CBX6 overexpression contributes to tumor progression and is predictive of a poor prognosis in hepatocellular carcinoma

Unravelling the impact of the chromobox proteins in human cancers

Chromobox (CBX) proteins play a crucial role in regulating epigenetic processes. They are extensively involved in various biological processes, including embryonic development, stem cell maintenance, cell proliferation and apoptosis control. The disruption and malfunction of CBXs in cancer typically results in the interference or abnormal activation of developmental pathways, which facilitate the onset, growth, and advancement of cancer. This review initially introduces the physiological properties and functions of the CBXs. Subsequently, it examines the involvement of CBXs in different cancer types. Cancer hallmarks driven by CBXs are mediated through multiple mechanisms, including changes in gene expression patterns, epigenetic dysregulation of chromatin control, disruption of intracellular signaling and alterations in cell metabolism. The study also highlights novel potential anticancer therapeutics targeting CBXs in cancer. In this review we provide novel perspectives and a solid foundation for future investigations on CBXs as promising therapeutic targets for cancer treatment.

Epigenetic regulatory protein chromobox family regulates multiple signalling pathways and mechanisms in cancer

Signal transduction plays a pivotal role in modulating a myriad of critical processes, including the tumour microenvironment (TME), cell cycle arrest, proliferation and apoptosis of tumour cells, as well as their migration, invasion, and the epithelial-mesenchymal transition (EMT). Epigenetic mechanisms are instrumental in the genesis and progression of tumours. The Chromobox (CBX) family proteins, which serve as significant epigenetic regulators, exhibit tumour-specific expression patterns and biological functionalities. These proteins are influenced by a multitude of factors and could modulate the activation of diverse signalling pathways within tumour cells through alterations in epigenetic modifications, thereby acting as either oncogenic agents or tumour suppressors. This review aims to succinctly delineate the composition, structure, function, and expression of CBXs within tumour cells, with an emphasis on synthesizing and deliberating the CBXs-mediated activation of intracellular signalling pathways and the intricate mechanisms governing tumourigenesis and progression. Moreover, a plethora of contemporary studies have substantiated that CBXs might represent a promising target for the diagnosis and therapeutic intervention of tumour patients. We have also compiled and scrutinized the current research landscape concerning inhibitors targeting CBXs, aspiring to aid researchers in gaining a deeper comprehension of the biological roles and mechanisms of CBXs in the malignant evolution of tumours, and to furnish novel perspectives for the innovation of targeted tumour therapeutics.

Integrated bioinformatics investigation and experimental validation reveals the clinical and biological significance of chromobox family in breast cancer

Chromobox (CBX) proteins are essential components of the Polycomb group and play pivotal roles in tumor onset, progression, and metastasis. However, the prognostic significance and functions of CBXs in the advancement of breast cancer (BC) have not been sufficiently investigated. A comprehensive analysis of the expression and prognostic relevance of CBX1-8 in BC was conducted comprehensively using The Cancer Genome Atlas (TCGA) and multiple databases. High mRNA expression of CBX2, CBX3, and CBX5 in BC patients was significantly associated with reduced overall survival (OS). Results from univariate and multivariate Cox regression analysis revealed that the mRNA expression level of CBX2 in BC patients served as an independent prognostic factor. In Luminal A and Luminal B BC subtypes, high expression of CBX2 correlated with unfavorable prognosis. Subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated a strong association between CBX2 and the cell cycle as well as DNA replication processes. CCK-8 and EdU assays demonstrated that silencing CBX2 inhibited the proliferation of T47D and MCF7 cell lines. Moreover, the cell cycle assay indicated that CBX2 silencing led to cell cycle arrest, accompanied by a significant decrease in the levels of CDK4 and CyclinD1. Elevated CBX2 expression significantly correlated with the infiltration of T cells, B cells, macrophages, and dendritic cells in BC. Our findings could provide new perspectives for identifying potential prognostic markers within the CBX family in BC. Targeting CBX2 may present a promising approach to address endocrine resistance in BC therapy.

