Chromobox protein homologue 7 protein, with decreased expression in human carcinomas, positively regulates E-cadherin expression by interacting with the histone deacetylase 2 protein

The Role of the MiR-181 Family in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fourth-leading cause of cancer-related death worldwide. Due to the high mortality rate in HCC patients, discovering and developing novel systemic treatment options for HCC is a vital unmet medical need. Among the numerous molecular alterations in HCCs, microRNAs (miRNAs) have been increasingly recognised to play critical roles in hepatocarcinogenesis. We and others have recently revealed that members of the microRNA-181 (miR-181) family were up-regulated in some, though not all, human cirrhotic and HCC tissues-this up-regulation induced epithelial-mesenchymal transition (EMT) in hepatocytes and tumour cells, promoting HCC progression. MiR-181s play crucial roles in governing the fate and function of various cells, such as endothelial cells, immune cells, and tumour cells. Previous reviews have extensively covered these aspects in detail. This review aims to give some insights into miR-181s, their targets and roles in modulating signal transduction pathways, factors regulating miR-181 expression and function, and their roles in HCC.

Critical Roles of Polycomb Repressive Complexes in Transcription and Cancer

Polycomp group (PcG) proteins are members of highly conserved multiprotein complexes, recognized as gene transcriptional repressors during development and shown to play a role in various physiological and pathological processes. PcG proteins consist of two Polycomb repressive complexes (PRCs) with different enzymatic activities: Polycomb repressive complexes 1 (PRC1), a ubiquitin ligase, and Polycomb repressive complexes 2 (PRC2), a histone methyltransferase. Traditionally, PRCs have been described to be associated with transcriptional repression of homeotic genes, as well as gene transcription activating effects. Particularly in cancer, PRCs have been found to misregulate gene expression, not only depending on the function of the whole PRCs, but also through their separate subunits. In this review, we focused especially on the recent findings in the transcriptional regulation of PRCs, the oncogenic and tumor-suppressive roles of PcG proteins, and the research progress of inhibitors targeting PRCs.

Liver-specific deletion of miR-181ab1 reduces liver tumour progression via upregulation of CBX7

MiR-181 expression levels increased in hepatocellular carcinoma (HCC) compared to non-cancerous tissues. MiR-181 has been widely reported as a possible driver of tumourigenesis but also acts as a tumour suppressor. In addition, the miR-181 family regulates the development and function of immune and vascular cells, which play vital roles in the progression of tumours. More complicatedly, many genes have been identified as miR-181 targets to mediate the effects of miR-181. However, the role of miR-181 in the development of primary tumours remains largely unexplored. We aimed to examine the function of miR-181 and its vital mediators in the progression of diethylnitrosamine-induced primary liver cancers in mice. The size of liver tumours was significantly reduced by 90% in global (GKO) or liver-specific (LKO) 181ab1 knockout mice but not in hematopoietic and endothelial lineage-specific knockout mice, compared to WT mice. In addition, the number of tumours was significantly reduced by 50% in GKO mice. Whole-genome RNA-seq analysis and immunohistochemistry showed that epithelial-mesenchymal transition was partially reversed in GKO tumours compared to WT tumours. The expression of CBX7, a confirmed miR-181 target, was up-regulated in GKO compared to WT tumours. Stable CBX7 expression was achieved with an AAV/Transposase Hybrid-Vector System and up-regulated CBX7 expression inhibited liver tumour progression in WT mice. Hepatic CBX7 deletion restored the progression of LKO liver tumours. MiR-181a expression was the lowest and CBX7 expression the highest in iClust2 and 3 subclasses of human HCC compared to iClust1. Gene expression profiles of GKO tumours overlapped with low-proliferative peri-portal-type HCCs. Liver-specific loss of miR-181ab1 inhibited primary liver tumour progression via up-regulating CBX7 expression, but tumour induction requires both hepatic and non-hepatic miR-181. Also, miR-181ab1-deficient liver tumours may resemble low-proliferative periportal-type human HCC.

CBX7, a Potential Prognostic Biomarker in Lung Adenocarcinoma

Background

Lung adenocarcinoma (LUAD) is a major type of NSCLC and has high morbidity and mortality. The identification of useful prognostic biomarkers for LUAD is important. CBX7 has been reported in various cancers yet its expression level and potential roles have not been fully understood.

Methods

GEPIA, Oncomine, TCGA, KM plotter and OSluca databases were used to explore the expression profile and prognostic effects of CBX7 mRNA expression in patients with LUAD. TIMER was used to explore the relationship between CBX7 and immune infiltrating cells. GSEA was used to further explore the potential biological process and pathways regulated by CBX7 in LUAD. Lastly, IHC detection of CBX7 in 95 samples was used to validate the result.

Results

We found CBX7 was downregulated in LUAD in GEPIA, Oncomine and TCGA databases. TCGA, KM plotter and OSluca databases suggested that CBX7 was associated with poor clinical outcomes and low survival rate. Using TIMER, we found that CBX7 might be associated with immune infiltration. Via gene set enrichment analysis, we found that tumor-associated biological processes and signaling pathways were enriched in the CBX7 downregulated group. Using clinical samples, we found that CBX7 protein has low expression in LUAD and was associated with poor survival.

Conclusion

CBX7 might serve as a promising biomarker and potential molecular target in LUAD.

CBX7 is Dualistic in Cancer Progression Based on its Function and Molecular Interactions

Chromobox protein homolog 7 (CBX7) is a member of the Chromobox protein family and participates in the formation of the polycomb repressive complex 1(PRC1). In cells, CBX7 often acts as an epigenetic regulator to regulate gene expression. However, pathologically, abnormal expression of CBX7 can lead to an imbalance of gene expression, which is closely related to the occurrence and progression of cancers. In cancers, CBX7 plays a dual role; On the one hand, it contributes to cancer progression in some cancers by inhibiting oncosuppressor genes. On the other hand, it suppresses cancer progression by interacting with different molecules to regulate the synthesis of cell cycle-related proteins. In addition, CBX7 protein may interact with different RNAs (microRNAs, long noncoding RNAs, circular RNAs) in different cancer environments to participate in a variety of pathways, affecting the development of cancers. Furthermore, CBX7 is involved in cancer-related immune response and DNA repair. In conclusion, CBX7 expression is a key factor in the occurrence and progression of cancers.

Genome-Wide Histone H3K27 Acetylation Profiling Identified Genes Correlated With Prognosis in Papillary Thyroid Carcinoma

Thyroid carcinoma (TC) is the most common endocrine malignancy, and papillary TC (PTC) is the most frequent subtype of TC, accounting for 85–90% of all the cases. Aberrant histone acetylation contributes to carcinogenesis by inducing the dysregulation of certain cancer-related genes. However, the histone acetylation landscape in PTC remains elusive. Here, we interrogated the epigenomes of PTC and benign thyroid nodule (BTN) tissues by applying H3K27ac chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) along with RNA-sequencing. By comparing the epigenomic features between PTC and BTN, we detected changes in H3K27ac levels at active regulatory regions, identified PTC-specific super-enhancer-associated genes involving immune-response and cancer-related pathways, and uncovered several genes that associated with disease-free survival of PTC. In summary, our data provided a genome-wide landscape of histone modification in PTC and demonstrated the role of enhancers in transcriptional regulations associated with prognosis of PTC.

