Coexpression of BMI-1 and EZH2 polycomb-group proteins is associated with cycling cells and degree of malignancy in B-cell non-Hodgkin lymphoma

Somatic mutations at EZH2 Y641 act dominantly through a mechanism of selectively altered PRC2 catalytic activity, to increase H3K27 trimethylation

Next-generation sequencing of follicular lymphoma and diffuse-large B-cell lymphoma has revealed frequent somatic, heterozygous Y641 mutations in the histone methyltransferase EZH2. Heterozygosity and the presence of equal quantities of both mutant and wild-type mRNA and expressed protein suggest a dominant mode of action. Surprisingly, B-cell lymphoma cell lines and lymphoma samples harboring heterozygous EZH2(Y641) mutations have increased levels of histone H3 Lys-27-specific trimethylation (H3K27me3). Expression of EZH2(Y641F/N) mutants in cells with EZH2(WT) resulted in an increase of H3K27me3 levels in vivo. Structural modeling of EZH2(Y641) mutants suggests a "Tyr/Phe switch" model whereby structurally neutral, nontyrosine residues at position 641 would decrease affinity for unmethylated and monomethylated H3K27 substrates and potentially favor trimethylation. We demonstrate, using in vitro enzyme assays of reconstituted PRC2 complexes, that Y641 mutations result in a decrease in monomethylation and an increase in trimethylation activity of the enzyme relative to the wild-type enzyme. This represents the first example of a disease-associated gain-of-function mutation in a histone methyltransferase, whereby somatic EZH2 Y641 mutations in lymphoma act dominantly to increase, rather than decrease, histone methylation. The dominant mode of action suggests that allele-specific EZH2 inhibitors should be a future therapeutic strategy for this disease.

Overexpression of BMI-1 promotes cell growth and resistance to cisplatin treatment in osteosarcoma

Background

BMI-1 is a member of the polycomb group of genes (PcGs), and it has been implicated in the development and progression of several malignancies, but its role in osteosarcoma remains to be elucidated.

Methodology/Principal Findings

In the present study, we found that BMI-1 was overexpressed in different types of osteosarcomas. Downregulation of BMI-1 by lentivirus mediated RNA interference (RNAi) significantly impaired cell viability and colony formation in vitro and tumorigenesis in vivo of osteosarcoma cells. BMI-1 knockdown sensitized cells to cisplatin-induced apoptosis through inhibition of PI3K/AKT pathway. Moreover, BMI-1-depletion-induced phenotype could be rescued by forced expression of BMI-1 wobble mutant which is resistant to inhibition by the small interfering RNA (siRNA).

Conclusions/Significance

These findings suggest a crucial role for BMI-1 in osteosarcoma pathogenesis.

Expression of BMI-1 and Mel-18 in breast tissue--a diagnostic marker in patients with breast cancer

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.

Coordinated activities of wild-type plus mutant EZH2 drive tumor-associated hypertrimethylation of lysine 27 on histone H3 (H3K27) in human B-cell lymphomas

EZH2, the catalytic subunit of the PRC2 complex, catalyzes the mono- through trimethylation of lysine 27 on histone H3 (H3K27). Histone H3K27 trimethylation is a mechanism for suppressing transcription of specific genes that are proximal to the site of histone modification. Point mutations of the EZH2 gene (Tyr641) have been reported to be linked to subsets of human B-cell lymphoma. The mutant allele is always found associated with a wild-type allele (heterozygous) in disease cells, and the mutations were reported to ablate the enzymatic activity of the PRC2 complex for methylating an unmodified peptide substrate. Here we demonstrate that the WT enzyme displays greatest catalytic efficiency (k(cat)/K) for the zero to monomethylation reaction of H3K27 and diminished efficiency for subsequent (mono- to di- and di- to trimethylation) reactions. In stark contrast, the disease-associated Y641 mutations display very limited ability to perform the first methylation reaction, but have enhanced catalytic efficiency for the subsequent reactions, relative to the WT enzyme. These results imply that the malignant phenotype of disease requires the combined activities of a H3K27 monomethylating enzyme (PRC2 containing WT EZH2 or EZH1) together with the mutant PRC2s for augmented conversion of H3K27 to the trimethylated form. To our knowledge, this is the first example of a human disease that is dependent on the coordinated activities of normal and disease-associated mutant enzymatic function.

BMI1-mediated histone ubiquitylation promotes DNA double-strand break repair

The polycomb repressor complex ubiquitylates γ-H2AX and other components of the DNA damage response pathway to facilitate genomic repair.

Polycomb group (PcG) proteins are major determinants of cell identity, stem cell pluripotency, and epigenetic gene silencing during development. The polycomb repressive complex 1, which contains BMI1, RING1, and RING2, functions as an E3-ubuiquitin ligase. We found that BMI1 and RING2 are recruited to sites of DNA double-strand breaks (DSBs) where they contribute to the ubiquitylation of γ-H2AX. In the absence of BMI1, several proteins dependent on ubiquitin signaling, including 53BP1, BRCA1, and RAP80, are impaired in recruitment to DSBs. Loss of BMI1 sensitizes cells to ionizing radiation to the same extent as loss of RNF8. The simultaneous depletion of both proteins revealed an additive increase in radiation sensitivity. These data uncover an unexpected link between the polycomb and the DNA damage response pathways, and suggest a novel function for BMI1 in maintaining genomic stability.

Expression and clinicopathological significance of Mel-18 and Bmi-1 mRNA in gastric carcinoma

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.

Genome-wide DNA methylation maps in follicular lymphoma cells determined by methylation-enriched bisulfite sequencing

Background

Follicular lymphoma (FL) is a form of non-Hodgkin's lymphoma (NHL) that arises from germinal center (GC) B-cells. Despite the significant advances in immunotherapy, FL is still not curable. Beyond transcriptional profiling and genomics datasets, there currently is no epigenome-scale dataset or integrative biology approach that can adequately model this disease and therefore identify novel mechanisms and targets for successful prevention and treatment of FL.

Methodology/Principal Findings

We performed methylation-enriched genome-wide bisulfite sequencing of FL cells and normal CD19⁺ B-cells using 454 sequencing technology. The methylated DNA fragments were enriched with methyl-binding proteins, treated with bisulfite, and sequenced using the Roche-454 GS FLX sequencer. The total number of bases covered in the human genome was 18.2 and 49.3 million including 726,003 and 1.3 million CpGs in FL and CD19⁺ B-cells, respectively. 11,971 and 7,882 methylated regions of interest (MRIs) were identified respectively. The genome-wide distribution of these MRIs displayed significant differences between FL and normal B-cells. A reverse trend in the distribution of MRIs between the promoter and the gene body was observed in FL and CD19⁺ B-cells. The MRIs identified in FL cells also correlated well with transcriptomic data and ChIP-on-Chip analyses of genome-wide histone modifications such as tri-methyl-H3K27, and tri-methyl-H3K4, indicating a concerted epigenetic alteration in FL cells.

Conclusions/Significance

This study is the first to provide a large scale and comprehensive analysis of the DNA methylation sequence composition and distribution in the FL epigenome. These integrated approaches have led to the discovery of novel and frequent targets of aberrant epigenetic alterations. The genome-wide bisulfite sequencing approach developed here can be a useful tool for profiling DNA methylation in clinical samples.

Prognostic relevance of Bmi-1 expression and autoantibodies in esophageal squamous cell carcinoma

Background

Overexpression of Bmi-1 has been observed in a variety of cancers, and it has been suggested to be an independent prognostic marker for the patients. The objective of this study was to determine the level of Bmi-1 expression or its autoantibodies in human esophageal squamous cell carcinoma (ESCC) and to correlate it with clinicopathologic data.

