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

Emerging trends in gastrointestinal cancers: Targeting developmental pathways in carcinogenesis and tumor progression

Gastrointestinal carcinomas are a group of cancers associated with the digestive system and its accessory organs. The most prevalent cancers related to the gastrointestinal tract are colorectal, gall bladder, gastric, hepatocellular, and esophageal cancers, respectively. Molecular aberrations in different signaling pathways, such as signal transduction systems or developmental pathways are the chief triggering mechanisms in different cancers Though a massive advancement in diagnostic and therapeutic interventions results in improved survival of patients with gastrointestinal cancer; the lower malignancy stages of these carcinomas are comparatively asymptomatic. Various gastrointestinal-related cancers are detected at advanced stages, leading to deplorable prognoses and increased rates of recurrence. Recent molecular studies have elucidated the imperative roles of several signaling pathways, namely Wnt, Hedgehog, and Notch signaling pathways, play in the progression, therapeutic responsiveness, and metastasis of gastrointestinal-related cancers. This book chapter gives an interesting update on recent findings on the involvement of developmental signaling pathways their mechanistic insight in gastrointestinalcancer. Subsequently, evidences supporting the exploration of gastrointestinal cancer related molecular mechanisms have also been discussed for developing novel therapeutic strategies against these debilitating carcinomas.

Polycomb repressor complex: Its function in human cancer and therapeutic target strategy

The Polycomb Repressor Complex (PRC) plays a pivotal role in gene regulation during development and disease, with dysregulation contributing significantly to various human cancers. The intricate interplay between PRC and cellular signaling pathways sheds light on cancer complexity. PRC presents promising therapeutic opportunities, with inhibitors undergoing rigorous evaluation in preclinical and clinical studies. In this review, we emphasize the critical role of PRC complex in gene regulation, particularly PcG proteins mediated chromatin compaction through phase separation. We also highlight the pathological implications of PRC complex dysregulation in various tumors, elucidating underlying mechanisms driving cancer progression. The burgeoning field of therapeutic strategies targeting PRC complexes, notably EZH2 inhibitors, has advanced significantly. However, we explore the need for combination therapies to enhance PRC targeted treatments efficacy, providing a glimpse into the future of cancer therapeutics.

Primary Cilium Identifies a Quiescent Cell Population in the Human Intestinal Crypt

Primary cilia are sensory antennae located at the cell surface which mediate a variety of extracellular signals involved in development, tissue homeostasis, stem cells and cancer. Primary cilia are found in an extensive array of vertebrae cells but can only be generated when cells become quiescent. The small intestinal epithelium is a rapidly self-renewing tissue organized into a functional unit called the crypt–villus axis, containing progenitor and differentiated cells, respectively. Terminally differentiated villus cells are notoriously devoid of primary cilia. We sought to determine if intestinal crypts contain a quiescent cell population that could be identified by the presence of primary cilia. Here we show that primary cilia are detected in a subset of cells located deep in the crypts slightly above a Paneth cell population. Using a normal epithelial proliferative crypt cell model, we show that primary cilia assembly and activity correlate with a quiescent state. These results provide further evidence for the existence of a quiescent cell population in the human small intestine and suggest the potential for new modes of regulation in stem cell dynamics.

Senolytic Therapy: A Potential Approach for the Elimination of Oncogene-Induced Senescent HPV-Positive Cells

Senescence represents a unique cellular stress response characterized by a stable growth arrest, macromolecular alterations, and wide spectrum changes in gene expression. Classically, senescence is the end-product of progressive telomeric attrition resulting from the repetitive division of somatic cells. In addition, senescent cells accumulate in premalignant lesions, in part, as a product of oncogene hyperactivation, reflecting one element of the tumor suppressive function of senescence. Oncogenic processes that induce senescence include overexpression/hyperactivation of H-Ras, B-Raf, and cyclin E as well as inactivation of PTEN. Oncogenic viruses, such as Human Papilloma Virus (HPV), have also been shown to induce senescence. High-risk strains of HPV drive the immortalization, and hence transformation, of cervical epithelial cells via several mechanisms, but primarily via deregulation of the cell cycle, and possibly, by facilitating escape from senescence. Despite the wide and successful utilization of HPV vaccines in reducing the incidence of cervical cancer, this measure is not effective in preventing cancer development in individuals already positive for HPV. Accordingly, in this commentary, we focus on the potential contribution of oncogene and HPV-induced senescence (OIS) in cervical cancer. We further consider the potential utility of senolytic agents for the elimination of HPV-harboring senescent cells as a strategy for reducing HPV-driven transformation and the risk of cervical cancer development.

Roles of BMI1 in the Initiation, Progression, and Treatment of Hepatocellular Carcinoma

Liver cancer has high rates of morbidity and mortality, and its treatment is a global health challenge. Hepatocellular carcinoma (HCC) accounts for 90% of all primary liver cancer cases. B-lymphoma Mo-MLV insertion region 1 (BMI1) has been identified as a proto-oncogene, which contributes to the initiation and progression of many malignant tumors. BMI1 expression is upregulated in HCC, and it influences the occurrence and development of HCC by various mechanisms, such as the INK4a/ARF locus, NF-κB signaling pathway, and PTEN/PI3K/AKT signaling pathway. In addition, the expression of BMI1 is related to prognosis and recurrence of HCC. Hence, there is clear evidence that BMI1 is a novel and valid therapeutic target for HCC. Accordingly, the development of therapeutic strategies targeting BMI1 has been a focus of recent research, providing new directions for HCC treatment. This review summarizes the role of BMI1 in the occurrence and treatment of HCC, which will provide a basis for using BMI1 as a potential target for the development of therapeutic strategies for HCC.

Downregulation of BORIS/CTCFL leads to ROS-dependent cellular senescence and drug sensitivity in MYCN-amplified neuroblastoma

Brother of Regulator of Imprinted Sites (BORIS) or CCCTC-binding factor like (CTCFL) is a nucleotide-binding protein, aberrantly expressed in various malignancies. Expression of BORIS has been found to be associated with the expression of oncogenes which regulate the reactive oxygen species (ROS) biogenesis, DNA double-strand break repair, regulation of stemness, and induction of cellular senescence. In the present study, we have analyzed the effects of knockdown of BORIS, a potential oncogene, on the induction of senescence and tumor suppression. Loss of BORIS downregulated the expression of critical oncogenes such as BMI1, Akt, MYCN, and STAT3, whereas overexpression increased their respective expression levels in MYCN-amplified neuroblastoma cells. BORIS knockdown exhibited high levels of ROS biogenesis, indicating an upregulated mitochondrial superoxide production and thereby induction of senescence. Our study also showed that the loss of BORIS facilitated cellular senescence through the disruption of telomere integrity via altering the expression of various proteins required for telomere capping (POT1, TRF2, and TIN1). In addition to affecting ROS production and DNA damage, BORIS knockdown sensitized the cells toward chemotherapeutic drugs and induced apoptosis. Tumor induction studies on in vivo xenograft mouse models showed that cells with loss of BORIS/CTCFL failed to induce tumors. From our study, we conclude that silencing BORIS/CTCFL influences tumor growth and proliferation by regulating key oncogenes. The results also indicated that the BORIS knockdown can cause cellular senescence and upon a combinatorial treatment with chemotherapeutic drugs can induce enhanced drug sensitivity in MYCN-amplified neuroblastoma cells.