CBX7 suppresses urinary bladder cancer progression via modulating AKR1B10-ERK signaling

The chromobox (CBX) proteins mediate epigenetic gene silencing and have been implicated in the cancer development. By analyzing eight CBX family members in TCGA dataset, we found that chromobox 7 (CBX7) was the most strikingly downregulated CBX family member in urinary bladder cancer (UBC), as compared to normal tissues. Though dysregulation of CBX7 has been reported in multiple cancers, its specific role and clinical relevance in UBC remain unclear. Herein, we found that frequent downregulation of CBX7 in UBC specimens, which was due to its promoter hypermethylation, was correlated with poor prognosis. The ectopic expression of CBX7 suppressed UBC cell proliferation, migration, invasion, and cancer stemness, whereas CBX7 depletion promoted cancer cell aggressiveness. Importantly, CBX7 overexpression in UBC cells inhibited tumorigenicity, whereas CBX7 depletion promoted the tumor development, indicating its tumor-suppressive role in UBC. Using RNA-seq and chromosome immunoprecipitation (ChIP) assays, we identified aldo-keto reductase family 1 member 10 (AKR1B10) as a novel downstream target of CBX7, which was negatively modulated by CBX7 in a PRC1-dependent manner and involved in stimulating ERK signaling. Consistently, AKR1B10 overexpression induced cancer cell aggressiveness, whereas suppression of AKR1B10 by siRNA or its small molecular inhibitor, oleanolic acid, reversed the CBX7 deficiency-induced cellular effects. AKR1B10 overexpression was negatively associated with CBX7 downregulation and predicted poor clinical outcomes in UBC patients. Taken together, our results indicate that CBX7 functions as a tumor suppressor to downregulate AKR1B10 and further inactivates ERK signaling. This CBX7/AKR1B10/ERK signaling axis may provide a new therapeutic strategy against UBC.

Protein-DNA/RNA Interactions: An Overview of Investigation Methods in the -Omics Era

The fields of application of functional proteomics are not limited to the study of protein–protein interactions; they also extend to those involving protein complexes that bind DNA or RNA. These interactions affect fundamental processes such as replication, transcription, and repair in the case of DNA, as well as transport, translation, splicing, and silencing in the case of RNA. Analytical or preparative experimental approaches, both in vivo and in vitro, have been developed to isolate and identify DNA/RNA binding proteins by exploiting the advantage of the affinity shown by these proteins toward a specific oligonucleotide sequence. The present review proposes an overview of the approaches most commonly employed in proteomics applications for the identification of nucleic acid-binding proteins, such as affinity purification (AP) protocols, EMSA, chromatin purification methods, and CRISPR-based chromatin affinity purification, which are generally associated with mass spectrometry methodologies for the unbiased protein identification.

Regulating Methylation at H3K27: A Trick or Treat for Cancer Cell Plasticity

Properly timed addition and removal of histone 3 lysine 27 tri-methylation (H3K27me3) is critical for enabling proper differentiation throughout all stages of development and, likewise, can guide carcinoma cells into altered differentiation states which correspond to poor prognoses and treatment evasion. In early embryonic stages, H3K27me3 is invoked to silence genes and restrict cell fate. Not surprisingly, mutation or altered functionality in the enzymes that regulate this pathway results in aberrant methylation or demethylation that can lead to malignancy. Likewise, changes in expression or activity of these enzymes impact cellular plasticity, metastasis, and treatment evasion. This review focuses on current knowledge regarding methylation and de-methylation of H3K27 in cancer initiation and cancer cell plasticity.

From classical to new generation approaches: An excursus of -omics methods for investigation of protein-protein interaction networks

Functional Proteomics aims to the identification of in vivo protein-protein interaction (PPI) in order to piece together protein complexes, and therefore, cell pathways involved in biological processes of interest. Over the years, proteomic approaches used for protein-protein interaction investigation have relied on classical biochemical protocols adapted to a global overview of protein-protein interactions, within so-called "interactomics" investigation. In particular, their coupling with advanced mass spectrometry instruments and innovative analytical methods led to make great strides in the PPIs investigation in proteomics. In this review, an overview of protein complexes purification strategies, from affinity purification approaches, including proximity-dependent labeling techniques and cross-linking strategy for the identification of transient interactions, to Blue Native Gel Electrophoresis (BN-PAGE) and Size Exclusion Chromatography (SEC) employed in the "complexome profiling", has been reported, giving a look to their developments, strengths and weakness and providing to readers several recent applications of each strategy. Moreover, a section dedicated to bioinformatic databases and platforms employed for protein networks analyses was also included.

The Prognostic Value of the Chromobox Family in Human Ovarian Cancer

Ovarian cancer is one of the most lethal gynecologic tumors in women and has a poor prognosis. The purpose of our study was to identify new prognostic markers in ovarian cancer. We examined the prognostic roles of mRNA expression of the chromobox (CBX) family in patients with ovarian cancer utilizing the Kaplan-Meier plotter database. The prognostic values and expression levels of CBX members associated with prognosis were further evaluated using KM plotter in diverse subgroups and immunohistochemistry (IHC) analysis in ovarian carcinoma. The results revealed that elevated CBX1-3 mRNA expression may predict poor overall survival (OS) and progression-free survival (PFS) outcomes in patients with ovarian cancer. Notably, in women with ovarian cancer, increased CBX1 mRNA expression was linked to a short OS in all stages and in the grade II and grade III subgroups. Additionally, CBX2 and CBX3 were strongly related to short OS in stage III+IV patients, and a link between high CBX3 mRNA expression and unfavorable OS in grade II patients was observed. High expression levels of CBX1 and CBX3 were significantly associated with chemotherapy resistance in ovarian cancer patients. IHC staining showed that the CBX1-3 proteins were upregulated in serous ovarian carcinoma tissues compared with normal ovarian tissues. Therefore, our results indicated that CBX1-3 could be attractive biomarkers for predicting poor prognosis of ovarian cancer.

Immunological Aspects of the Tumor Microenvironment and Epithelial-Mesenchymal Transition in Gastric Carcinogenesis

Infection with Helicobacter pylori, a Gram-negative, microaerophilic pathogen often results in gastric cancer in a subset of affected individuals. This explains why H. pylori is the only bacterium classified as a class I carcinogen by the World Health Organization. Several studies have pinpointed mechanisms by which H. pylori alters signaling pathways in the host cell to cause diseases. In this article, the authors have reviewed 234 studies conducted over a span of 18 years (2002-2020). The studies investigated the various mechanisms associated with gastric cancer induction. For the past 1.5 years, researchers have discovered new mechanisms contributing to gastric cancer linked to H. pylori etiology. Alongside alteration of the host signaling pathways using oncogenic CagA pathways, H. pylori induce DNA damage in the host and alter the methylation of DNA as a means of perturbing downstream signaling. Also, with H. pylori, several pathways in the host cell are activated, resulting in epithelial-to-mesenchymal transition (EMT), together with the induction of cell proliferation and survival. Studies have shown that H. pylori enhances gastric carcinogenesis via a multifactorial approach. What is intriguing is that most of the targeted mechanisms and pathways appear common with various forms of cancer.

