukemia cell line HL-60 via induction of HOXA7.
Biochem Biophys Res Commun. 2011; 416(1-2):86-91 [PubMed] Related Publications
This study tested the hypothesis that Polycomb Repressive Complex 1 (PRC1) may play a negative role in the granulocytic differentiation of acute promyelocytic leukemia (APL) cells. We first examined the expression of PRC1 genes during all-trans retinoic acid (ATRA)-mediated differentiation of human HL-60 cells, and identified PCGF2 as a gene down-regulated by ATRA in a time-dependent manner. Upon gene silencing of PCGF2 with lentiviral short hairpin RNA, granulocytic differentiation was induced as assessed by differentiation marker gene expression, nitroblue tetrazolium staining, Wright-Giemsa staining, and cell cycle analysis. We next identified HOXA7 as a homeobox gene up-regulated by ATRA and successfully induced granulocytic differentiation by overexpression of HOXA7. We next tested the relationship between PCGF2 and HOXA7 by quantifying the changes in HOXA7 and PCGF2 expression upon PCGF2 gene silencing and HOXA7 overexpression, respectively. HOXA7 expression was up-regulated by PCGF2 gene silencing, while PCGF2 expression remained unchanged by ectopic HOXA7 expression, suggesting PCGF2 as acting upstream of HOXA7. Finally, chromatin immunoprecipitation assay was performed with HOXA7 chromatin. We observed gene-specific reduction in direct binding of Pcgf2 protein to HOXA7 chromatin upon PCGF2 gene silencing. Taken together, these results support the notion that down-regulation of PCGF2 is sufficient to induce granulocytic differentiation of HL-60 cells via de-repression of HOXA7 gene expression. In conclusion, we report that PCGF2, a PRC1 gene, played a negative role in the granulocytic differentiation of human APL cells.

Park JH, Lee JY, Shin DH, et al.
Loss of Mel-18 induces tumor angiogenesis through enhancing the activity and expression of HIF-1α mediated by the PTEN/PI3K/Akt pathway.
Oncogene. 2011; 30(45):4578-89 [PubMed] Related Publications
Mel-18 has been implicated in several processes in tumor progression, in which the Akt pathway is involved as an important key molecular event. However, the function of Mel-18 in human cancers has not been fully established yet. Here, we examined the effect of Mel-18 on tumor angiogenesis in human breast cancer, and found that Mel-18 was a novel regulator of HIF-1α. Mel-18 negatively regulated the HIF-1α expression and its target gene VEGF transcription during both normoxia and hypoxia. We demonstrated that Mel-18 regulated the HIF-1α expression and activity via the PI3K/Akt pathway. Loss of Mel-18 downregulated Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression, consequently activating the PI3K/Akt/MDM2 pathway, and leading to an increase of HIF-1α protein level. Mel-18 modulated the HIF-1α transcriptional activity via regulating the cytoplasmic retention of FOXO3a, a downstream effector of Akt, and recruitment of HIF-1α/CBP complex to the VEGF promoter. Furthermore, our data shows that Mel-18 blocked tumor angiogenesis both in vitro and in vivo. Mel-18 overexpression inhibited in vitro tube formation in human umbilical endothelial cells (HUVECs). Xenografts in NOD/SCID mice derived from stably Mel-18 knocked down MCF7 human breast cancer cells showed increased tumor volume, microvessel density, and phospho-Akt and HIF-1α expression levels. In conclusion, our findings provide that Mel-18 is a novel regulator of tumor angiogenesis through regulating HIF-1α and its target VEGF expressions mediated by the PTEN/PI3K/Akt pathway, suggesting a new tumor-suppressive role of Mel-18 in human breast cancer.

