BMI1 as a novel target for drug discovery in cancer

O-GlcNAcylation modulates Bmi-1 protein stability and potential oncogenic function in prostate cancer

The Polycomb group transcriptional repressor Bmi-1 often overexpressed and participated in stem cells self-renewal and tumorigenesis initiating of prostate cancer. In this progression, Bmi-1 protein was regulated by transcription and post-translational modifications (PTMs). Nobly, the underlying PTMs regulation of Bmi-1 is poorly known. Here we use co-immunoprecipitation show that in C4-2 cell line, Bmi-1 directly interacted with OGT which is the only known enzyme catalyzed the O-GlcNAcylation in human. Furthermore, we identified that Ser255 is the site for Bmi-1 O-GlcNAcylation, and O-GlcNAcylation promoted Bmi-1 protein stability and its oncogenic activity. Finally, microarray analysis has characterized potential oncogenes associated pathway subject to repression via the OGT-Bmi-1 axis. Taken together, these results indicate that OGT-mediated O-GlcNAcylation at Ser255 stabilizes Bmi-1 and hence inhibits the TP53, PTEN and CDKN1A/CDKN2A pathway. The study not only uncovers a novel functional PTMs of Bmi-1 but also reveals a unique oncogenic role of O-GlcNAcylation in prostate cancer.

Fas signaling induces stemness properties in colorectal cancer by regulation of Bmi1

Fas signaling promotes colorectal cancer (CRC) metastasis by inducing epithelial-mesenchymal transition (EMT). The acquisition of EMT properties in turn induces stemness but the mechanism by which Fas signaling contributes to it still remains unclear. Hence, the aim of this study was to investigate how Fas signaling regulates CRC stemness. For this purpose, soft agar assay, sphere formation assay, cell survival analysis, immunoblot, qRT-PCR, chromatin immunoprecipitation, and luciferase reporter assay were performed. Expression of FasL, Bmi1, and the miR-200c in CRC specimens was examined through immunohistochemistry, qRT-PCR, and immunoblot. In our study, Fas signaling induced stem cell properties in CRC specimens, relying on ERK1/2 MAPK pathway, with Bmi1 being mainly responsible for FasL-induced stemness. FasL treatment promoted Bmi1 expression by inhibiting miR-200c, which targets Bmi1 3'UTR region. Furthermore, FasL-induced Zeb1 binded with miR-200c promoter and inhibited its expression. Moreover, FasL-induced β-catenin nuclear expression promoted Zeb1 expression by binding with Zeb1 promoter. GSK-3β, which regulates β-catenin, was inhibited by FasL-induced ERK1/2 MAPK signaling. Finally, FasL and Bmi1 expression in clinical samples increased during CRC progression, and a positive correlation between them was observed. Patients with high FasL and Bmi1 expression had a worse prognosis than patients with low expression. In conclusion, our results showed that Fas signaling can promote stemness in CRC through the modulation of Bmi1 expression via the ERK1/2 MAPK/GSK-3β/β-catenin/Zeb1/miR-200c axis, suggesting that Fas signaling-based cancer therapies should be administered cautiously, as the activation of this pathway not only leads to apoptosis but also induces stemness in CRC.

Deletion of RDINK4/ARF enhancer: A novel mutation to "inactivate" the INK4-ARF locus

The presence of an enhancer element, RD^INK4/ARF (RD), in the prominent INK4-ARF locus provides a novel en bloc mechanism to simultaneously regulate the transcription of the p15^INK4B (p15), p16^INK4A (p16), and p14^ARF tumor suppressor genes. While genetic inactivation of p15, p16, and p14^ARF in human cancers has been extensively studied, little is known about RD alteration and its potential contributions to cancer progression. In this review, we discuss recent developments in RD alteration and its association with p15, p16, and p14^ARF alterations in human cancers, and demonstrate that RD deletion may represent a novel mechanism to simultaneously down-regulate p15, p16, and p14^ARF, thus promoting carcinogenesis.

Identification of BMI1 Promoter Inhibitors from Beaumontia murtonii and Eugenia operculata

B-Cell-specific Moloney murine leukemia virus insertion region 1 (BMI1) is a core component of the polycomb repressive complex 1 (PRC1). Abnormal expression of BMI1 is associated with a number of human malignances and cancer stem cells (CSCs), which cause chemotherapy resistance. Therefore, small molecules that inhibit BMI1 expression are potential candidates for cancer therapy. In this study, a cell-based reporter gene assay was developed that allowed BMI1 promoter activity to be measured in 293T human embryonic kidney cells based on luciferase expression levels. Using this screening assay, the methanol-soluble extracts of Beaumontia murtonii and Eugenia operculata were selected as leads. Bioassay-guided fractionation of the extracts led to the isolation of three known cardenolides (1-3) and one new compound (4) from B. murtonii and two known triterpenoids (5 and 6) and one new compound (7) from E. operculata. These seven compounds inhibited BMI1 promoter activity (IC₅₀ range 0.093-23.0 μM), and the most active compound, wallichoside (1), was further evaluated. Western blot analysis revealed that wallichoside (1) decreases BMI1 protein levels in HCT116 human colon carcinoma cells, and flow cytometry analysis showed that it significantly reduced levels of the CSC biomarker epithelial cell adhesion molecule. Wallichoside (1) also inhibited sphere formation of Huh7 human hepatocellular carcinoma cells, indicating that it diminished the self-renewal capability of CSCs.

Negative regulation of Bmi-1 by AMPK and implication in cancer progression

Bmi-1 is a transcriptional regulator that promotes tumor cell self-renewal and epithelial to mesenchymal transition and its upregulation is associated with tumor progression, AMPK is an intracellular fuel-sensing enzyme and plays important roles in tumor cell growth and progression. Thus, the present study aims to examine the regulation of Bmi-1 by AMPK. First, our data revealed that, as compared to adjacent normal tissue, Bmi-1 was highly expressed in gastric cancer, whereas phosphorylation of AMPK (p-AMPK) was reduced. Similar findings were observed in lung adenocarcinomas and appeared that the expression of Bmi-1 was correlated with pathological grades of the cancer, where opposite changes were found in p-AMPK. Second, Metformin, a pharmacological AMPK activator and anti-diabetic drug, or ectopic expression of LKB1, diminished expression of Bmi-1 in cancer cells, an event that was reversed by silencing LKB1. Third, knockdown of LITAF, previously identified as a downstream target of AMPK, upregulated Bmi-1, associated with increased cell viability, colony formation, and migration of cancer cells in vitro. Fourth, metformin increased the abundance of miR-15a, miR-128, miR-192, and miR-194, which was prevented by knockdown of LITAF. Accordingly, transfection of these individual miRNAs downregulated Bmi-1. Altogether, our data for the first time suggest a regulatory axis in cancer cells: AMPK upregulates LITAF, which in turn increases miRNAs, leading to attenuation of Bmi-1 expression.

MicroRNA-194 represses glioma cell epithelial‑to‑mesenchymal transition by targeting Bmi1

MicroRNA-194 (miR-194) is frequently dysregulated in many types of cancer. However, the function of miR-194 in glioma remains unknown. In the present study, we aimed to investigate the biological functions of miR-194 in glioma and the potential molecular mechanism of miR-194 involved in glioma progression. We found that miR-194 expression was significantly reduced in glioma specimens and cell lines, as detected by real-time quantitative polymerase chain reaction (RT-qPCR) analysis. The overexpression of miR-194 inhibited while the suppression of miR-194 promoted cell migration, invasion and epithelial mesenchymal transition (EMT) in glioma cells. Bioinformatics analysis showed that the B cell-specific moloney murine leukemia virus insertion site 1 (Bmi1) was a direct target of miR-194, which was validated by dual-luciferase reporter assay, RT-qPCR and western blot analysis. The restoration of Bmi1 expression significantly abrogated the suppressive effect of miR-194 on glioma cell EMT. Taken together, the present study suggests that miR-194 inhibits glioma cell EMT by targeting Bmi1 providing novel insights into understanding the pathogenesis of glioma. The restoration of miR-194 may be a potential therapeutic strategy for glioma treatment.