The Long Non-Coding RNA Prader Willi/Angelman Region RNA5 (PAR5) Is Downregulated in Anaplastic Thyroid Carcinomas Where It Acts as a Tumor Suppressor by Reducing EZH2 Activity

Anaplastic thyroid carcinoma (ATC) represents one the most aggressive neoplasias in humans, and, nowadays, limited advances have been made to extend the survival and reduce the mortality of ATC. Thus, the identification of molecular mechanism underlying its progression is needed. Here, we evaluated the long non-coding RNA (lncRNA) expression profile of nine ATC in comparison with five normal thyroid tissues by a lncRNA microarray. By this analysis, we identified 19 upregulated and 28 downregulated lncRNAs with a fold change >1.1 or <−1.1 and p-value < 0.05, in ATC samples. Some of them were subsequently validated by qRT-PCR. Then, we investigated the role of the lncRNA Prader Willi/Angelman region RNA5 (PAR5), drastically and specifically downregulated in ATC. The restoration of PAR5 reduces proliferation and migration rates of ATC-derived cell lines indicating that its downregulation contributes to thyroid cancer progression. Our results suggest that PAR5 exerts its anti-oncogenic role by impairing Enhancer of Zeste Homolog 2 (EZH2) oncogenic activity since we demonstrated that PAR5 interacts with it in thyroid cancer cell lines, reducing EZH2 protein levels and its binding on the E-cadherin promoter, relieving E-cadherin from the negative regulation by EZH2. Consistently, EZH2 is overexpressed in ATC, but not in differentiated thyroid carcinomas. The results reported here define a tumor suppressor role for PAR5 in undifferentiated thyroid neoplasias, further highlighting the pivotal role of lncRNAs in thyroid carcinogenesis.

CBX7 Inhibits Cell Growth and Motility and Induces Apoptosis in Cervical Cancer Cells

The chromobox protein homolog 7 (CBX7), one member of the polycomb group family, has been characterized mainly to play a tumor-suppressive role in human malignant neoplasias. Moreover, downregulation of CBX7 is correlated with poor prognosis and aggressiveness in a variety of human cancers. However, the biological functions and role of CBX7 in cervical cancer have not been elucidated. In the present study, we explore whether CBX7 exerts its tumor-suppressive function in cervical cancer. To achieve this goal, molecular approaches were used to upregulate the expression of CBX7 or downregulation of CBX7 in cervical cancer cell lines. We observed that overexpression of CBX7 inhibited cell growth and induced apoptosis in cervical cancer cells. CBX7 overexpression retarded cell migration and invasion in cervical cancer cells. In line with this, downregulation of CBX7 promoted cell growth and migration as well as invasion in cervical cancer cells. Our findings suggest that CBX7 might be a tumor suppressor and could be a potential target in cervical cancer.

Investigating the structural features of chromodomain proteins in the human genome and predictive impacts of their mutations in cancers

Epigenetic readers are specific proteins which recognize histone marks and represents the underlying mechanism for chromatin regulation. Histone H3 lysine methylation is a potential epigenetic code for the chromatin organization and transcriptional control. Recognition of histone methylation is achieved by evolutionary conserved reader modules known as chromodomain, identified in several proteins, and is involved in transcriptional silencing and chromatin remodelling. Genetic perturbations within the structurally conserved chromodomain could potentially mistarget the reader protein and impair their regulatory pathways, ultimately leading to cellular chaos by setting the stage for tumor development and progression. Here, we report the structural conservations associated with diverse functions, prognostic significance and functional consequences of mutations within chromodomain of human proteins in distinct cancers. We have extensively analysed chromodomain containing human proteins in terms of their structural-functional ability to act as a molecular switch in the recognition of methyl-lysine recognition. We further investigated the combinatorial potential, target promiscuity and binding specificity associated with their underlying mechanisms. Indeed, the molecular mechanism of epigenetic silencing significantly underlies a newer cancer therapy approach. We hope that a critical understanding of chromodomains will pave the way for novel paths of research providing newer insights into the designing of effective anti-cancer therapies.

Beyond EZH2: is the polycomb protein CBX2 an emerging target for anti-cancer therapy?

Introduction: Epigenetic modifications are important regulators of transcription and appropriate gene expression answering an environmental stimulus. In cancer, these epigenetic modifications are altered, which impact the transcriptome, promoting initiation and cancer progression. Thus, targeting epigenetic machinery has proven to be an efficient cancer therapy. Areas covered: We review CBX2 as a therapeutic target. CBX2 is a polycomb protein, responsible for polycomb-repressive complex 1 (PRC1) targeting to chromatin via recognition of the repressive mark H3K27me3. Mechanistically, CBX2 overexpression may be implicated in poor survival by maintaining cancer stem cells in an undifferentiated state and via repression of tumor suppressors. We discuss strategies used to target CBX proteins and provide insights into biomarker considerations that may be important when targeting CBX family members for anti-cancer therapy. Expert opinion: CBX2 inhibition is a promising approach for the targeting of polycomb complexes in the cancer stem cell niche. However, extensive optimization of the current field of small molecules targeting CBX family proteins will be critical to reach in vivo, or clinical, utility.

The complex CBX7-PRMT1 has a critical role in regulating E-cadherin gene expression and cell migration

The Chromobox protein homolog 7 (CBX7) belongs to the Polycomb Group (PcG) family, and, as part of the Polycomb repressive complex (PRC1), contributes to maintain transcriptional gene repression. Loss of CBX7 expression has been reported in several human malignant neoplasias, where it often correlates with an advanced cancer state and poor survival, proposing CBX7 as a candidate tumor-suppressor gene in cancer progression. Indeed, CBX7 is able to positively or negatively regulate the expression of genes involved in cell proliferation and cancer progression, such as E-cadherin, cyclin E, osteopontin, EGR1. To understand the molecular mechanisms that underlie the involvement of CBX7 in cancer progression, we designed a functional proteomic experiment based on CHIP-MS to identify novel CBX7 protein partners. Among the identified CBX7-interacting proteins we focused our attention on the Protein Arginine Methyltransferase 1 (PRMT1) whose critical role in epithelial-mesenchymal transition (EMT), cancer cell migration and invasion has been already reported. We confirmed the interaction between CBX7 and PRMT1 and demonstrated that this interaction is crucial for PRMT1 enzymatic activity both in vitro and in vivo and for the regulation of E-cadherin expression, an important hallmark of EMT. These results suggest a general mechanism by which CBX7 interacting with histone modification enzymes like HDAC2 and PRMT1 enhances E-cadherin expression. Therefore, disruption of this equilibrium may induce impairment of E-cadherin expression and increased cell migration eventually leading to EMT and, then, cancer progression.

Penalized negative binomial models for modeling an overdispersed count outcome with a high-dimensional predictor space: Application predicting micronuclei frequency

Chromosomal aberrations, such as micronuclei (MN), have served as biomarkers of genotoxic exposure and cancer risk. Guidelines for the process of scoring MN have been presented by the HUman MicroNucleus (HUMN) project. However, these guidelines were developed for assay performance but do not address how to statistically analyze the data generated by the assay. This has led to the application of various statistical methods that may render different interpretations and conclusions. By combining MN with data from other high-throughput genomic technologies such as gene expression microarray data, we may elucidate molecular features involved in micronucleation. Traditional methods that can model discrete (synonymously, count) data, such as MN frequency, require that the number of explanatory variables (P) is less than the number of samples (N). Due to this limitation, penalized models have been developed to enable model fitting for such over-parameterized datasets. Because penalized models in the discrete response setting are lacking, particularly when the count outcome is over-dispersed, herein we present our penalized negative binomial regression model that can be fit when P > N. Using simulation studies we demonstrate the performance of our method in comparison to commonly used penalized Poisson models when the outcome is over-dispersed and applied it to MN frequency and gene expression data collected as part of the Norwegian Mother and Child Cohort Study. Our countgmifs R package is available for download from the Comprehensive R Archive Network and can be applied to datasets having a discrete outcome that is either Poisson or negative binomial distributed and a high-dimensional covariate space.