Riis ML, Lüders T, Nesbakken AJ, et al.
Expression of BMI-1 and Mel-18 in breast tissue--a diagnostic marker in patients with breast cancer.
BMC Cancer. 2010; 10:686 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Polycomb Group (PcG) proteins are epigenetic silencers involved in maintaining cellular identity, and their deregulation can result in cancer. Expression of Mel-18 and Bmi-1 has been studied in tumor tissue, but not in adjacent non-cancerous breast epithelium. Our study compares the expression of the two genes in normal breast epithelium of cancer patients and relates it to the level of expression in the corresponding tumors as well as in breast epithelium of healthy women.
METHODS: A total of 79 tumors, of which 71 malignant tumors of the breast, 6 fibroadenomas, and 2 DCIS were studied and compared to the reduction mammoplastic specimens of 11 healthy women. In addition there was available adjacent cancer free tissue for 23 of the malignant tumors. The tissue samples were stored in RNAlater, RNA was isolated to create expression microarray profile. These two genes were then studied more closely first on mRNA transcription level by microarrays (Agilent 44 K) and quantitative RT-PCR (TaqMan) and then on protein expression level using immunohistochemistry.
RESULTS: Bmi-1 mRNA is significantly up-regulated in adjacent normal breast tissue in breast cancer patients compared to normal breast tissue from noncancerous patients. Conversely, mRNA transcription level of Mel-18 is lower in normal breast from patients operated for breast cancer compared to breast tissue from mammoplasty. When protein expression of these two genes was evaluated, we observed that most of the epithelial cells were positive for Bmi-1 in both groups of tissue samples, although the expression intensity was stronger in normal tissue from cancer patients compared to mammoplasty tissue samples. Protein expression of Mel-18 showed inversely stronger intensity in tissue samples from mammoplasty compared to normal breast tissue from patients operated for breast cancer.
CONCLUSION: Bmi-1 mRNA level is consistently increased and Mel-18 mRNA level is consistently decreased in adjacent normal breast tissue of cancer patients as compared to normal breast tissue in women having had reduction mammoplasties. Bmi-1/Mel-18 ratio can be potentially used as a tool for stratifying women at risk of developing malignancy.

Lu YW, Li J, Guo WJ
Expression and clinicopathological significance of Mel-18 and Bmi-1 mRNA in gastric carcinoma.
J Exp Clin Cancer Res. 2010; 29:143 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The Polycomb group (PcG) genes are a class of regulators responsible for maintaining homeotic gene expression throughout cell division. PcG expression is deregulated in some types of human cancer. Both Bmi-1 and Mel-18 are of the key PcG proteins. We investigate the expression and clinicopathological roles of Mel-18 and Bmi-1 mRNA in gastric cancer.
METHODS: The expression of Mel-18 and Bmi-1 in a series of 71 gastric cancer tissues and paired normal mucosal tissues distant from the tumorous lesion was assayed by quantitative real time RT-PCR. The correlation between Mel-18 and Bmi-1 mRNA expression, and between Mel-18 or Bmi-1 mRNA level and clinicopathological characteristics were analyzed.
RESULTS: Expression of Mel-18 and Bmi-1 genes was variably detected, but overexpression of Bmi-1 mRNA and decreased expression of Mel-18 mRNA were the most frequent alteration. In addition, the expression of Bmi-1 and Mel-18 mRNA inversely correlates in gastric tumors. Moreover, a significant positive correlation between Bmi-1 overexpression and tumor size, depth of invasion, or lymph node metastasis, and a significant negative correlation between Mel-18 low-expression with lymph node metastasis or the clinical stage were observed.
CONCLUSION: Our data suggest that Mel-18 and Bmi-1 may play crucial but opposite roles in gastric cancer. Decreased Mel-18 and increased Bmi-1 mRNA expression was associated with the carcinogenesis and progression of gastric cancer. It is possible to list Bmi-1 and Mel-18 as biomarkers for predicting the prognosis of gastric cancer.