Methods

We first examined Bmi-1 expression in ESCC cell lines and tumor samples by RT-PCR and Western blot analysis. We then analyzed Bmi-1 protein expression in 171 clinicopathologically characterized ESCC cases by immunohistochemistry. In addition, we detected its autoantibodies in sera of patients with ESCC by ELISA.

Results

We found that Bmi-1 expression was higher in the immortalized cells, cancer cell lines and most cancer tissue than in non-tumorous control tissue at both mRNA and protein level. In addition, Bmi-1 expression was observed in 64.3% (110 of 171) archive ESCC specimen by immunohistochemistry analysis, and the location of Bmi-1 in ESCC was in the nuclei instead of cytoplasm of tumor cells. There was a significant difference of Bmi-1 expression in patients categorized according to stage (P = 0.003) and pN classification (P = 0.047). Multivariate analysis suggested that Bmi-1 expression was an independent prognostic marker for ESCC patients. A prognostic significance of Bmi-1 was also found in the subgroup of T3~T4 and N1 tumor classification. Bmi-1 autoantibodies were detected in sera of 39.0% (62 of 159) ESCC patients. The correlations between anti-Bmi-1 antibodies and tumor stage (P = 0.040), or lymph node status (P < 0.001) were significant.

Conclusions

Our results suggest that Bmi-1 protein is a valuable marker of ESCC progression. The presence of Bmi-1 autoantibodies in sera from patients with ESCC may have clinical utility in esophageal cancer diagnosis.

Deletion analysis of BMI1 oncoprotein identifies its negative regulatory domain

BACKGROUND

The polycomb group (PcG) protein BMI1 is an important regulator of development. Additionally, aberrant expression of BMI1 has been linked to cancer stem cell phenotype and oncogenesis. In particular, its overexpression has been found in several human malignancies including breast cancer. Despite its established role in stem cell maintenance, cancer and development, at present not much is known about the functional domains of BMI1 oncoprotein. In the present study, we carried out a deletion analysis of BMI1 to identify its negative regulatory domain.

RESULTS

We report that deletion of the C-terminal domain of BMI1, which is rich in proline-serine (PS) residues and previously described as PEST-like domain, increased the stability of BMI1, and promoted its pro-oncogenic activities in human mammary epithelial cells (HMECs). Specifically, overexpression of a PS region deleted mutant of BMI1 increased proliferation of HMECs and promoted an epithelial-mesenchymal transition (EMT) phenotype in the HMECs. Furthermore, when compared to the wild type BMI1, exogenous expression of the mutant BMI1 led to a significant downregulation of p16INK4a and an efficient bypass of cellular senescence in human diploid fibroblasts.

CONCLUSIONS

In summary, our data suggest that the PS domain of BMI1 is involved in its stability and that it negatively regulates function of BMI1 oncoprotein. Our results also suggest that the PS domain of BMI1 could be targeted for the treatment of proliferative disorders such as cancer and aging.

Deregulated expression of the polycomb-group protein SUZ12 target genes characterizes mantle cell lymphoma

Polycomb proteins are known to be of great importance in human cancer pathogenesis. SUZ12 is a component of the Polycomb PRC2 complex that, along with EZH2, is involved in embryonic stem cell differentiation. EZH2 plays an essential role in many cancer types, but an equivalent involvement of SUZ12 has not been as thoroughly demonstrated. Here we show that SUZ12 is anomalously expressed in human primary tumors, especially in mantle cell lymphoma (MCL), pulmonary carcinomas and melanoma, and is associated with gene locus amplification in some cases. Using MCL as a model, functional and genomic studies demonstrate that SUZ12 loss compromises cell viability, increases apoptosis, and targets genes involved in central oncogenic pathways associated with MCL pathogenesis. Our results support the hypothesis that the abnormal expression of SUZ12 accounts for some of the unexplained features of MCL, such as abnormal DNA repair and increased resistance to apoptosis.

High expression of EZH2 is associated with tumor aggressiveness and poor prognosis in patients with esophageal squamous cell carcinoma treated with definitive chemoradiotherapy

The enhancer of zeste homolog 2 (EZH2), a known repressor of gene transcription, has been reported to be associated with biological malignancy in several cancers. The potential oncogenic role of EZH2 and its clinical/prognostic significance, however, in esophageal squamous cell carcinoma (ESCC) are unclear. In this study, the methods of immunohistochemistry and fluorescence in-situ hybridization were used to examine protein expression and amplification of EZH2 in 98 pretreatment biopsy specimens of ESCC who received definitive chemoradiotherapy (CRT). High expression of EZH2 and amplification of EZH2 was found in 54.1% and 12.0% of ESCCs, respectively. High EZH2 expression was significantly correlated with increased cell proliferation (p = 0.009), high histopathological grade (p = 0.002), regional (p = 0.025) and distant lymph node metastasis (p < 0.001) and lack of clinical complete response to CRT (p = 0.028). Univariate analysis revealed that high expression of EZH2 was associated with poor metastasis-free survival (MFS) (p = 0.003), poor progression-free survival (PFS) (p = 0.001) and poor disease-specific survival (DSS) (p < 0.001). In multivariate analysis, high expression of EZH2, together with lack of clinical complete response, were evaluated as significant independent prognostic factors of MFS, PFS and DSS for patients with ESCC. These findings suggest that high expression of EZH2 correlates with tumor aggressiveness and adverse patient outcome in ESCC treated with definitive CRT. Evaluation of EZH2 expressions might be useful for predicting tumor response to CRT and prognosis for patients with ESCC.

Intensive expression of Bmi-1 is a new independent predictor of poor outcome in patients with ovarian carcinoma

BACKGROUND

It has been suggested that the B-cell specific moloney leukemia virus insertion site 1 (Bmi-1) gene plays an oncogenic role in several types of human cancer, but the status of Bmi-1 amplification and expression in ovarian cancer and its clinical/prognostic significance are unclear.

METHODS

The methods of immunohistochemistry and fluorescence in situ hybridization were utilized to examine protein expression and amplification of Bmi-1 in 30 normal ovaries, 30 ovarian cystadenomas, 40 borderline ovarian tumors and 179 ovarian carcinomas.

RESULTS

Intensive expression of Bmi-1 was detected in none of the normal ovaries, 3% cystadenomas, 10% borderline tumors, and 37% ovarian carcinomas, respectively. Amplification of Bmi-1 was detected in 8% of ovarian carcinomas. In ovarian carcinomas, significant positive associations were found between intensive expression of Bmi-1 and the tumors ascending histological grade, later pT/pN/pM and FIGO stages (P < 0.05). In univariate survival analysis of the ovarian carcinoma cohorts, a significant association of intensive expression of Bmi-1 with shortened patient survival (mean 49.3 months versus 100.3 months, p < 0.001) was demonstrated. Importantly, Bmi-1 expression provided significant independent prognostic parameters in multivariate analysis (p = 0.005).

CONCLUSIONS

These findings provide evidence that intensive expression of Bmi-1 might be important in the acquisition of an invasive and/or aggressive phenotype of ovarian carcinoma, and serve as a independent biomarker for shortened survival time of patients.