A regulatory BMI1/let-7i/ERK3 pathway controls the motility of head and neck cancer cells

Extracellular signal‐regulated kinase 3 (ERK3) is an atypical mitogen‐activated protein kinase (MAPK), whose biological activity is tightly regulated by its cellular abundance. Recent studies have revealed that ERK3 is upregulated in multiple cancers and promotes cancer cell migration/invasion and drug resistance. Little is known, however, about how ERK3 expression level is upregulated in cancers. Here, we have identified the oncogenic polycomb group protein BMI1 as a positive regulator of ERK3 level in head and neck cancer cells. Mechanistically, BMI1 upregulates ERK3 expression by suppressing the tumor suppressive microRNA (miRNA) let‐7i, which directly targets ERK3 mRNA. ERK3 then acts as an important downstream mediator of BMI1 in promoting cancer cell migration. Importantly, ERK3 protein level is positively correlated with BMI1 level in head and neck tumor specimens of human patients. Taken together, our study revealed a molecular pathway consisting of BMI1, miRNA let‐7i, and ERK3, which controls the migration of head and neck cancer cells, and suggests that ERK3 kinase is a potential new therapeutic target in head and neck cancers, particularly those with BMI1 overexpression.

BMI-1 interacts with sMEK1 and inactivates sMEK1-induced apoptotic cell death

The B lymphoma Mo-MLV insertion region 1 homolog (BMI-1) protein is activated in various types of tumors and associated with cancer development and tumor progression. However, the working role of BMI-1 in cellular signaling is not understood completely. In this study, we revealed one possible biologic mechanism of BMI-1 in cancer progression in vitro using a human ovarian tumor cell system. Suppressor of MEK1 (sMEK1), a pivotal regulator involved in the cellular biological response mechanism, was identified as a BMI-1-binding protein. Ectopic expression of BMI-1 activated cell growth by reducing sMEK1-stimulated apoptotic cell death and suppressing p21, p27 and p53 expression, while enhancing cyclin D1, CDK4 and Bcl-2 expression. The effect of BMI-1 on cell cycle and apoptotic regulatory proteins was also confirmed via silencing of BMI-1 expression. Subsequently, the promoter activities of p21 and p53 were inactivated significantly. However, BMI-1 overexpression noticeably increased Bcl-2 and NF-κB activities. In addition, BMI-1 activated the PI3K/mTOR/4E-BP1 signaling pathways, and sMEK1 significantly inhibited BMI-1-stimulated oncogenesis. These insights provide evidence that BMI-1 activates cell growth and suppresses apoptosis. Collectively, our data indicate that BMI-1 plays a pivotal role in the progression of ovarian cancer, thus representing a novel target for antitumor therapy of ovarian cancer.

BMI1 regulates PRC1 architecture and activity through homo- and hetero-oligomerization

BMI1 is a core component of the polycomb repressive complex 1 (PRC1) and emerging data support a role of BMI1 in cancer. The central domain of BMI1 is involved in protein-protein interactions and is essential for its oncogenic activity. Here, we present the structure of BMI1 bound to the polyhomeotic protein PHC2 illustrating that the central domain of BMI1 adopts an ubiquitin-like (UBL) fold and binds PHC2 in a β-hairpin conformation. Unexpectedly, we find that the UBL domain is involved in homo-oligomerization of BMI1. We demonstrate that both the interaction of BMI1 with polyhomeotic proteins and homo-oligomerization via UBL domain are necessary for H2A ubiquitination activity of PRC1 and for clonogenic potential of U2OS cells. Here, we also emphasize need for joint application of NMR spectroscopy and X-ray crystallography to determine the overall structure of the BMI1-PHC2 complex.

Polycomb and trithorax opposition in development and disease

Early discoveries in chromatin biology and epigenetics heralded new insights into organismal development. From these studies, two mediators of cellular differentiation were discovered: the Polycomb group (PcG) of transcriptional repressors, and the trithorax group (trxG) of transcriptional activators. These protein families, while opposed in function, work together to coordinate the appropriate cellular developmental programs that allow for both embryonic stem cell self-renewal and differentiation. Recently, both the PcG and trxG chromatin modulators have been observed to be deregulated in a wide spectrum diseases including developmental disorders and cancer. To understand the impact of these findings we outline the past, present, and future. WIREs Dev Biol 2016, 5:659-688. doi: 10.1002/wdev.244 For further resources related to this article, please visit the WIREs website.

B-cell-specific Moloney murine leukemia virus integration site 1: potential stratification factor and therapeutic target for epithelial ovarian cancer

Epithelial ovarian cancer, a vexing challenge for clinical management, still lacks biomarkers for early diagnosis, precise stratification, and prognostic evaluation of patients. B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1), a member of the polycomb group of proteins, engages in diverse cellular processes, including proliferation, differentiation, senescence, and stem cell renewal. In addition, BMI1, as a cancer stem-cell marker, participates in tumorigenesis through various pathways. Rewardingly, recent studies have also revealed a relationship between BMI1 expression and the clinical grade/stage, therapy response, and survival outcome in a majority of human malignancies, including epithelial ovarian cancer. Therefore, BMI1 might serve as a potential stratification factor and treatment target for epithelial ovarian cancer, pending evidence from further investigations.

BMI-1 Targeting Interferes with Patient-Derived Tumor-Initiating Cell Survival and Tumor Growth in Prostate Cancer

PURPOSE

Current prostate cancer management calls for identifying novel and more effective therapies. Self-renewing tumor-initiating cells (TICs) hold intrinsic therapy resistance and account for tumor relapse and progression. As BMI-1 regulates stem cell self-renewal, impairing BMI-1 function for TIC-tailored therapies appears to be a promising approach.

EXPERIMENTAL DESIGN

We have previously developed a combined immunophenotypic and time-of-adherence assay to identify CD49b^hiCD29^hiCD44^hi cells as human prostate TICs. We utilized this assay with patient-derived prostate cancer cells and xenograft models to characterize the effects of pharmacologic inhibitors of BMI-1.

RESULTS

We demonstrate that in cell lines and patient-derived TICs, BMI-1 expression is upregulated and associated with stem cell-like traits. From a screened library, we identified a number of post-transcriptional small molecules that target BMI-1 in prostate TICs. Pharmacologic inhibition of BMI-1 in patient-derived cells significantly decreased colony formation in vitro and attenuated tumor initiation in vivo, thereby functionally diminishing the frequency of TICs, particularly in cells resistant to proliferation- and androgen receptor-directed therapies, without toxic effects on normal tissues.

CONCLUSIONS

Our data offer a paradigm for targeting TICs and support the development of BMI-1-targeting therapy for a more effective prostate cancer treatment. Clin Cancer Res; 22(24); 6176-91. ©2016 AACR.

Beyond transcription factors: how oncogenic signalling reshapes the epigenetic landscape

Cancer, once thought to be caused largely by genetic alterations, is now considered to be a mixed genetic and epigenetic disease. The epigenetic landscape, which is dictated by covalent DNA and histone modifications, is profoundly altered in transformed cells. These abnormalities may arise from mutations in, or altered expression of, chromatin modifiers. Recent reports on the interplay between cellular signalling pathways and chromatin modifications add another layer of complexity to the already complex regulation of the epigenome. In this Review, we discuss these new studies and how the insights they provide can contribute to a better understanding of the molecular pathogenesis of neoplasia.