Zakrzewska M, Zakrzewski K, Grešner SM, et al.
Polycomb genes expression as a predictor of poor clinical outcome in children with medulloblastoma.
Childs Nerv Syst. 2011; 27(1):79-86 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: Medulloblastoma is the most frequent type of embryonal tumor in the pediatric population, accounting for 20-25% of all brain tumors in children. Recently, the suspected contribution of the Polycomb group (PcG) genes in medulloblastoma development was described. PcG genes play an important role in developmental processes; they are also involved in the self-renewal of hematopoietic and neural stem cells as well as in malignant transformation.
PURPOSE: In this study, we evaluated the expression of BMI1and PCGF2, members of family of PcG genes, and their potential target, MYC oncogene, and analyzed their association with demographic and clinical data.
MATERIALS AND METHODS: Thirty-one children (18 males and 13 females, aged from 0.4 to 17 years) with medulloblastoma were included in this study. The gene's expression level was measured by quantitative real-time PCR, obtained using the two-color multiplexing technique.
RESULTS: We found that the higher expression levels of BMI1 and PCGF2 genes were associated with significantly decreased patient survival (p = 0.02 and p = 0.012, respectively). Significant differences between gender were found, with a higher expression level of the PCGF2 gene observed among females (p = 0.02).
CONCLUSION: Our analysis showed correlation between BMI1 and PCGF2 gene's expression and survival in children with medulloblastoma.

Zhang XW, Sheng YP, Li Q, et al.
BMI1 and Mel-18 oppositely regulate carcinogenesis and progression of gastric cancer.
Mol Cancer. 2010; 9:40 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The BMI1 oncogene is overexpressed in several human malignancies including gastric cancer. In addition to BMI1, mammalian cells also express Mel-18, which is closely related to BMI1. We have reported that Mel-18 functions as a potential tumor suppressor by repressing the expression of BMI1 and consequent downregulation of activated AKT in breast cancer cells. However, the mechanisms of BMI1 overexpression and the role of Mel-18 in other cancers are still not clear. The purpose of this study is to investigate the role of BMI1 and Mel-18 in gastric cancer.
RESULTS: BMI1 was found to be overexpressed in gastric cancer cell lines and gastric tumors. Overexpression of BMI1 correlated with advanced clinical stage and lymph node metastasis; while the expression of Mel-18 negatively correlated with BMI1. BMI1 but not Mel-18 was found to be an independent prognostic factor. Downregulation of BMI1 by Mel-18 overexpression or knockdown of BMI1 expression in gastric cancer cell lines led to upregulation of p16 (p16INK4a or CDKN2A) in p16 positive cell lines and reduction of phospho-AKT in both p16-positive and p16-negative cell lines. Downregulation of BMI1 was also accompanied by decreased transformed phenotype and migration in both p16- positive and p16-negative gastric cancer cell lines.
CONCLUSIONS: In the context of gastric cancer, BMI1 acts as an oncogene and Mel-18 functions as a tumor suppressor via downregulation of BMI1. Mel-18 and BMI1 may regulate tumorigenesis, cell migration and cancer metastasis via both p16- and AKT-dependent growth regulatory pathways.

Wang W, Yuasa T, Tsuchiya N, et al.
The novel tumor-suppressor Mel-18 in prostate cancer: its functional polymorphism, expression and clinical significance.
Int J Cancer. 2009; 125(12):2836-43 [PubMed] Related Publications
Mel-18 is a member of the polycomb group (PcG) proteins, which are chromatin regulatory factors and play important roles in development and oncogenesis. This study was designed to investigate the clinical and prognostic significance of Mel-18 in patients with prostate cancer. A total of 539 native Japanese subjects consisting of 393 prostate cancer patients and 146 controls were enrolled in this study. Mel-18 genotyping was analyzed using a PCR-RFLP method and an automated sequencer using the GENESCAN software. Immunohistochemistry revealed that Mel-18 expression was diminished in high grade and high stage prostate cancers. Moreover, patients with positive Mel-18 expression had significantly longer PSA recurrence-free survival than patients negative for Mel-18 expression (p=0.038). A Mel-18 1805A/G SNP was located in the 3' untranslated region and was predicted to alter the secondary structure of the mRNA. Mel-18 mRNA expression of the 1805A allele was clearly higher than expression of the 1805G allele by allele specific quantitative RT-PCR. In multivariate analysis, a homozygous G allele genotype and negative Mel-18 expression were independent risk factors predicting high PSA recurrence after radical prostatectomy, with HRs of 2.757 (p=0.022) and 2.271 (p=0.045), respectively. Moreover, the G allele was also an independent predictor of poor cancer-specific survival with an HR of 4.658 (p=0.019) for patients with stage D2 prostate cancer. This is the first study to provide important evidence demonstrating that Mel-18 is a tumor suppressor and possible therapeutic target, as well as a diagnostic marker for poor prognosis in prostate cancer patients.