S100A8 promotes the proliferation, migration and invasion in bladder cancer cells

Background: There is mounting evidence that S100 calcium-binding A8 (S100A8) is involved in inflammation and cancer. However, whether S100A8 promotes the proliferation, invasion and migration of bladder cancer (BC) is still not completely clear. To investigate the influence of S100A8 on the proliferation, migration and invasion of BC. Methods: Based on Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases, genes related to the grading, staging, proliferation, migration and invasion of BC were screened, and S100A8 was selected as the target gene for further studies. Immunohistochemical staining were employed to examine the protein expression levels of S100A8 on adjacent tissues and BC tissues. The gene expression level of S100A8 in Pan cancer cell lines was analyzed through the Cancer Cell Line Encyclopedia (CCLE) database, and the HT-1376 cell line was selected for subsequent experiments. Overexpression recombinant lentivirus and short hairpin RNA-encoding lentivirus were used to overexpress and knock down S100A8 in HT-1376 cells via infection. The mRNA and protein expression levels of S100A8 were detected by reverse transcription-quantitative PCR and western blotting. The proliferation of BC cells was analyzed using Cell Counting Kit-8 and 5-ethynyl-2'-deoxyuridine assays. The Wound‑healing assay and Transwell assay were used to estimate the migration and invasion of BC cells. Results: The results demonstrated that S100A8 was highly expressed in BC based on the GEO and TCGA databases. In addition, compared with those of HT-1376 cells and the negative control group, the proliferation, migration and invasion of S100A8-overexpressing HT-1376 cells were enhanced, while those of S100A8-knockdown HT-1376 cells were reduced. Furthermore, S100A8 was differentially expressed in non-muscle invasive BC and muscle invasive BC, and in low- and high-grade BC. Conclusions: In this study, the bioinformatics and in vitro experiments revealed that S100A8 could promote the proliferation, invasion and migration of BC cells. Consequently, S1008A emerges as a promising diagnostic and therapeutic target for BC.

Identification of Cbx6 as a potential biomarker in renal ischemia/reperfusion injury

BACKGROUND

Renal ischemia/reperfusion injury (RIRI) is an inevitable consequence of kidney transplantation and has a negative impact on both short-term and long-term graft survival. The identification of key markers in RIRI to improve the prognosis of patients would be highly advantageous.

METHODS

Gene expression profile data of GSE27274 were obtained from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were analyzed using the Limma package. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment of DEGs were performed. Support vector machine-recursive feature elimination and least absolute shrinkage and selection operator regression modeling were both performed to identify potential biomarkers. The GSE148420 dataset, quantitative reverse transcriptase-PCR, and western blotting results of kidney tissue samples were used to validate the bioinformatic analysis. Lastly, exploring differences between different groups through gene set enrichment analysis and using DsigDB database to identify potential therapeutic drugs targeting hub genes.

RESULTS

A total of 160 upregulated and 180 downregulated DEGs were identified. Functional enrichment analysis identified significant enrichment in processes involving peroxisomes. As a subunit of Polycomb Repressive Complex 1(PRC1), chromobox 6(Cbx6) was identified as a potential biomarker with an area under the receiver operating characteristic curve of 0.875 (95% confidence interval 0.624-1.000) in the validation cohort, and it was highly expressed in the RIRI group (p < 0.05). In the high expression group Cbx6 was more enriched in the toll-like receptor signaling pathway. We predicted 15 potential drugs targeting hub genes of RIRI.

CONCLUSIONS

We identified Cbx6 as a potential biomarker for RIRI and 15 potential drugs for the treatment of RIRI, which might shed a light on the treatment of RIRI.

Construction of a novel nomogram based on competing endogenous RNAs and tumor-infiltrating immune cells for prognosis prediction in elderly patients with colorectal cancer

Competitive endogenous RNAs (ceRNAs) and tumor-infiltrating immune cells play essential roles in colorectal cancer (CRC) tumorigenesis. However, their prognostic role in elderly patients with CRC is unclear. Gene expression profiles and clinical information for elderly patients with CRC were downloaded from The Cancer Genome Atlas. Univariate, LASSO, and multivariate Cox regression analyses were utilized for screening key ceRNAs and prevent overfitting. A total of 265 elderly patients with CRC were included. We constructed a novel ceRNA network consisting of 17 lncRNAs, 35 miRNAs, and 5 mRNAs. We established three prognosis predictive nomograms based on four key ceRNAs (ceRNA nomogram), five key immune cells (immune cell nomogram), and their combination (ceRNA-immune cell nomogram). Among them, the ceRNA-immune cell nomogram had the best accuracy. Furthermore, the areas under the curve of the ceRNA-immune cell nomogram were also significantly greater than the TNM stage at 1 (0.818 vs. 0.693), 3 (0.865 vs. 0.674), and 5 (0.832 vs. 0.627) years. Co-expression analysis revealed that CBX6 was positively correlated with activated dendritic cells (R = 0.45, p < 0.01), whereas negatively correlated with activated mast cells (R =- 0.43, p < 0.01). In conclusion, our study constructed three nomograms to predict prognosis in elderly patients with CRC, among which the ceRNA-immune cell nomogram had the best prediction accuracy. We inferred that the mechanism underlying the regulation of activated dendritic cells and mast cells by CBX6 might play a crucial role in tumor development and prognosis of elderly patients with CRC.