TWIST1 and BMI1 in Cancer Metastasis and Chemoresistance

Purpose Increasing evidences revealed that cancer cells with the characteristics of epithelial-mesenchymal transition (EMT) or cancer stem cells (CSC) have high ability of progression, invasion, metastasis and chemoresistance. TWIST1 and BMI1 are crucial transcription factors required for EMT and CSC. Both TWIST1 and BMI1 are up-regulated in various cancers and have a positive correlation with poor prognosis. Although recent results showed that the two molecules function in promoting cancer metastasis and chemoresistance respectively, the correlation of TWIST1 and BMI1 is not well understood. Methods In this review, we summarize recent advance in cancer research focus on TWIST1 and BMI1 in cancer metastasis and chemoresistance, and emphasize the possible link between EMT and CSC. Results Further investigation of TWIST1 and BMI1 cooperately promote CSC proliferation due to EMT-associated effect will help to understand the mechanism of tumor cells metastasis and chemoresistance. Conclusions TWIST1 and BMI1 in cancer cells will be effective targets for treating chemoresistant metastatic lesions.

The nucleosome: orchestrating DNA damage signaling and repair within chromatin

DNA damage occurs within the chromatin environment, which ultimately participates in regulating DNA damage response (DDR) pathways and repair of the lesion. DNA damage activates a cascade of signaling events that extensively modulates chromatin structure and organization to coordinate DDR factor recruitment to the break and repair, whilst also promoting the maintenance of normal chromatin functions within the damaged region. For example, DDR pathways must avoid conflicts between other DNA-based processes that function within the context of chromatin, including transcription and replication. The molecular mechanisms governing the recognition, target specificity, and recruitment of DDR factors and enzymes to the fundamental repeating unit of chromatin, i.e., the nucleosome, are poorly understood. Here we present our current view of how chromatin recognition by DDR factors is achieved at the level of the nucleosome. Emerging evidence suggests that the nucleosome surface, including the nucleosome acidic patch, promotes the binding and activity of several DNA damage factors on chromatin. Thus, in addition to interactions with damaged DNA and histone modifications, nucleosome recognition by DDR factors plays a key role in orchestrating the requisite chromatin response to maintain both genome and epigenome integrity.

CDKN2A-independent role of BMI1 in promoting growth and survival of Ph+ acute lymphoblastic leukemia

BMI1 is a key component of the PRC1 complex (polycomb repressive complex-1) required for maintenance of normal and cancer stem cells. Its aberrant expression is detected in chronic myeloid leukemia and Ph+ acute lymphoblastic leukemia (ALL), but no data exist on BMI1 requirement in ALL cells.

We show here that BMI1 expression is important for proliferation and survival of Ph+ ALL cells and for leukemogenesis of Ph+ cells in vivo.

Levels of BIM, interferon-α (IFNα)-regulated genes, and E2F7 were upregulated in BMI1-silenced cells, suggesting that repressing their expression is important for BMI1 biological effects. Consistent with this hypothesis, we found that: i) downregulation of BIM or E2F7 abrogated apoptosis or rescued, in part, the reduced proliferation and colony formation of BMI1 silenced BV173 cells; ii) BIM/E2F7-double silencing further enhanced colony formation and in vivo leukemogenesis of BMI1-silenced cells; iii) overexpression of BIM and E2F7 mimicked the effect of BMI1 silencing in BV173 and SUP-B15 cells and iv) treatment with IFNα suppressed proliferation and colony formation of Ph+ ALL cells.

These studies indicate that the growth-promoting effects of BMI1 in Ph+ ALL cells depend on suppression of multiple pathways and support the use of IFNα in the therapy of Ph+ ALL.

Therapeutic evaluation of microRNA-15a and microRNA-16 in ovarian cancer

Treatment of chemo-resistant ovarian cancer (OvCa) remains clinically challenging and there is a pressing need to identify novel therapeutic strategies. Here we report that multiple mechanisms that promote OvCa progression and chemo-resistance could be inhibited by ectopic expression of miR-15a and miR-16. Significant correlations between low expression of miR-16, high expression of BMI1 and shortened overall survival (OS) were noted in high grade serous (HGS) OvCa patients upon analysis of The Cancer Genome Atlas (TCGA). Targeting BMI1, in vitro with either microRNA reduced clonal growth of OvCa cells. Additionally, epithelial to mesenchymal transition (EMT) as well as expression of the cisplatin transporter ATP7B were inhibited by miR-15a and miR-16 resulting in decreased degradation of the extra-cellular matrix and enhanced sensitization of OvCa cells to cisplatin. Nanoliposomal delivery of the miR-15a and miR-16 combination, in a pre-clinical chemo-resistant orthotopic mouse model of OvCa, demonstrated striking reduction in tumor burden compared to cisplatin alone. Thus, with the advent of miR replacement therapy some of which are in Phase 2 clinical trials, miR-15a and miR-16 represent novel ammunition in the anti-OvCa arsenal.

Epigenetic regulators: Polycomb-miRNA circuits in cancer

Polycomb group (PcG) proteins belong to a family of epigenetic modifiers and play a key role in dynamic control of their target genes. Several reports have found that aberrations in PcG-microRNA (miRNA) interplay in various cancer types often associated with poor clinical prognosis. This review discusses important PcG-miRNA molecular networks which act as critical interfaces between chromatin remodeling, and transcriptional and post-transcriptional regulation of their target genes in cancer. Moreover, here are discussed several compounds influencing the activity of PcG proteins entered in clinical arena for the treatment of solid tumors, multiple myeloma and B lymphomas, thus highlighting the therapeutic potential of targeting this protein family.

Targeting of BMI-1 with PTC-209 shows potent anti-myeloma activity and impairs the tumour microenvironment

Background

The polycomb complex protein BMI-1 (BMI-1) is a putative oncogene reported to be overexpressed in multiple myeloma (MM). Silencing of BMI-1 was shown to impair the growth and survival of MM cells. However, therapeutic agents specifically targeting BMI-1 were not available so far. Here, we investigated PTC-209, a novel small molecule inhibitor of BMI-1, for its activity in MM.

Methods

BMI-1 expression was analysed in human MM cell lines and primary MM cells by using publically available gene expression profiling (GEP) data. The anti-MM activity of PTC-209 was investigated by viability testing, cell cycle analysis, annexin V and 7-AAD staining, quantification of cleaved poly(ADP-ribose) polymerase (PARP), JC-1 as well as colony formation assays. Deregulation of central myeloma growth and survival genes was studied by quantitative PCR and flow cytometry, respectively. In addition, the impact of PTC-209 on in vitro osteoclast, osteoblast and tube formation was analysed.

Results

We confirmed overexpression of BMI-1 in MM patients by using publically available GEP datasets. Of note, BMI-1 expression was further increased at relapse which translated into significantly shorter overall survival in relapsed/refractory patients treated with bortezomib or dexamethasone.

Treatment with PTC-209 significantly decreased viable cell numbers in human MM cell lines, induced a G1 cell cycle arrest, promoted apoptosis and demonstrated synergistic activity with pomalidomide and carfilzomib. The anti-MM activity of PTC-209 was accompanied by a significant decrease of cyclin D1 (CCND1) and v-myc avian myelocytomatosis viral oncogene homolog (MYC) expression as well as upregulation of cyclin-dependent kinase inhibitor 1A (CDKN1A) and cyclin-dependent kinase inhibitor 1B (CDKN1B). We also observed upregulation of NOXA (up to 3.6 ± 1.2-fold induction, P = 0.009) and subsequent downregulation of myeloid cell leukemia 1 (MCL-1) protein levels, which likely mediates the apoptotic effects of PTC-209. Importantly, the anti-MM activity was upheld in the presence of stromal support or myeloma growth factors insulin-like growth factor 1 (IGF-1) and interleukin 6 (IL-6).