Wiederschain D, Wee S, Chen L, et al.
Single-vector inducible lentiviral RNAi system for oncology target validation.
Cell Cycle. 2009; 8(3):498-504 [PubMed] Related Publications
The use of RNA interference (RNAi) has enabled loss-of-function studies in mammalian cancer cells and has hence become critical for identifying and validating cancer drug targets. Current transient siRNA and stable shRNA systems, however, have limited utility in accurately assessing the cancer dependency due to their short-lived effects and limited in vivo utility, respectively. In this study, a single-vector lentiviral, Tet-inducible shRNA system (pLKO-Tet-On) was generated to allow for the rapid generation of multiple stable cell lines with regulatable shRNA expression. We demonstrate the advantages and versatility of this system by targeting two polycomb group proteins, Bmi-1 and Mel-18, in a number of cancer cell lines. Our data show that pLKO-Tet-On-mediated knockdown is tightly regulated by the inducer tetracycline and its derivative, doxycycline, in a concentration- and time-dependent manner. Furthermore, target gene expression is fully restored upon withdrawal of the inducing agent. An additional, 17 distinct gene products have been targeted by inducible shRNAs with robust regulation in all cases. Importantly, we functionally validate the ability of the pLKO-Tet-On vector to reversibly silence targeted transcripts in vivo. The versatile and robust inducible lentiviral RNAi system reported herein can therefore serve as a powerful tool to rapidly reveal tumor cell dependence.

Vékony H, Röser K, Löning T, et al.
Deregulated expression of p16INK4a and p53 pathway members in benign and malignant myoepithelial tumours of the salivary glands.
Histopathology. 2008; 53(6):658-66 [PubMed] Related Publications
AIMS: Myoepithelial salivary gland tumours are uncommon and follow an unpredictable biological course. The aim was to examine their molecular background to acquire a better understanding of their clinical behaviour.
METHODS AND RESULTS: Expression of protein (E2F1, p16(INK4a), p53, cyclin D1, Ki67 and Polycomb group proteins BMI-1, MEL-18 and EZH2) was investigated in 49 benign and 30 primary malignant myoepithelial tumours and five histologically benign recurrences by immunohistochemistry and the findings correlated with histopathological characteristics. Benign tumours showed a higher percentage of cells with expression of p16(INK4a) pathway members [p16(INK4a) and E2F1 (both P < 0.001), and cyclin D1, P = 0.002] compared with normal salivary gland. Furthermore, malignant tumours expressed p53 (P = 0.003) and EZH2 (P = 0.09) in a higher percentage. Recurrences displayed more p53 + tumour cells (P = 0.02) than benign primaries. Amongst the benign tumours, the clear cell type had the highest proliferation fraction (P = 0.05) and a higher percentage of EZH2 was detected in the plasmacytoid cell type (P = 0.002).
CONCLUSIONS: This study is the first to demonstrate that deregulation of the p16(INK4a) senescence pathway is involved in the development of myoepithelial tumours. We propose that additional inactivation of p53 in malignant primaries and benign recurrences contributes to myoepithelial neoplastic transformation and aggressive tumour growth.