PRL-2 increases Epo and IL-3 responses in hematopoietic cells

Dual specificity protein tyrosine phosphatase PRL-2 is overexpressed in pediatric acute myeloid leukemia (AML) and is located at human chromosome 1p35, a region often rearranged or amplified in malignant lymphoma and B-cell chronic lymphocytic leukemia (B-CLL). Little is known of the significance of PRL-2 expression in hematopoietic malignancies. Herein we demonstrated that ectopic expression of PRL-2 in murine pre-B-cell line Baf3ER and mouse bone marrow cells induced key features associated with malignant progression and metastasis. PRL-2-transfected Baf3ER cells had augmented growth responses to hematopoietic growth factors Epo or IL-3 with shortened cell cycle, reduced requirement (5x) for Epo in cell survival, increased cell migration (3x), reduced cell adhesion (5x), and conversion to an immature cell morphology in association with increased expression (3x) of stem cell marker Bmi-1. When transduced into mouse bone marrow cells, PRL-2 increased Epo-induced colony formation (4x) and gave rise to larger colonies. These observations provide evidences implicating PRL-2 as a pathogenic molecule in hematopoietic malignancies and suggest its potential as a novel therapeutic target.

Bmi-1 gene is upregulated in early-stage hepatocellular carcinoma and correlates with ATP-binding cassette transporter B1 expression

Overexpression of "stemness gene"Bmi-1 has been identified in some solid tumors. We investigated Bmi-1 expression in hepatocellular carcinoma (HCC) and ATP-binding cassette transporter B1 (ABCB1) as a new potential target for Bmi-1. Bmi-1 was highly expressed in HCC cell lines and the most well differentiated cell line, KIM-1, showed the highest expression. Immunohistochemical, immunocytochemical, and immunoelectron microscopic analysis showed the Bmi-1 protein as having a high intensity of small dots within the nucleus which reflected concentrated sites of Bmi-1 repressive activity. Clear "dot-pattern" staining was observed in 24 of 37 (65%) well differentiated HCC (including 13 of 21 early nodules [62%]), in 32 of 71 (45%) moderately differentiated HCC, and 7 of 14 (50%) poorly differentiated HCC. A similar expression was not observed in non-cancerous background regions. High Bmi-1 expression was observed in the early and well differentiated HCC. Furthermore, overexpression and suppression of Bmi-1 was followed by a respective increase and decrease in ABCB1 expression. As with Bmi-1, high ABCB1 expression was also observed in the early and well differentiated HCC. A strong correlation between ABCB1 and Bmi-1 mRNA expression was seen in HCC cell lines and clinical samples (Pearson's correlation coefficient 0.95 and 0.90, respectively). The Bmi-1 gene is upregulated in HCC, and in particular is highly expressed in early and well differentiated HCC. The fact that this expression correlated with that of ABCB1 suggests a new regulation target for Bmi-1, and gives new insight into early hepatocarcinogenesis mechanisms and potential targets for future HCC treatment.

Bmi-1 is critical for the proliferation and invasiveness of gastric carcinoma cells

BACKGROUND AND AIM

Bmi-1 is a transcriptional repressor belonging to the Polycomb group and is associated with the cell proliferation and carcinogenesis of a variety of human cancers. The level of Bmi-1 expression correlates with the aggressiveness of many cancers, and is considered an important marker for cancer diagnosis. However, its role in gastric carcinoma is unknown.

METHODS

We used lentiviral mediated interfering short hairpin RNA to knockdown Bmi-1 expression in gastric carcinoma human gastric cancer cell line (AGS cells), then tested the cell proliferation by MTT assay, rate of colony formation by colony formation assay, cell cycle distribution by fluorescence-activated cell sorting and cell invasiveness by cell invasion assay. To analyze the expression and localization of Bmi-1 in gastric tumor tissues, we further performed the immunohistochemistry analysis on a gastric cancer tissue array.

RESULTS

We found that knocking down Bmi-1 led to slower cell growth, lesser cell invasiveness, decelerated colony formation, and altered cell cycle progression. In addition, a positive relationship between nuclear expression of Bmi-1 and gastric cancer was observed, suggesting that nucleus localization of Bmi-1 in the cells may be a novel marker of gastric cancer.

CONCLUSIONS

Our study highlights critical roles for Bmi-1 in gastric cancer, and suggests that Bmi-1 nuclear localization could be an important marker for the diagnosis of gastric cancer.

Loss of the CBX7 protein expression correlates with a more aggressive phenotype in pancreatic cancer

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.

The role of nuclear organization in cancer

The functional significance of changes in nuclear structure and organization in transformed cells remains one of the most enigmatic questions in cancer biology. In this review, we discuss relationships between nuclear organization and transcription in terms of the three-dimensional arrangement of genes in the interphase cancer nucleus and the regulatory functions of nuclear matrix proteins. We also analyse the role of nuclear topology in the generation of gene fusions. We speculate that this type of multi-layered analysis will one day provide a framework for a more comprehensive understanding of the genetic origins of cancer and the identification of new therapeutic targets.

ShRNA-mediated silencing of the Bmi-1 gene promotes senescence and inhibits migration in human gastric caner cell line BGC823

AIM: To investigate the effects of B-cell-specific Moloney murine leukaemia virus insertion site 1 (Bmi-1) gene knock-down on cell senescence and migration in human gastric caner cell line BGC823.

METHODS: Two pairs of complementary small hairpin RNA (shRNA) oligonucleotides targeting the Bmi-1 gene were devised, synthesized, annealed and cloned into the pRNAT-U6.2 vector. After DNA sequencing to verify the correct insertion of the shRNA sequences, the recombinant plasmids were transfected into BGC823 cells. The expression of Bmi-1 mRNA and protein was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively. The effects of Bmi-1 knockdown on cell senescence and migration were determined by β-Gal activity assay and Boyden chamber assay, respectively.

RESULTS: The double-stranded shRNA oligonucleotides targeting the Bmi-1 gene were successfully cloned into the pRNAT-U6.2 vector. DNA sequencing results verified the correct insertion of the shRNA sequences. RT-PCR and Western blot analyses indicated that the expression levels of Bmi-1 mRNA and protein were significantly downregulated in cells transfected with the recombinant plasmids. Particularly, Bmi-1 protein expression was almost completely abolished in cells transfected with the recombinant vector harboring shRNA targeting the sequence GGAGGAGGTGAATGATAAA (nt 1 104-1 122). Compared with untransfected cells and cells transfected with the empty vector, the average percentage of senescent cells increased and the number of cells passing through the Matrigel decreased in cells transfected with the recombinant vectors.

CONCLUSION: ShRNA-mediated silencing of the Bmi-1 gene can effectively promote cell senescence and reduce migration in human gastric caner cell line BGC823.

Somatic mutations altering EZH2 (Tyr641) in follicular and diffuse large B-cell lymphomas of germinal-center origin

Follicular lymphoma (FL) and the GCB subtype of diffuse large B-cell lymphoma (DLBCL) derive from germinal center B cells. Targeted resequencing studies have revealed mutations in various genes encoding proteins in the NF-kappaB pathway that contribute to the activated B-cell (ABC) DLBCL subtype, but thus far few GCB-specific mutations have been identified. Here we report recurrent somatic mutations affecting the polycomb-group oncogene EZH2, which encodes a histone methyltransferase responsible for trimethylating Lys27 of histone H3 (H3K27). After the recent discovery of mutations in KDM6A (UTX), which encodes the histone H3K27me3 demethylase UTX, in several cancer types, EZH2 is the second histone methyltransferase gene found to be mutated in cancer. These mutations, which result in the replacement of a single tyrosine in the SET domain of the EZH2 protein (Tyr641), occur in 21.7% of GCB DLBCLs and 7.2% of FLs and are absent from ABC DLBCLs. Our data are consistent with the notion that EZH2 proteins with mutant Tyr641 have reduced enzymatic activity in vitro.