In the MM microenvironment, PTC-209 impaired tube formation, impaired osteoclast development and decreased osteoblast formation in a dose-dependent manner (P < 0.01 at 1 μM, respectively). The latter might be attributed to an induction of DKK1 and was reversed by concurrent anti-DKK1 antibody treatment.

Conclusions

We confirmed overexpression of BMI-1 in MM highlighting its role as an attractive drug target and reveal therapeutic targeting of BMI-1 by PTC-209 as a promising novel therapeutic intervention for MM.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0247-4) contains supplementary material, which is available to authorized users.

Association of BMI-1 and p16 as prognostic factors for head and neck carcinomas

CONCLUSIONS

BMI-1 is an upstream repressor of tumor suppressor p16 and their inverse expression patterns have been linked with patient survival in OPSCC. In this material only p16 remained a relevant prognostic marker in OPSCC.

OBJECTIVES

HNSCC tumors carry variable phenotypes and clinical outcomes depending on their anatomical location. In OPSCC, expression of tumor suppressor p16 is used as a surrogate marker of HPV infection and has prognostic value. There are no good prognostic biomarkers for HNSCC tumors of other anatomical locations.

AIM

To study the expression patterns of p16 and BMI-1 in not only oropharyngeal but also oral, hypopharyngeal, and laryngeal squamous cell carcinomas and to clarify their putative connections with clinical parameters, survival, and each other.

METHOD

Hospital records on 130 patients (59 OPSCC, 18 OSCC, 20 HPSCC, and 33 LSCC) diagnosed between 1997-2008 at the Helsinki University Hospital, Finland, were reviewed. BMI-1 and p16 expressions were studied by immunohistochemistry.

RESULTS

Sixty-eight per cent of OPSCC expressed p16 and expression correlated with lower age, lower T- and higher N-category, and with improved OS and DFS. BMI-1 expression was most prevalent in OPSCC and LSCC, but had no clinical correlations. No correlation between p16 and BMI-1 expression was found.

Polycomb Repressor Complex 1 Member, BMI1 Contributes to Urothelial Tumorigenesis through p16-Independent Mechanisms

Urothelial carcinoma (UC) causes significant morbidity and remains the most expensive cancer to treat because of the need for repeated resections and lifelong monitoring for patients with non-muscle-invasive bladder cancer (NMIBC). Novel therapeutics and stratification approaches are needed to improve the outlook for both NMIBC and muscle-invasive bladder cancer. We investigated the expression and effects of B Lymphoma Mo-MLV Insertion Region 1 (BMI1) in UC. BMI1 was found to be overexpressed in most UC cell lines and primary tumors by quantitative real-time polymerase chain reaction and immunohistochemistry. In contrast to some previous reports, no association with tumor stage or grade was observed in two independent tumor panels. Furthermore, upregulation of BMI1 was detected in premalignant bladder lesions, suggesting a role early in tumorigenesis. BMI1 is not located within a common region of genomic amplification in UC. The CDKN2A locus (which encodes the p16 tumor suppressor gene) is a transcriptional target of BMI1 in some cellular contexts. In UC cell lines and primary tissues, no correlation between BMI1 and p16 expression was observed. Retroviral-mediated overexpression of BMI1 immortalized normal human urothelial cells (NHUC) in vitro and was associated with induction of telomerase activity, bypass of senescence, and repression of differentiation. The effects of BMI1 on gene expression were identified by expression microarray analysis of NHUC-BMI1. Metacore analysis of the gene expression profile implicated downstream effects of BMI1 on α4/β1 integrin-mediated adhesion, cytoskeleton remodeling, and CREB1-mediated transcription.

ERα inhibits epithelial-mesenchymal transition by suppressing Bmi1 in breast cancer

In human breast cancer, estrogen receptor-α (ERα) suppresses epithelial-mesenchymal transition (EMT) and stemness, two crucial parameters for tumor metastasis; however, the underlying mechanism by which ERα regulates these two processes remains largely unknown. Bmi1, the polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog, regulates EMT transition, maintains the self-renewal capacity of stem cells, and is frequently overexpressed in human cancers. In the present study, ERα upregulated the expression of the epithelial marker, E-cadherin, in breast cancer cells through the transcriptional down-regulation of Bmi1. Furthermore, ERα overexpression suppressed the migration, invasion, and EMT of breast cancer cells. Notably, overexpression of ERα significantly decreased the CD44high/CD24low cell population and inhibited the capacity for mammosphere formation in ERα-negative breast cancer cells. In addition, overexpression of Bmi1 attenuated the ERα-mediated suppression of EMT and cell stemness. Immunohistochemistry revealed an inverse association of ERα and Bmi1 expression in human breast cancer tissue. Taken together, our findings suggest that ERα inhibits EMT and stemness through the downregulation of Bmi1.

BMI1 is expressed in canine osteosarcoma and contributes to cell growth and chemotherapy resistance

BMI1, a stem cell factor and member of the polycomb group of genes, has been shown to contribute to growth and chemoresistance of several human malignancies including primary osteosarcoma (OSA). Naturally occurring OSA in the dog represents a large animal model of human OSA, however the potential role of BMI1 in canine primary and metastatic OSA has not been examined. Immunohistochemical staining of canine primary and metastatic OSA tumors revealed strong nuclear expression of BMI1. An identical staining pattern was found in both primary and metastatic human OSA tissues. Canine OSA cell lines (Abrams, Moresco, and D17) expressed high levels of BMI1 compared with canine osteoblasts and knockdown or inhibition of BMI1 by siRNA or by small molecule BMI1-inhibitor PTC-209 demonstrated a role for BMI1 in canine OSA cell growth and resistance to carboplatin and doxorubicin chemotherapy. These findings suggest that inhibition of BMI1 in primary or metastatic OSA may improve response to chemotherapy and that the dog may serve as a large animal model to evaluate such therapy.

Interaction of tetraspan(in) TM4SF5 with CD44 promotes self-renewal and circulating capacities of hepatocarcinoma cells

Tumor metastasis involves circulating and tumor-initiating capacities of metastatic cancer cells. Epithelial-mesenchymal transition (EMT) is related to self-renewal capacity and circulating tumor cell (CTC) characteristics for tumor metastasis. Although tumor metastasis is a life-threatening, complicated process that occurs through circulation of tumor cells, mechanistic aspects of self-renewal and circulating capacities have been largely unknown. Hepatic transmembrane 4 L six family member 5 (TM4SF5) promotes EMT for malignant growth and migration, so it was rationalized that TM4SF5, as a hepatocellular carcinoma (HCC) biomarker, might be important for metastatic potential. Here, self-renewal capacity by TM4SF5 was mechanistically explored using hepatocarcinoma cells with or without TM4SF5 expression, and we explored whether they became CTCs using mouse liver-orthotopic model systems. We found that TM4SF5-dependent sphere growth correlated with CD24(-) , aldehyde dehydrogenase (ALDH) activity, as well as a physical association between CD44 and TM4SF5. Interaction between TM4SF5 and CD44 was through their extracellular domains with N-glycosylation modifications. TM4SF5/CD44 interaction activated proto-oncogene tyrosine-protein kinase Src (c-Src)/signal transducer and activator of transcription 3 (STAT3)/Twist-related protein 1 (Twist1)/B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi1) signaling for spheroid formation, whereas disturbing the interaction, expression, or activity of any component in this signaling pathway inhibited spheroid formation. In serial xenografts using 200∼5,000 cells per injection, TM4SF5-positive tumors exhibited subpopulations with locally increased CD44 expressions, supporting for tumor cell differentiation. TM4SF5-positive, but not TM4SF5- or CD44-knocked-down, cells were identified circulating in blood 4-6 weeks after orthotopic liver injection using in vivo laser scanning endomicroscopy. Anti-TM4SF5 reagent blocked their metastasis to distal intestinal organs.