Cigarette Smoke-Induced Respiratory Response: Insights into Cellular Processes and Biomarkers

Cigarette smoke (CS) poses a significant risk factor for respiratory, vascular, and organ diseases owing to its high content of harmful chemicals and reactive oxygen species (ROS). These substances are known to induce oxidative stress, inflammation, apoptosis, and senescence due to their exposure to environmental pollutants and the presence of oxidative enzymes. The lung is particularly susceptible to oxidative stress. Persistent oxidative stress caused by chronic exposure to CS can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), and lung cancer. Avoiding exposure to environmental pollutants, like cigarette smoke and air pollution, can help mitigate oxidative stress. A comprehensive understanding of oxidative stress and its impact on the lungs requires future research. This includes identifying strategies for preventing and treating lung diseases as well as investigating the underlying mechanisms behind oxidative stress. Thus, this review aims to investigate the cellular processes induced by CS, specifically inflammation, apoptosis, senescence, and their associated biomarkers. Furthermore, this review will delve into the alveolar response provoked by CS, emphasizing the roles of potential therapeutic target markers and strategies in inflammation and oxidative stress.

Comprehensive bioinformatics analysis of the expression, prognostic value, and immune infiltration of chromobox family members in cervical cancer

Objectives

Cervical cancer (CC) is the fourth most prevalent type of cancer in women worldwide and it is considered the leading cause of tumor-related death and malignancy. As part of complexes involved in epigenetic control, the proteins of the chromobox (CBX) family have been found to have a role in the growth of malignancies by preventing differentiation and increasing proliferation. Here, by a thorough investigation, we investigated the expression, prognostic significance, and immune infiltration of CBX in patients with CC.

Materials and Methods

Differential expression, clinicopathological parameters, immune cell infiltration, enrichment analysis, genetic alteration, and prognostic value of CBXs in patients with CC were examined using TIMER, Metascape, STRING, GeneMANIA, cBioPortal, UALCAN, The Human Protein Atlas, Gene Expression Profiling Interactive Analysis (GEPIA), and Oncomine.

Results

In CC tissues, CBX 2/3/4/5 and CBX 8 expression levels were considerably higher, whereas CBX 6/7 expression levels were lower. In CC, the CBX 5/6/8 promoters have elevated levels of methylation. The expression of CBX 2/6/8 and the pathological stage were connected. A 37% mutation rate of the differentially expressed CBX genes was observed. Also, there was a strong correlation of the CBXs expression with immune cell infiltration, such as T CD4⁺ cells, macrophages, neutrophils, B cells, T CD8⁺ cells, and dendritic cells.

Conclusion

The investigation discovered that members of the CBXs family may be therapeutic targets for CC patients and may play significant roles in the development of CC tumors.

S100A8 and S100A9 in Cancer

S100A8 and S100A9 are Ca²⁺ binding proteins that belong to the S100 family. Primarily expressed in neutrophils and monocytes, S100A8 and S100A9 play critical roles in modulating various inflammatory responses and inflammation-associated diseases. Forming a common heterodimer structure S100A8/A9, S100A8 and S100A9 are widely reported to participate in multiple signaling pathways in tumor cells. Meanwhile, S100A8/A9, S100A8, and S100A9, mainly as promoters, contribute to tumor development, growth and metastasis by interfering with tumor metabolism and the microenvironment. In recent years, the potential of S100A8/A9, S100A9, and S100A8 as tumor diagnostic or prognostic biomarkers has also been demonstrated. In addition, an increasing number of potential therapies targeting S100A8/A9 and related signaling pathways have emerged. In this review, we will first expound on the characteristics of S100A8/A9, S100A9, and S100A8 in-depth, focus on their interactions with tumor cells and microenvironments, and then discuss their clinical applications as biomarkers and therapeutic targets. We also highlight current limitations and look into the future of S100A8/A9 targeted anti-cancer therapy.