Polycomb group protein gene silencing, non-coding RNA, stem cells, and cancer

Epigenetic programming is an important facet of biology, controlling gene expression patterns and the choice between developmental pathways. The Polycomb group proteins (PcGs) silence gene expression, allowing cells to both acquire and maintain identity. PcG silencing is important for stemness, X chromosome inactivation (XCI), genomic imprinting, and the abnormally silenced genes in cancers. Stem and cancer cells commonly share gene expression patterns, regulatory mechanisms, and signalling pathways. Many microRNA species have oncogenic or tumor suppressor activity, and disruptions in these networks are common in cancer; however, long non-coding (nc)RNA species are also important. Many of these directly guide PcG deposition and gene silencing at the HOX locus, during XCI, and in examples of genomic imprinting. Since inappropriate HOX expression and loss of genomic imprinting are hallmarks of cancer, disruption of long ncRNA-mediated PcG silencing likely has a role in oncogenesis. Aberrant silencing of coding and non-coding loci is critical for both the genesis and progression of cancers. In addition, PcGs are commonly abnormally overexpressed years prior to cancer pathology, making early PcG targeted therapy an option to reverse tumor formation, someday replacing the blunt instrument of eradication in the cancer therapy arsenal.

The Bmi-1 polycomb protein antagonizes the (-)-epigallocatechin-3-gallate-dependent suppression of skin cancer cell survival

The polycomb group (PcG) proteins are epigenetic regulators of gene expression that enhance cell survival. This regulation is achieved via action of two multiprotein PcG complexes--PRC2 (EED) and PRC1 [B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1)]. These complexes modulate gene expression by increasing histone methylation and reducing acetylation--leading to a closed chromatin conformation. Activity of these proteins is associated with increased cell proliferation and survival. We show increased expression of key PcG proteins in immortalized keratinocytes and skin cancer cell lines. We examine the role of two key PcG proteins, Bmi-1 and enhancer of zeste homolog 2 (Ezh2), and the impact of the active agent in green tea, (-)-epigallocatechin-3-gallate (EGCG), on the function of these regulators. EGCG treatment of SCC-13 cells reduces Bmi-1 and Ezh2 level and this is associated with reduced cell survival. The reduction in survival is associated with a global reduction in histone H3 lysine 27 trimethylation, a hallmark of PRC2 complex action. This change in PcG protein expression is associated with reduced expression of key proteins that enhance progression through the cell cycle [cyclin-dependent kinase (cdk)1, cdk2, cdk4, cyclin D1, cyclin E, cyclin A and cyclin B1] and increased expression of proteins that inhibit cell cycle progression (p21 and p27). Apoptosis is also enhanced, as evidenced by increased caspase 9, 8 and 3 cleavage and increased poly(adenosine diphosphate ribose) polymerase cleavage. EGCG treatment also increases Bax and suppresses Bcl-xL expression. Vector-mediated enhanced Bmi-1 expression reverses these EGCG-dependent changes. These findings suggest that green tea polyphenols reduce skin tumor cell survival by influencing PcG-mediated epigenetic regulatory mechanisms.

The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells

The polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is dysregulated in various cancers, and its upregulation strongly correlates with an invasive phenotype and poor prognosis in patients with nasopharyngeal carcinomas. However, the underlying mechanism of Bmi-1-mediated invasiveness remains unknown. In the current study, we found that upregulation of Bmi-1 induced epithelial-mesenchymal transition (EMT) and enhanced the motility and invasiveness of human nasopharyngeal epithelial cells, whereas silencing endogenous Bmi-1 expression reversed EMT and reduced motility. Furthermore, upregulation of Bmi-1 led to the stabilization of Snail, a transcriptional repressor associated with EMT, via modulation of PI3K/Akt/GSK-3beta signaling. Chromatin immunoprecipitation assays revealed that Bmi-1 transcriptionally downregulated expression of the tumor suppressor PTEN in tumor cells through direct association with the PTEN locus. This in vitro analysis was consistent with the statistical inverse correlation detected between Bmi-1 and PTEN expression in a cohort of human nasopharyngeal carcinoma biopsies. Moreover, ablation of PTEN expression partially rescued the migratory/invasive phenotype of Bmi-1-silenced cells, indicating that PTEN might be a major mediator of Bmi-1-induced EMT. Our results provide functional and mechanistic links between the oncoprotein Bmi-1 and the tumor suppressor PTEN in the development and progression of cancer.

Polycomb group proteins: navigators of lineage pathways led astray in cancer

The Polycomb group (PcG) proteins are transcriptional repressors that regulate lineage choices during development and differentiation. Recent studies have advanced our understanding of how the PcG proteins regulate cell fate decisions and how their deregulation potentially contributes to cancer. In this Review we discuss the emerging roles of long non-coding RNAs (ncRNAs) and a subset of transcription factors, which we call cell fate transcription factors, in the regulation of PcG association with target genes. We also speculate about how their deregulation contributes to tumorigenesis.

Repression of BMI1 in normal and leukemic human CD34+ cells impairs self-renewal and induces apoptosis

High expression of BMI1 in acute myeloid leukemia (AML) cells is associated with an unfavorable prognosis. Therefore, the effects of down-modulation of BMI1 in normal and leukemic CD34+ AML cells were studied using a lentiviral RNA interference approach. We demonstrate that down-modulation of BMI1 in cord blood CD34+ cells impaired long-term expansion and progenitor-forming capacity, both in cytokine-driven liquid cultures as well as in bone marrow stromal cocultures. In addition, long-term culture-initiating cell frequencies were dramatically decreased upon knockdown of BMI1, indicating an impaired maintenance of stem and progenitor cells. The reduced progenitor and stem cell frequencies were associated with increased expression of p14ARF and p16INK4A and enhanced apoptosis, which coincided with increased levels of intracellular reactive oxygen species and reduced FOXO3A expression. In AML CD34+ cells, down-modulation of BMI1 impaired long-term expansion, whereby self-renewal capacity was lost, as determined by the loss of replating capacity of the cultures. These phenotypes were also associated with increased expression levels of p14ARF and p16INK4A. Together our data indicate that BMI1 expression is required for maintenance and self-renewal of normal and leukemic stem and progenitor cells, and that expression of BMI1 protects cells against oxidative stress.

BMI1 sustains human glioblastoma multiforme stem cell renewal

Glioblastoma multiforme (GBM) is one of the most common and aggressive types of brain tumors. In GBM, a subpopulation of CD133-positive cancer initiating cells displays stem cell characteristics. The Polycomb group (PcG) and oncogene BMI1 is part of the Polycomb repressive complex 1 (PRC1) that regulates gene expression by modifying chromatin organization. Here we show that BMI1 is expressed in human GBM tumors and highly enriched in CD133-positive cells. Stable BMI1 knockdown using short hairpin RNA-expressing lentiviruses resulted in inhibition of clonogenic potential in vitro and of brain tumor formation in vivo. Cell biology studies support the notion that BMI1 prevents CD133-positive cell apoptosis and/or differentiation into neurons and astrocytes, depending on the cellular context. Gene expression analyses suggest that BMI1 represses alternate tumor suppressor pathways that attempt to compensate for INK4A/ARF/P53 deletion and PI(3)K/AKT hyperactivity. Inhibition of EZH2, the main component of the PRC2, also impaired GBM tumor growth. Our results reveal that PcG proteins are involved in GBM tumor growth and required to sustain cancer initiating stem cell renewal.