Potential Use of Senolytics for Pharmacological Targeting of Precancerous Lesions

Senescence is a cell state that contributes to several homeostatic and pathologic processes. In addition to being induced in somatic cells in response to replicative exhaustion (replicative senescence) as part of organismal aging, senescence can also be triggered prematurely by oncogene hyperactivation or tumor suppressor dysfunction [oncogene-induced senescence (OIS)]. Consequently, senescent cells comprise a major component of precancerous lesions of skin, oral mucosa, nasopharynx, prostate, gut, and lung. Unfortunately, invasive (or minimally invasive) interventions are currently the only available approach employed to eradicate premalignant lesions that carry the potential for cancer progression. Senolytics are a newly emerging drug class capable of selectively eliminating senescent cells. Although senolytics have been successfully demonstrated to mitigate a myriad of aging-related pathologies and to cull senescent cancer cells, there is a paucity of evidence for the potential use of senolytics as a novel approach to eliminate oncogene-induced senescent cells. This Emerging Concepts commentary will 1) summarize evidence in established models of OIS including B-Raf-induced nevi, transgenic lung cancer, and pancreatic adenocarcinoma models, as well as evidence from clinical precancerous lesions; 2) suggest that OIS is targetable; and 3) propose the utilization of senolytic agents as a revolutionary means to interfere with the ability of senescent premalignant cells to progress to cancer in vitro and in vivo If proven to be effective, senolytics will represent an emerging tool to pharmacologically treat precancerous lesions. SIGNIFICANCE STATEMENT: The treatment of premalignant lesions is largely based on the utilization of invasive (or minimally invasive) measures. Oncogene-induced senescence (OIS) is one form of senescence that occurs in response to oncogene overexpression in somatic cells and is present in precancerous lesions. Although the contribution of OIS to disease progression is undetermined, recent evidence suggests that senescent cells are permissive for malignant transformation. Accordingly, the pharmacological targeting of oncogene-induced senescent cells could potentially provide a novel, less invasive, means for the treatment of premalignant disease.

Targeting BMI-1-mediated epithelial-mesenchymal transition to inhibit colorectal cancer liver metastasis

Liver is the most common metastatic site for colorectal cancer (CRC), there is no satisfied approach to treat CRC liver metastasis (CRCLM). Here, we investigated the role of a polycomb protein BMI-1 in CRCLM. Immunohistochemical analysis showed that BMI-1 expression in liver metastases was upregulated and associated with T4 stage, invasion depth and right-sided primary tumor. Knockdown BMI-1 in high metastatic HCT116 and LOVO cells repressed the migratory/invasive phenotype and reversed epithelial-mesenchymal transition (EMT), while BMI-1 overexpression in low metastatic Ls174T and DLD1 cells enhanced invasiveness and EMT. The effects of BMI-1 in CRC cells were related to upregulating snail via AKT/GSK-3β pathway. Furthermore, knockdown BMI-1 in HCT116 and LOVO cells reduced CRCLM using experimental liver metastasis mice model. Meanwhile, BMI-1 overexpression in Ls174T and DLD1 significantly increased CRCLM. Moreover, sodium butyrate, a histone deacetylase and BMI-1 inhibitor, reduced HCT116 and LOVO liver metastasis in immunodeficient mice. Our results suggest that BMI-1 is a major regulator of CRCLM and provide a potent molecular target for CRCLM treatment.

The Role of Polycomb Group Protein BMI1 in DNA Repair and Genomic Stability

The polycomb group (PcG) proteins are a class of transcriptional repressors that mediate gene silencing through histone post-translational modifications. They are involved in the maintenance of stem cell self-renewal and proliferation, processes that are often dysregulated in cancer. Apart from their canonical functions in epigenetic gene silencing, several studies have uncovered a function for PcG proteins in DNA damage signaling and repair. In particular, members of the poly-comb group complexes (PRC) 1 and 2 have been shown to recruit to sites of DNA damage and mediate DNA double-strand break repair. Here, we review current understanding of the PRCs and their roles in cancer development. We then focus on the PRC1 member BMI1, discussing the current state of knowledge of its role in DNA repair and genome integrity, and outline how it can be targeted pharmacologically.

Assessment of clinicopathological and prognostic relevance of BMI-1 in patients with colorectal cancer: A meta-analysis

B-cell-specific Moloney leukemia virus insertion site 1 (BMI-1) is one of the stemness markers. The prognostic and clinicopathological effects of BMI-1 expression in colorectal cancer (CRC) have been in dispute with different studies. Eligible studies were retrieved from international databases up to December 2019. Studies with a relationship between the clinicopathological and prognostic value of CRC patients with BMI-1 expression were selected. The correlations in the random-effect model were evaluated using the hazard ratios, odds ratio, and 95% confidence intervals (CIs). A total of nine studies comprising Asian cases (seven studies) and European cases (two studies) covering 1,294 samples of CRC were included for this meta-analysis. The analysis suggested that in Asian cases, increased expression of BMI-1 was associated with poor overall survival (OS) and death-free survival, whereas in European populations, high expression of BMI-1 was associated with better OS. Also, overexpression of BMI-1 in the Asian population was associated with the tumor size, distant metastasis, and patient's gender and age. Results suggested that high expression of BMI-1 can be involved in the progression and invasion of CRC, and so its inhibitor-based therapies could be used to prevent the progression of CRC.

The nutritional environment determines which and how intestinal stem cells contribute to homeostasis and tumorigenesis

Sporadic colon cancer accounts for approximately 80% of colorectal cancer (CRC) with high incidence in Western societies strongly linked to long-term dietary patterns. A unique mouse model for sporadic CRC results from feeding a purified rodent Western-style diet (NWD1) recapitulating intake for the mouse of common nutrient risk factors each at its level consumed in higher risk Western populations. This causes sporadic large and small intestinal tumors in wild-type mice at an incidence and frequency similar to that in humans. NWD1 perturbs intestinal cell maturation and Wnt signaling throughout villi and colonic crypts and decreases mouse Lgr5hi intestinal stem cell contribution to homeostasis and tumor development. Here we establish that NWD1 transcriptionally reprograms Lgr5hi cells, and that nutrients are interactive in reprogramming. Furthermore, the DNA mismatch repair pathway is elevated in Lgr5hi cells by lower vitamin D3 and/or calcium in NWD1, paralleled by reduced accumulation of relevant somatic mutations detected by single-cell exome sequencing. In compensation, NWD1 also reprograms Bmi1+ cells to function and persist as stem-like cells in mucosal homeostasis and tumor development. The data establish the key role of the nutrient environment in defining the contribution of two different stem cell populations to both mucosal homeostasis and tumorigenesis. This raises important questions regarding impact of variable human diets on which and how stem cell populations function in the human mucosa and give rise to tumors. Moreover, major differences reported in turnover of human and mouse crypt base stem cells may be linked to their very different nutrient exposures.