Altered Epigenetic Mechanisms in Thyroid Cancer Subtypes

Thyroid carcinoma (TC) is the most frequent malignant neoplasm of the endocrine system. Molecular methods for diagnosis of invasive thyroid disease can be effectively adopted. Epigenetic factors play an important role in the diversity patterns of gene expression and the phenotypic and biological characteristics of TC subtypes. We aimed to review epigenetic changes in the main subtypes of TC, along with a presentation of the methods that have examined these changes, and active clinical trials for the treatment of advanced TCs targeting epigenetic changes. A literature analysis was performed in MEDLINE using PubMed, Elsevier, and Google Scholar for studies published up to 2016, using the keywords: "Epigenetic alterations" OR "Epigenetic changes", "thyroid cancers", "papillary thyroid cancer", "medullary thyroid cancer", "follicular thyroid cancer", and "anaplastic thyroid cancer", which resulted in 310 articles in English. All related abstracts were reviewed and studies were included that were published in English, had available full text, and determined the details of the methods and materials associated with the epigenetic patterns of TC and its subtypes (100 articles). Analysis of epigenetic alterations in TC subtypes helps to identify pathogenesis and can play an important role in the classification and diagnosis of tumors. Epigenetic mechanisms, especially aberrant methylation of DNA and microRNAs (miRs), are likely to play an important role in thyroid tumorigenesis. Further studies are required to elucidate the role of histone modification mechanisms in TC development.

CBX7 is a glioma prognostic marker and induces G1/S arrest via the silencing of CCNE1

Chromobox homolog 7 (CBX7) cooperates with other polycomb group (PcG) proteins to maintain target genes in a silenced state. However, the precise role of CBX7 in tumor progression is still controversial. We found that the expression of CBX7 in four public databases was significantly lower in high grade glioma (HGG). The reduced expression of CBX7 correlated with poor outcome in HGG patients. Both KEGG and GO analyses indicated that genes that were negatively correlated to CBX7 were strongly associated with the cell cycle pathway. We observed that decreased CBX7 protein levels enhanced glioma cells proliferation, migration and invasion. Then, we verified that CBX7 overexpression arrested cells in the G₀/G₁ phase. Moreover, we demonstrated that the underlying mechanism involved in CBX7 induced repression of CCNE1 promoter requiring the recruitment of histone deacetylase 2 (HADC2). Finally, in vivo bioluminescence imaging and survival times of nude mice revealed that CBX7 behaved as a tumor suppressor in gliomas. In summary, our results validate the assumption that CBX7 is a tumor suppressor of gliomas. Moreover, CBX7 is a potential and novel prognostic biomarker in glioma patients. We also clarified that CBX7 silences CCNE1 via the combination of CCNE1 promoter and the recruitment of HDAC2.

CBX7 suppresses cell proliferation, migration, and invasion through the inhibition of PTEN/Akt signaling in pancreatic cancer

Chromobox protein homolog 7 (CBX7), one of the polycomb group (PcG) proteins, is a transcriptional repressor involved in the regulation of cell proliferation and senescence. In the present study, we showed that CBX7 negatively regulates the proliferation, viability, chemoresistance, and migration of pancreatic cancer cells. Overexpression of CBX7 significantly inhibited the proliferation of pancreatic cancer cells in vitro and in vivo. Depletion of CBX7 facilitated their growth. CBX7 also impaired the viability and chemoresistance of pancreatic cancer cells. Transwell assays showed that CBX7 reduces the migratory capacity of pancreatic cancer cells. Of note, CBX7 reduced PTEN/Akt signaling in pancreatic cancer cells by increasing PTEN transcription, suggesting involvement of PTEN/Akt pathway in the tumor suppressive activity of CBX7. In addition, immunohistochemical analysis the CBX7 and PTEN expression in 74 surgically resected pancreatic ductal adenocarcinoma (PDAC) specimens revealed that CBX7 expression is significantly downregulated in pancreatic ductal adenocarcinoma, compared to normal pancreatic tissues. Reduced expression of CBX7 and PTEN was associated with increased malignancy grade in pancreatic adenocarcinoma, whereas maintenance of CBX7 and PTEN expression showed a trend toward a longer survival. These findings suggest CBX7 is an important tumor suppressor that negatively modulates PTEN/Akt signaling during pancreatic tumorigenesis.

LncRNA FUNDC2P4 down-regulation promotes epithelial-mesenchymal transition by reducing E-cadherin expression in residual hepatocellular carcinoma after insufficient radiofrequency ablation

PURPOSE

Hepatocellular carcinoma (HCC) after insufficient radiofrequency ablation (RFA) could induce epithelial-mesenchymal transition (EMT) in residual tumours, resulting in rapid and aggressive recurrence. However, the role of EMT-related Long noncoding RNAs (lncRNAs) in residual tumour progression remains unclear.

METHODS

Insufficient RFA was simulated in vitro by heating Huh7 cells in water bath at 47 °C, named as Huh7-H. Cell invasion, migration assays and wound healing assay were conducted for functional analysis. Cell proliferation was determined by CCK8 assay. Differential expression profile of EMT-related lncRNAs between Huh7-H and Huh7 was analysed by LncPath human EMT array, and validated by qRT-PCR. Gain/loss-of-function assays of selected lncRNA were conducted by over-expressing or silencing its expression.

RESULTS

Huh7-H presented characteristic EMT morphological changes. WB analysis showed significantly decreased E-cadherin in Huh7-H cells. Transwell assays indicated the abilities of Huh7-H cells in migration and invasion were evidently strengthened. A new lncRNA, FUNDC2P4, was identified by LncPath human EMT array to be significantly down-regulated in Huh7-H cells. In vitro studies showed overexpression of FUNDC2P4 inhibited proliferation, invasion and migration potential and up-regulated E-cadherin expression in SMMC-7721 cells, whereas silencing FUNDC2P4 promoted these potentials and down-regulated E-cadherin expression in Huh7 cells.

CONCLUSIONS

We explored that lncRNA FUNDC2P4 down-regulation promoted EMT leading to tumour proliferation, invasion and migration by reducing E-cadherin expression in residual HCC after insufficient RFA in vitro. These results suggest that FUNDC2P4 may have potentially therapeutic value for prevention and treatment of HCC recurrence after RFA in the future.