Combined epigenetic therapy with the histone methyltransferase EZH2 inhibitor 3-deazaneplanocin A and the histone deacetylase inhibitor panobinostat against human AML cells

The polycomb repressive complex (PRC) 2 contains 3 core proteins, EZH2, SUZ12, and EED, in which the SET (suppressor of variegation-enhancer of zeste-trithorax) domain of EZH2 mediates the histone methyltransferase activity. This induces trimethylation of lysine 27 on histone H3, regulates the expression of HOX genes, and promotes proliferation and aggressiveness of neoplastic cells. In this study, we demonstrate that treatment with the S-adenosylhomocysteine hydrolase inhibitor 3-deazaneplanocin A (DZNep) depletes EZH2 levels, and inhibits trimethylation of lysine 27 on histone H3 in the cultured human acute myeloid leukemia (AML) HL-60 and OCI-AML3 cells and in primary AML cells. DZNep treatment induced p16, p21, p27, and FBXO32 while depleting cyclin E and HOXA9 levels. Similar findings were observed after treatment with small interfering RNA to EZH2. In addition, DZNep treatment induced apoptosis in cultured and primary AML cells. Furthermore, compared with treatment with each agent alone, cotreatment with DZNep and the pan-histone deacetylase inhibitor panobinostat caused more depletion of EZH2, induced more apoptosis of AML, but not normal CD34(+) bone marrow progenitor cells, and significantly improved survival of nonobese diabetic/severe combined immunodeficiency mice with HL-60 leukemia. These findings indicate that the combination of DZNep and panobinostat is effective and relatively selective epigenetic therapy against AML cells.

Bmi-1 over-expression plays a secondary role in chronic myeloid leukemia transformation

It has been demonstrated that over-expression of Bmi-1 occurs in a variety of cancers, including several types of leukemia. This gene plays a key role in the self-renewal of stem cells. Leukemic cells lacking Bmi-1 underwent proliferation arrest and showed signs of differentiation and apoptosis. These findings led to the proposal of Bmi-1 as a potential target for therapeutic intervention in cancer. In this study, we investigated the role of Bmi-1 in chronic myeloid leukemia (CML). Using qRT-PCR, we demonstrated a significantly increased level of Bmi-1 transcript in CML cells. Using array analysis, we determined the deregulation of several genes after Bmi-1 silencing. Proapoptotic genes BAD and TRADD, and CASP8, p16-INK4, BRCA2, Notch4 and Wnt-8B were elevated. PLK1, SOD1, E2F-3, two retinoblastoma binding proteins (RBQ1 and RBBP4) and HDGF were reduced after Bmi-1 inhibition. Additionally, we tested the impact of Bmi-1 siRNA on CML cell growth; however, there was no apparent change after Bmi-1 suppression. Despite the fact that Bmi-1 deregulation occurs in CML and its expression is connected to several oncogenic processes, Bmi-1 seems to play a secondary role in CML transformation.

BMI1 cooperates with H-RAS to induce an aggressive breast cancer phenotype with brain metastases

BMI1 is a member of the polycomb group of transcription repressors that functions in stem cell maintenance and oncogenesis through inhibition of the INK4A/ARF tumour suppressor locus. Overexpression of BMI1 is associated with poor prognosis in several human cancers, including breast cancer. We have previously shown that BMI1 collaborates with H-RAS to induce transformation of MCF10A human mammary epithelial cells via dysregulation of multiple growth pathways independent of the INK4A/ARF locus. In this study, we demonstrate that BMI1 collaborates with H-RAS to promote increased proliferation, invasion, and resistance to apoptosis in vitro, and an increased rate of spontaneous metastases from mammary fat pad xenografts including novel metastases to the brain. Furthermore, in collaboration with H-RAS, BMI1 induced fulminant metastatic disease in the lung using a tail vein model of haematogenous spread through accelerated cellular proliferation and inhibition of apoptosis. Finally, we show that knockdown of BMI1 in several established breast cancer cell lines leads to decreased oncogenic behaviour in vitro and in vivo. In summary, BMI1 collaborates with H-RAS to induce an aggressive and metastatic phenotype with the unusual occurrence of brain metastasis, making it an important target for diagnosis and treatment of aggressive breast cancer.

Effect of Bmi-1 gene on the proliferation of gastric cancer cells and its mechanism

AIM: To explore the effect of Bmi-1 knock-down on Akt/PKB activity, P16INK4a expression, cell proliferation and cell senescence.

METHODS: Bmi-1 expression in AGS was down-regulated using SiRNA approach; Bmi-1 protein and related proteins (pAkt, Akt, P16INK4a) were detected by Western blot. SA-β-Gal activity assay was applied for detection of the senescent cells, and soft-agar growth assay was used to detect the clone formation.

RESULTS: In the SA-β-Gal activity assay, the average senescent cell rate in Bmi-1 i group was 28% ± 3.5%, compared with 16% ± 2.7% in Ctrl i group (P < 0.01). In the soft-agar growth assay, the average clone formation number was 3.4 ± 1.4, compared with 11 ± 2.3 in Ctrl i group (P < 0.01). The Bmi-1 protein level was down-regulated significantly in the Bmi-1 i group, Akt activity was down-regulated and P16INK4a protein was up-regulated.

CONCLUSION: Bmi-1 knock-down may promote cell senescence and inhibit cell proliferation via down-regulating Akt/PKB activity and up-regulating P16INK4a.

Distinct expression of polycomb group proteins EZH2 and BMI1 in hepatocellular carcinoma

Polycomb gene products play a crucial role in the development of highly malignant phenotypes and aggressive cancer progression in a variety of cancers; however, their role in hepatocellular carcinoma remains unclear. First, we analyzed the impact of EZH2 and BMI1 modulation on cell growth of HepG2 cells. 3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays revealed marked growth inhibition after EZH2 or BMI1 knockdown. In addition, simultaneous knockdown of these 2 genes further augmented cell growth inhibitory effects. Next, we conducted immunohistochemical assessment of 86 hepatocellular carcinoma surgical specimens, evaluating the correlation between EZH2 and BMI1 protein expression and clinicopathologic features. High-level EZH2 and BMI1 expression was detected in 57 (66.3%) and 52 tumor tissues (60.5%), respectively. Among these, 48 tumor tissues (55.8%) showed colocalization of EZH2 and BMI1 in almost all tumor cells. The cumulative recurrence rate, but not survival rate, was significantly higher in patients positive for EZH2 (P = .029) and BMI1 (P = .039) than in their negative counterparts, as determined by Kaplan-Meier analysis. These data indicate that EZH2 and BMI1 may cooperate in initiation and progression of hepatocellular carcinoma.

Expression of Bmi-1 is a prognostic marker in bladder cancer

Background

The molecular mechanisms of the development and progression of bladder cancer are poorly understood. The objective of this study was to analyze the expression of Bmi-1 protein and its clinical significance in human bladder cancer.

Methods

We examined the expression of Bmi-1 mRNA and Bmi-1 protein by RT-PCR and Western blot, respectively in 14 paired bladder cancers and the adjacent normal tissues. The expression of Bmi-1 protein in 137 specimens of bladder cancer and 30 specimens of adjacent normal bladder tissue was determined by immunohistochemistry. Statistical analyses were applied to test the relationship between expression of Bmi-1, and clinicopathologic features and prognosis.