CONCLUSION

TM4SF5 promotes self-renewal and CTC properties supported by TM4SF5(+) /CD44(+(TM4SF5-bound)) /ALDH(+) /CD24(-) markers during HCC metastasis.

Bmi-1: At the crossroads of physiological and pathological biology

Bmi-1 is a member of the Polycomb repressor complex 1 that mediates gene silencing by regulating chromatin structure and is indispensable for self-renewal of both normal and cancer stem cells. Despite three decades of research that have elucidated the transcriptional regulation, post-translational modifications and functions of Bmi-1 in regulating the DNA damage response, cellular bioenergetics, and pathologies, the entire potential of a protein with such varied functions remains to be realized. This review attempts to synthesize the current knowledge on Bmi-1 with an emphasis on its role in both normal physiology and cancer. Additionally, since cancer stem cells are emerging as a new paradigm for therapy resistance, the role of Bmi-1 in this perspective is also highlighted. The wide spectrum of malignancies that implicate Bmi-1 as a signature for stemness and oncogenesis also make it a suitable candidate for therapy. Nonetheless, new approaches are vitally needed to further characterize physiological roles of Bmi-1 with the long-term goal of using Bmi-1 as a prognostic marker and a therapeutic target.

Role of Bmi-1 in regulation of ionizing irradiation-induced epithelial-mesenchymal transition and migration of breast cancer cells

Radiotherapy is a widely used treatment for cancer. However, recent studies suggest that ionizing radiation (IR) can promote tumor invasion and metastasis. Bmi-1, a member of the polycomb group protein family, has been observed as a regulator of oxidative stress and promotes metastasis in some tumors. But, its potential role in the metastasis induced by IR of breast cancer has not been explored. In our study, we found that increased levels of Bmi-1 were correlated to EMT of breast cancer cells. Through analyzing the EMT state and metastasis of breast cancer induced by IR, we found the metastatic potential of breast cancer cells can either be inhibited or accelerated by IR following a time-dependent pattern. Silencing Bmi-1 completely abolished the ability of the IR to alter, reduce or increase, the migration of breast cancer cells. Also, when Bmi-1 was knocked down, the effect of inhibition of PI3K/AKT signaling on EMT affected by IR was blocked. These results suggest that Bmi-1 is a key gene in regulation of EMT and migration of breast cancer cells induced by IR through activation of PI3K/AKT signaling; therefore, Bmi-1 could be a new target for inhibiting metastasis caused by IR.

α-Mangostin induces G1 cell cycle arrest in HCT116 cells through p38MAPK-p16INK4a pathway

α-Mangostin (α-MG), one of the active substances inGarcinia mangostana, has been shown to exhibit anti-cancer effects in HCT116 colon cancer cells.

Silencing BMI1 eliminates tumor formation of pediatric glioma CD133+ cells not by affecting known targets but by down-regulating a novel set of core genes

Clinical outcome of children with malignant glioma remains dismal. Here, we examined the role of over-expressed BMI1, a regulator of stem cell self-renewal, in sustaining tumor formation in pediatric glioma stem cells. Our investigation revealed BMI1 over-expression in 29 of 54 (53.7%) pediatric gliomas, 8 of 8 (100%) patient derived orthotopic xenograft (PDOX) mouse models, and in both CD133⁺ and CD133⁻ glioma cells. We demonstrated that lentiviral-shRNA mediated silencing of suppressed cell proliferation in vitro in cells derived from 3 independent PDOX models and eliminated tumor-forming capacity of CD133⁺ and CD133⁻ cells derived from 2 PDOX models in mouse brains. Gene expression profiling showed that most of the molecular targets of BMI1 ablation in CD133⁺ cells were different from that in CD133- cells. Importantly, we found that silencing BMI1 in CD133⁺ cells derived from 3 PDOX models did not affect most of the known genes previously associated with the activated BMI1, but modulated a novel set of core genes, including RPS6KA2, ALDH3A2, FMFB, DTL, API5, EIF4G2, KIF5c, LOC650152, C20ORF121, LOC203547, LOC653308, and LOC642489, to mediate the elimination of tumor formation. In summary, we identified the over-expressed BMI1 as a promising therapeutic target for glioma stem cells, and suggest that the signaling pathways associated with activated BMI1 in promoting tumor growth may be different from those induced by silencing BMI1 in blocking tumor formation. These findings highlighted the importance of careful re-analysis of the affected genes following the inhibition of abnormally activated oncogenic pathways to identify determinants that can potentially predict therapeutic efficacy.

Oncogenic roles of Bmi1 and its therapeutic inhibition by histone deacetylase inhibitor in tongue cancer

The polycomb complex protein Bmi1 (B lymphoma Mo-MLV insertion region 1 homolog) mediates epigenetic transcriptional silencing by modifying chromatin structure and is critical for stem cell homeostasis and tumorigenesis. Bmi1 is frequently overexpressed in human malignancies and therefore has key diagnostic and prognostic significance, and holds potential as a therapeutic target. Here we sought to characterize the expression patterns and oncogenic roles of Bmi1 in tongue squamous cell carcinoma and to determine the anticancer effects of histone deacetylase inhibitors (HDACis) via Bmi1 inhibition against tongue cancer. Our data revealed that Bmi1 was aberrantly overexpressed in a significant portion of tongue cancers. Elevated Bmi1 is associated with cervical node metastasis, Ki-67 abundance and reduced overall survival, and also serves as an independent prognostic factor for patient outcomes. Short-hairpin RNA-mediated Bmi1 knockdown inhibited cell proliferation and migration, induced cell apoptosis and senescence, reduced colony formation and CD44(+)CD133(+) sub-population as well as enhanced cisplatin chemosensitivity, presumably by modulation of p16, p14 and E-cadherin. Moreover, HDACi chemicals Trichostatin A (TSA) and sodium butyrate (NaB) potently inhibited Bmi1 and triggered similar phenotypic changes reminiscent of Bmi1 silencing, although TSA treatment seemed paradoxically to induce some epithelial-mesenchymal transition-like changes in tongue cancer cells. Importantly, NaB-induced antitumor effects were partially attenuated by enforced Bmi1 overexpression in vitro. Genetic Bmi1 silencing and pharmacological inhibition of Bmi1 by NaB treatment significantly impaired tumor growth in a tongue cancer xenograft model. Taken together, our results indicate that Bmi1 serves as a key driver and biomarker with multiple oncogenic functions underlying tongue tumorigenesis. Selected appropriate HDACi compounds like NaB may represent novel therapeutic agents against tongue cancer.

The role of polycomb repressive complexes in biliary tract cancer

INTRODUCTION

Polycomb group proteins are major epigenetic regulators that modify histone tails. They are organized in two multi-protein complexes called polycomb repressive complex (PRC) 1 and 2. Aberrant PRC activity is known to contribute to the development and aggressiveness of many cancers. Biliary tract cancer (BTC) is a rare malignancy associated with high chemoresistance and poor clinical outcome. Here we review the role of the PRC complexes and the effects of RNAi and drug-mediated inhibition of PRC1 and PRC2 in BTC.

AREAS COVERED

This review gives a short overview of the composition, biochemical functions and oncogenic role of PRC complexes. We then focus on and summarize the results of current studies that address the role of PRC in BTC. Finally, we discuss options and results of therapeutic targeting of PRC in BTC.

EXPERT OPINION

Pharmacological inhibition of the two PRC complexes seems to be a promising strategy for treatment of BTC. To date, only few studies have addressed the therapeutic effect of PRC inhibition in BTC. Therefore, it will be important to test established PRC inhibitors, such as DZNep, as well as newly developed drugs, for example, PTC209, to gain more insight into the role of the PRC complexes in BTC and potentially to develop new therapeutic strategies.