Ago-RIP-Seq identifies Polycomb repressive complex I member CBX7 as a major target of miR-375 in prostate cancer progression

Prostate cancer is a heterogeneous disease. MiR-375 is a marker for prostate cancer progression, but its cellular function is not characterized. Here, we provide the first comprehensive investigation of miR-375 in prostate cancer. We show that miR-375 is enriched in prostate cancer compared to normal cells. Furthermore, miR-375 enhanced proliferation, migration and invasion in vitro and induced tumor growth and reduced survival in vivo showing that miR-375 has oncogenic properties in prostate cancer. On the molecular level, we provide the targetome and genome-wide transcriptional changes of miR-375 expression by applying a generalized linear model for Ago-RIP-Seq and RNA-Seq, and show that miR-375 is involved in tumorigenic networks and Polycomb regulation. Integration of tissue and gene ontology data prioritized miR-375 targets and identified the tumor suppressor gene CBX7, a member of Polycomb repressive complex 1, as a major miR-375 target. MiR-375-mediated repression of CBX7 was accompanied by increased expression of its homolog CBX8 and activated transcriptional programs linked to malignant progression in prostate cancer cells. Tissue analysis showed association of CBX7 loss with advanced prostate cancer. Our study indicates that miR-375 exerts its tumor-promoting role in prostate cancer by influencing the epigenetic regulation of transcriptional programs through its ability to directly target the Polycomb complex member CBX7.

CBX7 negatively regulates migration and invasion in glioma via Wnt/β-catenin pathway inactivation

CBX7, a member of the Polycomb-group proteins, plays a significant role in normal and cancerous tissues and has been defined as a tumor suppressor in thyroid, breast and pancreatic cancers. However, its function in glioma remains undefined. CBX7 expression is decreased in glioma, especially in higher grade cases, according to data in the CGGA, GSE16001 and TCGA databases. Further experimental evidence has shown that exogenous CBX7 overexpression induced apoptosis and inhibited cell proliferation, colony formation and migration of glioma cells. In this study, we show that the invasive ability of glioma cells was decreased following CBX7 overexpression and CBX7 overexpression was associated with Wnt/β-catenin pathway inhibition, which also decreased downstream expression of ZEB1, a core epithelial-to-mesenchymal transition factor. This reduction in Wnt signaling is controlled by DKK1, a specific Wnt/β-catenin inhibitor. CBX7 enhances DKK1 expression by binding the DKK1 promoter, as shown in Luciferase reporter assays. Our data confirm that CBX7 inhibits EMT and invasion in glioma, which is manifested by influencing the expression of MMP2, MMP9, E-cadherin, N-cadherin and Vimentin in LN229, T98G cells and primary glioma cells (PGC). Furthermore, as a tumor suppressor, CBX7 expression is pivotal to reduce tumor invasion and evaluate prognosis.

Mithramycin inhibits epithelial-to-mesenchymal transition and invasion by downregulating SP1 and SNAI1 in salivary adenoid cystic carcinoma

Mithramycin exhibits certain anticancer effects in glioma, metastatic cerebral carcinoma, malignant lymphoma, chorionic carcinoma and breast cancer. However, its effects on salivary adenoid cystic carcinoma remain unclear. Here, we report that mithramycin significantly inhibited epithelial-to-mesenchymal transition and invasion in human salivary adenoid cystic carcinoma cell lines. The underlying mechanism for this activity was further demonstrated to involve decreasing the expression of the transcription factors specificity protein 1 and SNAI1. Specificity protein 1 is a pro-tumourigenic transcription factor that is overexpressed in SACC-LM and SACC-83 cells, and its expression is inhibited by mithramycin. Moreover, chromatin immunoprecipitation assays showed that specificity protein 1 induced SNAI1 transcription through direct binding to the SNAI1 promoter. In summary, this study uncovered the mechanism through which mithramycin inhibits epithelial-to-mesenchymal transition and invasion in salivary adenoid cystic carcinoma cell lines, namely, via downregulating specificity protein 1 and SNAI1 expression, which suggests mithramycin may be a promising therapeutic option for salivary adenoid cystic carcinoma.

Epigenetic alterations of gastrokine 1 gene expression in gastric cancer

The gastrokine 1 (GKN1) protein is important for maintaining the physiological function of the gastric mucosa. GKN1 is down-regulated in gastric tumor tissues and derived cell lines and its over-expression in gastric cancer cells induces apoptosis, suggesting a possible role for the protein as a tumor suppressor. However, the mechanism by which GKN1 is inactivated in gastric cancer remains unknown. Here, we investigated the causes of GKN1 silencing to determine if epigenetic mechanisms such as histonic modification could contribute to its down-regulation. To this end, chromatin immunoprecipitation assays for the trimethylation of histone 3 at lysine 9 (H3K9triMe) and its specific histone-lysine N-methyltransferase (SUV39H1) were performed on biopsies of normal and cancerous human gastric tissues. GKN1 down-regulation in gastric cancer tissues was shown to be associated with high levels of H3K9triMe and with the recruitment of SUV39H1 to the GKN1 promoter, suggesting the presence of an epigenetic transcriptional complex that negatively regulates GKN1 expression in gastric tumors. The inhibition of histone deacetylases with trichostatin A was also shown to increase GKN1 mRNA levels. Collectively, our results indicate that complex epigenetic machinery regulates GKN1 expression at the transcriptional level, and likely at the translational level.

miR-155 is positively regulated by CBX7 in mouse embryonic fibroblasts and colon carcinomas, and targets the KRAS oncogene

BACKGROUND

Loss of CBX7 expression has been described in several malignant neoplasias, including human colon and thyroid carcinomas proposing CBX7 as a tumor suppressor gene with a key role in cancer progression. This role is supported from the development of benign and malignant neoplasias in Cbx7 null mice. The aim of our work has been to investigate the mechanisms underlying the CBX7 oncosuppressor activity by analyzing the microRNAs (miRNAs) regulated by CBX7.

METHODS

The miRNA expression profiles of the mouse embryonic fibroblasts (MEFs) null for Cbx7 and the wild-type counterpart were analyzed by the miRNACHIP microarray and then validated by qRT-PCR. To asses KRAS as target of miR-155 we evaluated the protein levels after transfection of the synthetic miR-155. Human colon carcinoma samples have been investigated for the expression of CBX7 and miR-155.

RESULTS

Twenty miRNAs were found upregulated and nine, including miR-155, downregulated in cbx7-null MEFS in comparison with the wild-type ones. Then, we focused on miR-155 since several studies have shown its deregulated expression in several human malignancies and, moreover, was the most downregulated miRNA. Subsequently, we searched for miR-155 target genes demonstrating that KRAS protein levels are directly modulated by miR-155. A direct significant correlation (r = 0.6779) between CBX7 and miR-155 expression levels was found in a set of human colon carcinoma tissue samples.

CONCLUSION

miR-155 is positively regulated by CBX7 in MEFs and colon carcinomas, and has KRAS as one of the target genes likely accounting for the anti-apoptotic activity ascribed to miR-155 in some tissue contexts.

H3K27 Methylation: A Focal Point of Epigenetic Deregulation in Cancer

Epigenetics, the modification of chromatin without changing the DNA sequence itself, determines whether a gene is expressed, and how much of a gene is expressed. Methylation of lysine 27 on histone 3 (H3K27me), a modification usually associated with gene repression, has established roles in regulating the expression of genes involved in lineage commitment and differentiation. Not surprisingly, alterations in the homeostasis of this critical mark have emerged as a recurrent theme in the pathogenesis of many cancers. Perturbations in the distribution or levels of H3K27me occur due to deregulation at all levels of the process, either by mutation in the histone itself, or changes in the activity of the writers, erasers, or readers of this mark. Additionally, as no single histone mark alone determines the overall transcriptional readiness of a chromatin region, deregulation of other chromatin marks can also have dramatic consequences. Finally, the significance of mutations altering H3K27me is highlighted by the poor clinical outcome of patients whose tumors harbor such lesions. Current therapeutic approaches targeting aberrant H3K27 methylation remain to be proven useful in the clinic. Understanding the biological consequences and gene expression pathways affected by aberrant H3K27 methylation may lead to identification of new therapeutic targets and strategies.