Multifaceted Interpretation of Colon Cancer Stem Cells

Colon cancer is one of the leading causes of cancer-related deaths worldwide, despite recent advances in clinical oncology. Accumulating evidence sheds light on the existence of cancer stem cells and their role in conferring therapeutic resistance. Cancer stem cells are a minor fraction of cancer cells, which enable tumor heterogeneity and initiate tumor formation. In addition, these cells are resistant to various cytotoxic factors. Therefore, elimination of cancer stem cells is difficult but essential to cure the malignant foci completely. Herein, we review the recent evidence for intestinal stem cells and colon cancer stem cells, methods to detect the tumor-initiating cells, and clinical significance of cancer stem cell markers. We also describe the emerging problems of cancer stem cell theory, including bidirectional conversion and intertumoral heterogeneity of stem cell phenotype.

Hedgehog signaling pathway in colorectal cancer: function, mechanism, and therapy

Colorectal cancer (CRC) is one of the most common gastrointestinal cancers worldwide. It is a complicated and often fatal cancer, and is related to a high disease-related mortality. Around 90% of mortalities are caused by the metastasis of CRC. Current treatment statistics shows a less than 5% 5-year survival for patients with metastatic disease. The development and metastasis of CRC involve multiple factors and mechanisms. The Hedgehog (Hh) signaling plays an important role in embryogenesis and somatic development. Abnormal activation of the Hh pathway has been proven to be related to several types of human cancers. The role of Hh signaling in CRC, however, remains controversial. In this review, we will go through previous literature on the Hh signaling and its functions in the formation, proliferation, and metastasis of CRC. We will also discuss the potential of targeting Hh signaling pathway in the treatment, prognosis, and prevention of CRC.

New concept: cellular senescence in pathophysiology of cholangiocarcinoma

Cholangiocarcinoma, a malignant tumor arising in the hepatobiliary system, presents with poor prognosis because of difficulty in its early detection/diagnosis. Recent progress revealed that cellular senescence may be involved in the pathophysiology of cholangiocarcinoma. Cellular senescence is defined as permanent growth arrest caused by several cellular injuries, such as oncogenic mutations and oxidative stress. "Oncogene-induced" and/or stress-induced senescence may occur in the process of multi-step cholangiocarcinogenesis, and overexpression of a polycomb group protein EZH2 may play a role in the escape from, and/or bypassing of, senescence. Furthermore, senescent cells may play important roles in tumor development and progression via the production of senescence-associated secretory phenotypes. Cellular senescence may be a new target for the prevention, early diagnosis, and therapy of cholangiocarcinoma in the near future.

Bacterially-Associated Transcriptional Remodelling in a Distinct Genomic Subtype of Colorectal Cancer Provides a Plausible Molecular Basis for Disease Development

The relevance of specific microbial colonisation to colorectal cancer (CRC) disease pathogenesis is increasingly recognised, but our understanding of possible underlying molecular mechanisms that may link colonisation to disease in vivo remains limited. Here, we investigate the relationships between the most commonly studied CRC-associated bacteria (Enterotoxigenic Bacteroides fragilis, pks+ Escherichia coli, Fusobacterium spp., afaC+ E. coli, Enterococcus faecalis & Enteropathogenic E. coli) and altered transcriptomic and methylation profiles of CRC patients, in order to gain insight into the potential contribution of these bacteria in the aetiopathogenesis of CRC. We show that colonisation by E. faecalis and high levels of Fusobacterium is associated with a specific transcriptomic subtype of CRC that is characterised by CpG island methylation, microsatellite instability and a significant increase in inflammatory and DNA damage pathways. Analysis of the significant, bacterially-associated changes in host gene expression, both at the level of individual genes as well as pathways, revealed a transcriptional remodeling that provides a plausible mechanistic link between specific bacterial colonisation and colorectal cancer disease development and progression in this subtype; these included upregulation of REG3A, REG1A and REG1P in the case of high-level colonization by Fusobacterium, and CXCL10 and BMI1 in the case of colonisation by E. faecalis. The enrichment of both E. faecalis and Fusobacterium in this CRC subtype suggests that polymicrobial colonisation of the colonic epithelium may well be an important aspect of colonic tumourigenesis.

The Effect of Analogues of 1α,25-Dihydroxyvitamin D₂ on the Regrowth and Gene Expression of Human Colon Cancer Cells Refractory to 5-Fluorouracil

This study aimed to evaluate the capacity of hypocalcemic analogues of 1α,25-dihydroxyvitamin D₂ (1,25D2) and 1α,25-dihydroxyvitamin D₃ (1,25D3) to inhibit regrowth and regulate the stemness-related gene expression in colon cancer cells undergoing renewal after exposure to 5-fluorouracil (5-FU). All of the tested analogues of 1,25D2 equally potently decreased the clonogenicity and the proliferative activity of HT-29 cells which survived the exposure to 5-FU, but differently regulated gene expression of these cells during their renewal. 1,25D2 and analogues (PRI-1907 and PRI-1917), as well as 1,25D3 and analogue PRI-2191, decreased the relative expression level of several stemness-related genes, such as NANOG, OCT3/4, PROM1, SOX2, ALDHA1, CXCR4, in HT-29/5-FU cells during their renewal, in comparison to untreated HT-29/5-FU cells. The other 1,25D2 analogues (PRI-1906 and PRI-1916) were not capable of downregulating the expression of these stemness-related genes as the analogues PRI-1907 and PRI-1917 did. All of the tested vitamin D analogues upregulated CDH1, the gene encoding E-cadherin associated with epithelial phenotype. Out of the series of analogues studied, side-chain branched analogues of 1,25D2 (PRI-1907, PRI-1917) and the analogue of 1,25D3 (PRI-2191) might be used to target cancer cells with stem-like phenotypes that survive conventional chemotherapy.

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.