Lee JY, Jang KS, Shin DH, et al.
Mel-18 negatively regulates INK4a/ARF-independent cell cycle progression via Akt inactivation in breast cancer.
Cancer Res. 2008; 68(11):4201-9 [PubMed] Related Publications
Mel-18, a polycomb group (PcG) protein, has been suggested as a tumor suppressor in human breast cancer. Previously, we reported that Mel-18 has antiproliferative activity in breast cancer cells. However, its functional mechanism has not been fully elucidated. Here, we investigated the role of Mel-18 in human breast cancer. We saw an inverse correlation between Mel-18 and phospho-Akt, which were expressed at low and high levels, respectively, in primary breast tumor tissues from 40 breast cancer patients. The effect of Mel-18 on cell growth was examined in two breast cancer cell lines, SK-BR-3 and T-47D, which express relatively low and high levels of endogenous Mel-18, respectively. On Mel-18 overexpression in SK-BR-3 cells, cell growth was attenuated and G(1) arrest was observed. Likewise, suppression of Mel-18 by antisense expression in T-47D cells led to enhanced cell growth and accelerated G(1)-S phase transition. In these cells, cyclin-dependent kinase (Cdk)-4 and Cdk2 activities were affected by Mel-18, which were mediated by changes in cyclin D1 expression and p27(Kip1) phosphorylation at Thr(157), but not by INK4a/ARF genes. The changes were both dependent on the phosphatidylinositol 3-kinase/Akt signaling pathway. Akt phosphorylation at Ser(473) was reduced by Mel-18 overexpression in SK-BR-3 cells and enhanced by Mel-18 suppression in T-47D cells. Akt-mediated cytoplasmic localization of p27(Kip1) was inhibited by Mel-18 in SK-BR-3 cells. Moreover, Mel-18 overexpression showed reduced glycogen synthase kinase-3beta phosphorylation, beta-catenin nuclear localization, T-cell factor/lymphoid enhancer factor promoter activity, and cyclin D1 mRNA level. Taken together, we established a linear relationship between Mel-18-->Akt-->G(1) phase regulators.

Guo WJ, Zeng MS, Yadav A, et al.
Mel-18 acts as a tumor suppressor by repressing Bmi-1 expression and down-regulating Akt activity in breast cancer cells.
Cancer Res. 2007; 67(11):5083-9 [PubMed] Free Access to Full Article Related Publications
The Bmi-1 oncogene is overexpressed in a number of malignancies including breast cancer. In addition to Bmi-1, mammalian cells also express four other polycomb group (PcG) proteins that are closely related to Bmi-1. Virtually nothing is known about the role of these PcG proteins in oncogenesis. We have recently reported that Mel-18, a Bmi-1-related PcG protein, negatively regulates Bmi-1 expression, and that its expression negatively correlates with Bmi-1 in proliferating and senescing human fibroblasts. Here, we report that the expression of Bmi-1 and Mel-18 inversely correlates in a number of breast cancer cell lines and in a significant number of breast tumor samples. Overexpression of Mel-18 results in repression of Bmi-1 and reduction of the transformed phenotype in malignant breast cancer cells. Furthermore, the repression of Bmi-1 by Mel-18 is accompanied by the reduction of Akt/protein kinase B (PKB) activity in breast cancer cells. Similarly, Bmi-1 knockdown using RNA interference approach results in down-regulation of Akt/PKB activity and reduction in transformed phenotype of MCF7 cells. Importantly, we show that overexpression of constitutively active Akt overrides tumor-suppressive effect of Mel-18 overexpression and the knockdown of Bmi-1 expression. Thus, our studies suggest that Mel-18 and Bmi-1 may regulate the Akt pathway in breast cancer cells, and that Mel-18 functions as a tumor suppressor by repressing the expression of Bmi-1 and consequently down-regulating Akt activity.