Cbx7 is epigenetically silenced in glioblastoma and inhibits cell migration by targeting YAP/TAZ-dependent transcription

Glioblastomas (GBM) are the most malignant form of astrocytomas which are difficult to treat and portend a grave clinical course and poor prognosis. In this study, we identified Chromobox homolog 7 (Cbx7), a member of Polycomb Repressive Complex 1 (PRC1), as a downregulated gene in GBM owing to its promoter hypermethylation. Bisulphite sequencing and methylation inhibitor treatment established the hypermethylation of Cbx7 in GBM. Exogenous overexpression of Cbx7 induced cell death, inhibited cell proliferation, colony formation and migration/invasion of the glioma cells. GSEA of Cbx7 regulated genes identified Cbx7 as a repressor of transcription co-activators YAP/TAZ, the inhibitory targets of the Hippo signalling pathway. In good correlation, the exogenous expression of Cbx7 repressed the YAP/TAZ-dependent transcription and downregulated CTGF, a bonafide YAP/TAZ target. We also observed reduced levels of phospho-JNK in Cbx7 expressing cells. Additionally, CTGF silencing and pharmacological inhibition of JNK also inhibited glioma cell migration. Further, Cbx7 failed to inhibit cell migration significantly in the presence of exogenously overexpressed CTGF or constitutively active JNK. Thus, our study identifies Cbx7 as an inhibitor of glioma cell migration through its inhibitory effect on YAP/TAZ-CTGF-JNK signalling axis and underscores the importance of epigenetic inactivation of Cbx7 in gliomagenesis.

CBX7 and HMGA1b proteins act in opposite way on the regulation of the SPP1 gene expression

Several recent studies have reported the Polycomb Repressive Complex 1 member CBX7 as a tumor-suppressor gene whose expression progressively decreases in different human carcinomas in relation with tumor grade, malignant stage and poor prognosis. We have previously demonstrated that CBX7 is able to inhibit the expression of the SPP1 gene, encoding the chemokine osteopontin that is over-expressed in cancer and has a critical role in cancer progression. Here, we have analyzed the mechanism by which CBX7 regulates the SPP1 gene expression. We show that the SPP1 transcriptional regulation mechanism involves the CBX7-interacting protein HMGA1b, that acts as a positive regulator of the SPP1 gene. In fact, we demonstrate that, in contrast with the transcriptional activity of CBX7, HMGA1b is able to increase the SPP1 expression by inducing the activity of its promoter. Moreover, we show that CBX7 interferes with HMGA1b on the SPP1 promoter and counteracts the positive transcriptional activity of HMGA1b on the SPP1 expression. Furthermore, since we found that also the NF-κB complex resulted involved in the modulation of the SPP1 expression in thyroid cells, we suppose that CBX7/HMGA1b/NF-κB could take part in the same transcriptional mechanism that finally leads to the regulation of the SPP1 gene expression. Taken together, our data show the important role played by CBX7 in the negative regulation of the SPP1 gene expression, thus contributing to prevent the acquisition of a malignant 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.

Generalized monotone incremental forward stagewise method for modeling count data: application predicting micronuclei frequency

The cytokinesis-block micronucleus (CBMN) assay can be used to quantify micronucleus (MN) formation, the outcome measured being MN frequency. MN frequency has been shown to be both an accurate measure of chromosomal instability/DNA damage and a risk factor for cancer. Similarly, the Agilent 4×44k human oligonucleotide microarray can be used to quantify gene expression changes. Despite the existence of accepted methodologies to quantify both MN frequency and gene expression, very little is known about the association between the two. In modeling our count outcome (MN frequency) using gene expression levels from the high-throughput assay as our predictor variables, there are many more variables than observations. Hence, we extended the generalized monotone incremental forward stagewise method for predicting a count outcome for high-dimensional feature settings.

HMGA1 silencing restores normal stem cell characteristics in colon cancer stem cells by increasing p53 levels

High-mobility group A1 (HMGA1) proteins are architectural chromatinic proteins, abundantly expressed during embryogenesis and in most cancer tissues, but expressed at low levels or absent in normal adult tissues. Several studies have demonstrated that HMGA1 proteins play a causal role in neoplastic cell transformation. The aim of this study was to investigate the role of these proteins in the control of cancer stem cells (CSCs), which have emerged as a preferred target in cancer therapy, because of their role in cancer recurrence. We observed that HMGA1 is overexpressed in colon tumour stem cell (CTSC) lines compared to normal and colon cancer tissues. We demonstrated that HMGA1 silencing in CTSCs increases stem cell quiescence and reduces self-renewal and sphere-forming efficiency (SFE). The latter, together with the upregulation and asymmetric distribution of NUMB, is indicative of the recovery of an asymmetric division pattern, typical of normal stem cells. We further found that HMGA1 transcriptionally regulates p53, which is known to control the balance between symmetric and asymmetric divisions in CSCs. Therefore, our data indicate a critical role for HMGA1 in regulating both self-renewal and the symmetric/asymmetric division ratio in CSCs, suggesting that blocking HMGA1 function may be an effective anti-cancer therapy.

Up-regulation of miR-9 target CBX7 to regulate invasion ability of bladder transitional cell carcinoma

BACKGROUND

Bladder urothelial carcinoma is the most common genitourinary system cancer in China. The objective of this study was to investigate whether the miR-9 can regulate the invasion ability of human bladder transitional cell carcinoma cells by down-regulation of CBX7.

MATERIAL/METHODS

The expression of miR-9 was detected by quantitative real-time PCR in bladder transitional cell carcinomas (TCC) and normal bladder transitional cell (NBTC) samples. Bioinformatics software was used to predict some potential target genes of miR-9. T24 cells were transfected with pre-miR-9, and the CBX7 protein expression was detected by Western blot. Luciferase activities assay was selected to verify that CBX7 was a direct and specific gene of miR-9. T24 cells were transfected with pcDNA-CBX7, and the expression of CBX7 gene was detected. Then, the transwell assay was used to detect the invasion ability of T24 cells with CBX7 over-expression.

RESULTS

The expression of miR-9 increased significantly in human TCC specimens compared to that in NBTC specimens. TargetScan and PicTar software programs predicted CBX7 gene was a target gene of miR-9. The pre-miR-9 could up-regulate the miR-9 expression and down-regulate CBX7 protein expression. The luciferase activities assay verified that CBX7 gene was a direct and specific target gene of miR-9. The pcDNA-CBX7 transfection could up-regulate the CBX7 protein expression, and the invasion ability of T24 cells with CBX7 over-expression decreased significantly.

CONCLUSIONS

Aberrantly expressed miR-9 contributes to T24 cells invasion, partly through directly down-regulating CBX7 protein expression in TCC. This miRNA signature offers a new potential therapeutic target for TCC.

CBX7 Expression in Oncocytic Thyroid Neoplastic Lesions (Hürthle Cell Adenomas and Carcinomas)

BACKGROUND

Previous analysis of CBX7 expression in a large number of thyroid adenoma and carcinoma samples revealed a progressive reduction of CBX7 levels that was well related with the malignant grade of thyroid neoplasias. Hürthle cell tumors are unusual thyroid neoplasms characterized by the presence of particular cells called oncocytes.