Geroconversion of aged muscle stem cells under regenerative pressure

Regeneration of skeletal muscle relies on a population of quiescent stem cells (satellite cells) and is impaired in very old (geriatric) individuals undergoing sarcopenia. Stem cell function is essential for organismal homeostasis, providing a renewable source of cells to repair damaged tissues. In adult organisms, age-dependent loss-of-function of tissue-specific stem cells is causally related with a decline in regenerative potential. Although environmental manipulations have shown good promise in the reversal of these conditions, recently we demonstrated that muscle stem cell aging is, in fact, a progressive process that results in persistent and irreversible changes in stem cell intrinsic properties. Global gene expression analyses uncovered an induction of p16(INK4a) in satellite cells of physiologically aged geriatric and progeric mice that inhibits satellite cell-dependent muscle regeneration. Aged satellite cells lose the repression of the INK4a locus, which switches stem cell reversible quiescence into a pre-senescent state; upon regenerative or proliferative pressure, these cells undergo accelerated senescence (geroconversion), through Rb-mediated repression of E2F target genes. p16(INK4a) silencing rejuvenated satellite cells, restoring regeneration in geriatric and progeric muscles. Thus, p16(INK4a)/Rb-driven stem cell senescence is causally implicated in the intrinsic defective regeneration of sarcopenic muscle. Here we discuss on how cellular senescence may be a common mechanism of stem cell aging at the organism level and show that induction of p16(INK4a) in young muscle stem cells through deletion of the Polycomb complex protein Bmi1 recapitulates the geriatric phenotype.

Polycomb Group (PcG) Proteins and Human Cancers: Multifaceted Functions and Therapeutic Implications

Polycomb group (PcG) proteins are transcriptional repressors that regulate several crucial developmental and physiological processes in the cell. More recently, they have been found to play important roles in human carcinogenesis and cancer development and progression. The deregulation and dysfunction of PcG proteins often lead to blocking or inappropriate activation of developmental pathways, enhancing cellular proliferation, inhibiting apoptosis, and increasing the cancer stem cell population. Genetic and molecular investigations of PcG proteins have long been focused on their PcG functions. However, PcG proteins have recently been shown to exert non-classical-Pc-functions, contributing to the regulation of diverse cellular functions. We and others have demonstrated that PcG proteins regulate the expression and function of several oncogenes and tumor suppressor genes in a PcG-independent manner, and PcG proteins are associated with the survival of patients with cancer. In this review, we summarize the recent advances in the research on PcG proteins, including both the Pc-repressive and non-classical-Pc-functions. We specifically focus on the mechanisms by which PcG proteins play roles in cancer initiation, development, and progression. Finally, we discuss the potential value of PcG proteins as molecular biomarkers for the diagnosis and prognosis of cancer, and as molecular targets for cancer therapy.

Bmi1 is required for the initiation of pancreatic cancer through an Ink4a-independent mechanism

Epigenetic dysregulation is involved in the initiation and progression of many epithelial cancers. BMI1, a component of the polycomb protein family, plays a key role in these processes by controlling the histone ubiquitination and long-term repression of multiple genomic loci. BMI1 has previously been implicated in pancreatic homeostasis and the function of pancreatic cancer stem cells. However, no work has yet addressed its role in the early stages of pancreatic cancer development. Here, we show that BMI1 is required for the initiation of murine pancreatic neoplasia using a novel conditional knockout of Bmi1 in combination with a Kras(G12D)-driven pancreatic cancer mouse model. We also demonstrate that the requirement for Bmi1 in pancreatic carcinogenesis is independent of the Ink4a/Arf locus and at least partially mediated by dysregulation of reactive oxygen species. Our data provide new evidence of the importance of this epigenetic regulator in the genesis of pancreatic cancer.

Biomarkers and signaling pathways of colorectal cancer stem cells

The progression of colorectal cancer is commonly characterized by accumulation of genetic or epigenetic abnormalities, altering regulation of gene expression as well as normal protein structures and functions. Nonetheless, there are some questions that remain to be elucidated, such as the origin of cancer cells and populations of cells initiating and propagating tumor development. Currently, there are two rival theories describing the process of carcinogenesis. One is the stochastic model, arguing that any cell is capable of initiating and triggering the development of cancer. Meanwhile, the cancer stem cell model hypothesizes that only a small fraction of stem cells possesses cancer-promoting properties. Typically, colorectal cancer stem cells (CSCs) share the same molecular signaling profiles with normal stem cells or embryonic stem cells, such as Wnt, Notch, TGF-β, and Hedgehog. Nevertheless, CSCs differ from normal stem cells and the bulk of tumor cells in their tumorigenic potential and susceptibility to chemotherapeutic drugs. This may be a possible explanation of the high percentage of cancer recurrence in patients who underwent chemotherapeutic treatment and surgery. This review article focuses on the colorectal cancer stem cell biomarkers and the role of upregulated signaling pathways implicated in the initiation and progression of colorectal cancer.

Direct serum assay for cell-free bmi-1 mRNA and its potential diagnostic and prognostic value for colorectal cancer

PURPOSE

Cell-free Bmi-1 mRNA is stably detectable in the serum/plasma and is associated with the development and progression of some tumors. Previous methods detecting extracellular Bmi-1 mRNA with RNA extraction are inefficient. This study developed a novel reverse transcription quantitative PCR (RT-qPCR) approach directly applied in serum (RT-qPCR-D) to quantify Bmi-1 mRNA, and assessed its diagnostic and prognostic potential in colorectal cancer.

EXPERIMENTAL DESIGN

The feasibility of the RT-qPCR-D method was first analyzed in 50 serum samples. Then, using the RT-qPCR-D method, Bmi-1 mRNA expression was validated in serum from an independent cohort of patients with 87 normal colonoscopy, 76 hyperplastic polyp, 82 inflammatory bowel disease, 68 adenoma, and 158 colorectal cancer. Receiver operating characteristic (ROC) curves and Cox analyses were used to evaluate its diagnosis and prognosis value, respectively.

RESULTS

In a pilot study, levels of Bmi-1 mRNA were increased in colorectal cancer serum samples detected by RT-qPCR-D and significantly associated with results obtained by RT-qPCR. In a validation cohort, serum Bmi-1 mRNA levels were significantly elevated in the colorectal cancer group and the adenoma group when compared with other groups. The area under ROC curve distinguishing colorectal cancer from benign colorectal diseases was 0.888, with 72.2% sensitivity and 94.9% specificity, which was superior to carcinoembryogenic antigen. Bmi-1 mRNA levels were significantly associated with survival. Cox analysis indicated Bmi-1 mRNA was an independent prognostic factor for overall survival.

CONCLUSIONS

Detection of cell-free Bmi-1 mRNA in serum by RT-qPCR-D is a simple and noninvasive approach and may be used for colorectal cancer diagnosis and prognosis.