Wiederschain D, Chen L, Johnson B, et al.
Contribution of polycomb homologues Bmi-1 and Mel-18 to medulloblastoma pathogenesis.
Mol Cell Biol. 2007; 27(13):4968-79 [PubMed] Free Access to Full Article Related Publications
Bmi-1 and Mel-18 are structural homologues that belong to the Polycomb group of transcriptional regulators and are believed to stably maintain repression of gene expression by altering the state of chromatin at specific promoters. While a number of clinical and experimental observations have implicated Bmi-1 in human tumorigenesis, the role of Mel-18 in cancer cell growth has not been investigated. We report here that short hairpin RNA-mediated knockdown of either Bmi-1 or Mel-18 in human medulloblastoma DAOY cells results in the inhibition of proliferation, loss of clonogenic survival, anchorage-independent growth, and suppression of tumor formation in nude mice. Furthermore, overexpression of both Bmi-1 and Mel-18 significantly increases the clonogenic survival of Rat1 fibroblasts. In contrast, stable downregulation of Bmi-1 or Mel-18 alone does not affect the growth of normal human WI38 fibroblasts. Proteomics-based characterization of Bmi-1 and Mel-18 protein complexes isolated from cancer cells revealed substantial similarities in their respective compositions. Finally, gene expression analysis identified a number of cancer-relevant pathways that may be controlled by Bmi-1 and Mel-18 and also showed that these Polycomb proteins regulate a set of common gene targets. Taken together, these results suggest that Bmi-1 and Mel-18 may have overlapping functions in cancer cell growth.

Silva J, García JM, Peña C, et al.
Implication of polycomb members Bmi-1, Mel-18, and Hpc-2 in the regulation of p16INK4a, p14ARF, h-TERT, and c-Myc expression in primary breast carcinomas.
Clin Cancer Res. 2006; 12(23):6929-36 [PubMed] Related Publications
PURPOSE: Deregulation of mammalian Polycomb group (PcG) members may contribute to human carcinogenesis. p16INK4a and p14ARF tumor suppressors, human telomerase reverse transcriptase (h-TERT), and oncoprotein c-Myc have been implicated in the regulation of the cell cycle and proliferation mediated by PcG proteins, mainly Bmi-1, in mice and in cell culture experiments. Here, we examine whether these in vitro findings can be extrapolated to the in vivo situation.
EXPERIMENTAL DESIGN: We measure the expression of PcG members Bmi-1, Mel-18, and Hpc-2 and their potential targets by reverse transcription-PCR, immunostaining, and Western blotting in a series of 134 breast carcinomas and correlate the data with several clinical-pathologic variables of the tumors.
RESULTS: Expression of PcG genes was variably detected, but overexpression of Bmi-1 was the most frequent PcG alteration observed. In addition, statistical direct correlation in expression level of the three PcG members was detected. A correlation between c-Myc and Bmi-1 expression levels was observed; however, there was no correlation between expression of Bmi-1 and p16INK4a, p14ARF, or h-TERT. However, expression of the other PcG members Mel-18 and Hpc-2 correlated with the cell cycle regulators. Moreover, PcG mRNA-altered expression correlated significantly with certain clinical-pathologic variables associated with poor prognosis.
CONCLUSIONS: Our data suggest that the oncogenic role of Bmi-1 in human primary breast carcinomas is not determined by its capacity to inhibit INK4a/ARF proteins or to induce telomerase activity.

Sánchez-Beato M, Sánchez E, González-Carreró J, et al.
Variability in the expression of polycomb proteins in different normal and tumoral tissues. A pilot study using tissue microarrays.
Mod Pathol. 2006; 19(5):684-94 [PubMed] Related Publications
In spite of the known function of polycomb group (PcG) genes in stem cell self-renewal, control of cellular proliferation and differentiation, its role in cancer pathogenesis is still poorly understood. We studied the expression by immunohistochemistry of several PcG-maintenance complex proteins (RING1, RNF2, BMI1, MEL18, HPH1 and RYBP) in nontumoral (154 samples) and tumoral (550 samples) human tissues using Tissue Microarrays. For selected genes (BMI1 and RING1) FISH analysis has been also carried out. PcG proteins had a tissue- and cell-type-specific expression pattern. Some of them were highly selectively expressed, such as HPH1, which was detected in germ cells in testis, pituitary and parathyroid glands and Langerhans islets, and RYBP, which was found in placenta, umbilical cord and thyroid gland. By contrast, RING1 was ubiquitously expressed in every normal tissue analyzed. Changes in expression associated with tumoral transformation have been found for BMI1 and RNF2, which exhibited increased expression in a large series of tumors, including gastrointestinal tumors, pituitary and parathyroid adenomas, and lymphomas, compared with their expression in normal-cell counterparts. The high level of expression of BMI1 protein observed in mantle-cell lymphomas and pituitary adenomas is associated in some cases with amplification of BMI1 locus. These findings imply that upregulation of BMI1 may constitute a malignancy marker in different types of cancer, mainly in lymphoid and endocrine tumors. RING1 was lost in a group of renal-cell carcinomas and testicular germ-cell tumors. Lastly, RYBP is anomalously expressed in Hodgkin's lymphomas and oligodendrogliomas, among others tumors. A significant finding of the study is the identification of unique PcG profiles for some tumors, such as testicular germ-cell tumors, which have high levels of HPH1 expression and loss of RING1 and/or BMI1; pituitary adenomas, which expressed every PcG protein analyzed; and clear-cell renal-cell carcinoma, which was the only tumor other than testicular germ-cell tumors that did not express RING1.