Results

Expression of Bmi-1 mRNA and protein was higher in bladder cancers than in the adjacent normal tissues in 14 paired samples (P < 0.01). By immunohistochemical examination, five of 30 adjacent normal bladder specimens (16.7%) versus 75 of 137 bladder cancers (54.3%) showed Bmi-1 protein expression (P < 0.05). Bmi-1 protein expression was intense in 20.6%, 54.3%, and 78.8% of tumors of histopathological stages G1, G2, and G3, respectively (P < 0.05). Expression of Bmi-1 protein was greater in invasive bladder cancers than in superficial bladder cancers (81.5% versus 32.5%, P < 0.05). In invasive bladder cancers, the expression of Bmi-1 protein in progression-free cancers was similar to that of cancers that have progressed (80.0% versus 82.4%, P > 0.5). In superficial bladder cancers, the expression of Bmi-1 protein in recurrent cases was higher than in recurrence-free cases (62.5% versus 13.7%, P < 0.05). Bmi-1 expression was positively correlated with tumor classification and TNM stage (P < 0.05), but not with tumor number (P > 0.05). Five-year survival in the group with higher Bmi-1 expression was 50.8%, while it was 78.5% in the group with lower Bmi-1 expression (P < 0.05). Patients with higher Bmi-1 expression had shorter survival time, whereas patients with lower Bmi-1 expression had longer survival time (P < 0.05).

Conclusion

Expression of Bmi-1 was greater in bladder cancers than in the adjacent normal tissues. The examination of Bmi-1 protein expression is potentially valuable in prognostic evaluation of bladder cancer.

Oncoprotein BMI-1 induces the malignant transformation of HaCaT cells

BMI-1 (B-cell-specific Moloney murine leukemia virus integration site 1), a novel oncogene, has attracted much attention in recent years for its involvement in the initiation of a variety of tumors. Recent evidence showed that BMI-1 was highly expressed in neoplastic skin lesions. However, whether dysregulated BMI-1 expression is causal for the transformation of skin cells remains unknown. In this study, we stably expressed BMI-1 in a human keratinocyte cell line, HaCaT. The expression of wild-type BMI-1 induced the malignant transformation of HaCaT cells in vitro. More importantly, we found that expression of BMI-1 promoted formation of squamous cell carcinomas in vivo. Furthermore, we showed that BMI-1 expression led to the downregulation of tumor suppressors, such as p16INK4a and p14ARF, cell adhesion molecules, such as E-Cadherin, and differentiation related factor, such as KRT6. Therefore, our findings demonstrated that dysregulated BMI-1 could indeed lead to keratinocytes transformation and tumorigenesis, potentially through promoting cell cycle progression and increasing cell mobility.

Roles of the EZH2 histone methyltransferase in cancer epigenetics

EZH2 is the catalytic subunit of Polycomb repressive complex 2 (PRC2), which is a highly conserved histone methyltransferase that targets lysine-27 of histone H3. This methylated H3-K27 chromatin mark is commonly associated with silencing of differentiation genes in organisms ranging from plants to flies to humans. Studies on human tumors show that EZH2 is frequently over-expressed in a wide variety of cancerous tissue types, including prostate and breast. Although the mechanistic contributions of EZH2 to cancer progression are not yet determined, functional links between EZH2-mediated histone methylation and DNA methylation suggest partnership with the gene silencing machinery implicated in tumor suppressor loss. Here we review the basic molecular biology of EZH2 and the findings that implicate EZH2 in different cancers. We also discuss EZH2 connections to other silencing enzymes, such as DNA methyltransferases and histone deacetylases, and we consider progress on deciphering mechanistic consequences of EZH2 overabundance and its potential roles in tumorigenesis. Finally, we review recent findings that link EZH2 roles in stem cells and cancer, and we consider prospects for integrating EZH2 blockade into strategies for developing epigenetic therapies.

Expression of VEGF-A/C, VEGF-R2, PDGF-alpha/beta, c-kit, EGFR, Her-2/Neu, Mcl-1 and Bmi-1 in Merkel cell carcinoma

Merkel cell carcinoma is a rare but very aggressive tumor of the skin. With current treatment options, Merkel cell carcinoma is associated with a high incidence of recurrence and metastasis. Targeted anticancer therapies such as receptor tyrosine kinase inhibitors and antisense oligonucleotides have been found to be a promising new type of treatment for various types of cancer. To evaluate whether the use of targeted therapies is a possible treatment option in Merkel cell carcinoma, we determined the expression of the target molecules c-kit, Mcl-1, Bmi-1, vascular endothelial growth factor (VEGF)-A, VEGF-C, VEGF-receptor 2 (VEGF-R2), platelet-derived growth factor (PDGF)-alpha, PDGF-beta, epidermal growth factor receptor (EGFR) and Her-2/Neu in a tissue microarray of 32 samples of 29 patients with Merkel cell carcinoma. C-kit-positive samples were analyzed for mutations in exons 9 and 11. The tissue microarray was stained immunohistochemically with antibodies directed against the above-mentioned proteins, and an immunoreactivity score was calculated. DNA was extracted from c-kit-positive samples and was analyzed for exon 9 and 11 mutations using direct DNA sequencing. We found that c-kit (7%), Mcl-1 (88%), Bmi-1 (78%), VEGF-A (91%), VEGF-C (75%) VEGF-R2 (88%), PDGF-alpha (72%) and PDGF-beta (13%) were expressed in Merkel cell carcinomas. All samples showed a lack of EGFR and Her-2/Neu expression. Analysis of c-kit revealed no mutations. As VEGF-A, VEGF-C, VEGF-R2, PDGFs and c-kit are targets of new cytostatic agents used in the treatment of other cancers, inhibition by a multitargeted chemotherapy could be a very promising treatment option. High expression of Bmi-1 and Mcl-1 warrants further studies on the use of antisense oligonucleotides in Merkel cell carcinoma.

Epigenetic plasticity of chromatin in embryonic and hematopoietic stem/progenitor cells: therapeutic potential of cell reprogramming

During embryonic development and adult life, the plasticity and reversibility of modifications that affect the chromatin structure is important in the expression of genes involved in cell fate decisions and the maintenance of cell-differentiated state. Epigenetic changes in DNA and chromatin, which must occur to allow the accessibility of transcriptional factors at specific DNA-binding sites, are regarded as emerging major players for embryonic and hematopoietic stem cell (HSC) development and lineage differentiation. Epigenetic deregulation of gene expression, whether it be in conjunction with chromosomal alterations and gene mutations or not, is a newly recognized mechanism that leads to several diseases, including leukemia. The reversibility of epigenetic modifications makes DNA and chromatin changes attractive targets for therapeutic intervention. Here we review some of the epigenetic mechanisms that regulate gene expression in pluripotent embryonic and multipotent HSCs but may be deregulated in leukemia, and the clinical approaches designed to target the chromatin structure in leukemic cells.

Epigenetic regulator polycomb group protein complexes control cell fate and cancer

The chromatin-associated Polycomb group (PcG) proteins were first identified in genetic screens for homeotic transformations in Drosophila melanogaster. Besides body patterning, members of the PcG are now known to regulate epigenetic cellular memory, stem cell self-renewal, and cancer development. Here, we discuss the multifarious functions of the PcG family, isoforms of protein complexes, and its enzymatic activities, for example histone methylation, links to DNA methylation, its phosphorylation status, H2A mono-ubiquitination, SUMOylation, and links to non-coding RNA. We also discuss the function of cytosolic PcG complexes as a regulator of receptor-induced actin polymerization and proliferation in a methylation-dependent manner. We propose that the functional versatility of PcG protein complexes contributed significantly to the complexity of heritable gene repression mechanisms, signal transduction, and cell proliferation in cancer development.

Myelodysplastic syndromes

There has been a remarkable explosion of knowledge into the molecular defects that underlie the acute and chronic leukemias, leading to the introduction of targeted therapies that can block key cellular events essential for the viability of the leukemic cell. Our understanding of the pathogenesis of the myelodysplastic syndromes (MDSs) has lagged behind, at least in part, because they represent a more heterogeneous group of disorders. The significant immunologic abnormalities described in this disease, coupled with the admixture of MDS stem or progenitor cells within the myriad types of dysplastic and normal cells in the bone marrow and peripheral blood, have made it difficult to molecularly characterize and model MDS. The recent availability of several, effective (ie, FDA-approved) therapies for MDS and newly described mouse models that mimic aspects of the human disease provide an opportune moment to try to leverage this new knowledge into a better understanding of and better therapies for MDS.