Plasma Bmi1 mRNA as a potential prognostic biomarker for distant metastasis in colorectal cancer patients

Bmi1 is overexpressed in gastrointestinal cancers, including colorectal cancer (CRC); however, its role as a non-invasive biomarker in CRC has not been established. The aim of this study was to compare the plasma Bmi1 mRNA levels prior to and following curative resection of the primary tumor in CRC patients and to determine their association with the clinicopathological parameters. The plasma Bmi1 mRNA level was measured by quantitative polymerase chain reaction and expressed as cycle threshold value. There was no significant difference between the overall pre- and postoperative plasma Bmi1 mRNA level (31.73±2.63 vs. 31.93±2.88, respectively; P=0.614) in 45 CRC patients. However, when grouped into non-metastatic and metastatic CRC patients, the postoperative Bmi1 transcript level was found to be significantly lower compared to the preoperative level in patients with non-metastatic CRC (32.13±2.677 31.44±2.764, respectively; P=0.041), whereas there was a trend towards a higher postoperative Bmi1 transcript level compared to the preoperative level in the metastatic counterpart (30.85±3.916 vs. 33.27±0.718, respectively; P=0.164). Furthermore, when the patients were categorized into two groups according to their plasma Bmi1 postoperative vs. preoperative level status, we observed that patients without a reduction in the postoperative plasma Bmi1 mRNA levels exhibited a significantly higher rate of distant metastasis following primary resection (P=0.017) and a significantly worse prognosis regarding disease-free survival (P=0.016) when compared to the reduced postoperative plasma Bmi1 level counterparts. In conclusion, plasma Bmi1 mRNA levels may serve as a non-invasive biomarker for monitoring occult metastasis and predicting the development of distant metastasis.

Modulation of miR-203 and its regulators as a function of time during the development of 7, 12 dimethylbenz [a] anthracene induced mouse skin tumors in presence or absence of the antitumor agents

We investigated the chemopreventive effects of naturally occurring compounds like butyric acid (BA), nicotinamide (NA) and calcium glucarate (CAG) individually or in combination in 7, 12-dimethylbenz [a] anthracene (DMBA) treated mouse skin at 4 and 16 weeks, the time before and after the tumor development. DMBA application did not show any skin tumors at 4 weeks but well defined tumors appeared at 16 weeks. BA, NA or CAG prevented the tumor development significantly but the protection was highly enhanced when all these compounds were given together. In order to see the molecular changes progressing with tumors, we showed the downregulation of tumor suppressor miR-203 at 16 weeks and upregulation of histone deacetylases (HDAC), DNA methyltransferase, promoter methylation of miR-203 at 4 or 16 weeks. Regulators of micro RNA biogenesis such as DICER1 and Ago2 were also deregulated by DMBA. Proto-oncogene c-myc and BMI1 were upregulated and tumor suppressor gene p16 was downregulated by DMBA as a function of time. Effects of BA, NA or CAG were more pronounced after 16 weeks as compared to 4 weeks in preventing the tumor development and altered gene expression. Concomitant administration of BA, NA and CAG tried to prevent these alterations more effectively than that of individual compound possibly by regulating miR-203 status through epigenetic or biogenetic modulations before and after the tumor development. Study provides a rationale for chemoprevention by combination of different compounds targeting miR-203.

Self-renewal as a therapeutic target in human colorectal cancer

Tumor recurrence following treatment remains a major clinical challenge. Evidence from xenograft models and human trials indicates selective enrichment of cancer-initiating cells (CICs) in tumors that survive therapy. Together with recent reports showing that CIC gene signatures influence patient survival, these studies predict that targeting self-renewal, the key 'stemness' property unique to CICs, may represent a new paradigm in cancer therapy. Here we demonstrate that tumor formation and, more specifically, human colorectal CIC function are dependent on the canonical self-renewal regulator BMI-1. Downregulation of BMI-1 inhibits the ability of colorectal CICs to self-renew, resulting in the abrogation of their tumorigenic potential. Treatment of primary colorectal cancer xenografts with a small-molecule BMI-1 inhibitor resulted in colorectal CIC loss with long-term and irreversible impairment of tumor growth. Targeting the BMI-1-related self-renewal machinery provides the basis for a new therapeutic approach in the treatment of colorectal cancer.

Bmi1 is required for tumorigenesis in a mouse model of intestinal cancer

The epigenetic regulator BMI1 is upregulated progressively in a wide variety of human tumors including colorectal cancer. In this study, we assessed the requirement for Bmi1 in intestinal tumorigenesis using an autochthonous mouse model in which Apc was conditionally ablated in the intestinal epithelium. Germline mutation of Bmi1 significantly reduced both the number and size of small intestinal adenomas arising in this model, and it acted in a dose-dependent manner. Moreover, in contrast to wild-type controls, Bmi1(-/-) mice showed no increase in median tumor size, and a dramatic decrease in tumor number, between 3 and 4 months of age. Thus, Bmi1 is required for both progression and maintenance of small intestinal adenomas. Importantly, Bmi1 deficiency did not disrupt oncogenic events arising from Apc inactivation. Instead, the Arf tumor suppressor, a known target of Bmi1 epigenetic silencing, was upregulated in Bmi1 mutant tumors. This was accompanied by significant upregulation of p53, which was confirmed by sequencing to be wild-type, and also elevated apoptosis within the smallest Bmi1(-/-) adenomas. By crossing Arf into this cancer model, we showed that Arf is required for the induction of both p53 and apoptosis, and it is a key determinant of the ability of Bmi1 deficiency to suppress intestinal tumorigenesis. Finally, a conditional Bmi1 mutant strain was generated and used to determine the consequences of deleting Bmi1 specifically within the intestinal epithelium. Strikingly, intestinal-specific Bmi1 deletion suppressed small intestinal adenomas in a manner that was indistinguishable from germline Bmi1 deletion. Thus, we conclude that Bmi1 deficiency impairs the progression and maintenance of small intestinal tumors in a cell autonomous and highly Arf-dependent manner.

Bmi1 expression in oral lichen planus and the risk of progression to oral squamous cell carcinoma

Oral lichen planus (OLP) is a potentially malignant disorder associated with an increased risk of progression to oral squamous cell carcinoma (OSCC). The objective of this study was to determine protein expression of cancer stem cell factor Bmi1 in a longitudinal series of patients with OLP and evaluate the correlation between Bmi1 expression and the risk of progression to OSCC. In a retrospective study, Bmi1 expression was determined using immunohistochemistry in samples from 96 patients with OLP who received a mean follow-up of 54 months, including patients who did not progress to OSCC (n=87) and patients who had progressed to OSCC (n=9). Analysis of 10 cases of normal oral mucosa and 6 cases of postmalignant OSCC form previously diagnosed OLP was also performed. The results showed that Bmi1 expression was observed in 32 (36.8%) of 87 cases of nonprogressing OLP and in 8 (88.9%) of 9 cases of progressing OLP. Bmi1 was not expressed in normal oral mucosa, but it was positively expressed in the 6 (100%) cases of OSCC. Multivariate analysis revealed that the risk of malignant progression in the patients with Bmi1-positive expression was significantly higher than those with Bmi1 negativity (odds ratio, 20.75; 95% confidence interval, 2.21-194.57; P=.008). Collectively, Bmi1 expression was significantly associated with malignant transformation in a large series of patients with OLP who received a longitudinal observation. Our findings suggested that Bmi1 may serve as a useful marker for the identification of a high risk of malignant progression of OLP.