OBJECTIVES

In order to develop new tools for a more accurate diagnosis of Hürthle cell tumors of the thyroid, we evaluated CBX7 protein levels to verify the possible presence of an expression signature.

METHODS

CBX7 expression was evaluated by immunohistochemistry in a panel of thyroid tissue sections including normal thyroids, goiters, follicular adenomas and oncocytic lesions.

RESULTS

CBX7 expression was low or null in 68% of Hürthle adenomas, whereas it was comparable to normal thyroid tissue in Hürthle hyperplasias and follicular adenomas.

CONCLUSIONS

Reduced expression of CBX7 suggests a more aggressive identity of Hürthle adenomas with respect to non-Hürthle ones.

CBX7 inhibits breast tumorigenicity through DKK-1-mediated suppression of the Wnt/β-catenin pathway

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

CBX7 gene expression plays a negative role in adipocyte cell growth and differentiation

We have recently generated knockout mice for the Cbx7 gene, coding for a polycomb group protein that is downregulated in human malignant neoplasias. These mice develop liver and lung adenomas and carcinomas, which confirms a tumour suppressor role for CBX7. The CBX7 ability to downregulate CCNE1 expression likely accounts for the phenotype of the Cbx7-null mice.

Unexpectedly, Cbx7-knockout mice had a higher fat tissue mass than wild-type, suggesting a role of CBX7 in adipogenesis. Consistently, we demonstrate that Cbx7-null mouse embryonic fibroblasts go towards adipocyte differentiation more efficiently than their wild-type counterparts, and this effect is Cbx7 dose-dependent. Similar results were obtained when Cbx7-null embryonic stem cells were induced to differentiate into adipocytes. Conversely, mouse embryonic fibroblasts and human adipose-derived stem cells overexpressing CBX7 show an opposite behaviour.

These findings support a negative role of CBX7 in the control of adipocyte cell growth and differentiation.

PRC1 complex diversity: where is it taking us?

Polycomb group proteins (PcGs) are essential epigenetic regulators that play key roles in development, pluripotency, senescence, and cancer. Recent reports have found that the composition of mammalian Polycomb repressive complex 1 (PRC1) is far more varied than previously thought. PRC1 diversity largely depends on the presence of CBX proteins, dividing them into canonical and non-canonical, the existence of redundant subunits, and different binding affinities and/or regulation. However, there is no clear insight into how many functional PRC1 complexes exist and what the biological relevance is for such diversification. In this review we focus on mammalian PRC1 and discuss the mechanisms by which canonical and non-canonical PRC1 are recruited to chromatin, their role in normal development and disease, and emerging evidence for PRC1 as a transcriptional activator.

CBX7 modulates the expression of genes critical for cancer progression

Background

We have previously shown that the expression of CBX7 is drastically decreased in several human carcinomas and that its expression progressively decreases with the appearance of a highly malignant phenotype. The aim of our study has been to investigate the mechanism by which the loss of CBX7 expression may contribute to the emergence of a more malignant phenotype.

Methods

We analyzed the gene expression profile of a thyroid carcinoma cell line after the restoration of CBX7 and, then, analyzed the transcriptional regulation of identified genes. Finally, we evaluated the expression of CBX7 and regulated genes in a panel of thyroid and lung carcinomas.

Results

We found that CBX7 negatively or positively regulates the expression of several genes (such as SPP1, SPINK1, STEAP1, and FOS, FOSB, EGR1, respectively) associated to cancer progression, by interacting with their promoter regions and modulating their transcriptional activity. Quantitative RT-PCR analyses in human thyroid and lung carcinoma tissues revealed a negative correlation between CBX7 and its down-regulated genes, while a positive correlation was observed with up-regulated genes.

Conclusion

In conclusion, the loss of CBX7 expression might play a critical role in advanced stages of carcinogenesis by deregulating the expression of specific effector genes.

Hmga1/Hmga2 double knock-out mice display a "superpygmy" phenotype

The HMGA1 and HMGA2 genes code for proteins belonging to the High Mobility Group A family. Several genes are negatively or positively regulated by both these proteins, but a number of genes are specifically regulated by only one of them. Indeed, knock-out of the Hmga1 and Hmga2 genes leads to different phenotypes: cardiac hypertrophy and type 2 diabetes in the former case, and a large reduction in body size and amount of fat tissue in the latter case. Therefore, to better elucidate the functions of the Hmga genes, we crossed Hmga1-null mice with mice null for Hmga2. The Hmga1(-/-)/Hmga2(-/-) mice showed reduced vitality and a very small size (75% smaller than the wild-type mice); they were even smaller than pygmy Hmga2-null mice. The drastic reduction in E2F1 activity, and consequently in the expression of the E2F-dependent genes involved in cell cycle regulation, likely accounts for some phenotypic features of the Hmga1(-/-)/Hmga2(-/-) mice.

Expression of chromobox homolog 7 (CBX7) is associated with poor prognosis in ovarian clear cell adenocarcinoma via TRAIL-induced apoptotic pathway regulation

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

Altered expression of polycomb group genes in glioblastoma multiforme

The Polycomb group (PcG) proteins play a critical role in histone mediated epigenetics which has been implicated in the malignant evolution of glioblastoma multiforme (GBM). By systematically interrogating The Cancer Genome Atlas (TCGA), we discovered widespread aberrant expression of the PcG members in GBM samples compared to normal brain. The most striking differences were upregulation of EZH2, PHF19, CBX8 and PHC2 and downregulation of CBX7, CBX6, EZH1 and RYBP. Interestingly, changes in EZH2, PHF19, CBX7, CBX6 and EZH1 occurred progressively as astrocytoma grade increased. We validated the aberrant expression of CBX6, CBX7, CBX8 and EZH2 in GBM cell lines by Western blotting and qRT-PCR, and further the aberrant expression of CBX6 in GBM tissue samples by immunohistochemical staining. To determine if there was functional significance to the diminished CBX6 levels in GBM, CBX6 was overexpressed in GBM cells resulting in decreased proliferative capacity. In conclusion, aberrant expression of PcG proteins in GBMs may play a role in the development or maintenance of the malignancy.

Mitogen-activated protein kinase signaling mediates phosphorylation of polycomb ortholog Cbx7

Cbx7 is one of five mammalian orthologs of the Drosophila Polycomb. Cbx7 recognizes methylated lysine residues on the histone H3 tail and contributes to gene silencing in the context of the Polycomb repressive complex 1 (PRC1). However, our knowledge of Cbx7 post-translational modifications remains limited. Through combined biochemical and mass spectrometry approaches, we report a novel phosphorylation site on mouse Cbx7 at residue Thr-118 (Cbx7T118ph), near the highly conserved Polycomb box. The generation of a site-specific antibody to Cbx7T118ph demonstrates that Cbx7 is phosphorylated via MAPK signaling. Furthermore, we find Cbx7T118 phosphorylation in murine mammary carcinoma cells, which can be blocked by MEK inhibitors. Upon EGF stimulation, Cbx7 interacts robustly with other members of PRC1. To test the role of Cbx7T118 phosphorylation in gene silencing, we employed a RAS-induced senescence model system. We demonstrate that Cbx7T118 phosphorylation moderately enhances repression of its target gene p16. In summary, we have identified and characterized a novel MAPK-mediated phosphorylation site on Cbx7 and propose that mitogen signaling to the chromatin template regulates PRC1 function.