Expression of the Polycomb-Group protein BMI1 and correlation with p16 in astrocytomas an immunohistochemical study on 80 cases

A number of studies on the putative relation between Polycomb-Group (PcG) proteins overexpression and carcinogenesis have been published recently. BMI1, the prototype PcG gene, is critically involved in cell cycle control and differentiation, and despite the regulatory role demonstrated in central nervous system (CNS) development, its implication in brain tumorigenesis is scarcely known. Moreover, to the best of our knowledge, large studies on human brain tumors tissue are lacking. To gain a new insight, we tested 80 primary brain astrocytomas for BMI1 expression using immunohistochemistry and established a correlation with the expression of p16, a negatively regulated target of BMI1 function. Fifty-four cases (72.5%) were BMI1 + /p16-, and 22 cases (27.5%) were BMI1 + /p16+. Slight non-significant differences were noted in the expression profile between grades II, III, and IV astrocytomas. However, when the 22 BMI1 + /p16+ tumors were examined cytologically, a substantial proportion contained a significant gemistocytic component, which is thought to be an adverse prognostic factor or to display a high degree of anaplasia, suggesting a common molecular mechanism of BMI1/p16 pathway disruption, which may have prognostic implications.

Loss of BMI-1 expression is associated with clinical progress of malignant melanoma

BMI-1 is a member of the Polycomb group of genes (PcGs) and is involved in embryonic gene regulation and maintenance of adult stem cells. It has been suggested that BMI-1 protein is important in cell cycle regulation, since both p16/INK4a and p14/ARF are downstream BMI-1 targets. BMI-1 has been implicated in the development and progression of several malignancies, but its role in melanocytic tumors of the skin is unknown. In the present study, using immunohistochemistry on 178 benign and malignant melanocytic lesions and two different antibodies, BMI-1 expression was reduced in melanomas compared with benign nevi. In established melanomas, loss of BMI-1 expression was associated with features of aggressive tumors, such as increased tumor cell proliferation, presence of necrosis and increased expression of both N-cadherin and beta3-integrin, indicating a more invasive and mesenchymal phenotype. Low BMI-1 expression was associated with low p14 and CDK4 but not with p16 expression. Low levels of BMI-1 expression were also significantly associated with decreased patient survival.

Bmi-1 expression predicts prognosis for patients with gastric carcinoma

BACKGROUND AND OBJECTIVE

The Bmi-1 gene is a transcriptional repressor involved in oncogenesis in various human cancers. Here, we examine Bmi-1 expression in gastric carcinoma (GC) and investigates whether its expression correlates with patient prognosis.

METHODS

Immunohistochemistry was performed using an anti-Bmi-1 antibody on primary tumor samples of 146 cases of GC. The association between Bmi-1 expression and the clinicopathological status and prognosis of GC patients was statistically analyzed. Furthermore, reverse transcription-PCR (RT-PCR) and Western blotting were performed to determine the expression levels of Bmi-1 in an additional 8 GC and the adjacent non-cancerous samples.

RESULTS

Using immunohistochemistry, we found that 99 of 146 paraffin-embedded GC samples expressed Bmi-1 extensively. Statistical analysis showed that Bmi-1 overexpression was highly correlated with tumor size, clinical stage, lymph node metastasis and T classification (P < 0.05), Patients with Bmi-1 expression had shorter overall survival time than those without Bmi-1 expression (P < 0.01). Multivariate analysis indicated that Bmi-1 expression is an independent prognostic factor of GC. RT-PCR and Western blotting showed that Bmi-1 was up-regulated at both the transcriptional and translational levels in the GC tissues compared with the adjacent non-cancerous tissues.

CONCLUSIONS

Bmi-1 may serve as a valuable marker for diagnosis and prognosis of GC.

Enhancer of zeste homolog 2 downregulates E-cadherin by mediating histone H3 methylation in gastric cancer cells

Overexpression of enhancer of zeste homolog 2 (EZH2), an epigenetic repressor, occurs in various malignancies and is associated with poor prognosis; however, the functional role of EZH2 overexpression in cancer versus non-cancerous tissue remains unclear. In this study, we found an inverse correlation between EZH2 and E-cadherin gene expression in gastric cancer cells. Knockdown of EZH2 by short interfering RNA in gastric cancer cells resulted in a restoration of the E-cadherin gene. We showed that the EZH2 complex existed with histone H3 and Lys27, which were methylated on E-cadherin promoter regions in gastric cancer cells. The restoration of E-cadherin was not involved in the change of the DNA methylation status in the E-cadherin promoter region. Immunofluorescence staining confirmed the expression of E-cadherin protein present in the cell membrane was restored after knockdown of EZH2, resulting in changing the cancer phenotype, such as its invasive capacity. In vivo, the relationship of inverse expression between EZH2 protein and E-cadherin protein was observed at the individual cellular level in gastric cancer tissue. This study provides into the mechanisms underlying the functional role of EZH2 overexpression in gastric cancer cells and a new modality of regulation of E-cadherin expression in silencing mechanisms of tumor suppressor genes. Our present study paves the way for exploring the blockade of EZH2 overexpression as a novel approach to treating cancer.

BMI-1 expression is inversely correlated with the grading of renal clear cell carcinoma

BMI-1 regulates cell proliferation and differentiation, is involved in stem cell maintenance and can act as an oncogene. We investigated BMI-1 expression in healthy normal kidney and in 77 renal tumours by immunohistochemistry, and correlated it with tumour differentiation. BMI-1 could regularly be demonstrated in distal tubules and in Bowman's capsule, whereas it was mostly lacking in proximal tubules, indicating that it may rather be a differentiation marker of different renal cell populations than a stem cell marker. In contrast to previous studies demonstrating a correlation between BMI-1 expression and malignancy, we showed that its expression was inversely correlated with the differentiation grade of clear cell carcinoma. Furthermore, despite their different biologies, BMI-1 was strongly expressed in both papillary carcinomas and oncocytomas. Thus, in renal clear cell carcinomas BMI-1 is rather a differentiation marker lost in carcinomas with high malignancy than an oncogene involved in tumour progression.

Independent prognostic value of the basal-like phenotype of breast cancer and associations with EGFR and candidate stem cell marker BMI-1

AIMS

To study the relationship between basal-like breast cancers, epidermal growth factor receptor (EGFR) and candidate stem cell markers (BMI-1, EZH2, Oct-4) in a population-based setting.

METHODS AND RESULTS

Immunohistochemistry was evaluated in a series of 190 breast cancers. Basal-like phenotype (BLP) 1-5 was found in 4.3-14.3% of cases. EGFR was expressed in 9% of cases and associated with cytokeratin (CK) 5 and P-cadherin positivity, but not with survival; 28% of CK5+ cases were EGFR+. On multivariate analysis, basal-like differentiation and lymph node status were independent prognostic factors of comparable strength. BMI-1 positivity (42.6%) was associated with absence of basal-like features, oestrogen receptor positivity and low Ki67, but not related to survival. BMI was not associated with EZH2 expression, and these markers tended to show opposite associations with other variables, suggesting different roles in breast cancer. Oct-4 expression was not detected in this series.