Intestinal stem cells - types and markers

Intestinal epithelium is a rapidly cycling tissue, always renewing every 4-5 days under normal conditions, which is maintained by intestinal stem cells (ISCs). Using the fluorescence labelling trace, ISCs can be divided into two different types: active intestinal stem cells (A-ISCs) located in bottom of the intestinal crypt and the quiescent intestinal stem cells (Q-ISCs) in the +4 position of the crypt. There is a complex signal regulation net between the ISCs and other intestinal cells, such as Wnt and Notch pathways. ISCs have an intimate relationship with the colorectal cancer (CRC). However, a deficiency of stem cells markers severely limits research on the biological characteristics of ISCs. We have reviewed several ISCs markers, including Lgr5, PHLDA1, Bmi1 and Lrig1. These markers have widely different biological functions, but also have a close relationship with cancers, especially CRC. Our hypothesis concerns the reasons for ISCs having two distinct types and why endless ISCs markers have emerged.

Bmi1 enhances tumorigenicity and cancer stem cell function in pancreatic adenocarcinoma

Background

Bmi1 is an integral component of the Polycomb Repressive Complex 1 (PRC1) and is involved in the pathogenesis of multiple cancers. It also plays a key role in the functioning of endogenous stem cells and cancer stem cells. Previous work implicated a role for cancer stem cells in the pathogenesis of pancreatic cancer. We hypothesized that Bmi1 plays an integral role in enhancing pancreatic tumorigenicity and the function of cancer stem cells in pancreatic ductal adenocarcinoma.

Methods

We measured endogenous Bmi1 levels in primary human pancreatic ductal adenocarcinomas, pancreatic intraepithelial neoplasias (PanINs) and normal pancreas by immunohistochemistry and Western blotting. The function of Bmi1 in pancreatic cancer was assessed by alteration of Bmi1 expression in several cell model systems by measuring cell proliferation, cell apoptosis, in vitro invasion, chemotherapy resistance, and in vivo growth and metastasis in an orthotopic model of pancreatic cancer. We also assessed the cancer stem cell frequency, tumorsphere formation, and in vivo growth of human pancreatic cancer xenografts after Bmi1 silencing.

Results

Bmi1 was overexpressed in human PanINs, pancreatic cancers, and in several pancreatic cancer cell lines. Overexpression of Bmi1 in MiaPaCa2 cells resulted in increased proliferation, in vitro invasion, larger in vivo tumors, more metastases, and gemcitabine resistance while opposite results were seen when Bmi1 was silenced in Panc-1 cells. Bmi1 was overexpressed in the cancer stem cell compartment of primary human pancreatic cancer xenografts. Pancreatic tumorspheres also demonstrated high levels of Bmi1. Silencing of Bmi1 inhibited secondary and tertiary tumorsphere formation, decreased primary pancreatic xenograft growth, and lowered the proportion of cancer stem cells in the xenograft tissue.

Conclusions

Our results implicate Bmi1 in the invasiveness and growth of pancreatic cancer and demonstrate its key role in the regulation of pancreatic cancer stem cells.

MicroRNA-218 inhibits cell cycle progression and promotes apoptosis in colon cancer by downregulating BMI1 polycomb ring finger oncogene

Deregulated miRNAs participate in colorectal carcinogenesis. In this study, miR-218 was found to be downregulated in human colorectal cancer (CRC) by miRNA profile assay. miR-218 was silenced or downregulated in all five colon cancer cells (Caco2, HT29, SW620, HCT116 and LoVo) relative to normal colon tissues. miR-218 expression was significantly lower in 46 CRC tumor tissues compared with their adjacent normal tissues (P < 0.001). Potential target genes of miR-218 were predicted and BMI1 polycomb ring finger oncogene (BMI-1), a polycomb ring finger oncogene, was identified as one of the potential targets. Upregulation of BMI-1 was detected in CRC tumors compared with adjacent normal tissues (P < 0.001) and in all five colon cancer cell lines. Transfection of miR-218 in colon cancer cell lines (HCT116, HT29) significantly reduced luciferase activity of the wild-type construct of BMI-1 3' untranslated region (3'UTR) (P < 0.001), whereas this effect was not seen in the construct with mutant BMI-1 3'UTR, indicating a direct and specific interaction of miR-218 with BMI-1. Ectopic expression of miR-218 in HCT116 and HT29 cells suppressed BMI-1 mRNA and protein expression. In addition, miR-218 suppressed protein expression of BMI-1 downstream targets of cyclin-dependent kinase 4, a cell cycle regulator, while upregulating protein expression of p53. We further revealed that miR-218 induced apoptosis (P < 0.01), inhibited cell proliferation (P < 0.05) and promoted cell cycle arrest in the G2 phase (P < 0.01). In conclusion, miR-218 plays a pivotal role in CRC development through inhibiting cell proliferation and cycle progression and promoting apoptosis by downregulating BMI-1.

Oncogenicity of the developmental transcription factor Sox9

SOX9 [sex-determining region Y (SRY)-box 9 protein], a high mobility group box transcription factor, plays critical roles during embryogenesis and its activity is required for development, differentiation, and lineage commitment in various tissues including the intestinal epithelium. Here, we present functional and clinical data of a broadly important role for SOX9 in tumorigenesis. SOX9 was overexpressed in a wide range of human cancers, where its expression correlated with malignant character and progression. Gain of SOX9 copy number is detected in some primary colorectal cancers. SOX9 exhibited several pro-oncogenic properties, including the ability to promote proliferation, inhibit senescence, and collaborate with other oncogenes in neoplastic transformation. In primary mouse embryo fibroblasts and colorectal cancer cells, SOX9 expression facilitated tumor growth and progression whereas its inactivation reduced tumorigenicity. Mechanistically, we have found that Sox9 directly binds and activates the promoter of the polycomb Bmi1, whose upregulation represses the tumor suppressor Ink4a/Arf locus. In agreement with this, human colorectal cancers showed a positive correlation between expression levels of SOX9 and BMI1 and a negative correlation between SOX9 and ARF in clinical samples. Taken together, our findings provide direct mechanistic evidence of the involvement of SOX9 in neoplastic pathobiology, particularly, in colorectal cancer.

Epigenetic factors in cancer development: polycomb group proteins

The role of chromatin-modifying factors in cancer biology emerged exponentially in the last 10 years, and increased attention has been focused on Polycomb group (PcG) proteins and their enzymatic activities. PcG proteins are repressive chromatin modifiers required for proliferation and development. The frequent deregulation of PcG activities in human tumors has direct oncogenic effects and results, essential for cancer cell proliferation. Here we will review the recent findings regarding PcG proteins in prospective tumor development, focusing on the molecular mechanisms that deregulate PcG expression in different tumors, at the downstream pathways to PcG expression (that contribute to cancer development) and at the mechanisms that regulate PcG recruitment to specific targets. Finally, we will speculate on the benefit of PcG inhibition for cancer treatment, reviewing potential pharmacological strategies.