Cancer development, progression, and therapy: an epigenetic overview

Carcinogenesis involves uncontrolled cell growth, which follows the activation of oncogenes and/or the deactivation of tumor suppression genes. Metastasis requires down-regulation of cell adhesion receptors necessary for tissue-specific, cell-cell attachment, as well as up-regulation of receptors that enhance cell motility. Epigenetic changes, including histone modifications, DNA methylation, and DNA hydroxymethylation, can modify these characteristics. Targets for these epigenetic changes include signaling pathways that regulate apoptosis and autophagy, as well as microRNA. We propose that predisposed normal cells convert to cancer progenitor cells that, after growing, undergo an epithelial-mesenchymal transition. This process, which is partially under epigenetic control, can create a metastatic form of both progenitor and full-fledged cancer cells, after which metastasis to a distant location may occur. Identification of epigenetic regulatory mechanisms has provided potential therapeutic avenues. In particular, epigenetic drugs appear to potentiate the action of traditional therapeutics, often by demethylating and re-expressing tumor suppressor genes to inhibit tumorigenesis. Epigenetic drugs may inhibit both the formation and growth of cancer progenitor cells, thus reducing the recurrence of cancer. Adopting epigenetic alteration as a new hallmark of cancer is a logical and necessary step that will further encourage the development of novel epigenetic biomarkers and therapeutics.

Tumor suppressor role of the CL2/DRO1/CCDC80 gene in thyroid carcinogenesis

CONTEXT

Thyroid carcinoma is one of the most common malignancies of the endocrine system, and, despite the high frequency of oncogene activation in thyroid neoplastic lesions, the tumor suppressor genes involved in thyroid carcinogenesis remain unidentified. Our previous data implicated a link between the CL2/CCDC80 gene and thyroid cancer.

OBJECTIVE

The objective of the study was to examine the expression of the CL2/CCDC80 gene in human thyroid carcinomas in the attempt to determine whether it plays a role in thyroid carcinogenesis.

DESIGN

We evaluated the expression of CL2/CCDC80 in a large number of thyroid neoplastic tissue samples differing in degree of malignancy. We also investigated the effects of its restoration in 2 human thyroid carcinoma cell lines characterized by very low levels of CL2/CCDC80 expression.

RESULTS

CL2/CCDC80 expression was much lower in almost all the thyroid carcinomas analyzed than in normal thyroid tissues and was lowest in follicular variants of papillary carcinomas. Loss of heterozygosity partially accounted for CL2/CCDC80 down-regulation in thyroid carcinoma samples. Restoration of CL2/CCDC80 expression in the 2 human thyroid anaplastic carcinoma cell lines resulted in a higher susceptibility to apoptosis and suppression of the malignant phenotype. CL2/CCDC80 expression positively regulated the expression of E-cadherin, thereby halting cancer progression.

CONCLUSIONS

These results indicate that CL2/CCDC80 is a putative tumor suppressor gene in thyroid carcinogenesis.

Comparative RNA-seq analysis in the unsequenced axolotl: the oncogene burst highlights early gene expression in the blastema

The salamander has the remarkable ability to regenerate its limb after amputation. Cells at the site of amputation form a blastema and then proliferate and differentiate to regrow the limb. To better understand this process, we performed deep RNA sequencing of the blastema over a time course in the axolotl, a species whose genome has not been sequenced. Using a novel comparative approach to analyzing RNA-seq data, we characterized the transcriptional dynamics of the regenerating axolotl limb with respect to the human gene set. This approach involved de novo assembly of axolotl transcripts, RNA-seq transcript quantification without a reference genome, and transformation of abundances from axolotl contigs to human genes. We found a prominent burst in oncogene expression during the first day and blastemal/limb bud genes peaking at 7 to 14 days. In addition, we found that limb patterning genes, SALL genes, and genes involved in angiogenesis, wound healing, defense/immunity, and bone development are enriched during blastema formation and development. Finally, we identified a category of genes with no prior literature support for limb regeneration that are candidates for further evaluation based on their expression pattern during the regenerative process.

Distinct SNP combinations confer susceptibility to urinary bladder cancer in smokers and non-smokers

Recently, genome-wide association studies have identified and validated genetic variations associated with urinary bladder cancer (UBC). However, it is still unknown whether the high-risk alleles of several SNPs interact with one another, leading to an even higher disease risk. Additionally, there is no information available on how the UBC risk due to these SNPs compare to the risk of cigarette smoking and to occupational exposure to urinary bladder carcinogens, and whether the same or different SNP combinations are relevant in smokers and non-smokers. To address these questions, we analyzed the genotypes of six SNPs, previously found to be associated with UBC, together with the GSTM1 deletion, in 1,595 UBC cases and 1,760 controls, stratified for smoking habits. We identified the strongest interactions of different orders and tested the stability of their effect by bootstrapping. We found that different SNP combinations were relevant in smokers and non-smokers. In smokers, polymorphisms involved in detoxification of cigarette smoke carcinogens were most relevant (GSTM1, rs11892031), in contrast to those in non-smokers with MYC and APOBEC3A near polymorphisms (rs9642880, rs1014971) being the most influential. Stable combinations of up to three high-risk alleles resulted in higher odds ratios (OR) than the individual SNPs, although the interaction effect was less than additive. The highest stable combination effects resulted in an OR of about 2.0, which is still lower than the ORs of cigarette smoking (here, current smokers' OR: 3.28) and comparable to occupational carcinogen exposure risks which, depending on the workplace, show mostly ORs up to 2.0.

Akt mediates metastasis-associated gene 1 (MTA1) regulating the expression of E-cadherin and promoting the invasiveness of prostate cancer cells

Human metastasis-associated gene 1 (MTA1) is highly associated with the metastasis of prostate cancer; however, the molecular functions of MTA1 that facilitate metastasis remain unclear. In this study, we demonstrate that the silencing of MTA1 by siRNA treatment results in the upregulation of E-cadherin expression by the phosphorylation of AKT (p-AKT) and decreases the invasiveness of prostate cancer cells. We show that MTA1 is expressed in over 90% of prostate cancer tissues, especially metastatic prostate cancer tissue, comparing to non-expression in normal prostate tissue. RT-PCR analysis and Western blot assay showed that MTA1 expression is significantly higher in highly metastatic prostate cancer PC-3M-1E8 cells (1E8) than in poorly metastatic prostate cancer PC-3M-2B4 cells (2B4). Silencing MTA1 expression by siRNA treatment in 1E8 cells increased the cellular malignant characters, including the cellular adhesive ability, decreased the cellular invasive ability and changed the polarity of cellular cytoskeleton. 1E8 cells over-expressing MTA1 had a reduced expression of E-cadherin, while 1E8 cells treated with MTA1 siRNA had a higher expression of E-cadherin. The expression of phosphorylated AKT (p-AKT) or the inhibition of p-AKT by wortmannin treatment (100 nM) significantly altered the function of MTA1 in the regulation of E-cadherin expression. Alterations in E-cadherin expression changed the role of p-AKT in cellular malignant characters. All of these results demonstrate that MTA1 plays an important role in controlling the malignant transformation of prostate cancer cells through the p-AKT/E-cadherin pathway. This study also provides a new mechanistic role for MTA1 in the regulation of prostate cancer metastasis.