Bmi1 regulates self-renewal and epithelial to mesenchymal transition in breast cancer cells through Nanog

Background

The Bmi1 polycomb ring finger oncogene, a transcriptional repressor belonging to the Polycomb group of proteins plays an important role in the regulation of stem cell self-renewal and is elevated in several cancers. In the current study, we have explored the role of Bmi1 in regulating the stemness and drug resistance of breast cancer cells.

Methods

Using real time PCR and immunohistochemistry primary breast tissues were analyzed. Retro- and lentiviruses were utilized to overexpress and knockdown Bmi1, RT-PCR and Western blot was performed to evaluate mRNA and protein expression. Stemness properties were analyzed by flow cytometry and sphere-formation and tumor formation was determined by mouse xenograft experiments. Dual luciferase assay was employed to assess promoter activity and MTT assay was used to analyze drug response.

Results

We found Bmi1 overexpression in 64% of grade III invasive ductal breast adenocarcinomas compared to normal breast tissues. Bmi1 overexpression in immortalized and transformed breast epithelial cells increased their sphere-forming efficiency, induced epithelial to mesenchymal transition (EMT) with an increase in the expression of stemness-related genes. Knockdown of Bmi1 in tumorigenic breast cells induced epithelial morphology, reduced expression of stemness-related genes, decreased the IC₅₀ values of doxorubicin and abrogated tumor-formation. Bmi1-high tumors showed elevated Nanog expression whereas the tumors with lower Bmi1 showed reduced Nanog levels. Overexpression of Bmi1 increased Nanog levels whereas knockdown of Bmi1 reduced its expression. Dual luciferase promoter-reporter assay revealed Bmi1 positively regulated the Nanog and NFκB promoter activity. RT-PCR analysis showed that Bmi1 overexpression activated the NFκB pathway whereas Bmi1 knockdown reduced the expression of NFκB target genes, suggesting that Bmi1 might regulate Nanog expression through the NFκB pathway.

Conclusions

Our study showed that Bmi1 is overexpressed in several high-grade, invasive ductal breast adenocarcinomas, thus supporting its role as a prognostic marker. While Bmi1 overexpression increased self-renewal and promoted EMT, its knockdown reversed EMT, reduced stemness, and rendered cells drug sensitive, thus highlighting a crucial role for Bmi1 in regulating the stemness and drug response of breast cancer cells. Bmi1 may control self-renewal through the regulation of Nanog expression via the NFκB pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-785) contains supplementary material, which is available to authorized users.

Ethyl acetate extract from Jiedu Xiaozheng Yin inhibits the proliferation of human hepatocellular carcinoma cells by suppressing polycomb gene product Bmi1 and Wnt/β-catenin signaling

Jiedu Xiaozheng Yin (JXY) is a Chinese herbal decoction used to treat hepatocellular carcinoma (HCC). Previous studies have demonstrated that JXY can inhibit HCC cell proliferation via induction of G0/G1 phase arrest. In this study, we investigated whether the inhibitory effect of JXY on HCC cells is associated with the inhibition of the Wnt/β‑catenin pathway and the polycomb gene product Bmi1. Ethyl acetate extract from JXY (EE-JXY) was prepared. Methyl thiazolyl tetrazolium (MTT) and colony formation assays were used to measure cell proliferation. Immunofluorescence was used to analyze the expression and location of β-catenin and Bmi1. Immunohistochemistry was used to examine the expression of proliferating cell nuclear antigen (PCNA), c-myc and cyclin D1. β-catenin, Bmi1, c-myc, cyclin D1 and p16INK4A mRNA levels were detected by RT-PCR. The results demonstrated that EE-JXY inhibited the expression of PCNA, c-myc, cyclin D1 and Bmi1, and upregulated the expression of p16INK4A. We also found that EE-JXY could facilitate β-catenin translocation from the cytoplasm and nuclei to the cytomembrane. Finally, suppression of cell proliferation and expression of Bmi1 and Wnt/β-catenin by EE-JXY was confirmed in a mouse xenograft model of HCC. Thus, EE-JXY can inhibit the proliferation of HCC partially via suppression of the Bmi1 and Wnt/β-catenin signaling pathways.

Deletions of RDINK4/ARF enhancer in gastrinomas and nonfunctioning pancreatic neuroendocrine tumors

OBJECTIVE

The presence of an enhancer element, RD (RD), in the prominent INK4-ARF locus provides a novel en bloc mechanism to simultaneously regulate the transcription of p15, p14ARF, and p16 genes. However, knowledge about RD alterations and its potential contributions to cancer progression remains limited. In this study, we aimed to evaluate the incidence of RD alterations in pancreatic tumors.

METHODS

DNAs from 14 gastrinomas and 6 nonfunctioning pancreatic neuroendocrine tumors were subjected to quantitative real-time polymerase chain reaction-based assays to determine deletions in p15, p14ARF, and p16 (both exons 1 and 2).

RESULTS

RD was frequently deleted in gastrinomas and nonfunctioning pancreatic neuroendocrine tumors with an incidence of 30% (6/20 samples). In comparison, the incidences of deletions of p15 (exon 1), p14ARF (exon 1β), and p16 (exon 1α) are 10% (2/20 samples), 10% (2/20 samples), and 45% (9/20 samples), respectively. Whereas some RD deletion events arose from deletions of the entire INK4-ARF locus, RD deletions in some specimens seemed to be independent of genetic alterations in any of the p15, p14ARF, and p16 genes.

CONCLUSIONS

Our results strongly support that the deletion of RD may represent a novel mechanism to simultaneously downregulate p15, p14ARF, and p16, thus contributing to the development of human pancreatic cancers.

Genotranscriptomic meta-analysis of the Polycomb gene CBX2 in human cancers: initial evidence of an oncogenic role

Background:

Polycomb group (PcG) proteins are histone modifiers known to transcriptionally silence key tumour suppressor genes in multiple human cancers. The chromobox proteins (CBX2, 4, 6, 7, and 8) are critical components of PcG-mediated repression. Four of them have been associated with tumour biology, but the role of CBX2 in cancer remains largely uncharacterised.

Methods:

Addressing this issue, we conducted a comprehensive and unbiased genotranscriptomic meta-analysis of CBX2 in human cancers using the COSMIC and Oncomine databases.

Results:

We discovered changes in gene expression that are suggestive of a widespread oncogenic role for CBX2. Our genetic analysis of 8013 tumours spanning 29 tissue types revealed no inactivating chromosomal aberrations and only 40 point mutations at the CBX2 locus. In contrast, the overall rate of CBX2 amplification averaged 10% in all combined neoplasms but exceeded 30% in ovarian, breast, and lung tumours. In addition, transcriptomic analyses revealed a strong tendency for increased CBX2 mRNA levels in many cancers compared with normal tissues, independently of CDKN2A/B silencing. Furthermore, CBX2 upregulation and amplification significantly correlated with metastatic progression and lower overall survival in many cancer types, particularly those of the breast.

Conclusions:

Overall, we report that the molecular profile of CBX2 is suggestive of an oncogenic role. As CBX2 has never been studied in human neoplasms, our results provide the rationale to further investigate the function of CBX2 in the context of cancer cells.