Two stem cell markers, ATP-binding cassette, G2 subfamily (ABCG2) and BMI-1, predict the transformation of oral leukoplakia to cancer: a long-term follow-up study

BACKGROUND

Although oral leukoplakia (OL) is the best-known potentially malignant disorder, the risk of OL malignant transformation is difficult to assess. ATP-binding cassette, G2 subfamily (ABCG2) and BMI-1 are stem cell markers that have been found to be associated with head and neck tumorigenesis. The objective of the current study was to evaluate the usefulness of ABCG2 and BMI-1 in predicting OL transformation.

METHODS

In a retrospective cohort of 135 patients with OL from the study institution who had a mean follow-up of 5.5 years, 32 developed cancer between 1985 and 2008. The expression of ABCG2 and BMI-1 was determined using immunohistochemistry in samples from these patients, and included untransformed OL (n = 103) and malignant-transformed OL (n = 32). The association between protein expression and clinicopathological parameters and transformation was analyzed.

RESULTS

Expression of ABCG2 and BMI-1 was observed in 58 (43.0%) and 44 (32.6%) of 135 patients, respectively. The correlation between ABCG2 and BMI-1 expression was significant (P = .024). Kaplan-Meier analysis revealed that 37.9% of patients with ABCG2 positivity developed cancer compared with 13.0% of patients with ABCG2 negativity (P = .014, log-rank test). Approximately 40.9% of patients with BMI-1 positivity developed cancer compared with 15.4% of patients with BMI-1 negativity (P = .029, log-rank test). Multivariate analysis revealed that ABCG2 and BMI-1 expression was associated with a 3.24-fold (95% confidence interval [95% CI], 1.31-7.98; P = .011) and 4.03-fold (95% CI, 1.59-10.26; P = .003) increased the risk of transformation, respectively.

CONCLUSIONS

ABCG2 and BMI-1 expression was found to be associated with the development of oral cancer in a large cohort of patients with OL for whom long-term follow-up was available, which suggests that ABCG2 and BMI-1 may be used as predictors of OL transformation.

Colon cancer stem cells: implications in carcinogenesis

The cancer stem cell model was described for hematologic malignancies in 1997 and since then evidence has emerged to support it for many solid tumors as well, including colon cancer. This model proposes that certain cells within the tumor mass are pluripotent and capable of self-renewal and have an enhanced ability to initiate distant metastasis. The cancer stem cell model has important implications for cancer treatment, since most current therapies target actively proliferating cells and may not be effective against the cancer stem cells that are responsible for recurrence. In recent years great progress has been made in identifying markers of both normal and malignant colon stem cells. Proteins proposed as colon cancer stem cell markers include CD133, CD44, CD166, ALDH1A1, Lgr5, and several others. In this review we consider the evidence for these proteins as colon cancer stem cell markers and as prognostic indicators of colon cancer survival. Additionally, we discuss potential functions of these proteins and the implications this may have for development of therapies that target colon cancer stem cells.

Bmi-1 is related to proliferation, survival and poor prognosis in pancreatic cancer

B-cell-specific Moloney murine leukemia virus insertion site 1 (BMI1) is a member of the polycomb group of transcriptional repressors. Until now, its expression and functional significance in pancreatic carcinogenesis was unknown. In the present study, we demonstrated that expression of BMI1 was markedly up-regulated in pancreatic cancer cell lines and surgically resected cancer specimens. In addition, BMI1 expression levels correlated positively with the presence of lymph node metastases and negatively with patient survival rates, suggesting a role for BMI1 in the progression of pancreatic cancer. Furthermore, stable down-regulation of BMI1 suppressed cell growth, delayed the G1/S transition, and enhanced the susceptibility of different pancreatic cell lines to apoptosis following expression of a lentiviral-mediated shRNA targeted for BMI1. Expression of the short-hairpin RNA also correlated with the up-regulation of p21 and Bax and the down-regulation of cyclin D1, cyclin-dependent kinase (CDK)-2 and -4, Bcl-2, and phospho-Akt. Finally, growth suppression following BMI1 depletion was confirmed in a nude mouse model. In conclusion, our findings indicate that BMI1 plays an important role in the late progression of pancreatic cancer and may represent a novel therapeutic target for the treatment of pancreatic cancer.

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.

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.

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.

Expression level of Bmi-1 oncoprotein is associated with progression and prognosis in colon cancer

PURPOSE

To investigate the clinicopathologic significance and predictive value of Bmi-1 expression in patients with colon cancer.

METHODS

Bmi-1 expression was assessed by immunohistochemistry, PCR, and western blotting in specimens from 203 patients and by immunohistochemistry in 66 specimens of lymph node metastasis (LNM).

RESULTS

Positive staining of Bmi-1 occurred in 7.9% (16/203), 66.5% (135/203), and 86.4% (57/66) of specimens from normal tissue, colon cancer, and LNM, respectively. Staining was significantly correlated with clinical stage, depth of invasion, nodal involvement, distant metastasis, and Ki67 level. Bmi-1 was upregulated at the transcriptional and translational levels. Patients with Bmi-1-positive localized tumors had a much lower 5-year disease-free survival (relative risk 2.919, P < 0.0001) and overall survival (relative risk 5.056, P < 0.0001). Bmi-1 immunoreactivity emerged as an independent prognostic factor in the multivariate analysis.

CONCLUSIONS

We have shown that expression of Bmi-1 was elevated in colon cancer and might serve as an independent prognostic marker.

Polycomb group protein Bmi1 is overexpressed and essential in anchorage-independent colony formation, cell proliferation and repression of cellular senescence in cholangiocarcinoma: tissue and culture studies

Polycomb-group proteins Bmi1 is regarded as a "stemness" gene involved in the maintenance of stem cells, malignant transformation, and biologic aggressiveness of several human carcinomas. We examined the significance of the Bmi1 expression in intrahepatic cholangiocarcinoma. The expression of Bmi1 was examined in intrahepatic cholangiocarcinoma (n = 30; 9 bile ductular carcinoma, 8 intrahepatic cholangiocarcinoma of peripheral type, and 13 of hilar type) by using immunohistochemistry and real-time polymerase chain reaction. The expression level of Bmi1 was assessed in 7 cholangiocarcinoma cell lines. The effect of Bmi1 knockdown was examined in cultured cholangiocarcinoma cells (HuCCT1 and TFK-1) using small interfering RNA. Bmi1 was consistently expressed in nonneoplastic biliary epithelial cells and in all intrahepatic cholangiocarcinoma, irrespective of the location and histological degree of differentiation. The level of mRNA expression was significantly higher in 13 (81.3%) of 16 intrahepatic cholangiocarcinoma compared with the corresponding nonneoplastic tissues. All 7 cultured cholangiocarcinoma cells overexpressed Bmi1 to various degrees. The knockdown of Bmi1 resulted in decreased colony formation, decreased cell proliferation activities, and increased cellular senescence. The overexpression of polycomb-group protein Bmi1 is essential for colony formation and cell proliferation, probably by the repression of cellular senescence in intrahepatic cholangiocarcinoma.