Sánchez-Beato M, Sánchez E, García JF, et al.
Abnormal PcG protein expression in Hodgkin's lymphoma. Relation with E2F6 and NFkappaB transcription factors.
J Pathol. 2004; 204(5):528-37 [PubMed] Related Publications
The Polycomb group (PcG) of proteins comprises a family of repressors of homeobox genes that play key roles in body formation, haematopoiesis and cell cycle control. In this study, a large-scale analysis of PcG protein expression (BMI1, MEL18, PH1, RNF2, RING1, and RYBP) was performed in 321 Hodgkin's lymphoma (HL) biopsies and in reactive lymphoid tissues using tissue microarrays. The relevance of PcG proteins in HL was also investigated by the simultaneous analysis of PcG and other proteins involved in the control of cell cycle, transcription machinery and lymphoid differentiation. The analysis revealed increased expression of a set of PcG proteins (particularly RYBP and BMI1) in tumour cells in comparison with reactive lymphoid tissue. One of the most striking findings was anomalous RYBP expression in 55% of classical HL cases associated with an unfavourable response to treatment and shorter survival. The data obtained in this study also show an association of PcG proteins with E2F6 and NFkappaB transcription factors. The statistical relationship between PcG and NFkappaB activation was further explored in HL-derived cell lines treated with curcumin, an NFkappaB inhibitor, and TNFalpha. Up- or downregulation of MEL18 was paralleled by loss or gain of activated NFkappaB, which suggests that NFkappaB may regulate expression of this protein. Investigation of the relationship between E2F6 and RING1 by immunofluorescence and confocal analysis, in HL cell lines and paraffin sections, revealed co-expression of both proteins in the same tumour cells. These results allow us to propose that the formation of transcription complexes with E2F6 may modify the functional status of PcG proteins in HSR cells.

Dukers DF, van Galen JC, Giroth C, et al.
Unique polycomb gene expression pattern in Hodgkin's lymphoma and Hodgkin's lymphoma-derived cell lines.
Am J Pathol. 2004; 164(3):873-81 [PubMed] Free Access to Full Article Related Publications
Human Polycomb-group (PcG) genes play a crucial role in the regulation of embryonic development and regulation of the cell cycle and hematopoiesis. PcG genes encode proteins that form two distinct PcG complexes, involved in maintenance of cell identity and gene silencing patterns. We recently showed that expression of the BMI-1 and EZH2 PcG genes is separated during normal B-cell development in germinal centers, whereas Hodgkin/Reed-Sternberg (H/RS) cells co-express BMI-1 and EZH2. In the current study, we used immunohistochemistry and immunofluorescence to determine whether the binding partners of these PcG proteins are also present in H/RS cells and H/RS-derived cell lines. PcG expression profiles were analyzed in combination with expression of the cell cycle inhibitor p16INK4a, because experimental model systems indicate that p16 is a downstream target of Bmi-1. We found that H/RS cells and HL-derived cell lines co-express all core proteins of the two known PcG complexes, including BMI-1, MEL-18, RING1, HPH1, HPC1, and -2, EED, EZH2, YY1, and the HPC2 binding partner, CtBP. Expression of HPC1 has not been found in normal mature B cells and other malignant lymphomas of B-cell origin, suggesting that the PcG expression profile of H/RS is unique. In contrast to Bmi-1 transgenic mice where p16INK4a is down-regulated, 27 of 52 BMI-1POS cases of HL revealed strong nuclear expression of p16INK4a. We propose that abnormal expression of BMI-1 and its binding partners in H/RS cells contributes to development of HL. However, abnormal expression of BMI-1 in HL is not necessarily associated with down-regulation of p16INK4a.