A retrospective review of the prognostic value of ALDH-1, Bmi-1 and Nanog stem cell markers in esophageal squamous cell carcinoma

Stem cell markers are upregulated in various cancers and have potential as prognostic indicators. The objective of this study was to determine the expression of three stem cell markers, aldehyde dehydrogenase 1 (ALDH-1), B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1), and Nanog, in esophageal squamous cell carcinoma (ESCC) tissues. Immunohistochemistry was used to measure the expression of ALDH-1, Bmi-1, and Nanog in ESCC tissues from 41 patients who received pre-operative chemoradiation. We evaluated the relationship between expression of these markers, and clinicopathological features, tumor regression grade (TRG), and 5-year overall survival (OS). There were no significant associations of ALDH-1 or Bmi-1 expression with age, gender, clinical stage, and treatments (p>0.05). However, patients with Nanog-positive tumors were significantly older than those whose tumors were Nanog-negative (p = 0.033). TRG after treatment was significantly associated with expression of ALDH-1 (p = 0.001), Bmi-1 (p = 0.004), and Nanog (p<0.001). Although OS was significantly better in patients with low TRGs (p = 0.001), there were no significant correlations between ALDH-1, Bmi-1, or Nanog with OS. Expression of ALDH-1, Bmi-1, and Nanog correlated with TRG, but not OS. Further large studies are necessary to fully elucidate the prognostic value of these stem cell markers for ESCC patients.

Epigenetic mechanisms of tumorigenicity manifesting in stem cells

One of the biggest roadblocks to using stem cells as the basis for regenerative medicine therapies is the tumorigenicity of stem cells. Unfortunately, the unique abilities of stem cells to self-renew and differentiate into a variety of cell types are also mechanistically linked to their tumorigenic behaviors. Understanding the mechanisms underlying the close relationship between stem cells and cancer cells has therefore become a primary goal in the field. In addition, knowledge gained from investigating the striking parallels between mechanisms orchestrating normal embryogenesis and those that invoke tumorigenesis may well serve as the foundation for developing novel cancer treatments. Emerging discoveries have demonstrated that epigenetic regulatory machinery plays important roles in normal stem cell functions, cancer development, and cancer stem cell identity. These studies provide valuable insights into both the shared and distinct mechanisms by which pluripotency and oncogenicity are established and regulated. In this review, the cancer-related epigenetic mechanisms found in pluripotent stem cells and cancer stem cells will be discussed, focusing on both the similarities and the differences.

Modeling colorectal cancer as a 3-dimensional disease in a dish: the case for drug screening using organoids, zebrafish, and fruit flies

This review discusses recent shifts in the understanding of colorectal cancer as a stem cell based disease, based on findings that tie patient prognosis to the presence of cancer stem cells in colorectal tumors. Currently no drugs specifically target CSCs in colorectal tumors. However, recent advances in the culturing of colorectal stem cells using mammalian organoids, zebrafish, and Drosophila offer promising avenues for anti-CSC drug discovery.

Kinase-inhibitor-insensitive cancer stem cells in chronic myeloid leukemia

INTRODUCTION

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the translocation t(9;22), coding for the chimeric protein BCR-ABL. The development of BCR-ABL tyrosine kinase inhibitors (TKIs) has dramatically revolutionized and improved CML therapy. However, TKI-based therapy faces a major challenge: the insensitivity of CML leukemic stem cells (LSCs) to TKIs. In particular, while CML progenitor cells and differentiated cells are oncogene addicted, BCR-ABL tyrosine kinase is dispensable for CML LSC survival and maintenance. Notably, in CML, additional cellular mechanisms promote LSC survival and maintenance, rendering these cells able to survive even in the presence of TKI and to eventually promote relapse.

AREAS COVERED

This review will focus on the mechanisms of LSC insensitivity to TKI and on the strategies to obtain synthetic lethality with combination therapies.

EXPERT OPINION

Several pathways have been proposed to promote LSC maintenance and described as ideal targets to induce CML LSC exhaustion in combination with TKI. Ongoing clinical trials designed to target some of these pathways will assess which molecular target is relevant for in vivo human LSC survival in a new 'stem-cell targeting' perspective.

Alterations in RD(INK4/ARF) -mediated en bloc regulation of the INK4-ARF locus in human squamous cell carcinoma of the head and neck

The presence of RD(INK4/ARF) (RD) enhancer in the INK4-ARF locus provides a novel mechanism to simultaneously increase the transcription of p15(INK4b) (p15), p14ARF (p14), and p16(INK4a) (p16). While such upregulation can be repressed through interactions between RD and oncoproteins CDC6 and BMI1, little is known about the involvement of RD in cancer. In this study we investigated RD deletions in 30 squamous cell carcinoma of the head and neck (SCCHN) and the patient-matched High At-Risk Mucosa specimens (HARM, "phenotypically normal" tissues neighboring SCCHN foci but beyond the surgical resection margin). RD was deleted (homozygously/heterozygously) in SCCHN and HARM at the incidence of 36.7% (11/30) and 13.3% (4/30), respectively. In comparison, no RD deletion was detected in 26 oral buccal brush biopsy specimens from healthy donors. Both p16 and p14 were lowly expressed in SCCHN and HARM, and their mRNA expression levels were positively associated with each other (P < 0.01). Moreover, BMI1 was highly expressed in both SCCHN and HARM, and BMI1 overexpression was associated with p16 downregulation in SCCHN (P < 0.05). These results indicate that RD deletion and BMI1 overexpression frequently occur in the early stage of oral carcinogenesis and BMI1 overexpression may downregulate the transcription of p16 and p14 through interfering with RD.

Immunohistochemical expression and prognostic relevance of Bmi-1, a stem cell factor, in epithelial ovarian cancer

Ovarian cancer is the fourth most common cause of cancer-related death in women. Bmi-1 is a stem cell factor implicated in many human malignancies with poor outcome. Few published reports on the expression of Bmi-1 in epithelial ovarian cancer were either experimental or performed on cell lines. This study evaluates the immunohistochemical expression of Bmi-1 protein in epithelial ovarian cancer tissue specimens and its relevance to the clinicopathologic prognostic variables and patient survival. Forty cases of epithelial ovarian cancer were selected according to the availability of paraffin-embedded tissue and the clinicopathologic and survival data. Immunohistochemistry was performed for anti-Bmi-1 antibody. Low and high Bmi-1 expression groups were compared with age, tumor stage, laterality, grade, histology, and patient survival. Bmi-1 expression was detected in 72.5% of cases, of which 42.5% had high expression. High Bmi-1 expression strongly associated with advanced International Federation of Gynecology and Obstetrics stages (P = .007), bilaterality (P = .01), and higher Gynecologic Oncology Group grades (P = .031) and carcinomas of serous histology (P = .027). It had no association with patient age. Bmi-1 expression displayed a significant inverse association with patient overall and mean survival (P = .006, P < .001). These observations suggested correlation between increased Bmi-1 expression and clinical progression in ovarian epithelial cancer.

Combined aberrant expression of Bmi1 and EZH2 is predictive of poor prognosis in glioma patients

BACKGROUND AND OBJECTIVES

Bmi1 and EZH2 are involved in tumorigenesis of gliomas. However, clinicopathologic significance of their expression in gliomas is unknown; especially, the prognostic value of combined expression of Bmi1 and EZH2 has not been explored.

METHODS

Bmi1 and EZH2 expression in human gliomas and nonneoplastic brain tissues was measured by immunohistochemistry.

RESULTS

Both Bmi1 and EZH2 expressions in glioma tissues were significantly higher than those in corresponding nonneoplastic brain tissues (both P<0.001). Additionally, the upregulations of Bmi1 and EZH2 proteins were both significantly associated with advanced WHO grades (both P<0.001) and low KPS (P=0.008 and 0.01, respectively). Moreover, the overall survival of patients with high Bmi1 protein expression (P=0.006) or high EZH2 protein expression (P=0.01) was obviously lower than those with low expressions. More interestingly, glioma patients with combined overexpression of Bmi1 and EZH2 proteins had the shortest overall survival (P<0.001). Furthermore, multivariate analysis showed that Bmi1n expression (P=0.02), EZH2 expression (P=0.03), and combined expression of Bmi1 and EZH2 (P=0.008), were all independent prognostic factors for overall survival in glioma patients.