CONCLUSIONS

Basal-like features and lymph node status were strong and independent prognostic factors in this population-based series of breast cancer. Neither EGFR nor BMI-1 had significant prognostic impact, whereas EZH2 expression was associated with decreased survival. BMI-1 was inversely related to basal-like factors, and a stem cell phenotype of the basal-like subgroup could not be verified by this marker.

Circulating Bmi-1 mRNA as a possible prognostic factor for advanced breast cancer patients

Introduction

Deregulation of Polycomb member Bmi-1 is involved in cell proliferation and human oncogenesis. Modulation of Bmi-1 is found in several tumor tissues, including primary breast carcinomas; however, analysis of Bmi-1 in plasma of cancer patients has not been reported. This is the first study that evaluates Bmi-1 in plasma by using a large series of primary breast carcinomas to investigate the presence at diagnosis of detectable Bmi-1 mRNA in plasma and possible correlations between this event and a series of clinical-pathological parameters of the tumors.

Methods

Bmi-1 expression levels were quantified in plasma of 111 breast cancer patients and in 20 healthy controls by real-time quantitative polymerase chain reaction.

Results

Cancer patients with the presence of Bmi-1 mRNA in plasma had higher levels of Bmi-1 expression than healthy controls with Bmi-1 mRNA in plasma. The higher expression levels of Bmi-1 correlated with well-established markers of poor clinical outcome in breast cancer such as positive p53 immunostaining and negative progesterone receptors. Moreover, we described for the first time a statistically significant correlation between Bmi-1 expression in plasma of breast cancer patients and disease-free and overall survival in advanced stages.

Conclusion

Our results suggest that levels of Bmi-1 expression may be a surrogate marker of poor prognosis and may become clinically useful as noninvasive diagnostic markers.

Long-term maintenance of human hematopoietic stem/progenitor cells by expression of BMI1

The polycomb group (PcG) gene BMI1 has been identified as one of the key epigenetic regulators of cell fates during different stages of development in multiple murine tissues. In a clinically relevant model, we demonstrate that enforced expression of BMI1 in cord blood CD34+ cells results in long-term maintenance and self-renewal of human hematopoietic stem and progenitor cells. Long-term culture-initiating cell frequencies were increased upon stable expression of BMI1 and these cells engrafted more efficiently in NOD-SCID mice. Week 5 cobblestone area-forming cells (CAFCs) were replated to give rise to secondary CAFCs. Serial transplantation studies in NOD-SCID mice revealed that secondary engraftment was only achieved with cells overexpressing BMI1. Importantly, BMI1-transduced cells proliferated in stroma-free cytokine-dependent cultures for more than 20 weeks, while a stable population of approximately 1% to 5% of CD34+ cells was preserved that retained colony-forming capacity. Whereas control cells lost most of their NOD-SCID engraftment potential after 10 days of ex vivo culturing in absence of stroma, NOD-SCID multilineage engraftment was retained by overexpression of BMI1. Thus, our data indicate that self-renewal of human hematopoietic stem cells is enhanced by BMI1, and we classify BMI1 as an intrinsic regulator of human stem/progenitor cell self-renewal.

Prognostic value of Bmi-1 oncoprotein expression in NSCLC patients: a tissue microarray study

PURPOSE

Bmi-1 is a Polycomb group member which participates in many physiological processes as well as in a wide spectrum of cancers. The aim of this study was to investigate Bmi-1 expression in non-small cell lung cancer (NSCLC) in respect to clinicopathological features and therapeutic outcomes.

METHODS

Immunohistochemical staining for Bmi-1 was performed on tissue microarrays (TMAs) constructed from 179 formalin-fixed and paraffin-embedded NSCLC samples (106 squamous, 58 adeno-, and 15 large cell carcinomas). Data were subject to statistical analysis by SPSS.

RESULTS

Overall evaluation of all tumor cases showed that 20 (11.43%) were negative, 37 (21.14%) showed weak, 65 (37.14%) moderate and 57 (32.57%) strong nuclear positivity for Bmi-1. Statistical analysis of our data revealed that the expression of Bmi-1 was significantly higher in stage III (P = 10(-6)) and stage IV (P = 10(-5)) tumors compared to stages I and II tumors. The administration of adjuvant chemotherapy significantly increased DFS at stage I and II patients who did not express Bmi-1 when compared to their Bmi-1 positive counterparts (P = 0.05).

CONCLUSIONS

Our results suggest that Bmi-1 is significantly associated with progression of NSCLC and might serve as a prognostic marker of adverse disease outcome.

Chromatin-modifying proteins in cancer

Chromatin-modifying proteins mold the genome into areas that are accessible for transcriptional activity and areas that are transcriptionally silent. This epigenetic gene regulation allows for different transcriptional programs to be conducted in different cell types at different timepoints-despite the fact that all cells in the organism contain the same genetic information. A large amount of data gathered over the last decades has demonstrated that deregulation of chromatin-modifying proteins is etiologically involved in the development and progression of cancer. Here we discuss how epigenetic alterations influence cancer development and review known cancer-associated alterations in chromatin-modifying proteins.

Importance of Ezh2 polycomb protein in tumorigenesis process interfering with the pathway of growth suppressive key elements

An understanding of the mechanisms that uncover the dynamic changes in the distribution of the chromatin modifying enzymes and regulatory proteins on their target loci could provide further insight into the phenomenon of malignant transformation. Based on the current available data, it seems more and more clear that an abnormal expression of Ezh2, a member of the Polycomb group (PcG) protein, may be involved in the tumorigenesis process, in addition, different studies identify Ezh2 as a potential marker that distinguish aggressive prostate and breast cancer from indolent one. Recent investigation show that ectopic expression of Ezh2 provides proliferative advantage to primary cells through interaction with the pathways of key elements that control cell growth arrest and differentiation, like members of the retinoblastoma (Rb) family. Here, we outline how these pathways converge and we review the recent advances on the molecular mechanisms that promote cell cycle progression through deregulation of Ezh2 protein level, providing novel links between cancer progression and chromatin remodeling machineries.

Dysregulated expression of stem cell factor Bmi1 in precancerous lesions of the gastrointestinal tract

PURPOSE

It is important to identify the definitive molecular switches involved in the malignant transformation of premalignant tissues. Cellular senescence is a specific characteristic of precancerous tissues, but not of cancers, which might reflect tumorigenesis-protecting mechanisms in premalignant lesions. Polycomb protein Bmi1, which is a potent negative regulator of the p16INK4 gene, suppresses senescence in primary cells and is overexpressed in various cancers. We hypothesized that Bmi1 expression would also be dysregulated in precancerous lesions in human digestive precancerous tissues.

EXPERIMENTAL DESIGN

Bmi1 expression was investigated in cancerous and precancerous tissues of the digestive tract. The expression of p16, beta-catenin, and Gli1 and the in vivo methylation status of the p16 gene were also analyzed in serial sections of colonic precancerous lesions.

RESULTS

Bmi1 was clearly overexpressed across a broad spectrum of gastrointestinal cancers, and the expression of Bmi1 increased in a manner that reflected the pathologic malignant features of precancerous colonic tissues (low-grade dysplasia, 12.9 +/- 2.0%; high-grade dysplasia, 82.9 +/- 1.6%; cancer, 87.5 +/- 2.4%). p16 was also strongly expressed in high-grade dysplasia, but not in cancers. p16 promoter methylation was detected only in some Bmi1-positive neoplastic cells.

CONCLUSIONS

Bmi1 overexpression was correlated with the malignant grades of human digestive precancerous tissues, which suggests that advanced Bmi1 dysregulation might predict malignant progression. The abnormal Bmi1 expression might link to malignant transformation via the disturbance of orderly histone modification.