Matsuo F, Yano K, Saito H, et al.
Mutation analysis of the mel-18 gene that shows decreased expression in human breast cancer cell lines.
Breast Cancer. 2002; 9(1):33-8 [PubMed] Related Publications
BACKGROUND: Mammalian mel-18 is a member of the polycomb group, and it acts as a transcriptional repressor with DNA binding activity. Murine mel-18 negatively regulates the cell cycle through the c-myc/cdc25 cascade, and mice haploinsufficient for mel-18 develop mammary gland tumors. In addition, the human homolog of mel-18 is located at 17q, on which candidate tumor suppressor genes for breast cancer have been suggested for a long time. These observations indicate that the mel-18 gene may be a tumor suppressor gene for breast cancer. To investigate this possibility, we examined the expression of mel-18 mRNA in human breast cancer cell lines and searched for mel-18 gene mutations in sporadic and familial breast cancers.
METHODS: The expression of mel-18 mRNA was examined in five breast cancer cell lines by RT-PCR, and somatic and germline mutations of the mel-18 gene were analyzed by the PCR-SSCP and sequence methods in 48 sporadic breast cancers, including 16 cases with loss of heterozygosity (LOH) at the mel-18 locus, and in 23 cases from 18 breast cancer families, respectively.
RESULTS: We found that most cell lines examined here showed decreased expression of mel-18 mRNA, however, no alteration other than a single nucleotide change that did not lead to amino acid alteration in one patient was identified.
CONCLUSION: Our results reveal that mel-18 gene mutations are exceedingly rare in human breast cancers, and a reduction of mel-18 expression in human breast cancer cell lines would support a role for mel-18 haploinsufficiency in breast carcinogenesis.

Ishiwatari H, Nakanishi K, Kondoh G, et al.
Suppression of tumor growth by the 3' untranslated region of mel-18 in 3Y1 cells transformed by the E6 and E7 genes of human papillomavirus type 18.
Cancer Lett. 1997; 117(1):57-65 [PubMed] Related Publications
By introducing a cDNA library derived from rat embryonic fibroblast cells, we isolated several morphologically flat revertants of rat 3Y1 cells transformed by the E6 and E7 genes of human papillomavirus type 18 (HPV18). From one of the revertants, we recovered a 0.2-kb cDNA, N56, that suppresses the tumor growth of the transformed 3Y1 cells irrespective of the expression of the E6 and E7 genes. The nucleotide sequence of the cDNA was shown to be identical to that of the 3' untranslated region of a putative mammalian polycomb group gene, mel-18.

Tagawa M, Sakamoto T, Shigemoto K, et al.
Expression of novel DNA-binding protein with zinc finger structure in various tumor cells.
J Biol Chem. 1990; 265(32):20021-6 [PubMed] Related Publications
We have isolated from B16 mouse melanoma cells a complementary DNA (Mel-18), whose deduced amino acid sequence possesses a characteristic zinc finger structure. Immunostaining with antibodies raised against partial Mel-18 peptide sequences demonstrated nuclear localization of the gene product. We have also demonstrated that this protein has DNA-binding capacity, and the zinc finger is responsible for the DNA binding. At the transcriptional level the Mel-18 mRNA was detected in all tumor cells examined as well as melanoma cells (ontogenically of neural origin) but was scarcely present in normal tissues except neural organs. The transcript is developmentally regulated. These data suggest that Mel-18 may play a role in transcriptional regulation and also in control of cell proliferation and/or neural cell development.

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