CONCLUSIONS

Our data suggest for the first time that the combination of Bmi1 and EZH2 overexpression may be a highly sensitive marker for the prognosis in glioma patients.

A Bmi1-miRNAs cross-talk modulates chemotherapy response to 5-fluorouracil in breast cancer cells

The polycomb group transcriptional modifier Bmi1 is often upregulated in numerous cancers and is intensely involved in normal and cancer stem cells, and importantly is as a prognostic indicator for some cancers, but its role in breast cancer remains unclear. Here, we found Bmi1 overexpression in 5-Fu (5-fluorouracil)-resistant MCF-7 cells (MCF-7/5-Fu) derived from MCF-7 breast cancer cells, MDA-MB-231 and MDA-MB-453 breast cancer cells compared to MCF-7 cells, was related with 5-Fu resistance and enrichment of CD44⁺/CD24^- stem cell subpopulation. Bmi1 knockdown enhanced the sensitivity of breast cancer cells to 5-Fu and 5-Fu induced apoptosis via mitochondrial apoptotic pathway, and decreased the fraction of CD44⁺/CD24^- subpopulation. In addition, our analysis showed inverse expression pattern between Bmi1 and miR-200c and miR-203 in selected breast cancer cell lines, and miR-200c and miR-203 directly repressed Bmi1 expression in protein level confirmed by luciferase reporter assay. MiR-200c and miR-203 overexpression in breast cancer cells downregulated Bmi1 expression accompanied with reversion of resistance to 5-Fu mediated by Bmi1. Inversely, Bmi1 overexpression inhibited miR-200c expression in MCF-7 cells, but not miR-203, however ectopic wild-type p53 expression reversed Bmi1 mediated miR-200c downregulation, suggesting the repressive effect of Bmi1 on miR-200c maybe depend on p53. Thus, our study suggests a cross-talk between Bmi1 and miR-200c mediated by p53, and Bmi1 interference would improve chemotherapy efficiency in breast cancer via susceptive apoptosis induction and cancer stem cell enrichment inhibition.

BMI1, the polycomb-group gene, is recurrently targeted by genomic rearrangements in progressive B-cell leukemia/lymphoma

BMI1, a Polycomb-group gene located at 10p12.2, is implicated in the pathogenesis of a variety of tumors. However, the genetic molecular mechanisms underlying its aberrant expression in cancer cells remain largely unknown. In this study, we show that BMI1 is recurrently targeted by chromosomal aberrations in B-cell leukemia/lymphoma. We identified a novel t(10;14)(p12;q32)/IGH-BMI1 rearrangement and its IGL variant in six cases of chronic lymphocytic leukemia (CLL) and found that these aberrations were consistently acquired at time of disease progression and high grade transformation of leukemia (Richter syndrome). The IG-BMI1 translocations were not associated with any particular molecular subtype of CLL and the leukemias were negative for common mutations of NOTCH1 and TP53, known to increase a risk of progression and transformation in CLL. In addition, using FISH and SNP array analysis, we identified a wide range of BMI1-involving 10p12 lesions in 17 cases of mantle cell lymphoma (MCL). These aberrations included various balanced and unbalanced structural abnormalities and very frequently but not exclusively, were associated with gain of the BMI1 locus and loss of the 10p terminal sequences. These findings point to genomic instability at the 10p region in MCL which likely promotes rearrangements and deregulation of BMI1. Our findings are in line with previously published observations correlating overexpression of BMI1 with tumor progression and chemoresistance. In summary, our study provides new insights into genetic molecular mechanisms underlying aberrant expression of BMI1 in lymphoma and documents its contribution in the pathogenesis of Richter syndrome and MCL.

Tumours associated with BAP1 mutations

BAP1 (BRCA1-Associated Protein 1) was initially identified as a protein that binds to BRCA1. BAP1 is a tumour suppressor that is believed to mediate its effects through chromatin modulation, transcriptional regulation, and possibly via the ubiquitin-proteasome system and the DNA damage response pathway. Germline mutations of BAP1 confer increased susceptibility for the development of several tumours, including uveal melanoma, epithelioid atypical Spitz tumours, cutaneous melanoma, and mesothelioma. However, the complete tumour spectrum associated with germline BAP1 mutations is not yet known. Somatic BAP1 mutations are seen in cutaneous melanocytic tumours (epithelioid atypical Spitz tumours and melanoma), uveal melanoma, mesothelioma, clear cell renal cell carcinoma, and other tumours. Here, we review the current state of knowledge about the functional roles of BAP1, and summarise data on tumours associated with BAP1 mutations. Awareness of these tumours will help pathologists and clinicians to identify patients with a high likelihood of harbouring germline or somatic BAP1 mutations. We recommend that pathologists consider testing for BAP1 mutations in epithelioid atypical Spitz tumours and uveal melanomas, or when other BAP1-associated tumours occur in individual patients. Tumour tissues may be screened for BAP1 mutations/loss/inactivation by immunohistochemistry (IHC) (demonstrated by loss of nuclear staining in tumour cells). Confirmatory sequencing may be considered in tumours that exhibit BAP1 loss by IHC and in those with equivocal IHC results. If a BAP1 mutation is confirmed in a tumour, the patient's treating physician should be informed of the possibility of a BAP1 germline mutation, so they can consider whether genetic counselling and further testing of the patient and investigation of their family is appropriate. Recognition and evaluation of larger numbers of BAP1-associated tumours will also be necessary to facilitate identification of additional distinct clinico-pathological characteristics or other genotype-phenotype correlations that may have prognostic and management implications.

Nigericin selectively targets cancer stem cells in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is prevalent in southern China, northern Africa, and Alaska. The prognosis for NPC patients at early stage is good, while it is poor for patients at late stages. Cancer stem cells (CSCs) have been proposed to be associated with tumor initiation, relapse and metastasis, and the poor prognosis of NPC likely results from residual CSCs after therapy. Study on the therapy targeting CSCs in NPC remains poor, though it received intensive attentions in other cancers. Here, we used NPC cell lines with high and low proportion of CSCs as models to explore the effect of nigericin, an antibiotic, on CSCs. We found that nigericin could selectively target CSCs and sensitize CSCs in NPC to the widely used clinical drug cisplatin both in vitro and in vivo. Moreover, downregulation of the polycomb group protein Bmi-1 may contribute to the inhibitory effect of nigericin on CSCs. Furthermore, by using the in vitro NPC cell models, we found that nigericin could significantly decrease the migration and invasion abilities, which are known to be associated with CSCs. Taken together, our results suggest that nigericin can selectively target CSCs in NPC, which could be a candidate CSCs targeting drug for clinical evaluation.

Synergistic effects of curcumin with emodin against the proliferation and invasion of breast cancer cells through upregulation of miR-34a

Curcumin, a biphenyl compound derived from rhizome, is a powerful anti-cancer agent. Emodin is an active component isolated from the root and rhizome of Rheum palmatum that has been widely used in traditional Chinese medicine for the treatment of various diseases. Currently, there are no studies examining the effect of curcumin in combination with emodin on tumor cell growth. In this study, we report for the first time that combined curcumin and emodin administration synergistically inhibits proliferation (MTT assay), survival (flow cytometry), and invasion (transwell migration assay) of breast cancer cells. Synergism is determined by the Chou-Talalay method. Moreover, we demonstrate that miR-34a is upregulated by curcumin and emodin. This microRNA helps mediate the anti-tumor effects of curcumin and emodin by downregulating Bcl-2 and Bmi-1. Our results not only provide insight into the mechanism of synergy between curcumin and emodin in breast cancer cells, but also suggest a new and potentially useful approach for breast cancer therapy.