Epigenetics, stem cells and epithelial cell fate

Establishment and maintenance of epigenetic profiles are essential steps of development during which stem cells, despite identical genetic information, will acquire different and selective gene expression patterns, specific for their fate. This highly complex programming process involves mechanisms that are not yet completely understood although it has been established over the past few years that chromatin modifier enzymes (i.e. DNA and histone methyltransferases, histone deacetylases, histone demethylases, histone acetyltransferases) play essential roles in the establishment of transcriptional programs accompanying cell differentiation. Investigators in this field have been studying a wide variety of cell types including neural, muscular, mesenchymal and blood cells. This review will focus on epithelial cells of the digestive tract, intestinal stem cell niches being a model of choice to understand how epigenetic changes can drive nuclear programming and specific cell differentiation. Moreover, deregulation of epigenetic programming is frequently observed in human tumours and therefore, decoding these molecular mechanisms is essential to better understand both developmental and cancerous processes.

Type I collagen inhibits differentiation and promotes a stem cell-like phenotype in human colorectal carcinoma cells

Background:

Human colorectal cancer is caused by mutations and is thought to be maintained by a population of cancer stem cells. Further phenotypic changes occurring at the invasive edge suggest that colon cancer cells are also regulated by their microenvironment. Type I collagen, a promoter of the malignant phenotype in pancreatic carcinoma cells, is highly expressed at the invasive front of human colorectal cancer.

Methods:

This study investigates the role of type I collagen in specifying the colorectal cancer cell phenotype. The effect of type I collagen on morphology, localisation of cell–cell adhesion proteins, differentiation and stem cell-like characteristics was examined in a panel of human colorectal carcinoma cell lines.

Results:

Human colorectal carcinoma cells grown on type I collagen in serum-free medium show an epithelial–mesenchymal-like transition (EMT-like), assuming a more flattened less cohesive morphology. Type I collagen downregulates E-cadherin and β-catenin at cell–cell junctions. Furthermore, type I collagen inhibits differentiation, increases clonogenicity and promotes expression of stem cell markers CD133 and Bmi1. Type I collagen effects were partially abrogated by a function-blocking antibody to α2 integrin.

Conclusion:

Together, these results indicate that type I collagen promotes expression of a stem cell-like phenotype in human colorectal cancer cells likely through α2β1 integrin.

Clinicopathological significance of B-cell-specific Moloney murine leukemia virus insertion site 1 expression in gastric carcinoma and its precancerous lesion

AIM: To explore the relation between B-cell-specific Moloney murine leukemia virus insertion site 1 (Bmi-1) expression and the clinicopathological features of gastric carcinoma (GC).

METHODS: Immunohistochemistry was used to detect the expression of Bmi-1 and ki-67. Double-labeling staining was used to display the distribution of Bcl-2⁺/ki-67^- cells in 162 cases of GC and its matched normal mucosa and precancerous lesion.

RESULTS: The positive rate of Bmi-1 expression in GC (52.5%) was significantly higher than that in normal gastric mucosa (21.6%, χ² = 33.088, P < 0.05). The Bmi-1 expression in GC was closely related with the Lauren’s and Borrmann’s classification and clinical stage (χ² = 4.400, 6.122 and 11.190, respectively, P < 0.05). The expression of ki-67 was related to the Borrmann’s classification (χ² = 13.380, P < 0.05). Bcl-2 expression was correlated with the Lauren’s classification (χ² = 4.725, P < 0.05), and the Bmi-1 expression both in GC (r_k = 0.157, P < 0.05) and in intestinal metaplasia (r_k = 0.270, P < 0.05).

CONCLUSION: Abnormal Bmi-1 expression in GC may be involved in cell proliferation, apoptosis and cancerization. This marker can objectively indicate the clinicopathological characteristics of GC.

Bmi-1 over-expression in neural stem/progenitor cells increases proliferation and neurogenesis in culture but has little effect on these functions in vivo

The polycomb gene Bmi-1 is required for the self-renewal of stem cells from diverse tissues, including the central nervous system (CNS). Bmi-1 expression is elevated in most human gliomas, irrespective of grade, raising the question of whether Bmi-1 over-expression is sufficient to promote self-renewal or tumorigenesis by CNS stem/progenitor cells. To test this we generated Nestin-Bmi-1-GFP transgenic mice. Analysis of two independent lines with expression in the fetal and adult CNS demonstrated that transgenic neural stem cells formed larger colonies, more self-renewing divisions, and more neurons in culture. However, in vivo, Bmi-1 over-expression had little effect on CNS stem cell frequency, subventricular zone proliferation, olfactory bulb neurogenesis, or neurogenesis/gliogenesis during development. Bmi-1 transgenic mice were born with enlarged lateral ventricles and a minority developed idiopathic hydrocephalus as adults, but none of the transgenic mice formed detectable CNS tumors, even when aged. The more pronounced effects of Bmi-1 over-expression in culture were largely attributable to the attenuated induction of p16(Ink4a) and p19(Arf) in culture, proteins that are generally not expressed by neural stem/progenitor cells in young mice in vivo. Bmi-1 over-expression therefore has more pronounced effects in culture and does not appear to be sufficient to induce tumorigenesis in vivo.

Genes involved in differentiation, stem cell renewal, and tumorigenesis are modulated in telomerase-immortalized human urothelial cells

The expression of hTERT, the catalytic subunit of telomerase, immortalizes normal human urothelial cells (NHUC). Expression of a modified hTERT, without the ability to act in telomere maintenance, did not immortalize NHUC, confirming that effects at telomeres are required for urothelial immortalization. Previous studies indicate that inhibition of telomerase has an immediate effect on urothelial carcinoma (UC) cell line viability, before sufficient divisions to account for telomere attrition, implicating non-telomere effects of telomerase in UC. We analyzed the effects of telomerase on gene expression in isogenic mortal and hTERT-transduced NHUC. hTERT expression led to consistent alterations in the expression of genes predicted to be of phenotypic significance in tumorigenesis. A subset of expression changes were detected soon after transduction with hTERT and persisted with continued culture. These genes (NME5, PSCA, TSPYL5, LY75, IGFBP2, IGF2, CEACAM6, XG, NOX5, KAL1, and HPGD) include eight previously identified as polycomb group targets. TERT-NHUC showed overexpression of the polycomb repressor complex (PRC1 and PRC4) components, BMI1 and SIRT1, and down-regulation of multiple PRC targets and genes associated with differentiation. TERT-NHUC at 100 population doublings, but not soon after transduction, showed increased saturation density and an attenuated differentiation response, indicating that these are not acute effects of telomerase expression. Some of the changes in gene expression identified may contribute to tumorigenesis. Expression of NME5 and NDN was down-regulated in UC cell lines and tumors. Our data supports the concept of both telomere-based and non-telomere effects of telomerase and provides further rationale for the use of telomerase inhibitors in UC.