Epigenome-wide analysis of aging effects on liver regeneration

BACKGROUND

Aging is known to exert an effect on liver regeneration, with the ability of liver to regenerate displaying a significant decline over time. Liver physiological parameters such as liver volume, blood flow, and metabolism, as well as the ability to regenerate after injury have all been shown to decrease at old age in humans and model systems, with a number of molecular mechanisms proposed to be involved, including DNA methylation-dependent genome remodeling. To address how changes in DNA methylation mediate the adverse aging effect on liver regeneration, we searched for differentially methylated genomic regions (DMRs) in mouse livers co-regulated by aging and regeneration and determined their associated genes and enriched pathways.

RESULTS

DMRs were identified using whole-genome bisulfite sequencing (WGBS). Pathway analysis of aging DMR-mapped genes revealed two distinct phases of aging, 2-to-8 and 8-to-16 months old (m/o). Regenerative DMR-mapped differentially expressed genes (DEGs) were enriched in pathways controlling cell proliferation and differentiation. Most DMRs shared by both aging and regeneration changed in the same methylation direction between 2 and 8 m/o but in the opposite direction between 8 and 16 m/o. Regenerative DMRs inversely affected by aging during 8-to-16 m/o were found in the promoter/gene regions of 12 genes. Four regenerative DEGs were synchronously regulated by early aging and inversely regulated by mid-to-late aging DMRs. Lead DMR-mapped genes were validated by their expression profiles in liver aging and regeneration.

CONCLUSIONS

Our study has uncovered new DMRs and gene targets inversely affected by liver aging and regeneration to explain the adverse aging effect on liver regeneration. These findings will be of fundamental importance to understand the epigenomic changes underlying the biology of aging on liver regeneration.

Chromobox proteins in cancer: Multifaceted functions and strategies for modulation (Review)

Chromobox (CBX) proteins are important epigenetic regulatory proteins and are widely involved in biological processes, such as embryonic development, the maintenance of stem cell characteristics and the regulation of cell proliferation and apoptosis. Disorder and dysfunction of CBXs in cancer usually lead to the blockade or ectoptic activation of developmental pathways, promoting the occurrence, development and progression of cancer. In the present review, the characteristics and functions of CBXs were first introduced. Subsequently, the expression of CBXs in cancers and the relationship between CBXs and clinical characteristics (mainly cancer grade, stage, metastasis and relapse) and prognosis were discussed. Finally, it was described how CBXs regulate cell proliferation and self‑renewal, apoptosis and the acquisition of malignant phenotypes, such as invasion, migration and chemoresistance, through mechanisms involving epigenetic modification, nuclear translocation, noncoding RNA interactions, transcriptional regulation, posttranslational modifications, protein‑protein interactions, signal transduction and metabolic reprogramming. The study also focused on cancer therapies targeting CBXs. The present review provides new insight and a comprehensive basis for follow‑up research on CBXs and cancer.

Pan-cancer analysis of Chromobox (CBX) genes for prognostic significance and cancer classification

Polycomb group of proteins play a significant role in chromatin remodelling essential for epigenetic regulation of transcription. Chromobox (CBX) gene family is an important part of canonical polycomb repressive complex 1 (PRC1), belonging to the polycomb group involved in chromatin remodelling. Aberrations in CBX expression are linked to various cancers. To assess their biomarker significance, we performed a pan-cancer analysis of CBX mRNA levels in 18 cancer types. We also performed cancer classification using CBX genes as distinctive features for machine learning model development. Logistic regression (L.R.), support vector machine (SVM), random forest (R.F.), decision tree (D.T.), and XGBoost (XGB) algorithms for model training and classification. The expression of CBX genes was significantly changed in four cancer types, i.e., cholangiocarcinoma (CHOL), colon adenocarcinoma (COAD), lung adenocarcinoma (LUAD), and lung squamous cell carcinoma (LUSC). The fold change (FC) values suggest that CBX2 was significantly upregulated in CHOL (FC = 1.639), COAD (FC = 1.734), and LUSC (FC = 1.506). On the other hand, CBX7 was found downregulated in COAD (FC = -1.209), LUAD (FC = -1.190), and LUSC (FC = -1.214). The performance of machine learning models for classification was excellent. L.R., R.F., SVM, and XGB obtained a prediction accuracy of 100 % for most cancers. However, D.T. performed comparatively poorly in prediction accuracy. The results suggest that CBX expression is significantly altered in all the cancers studied; therefore, they might be treated as potential biomarkers for therapeutic intervention of these cancers.

Chromobox Family Proteins as Putative Biomarkers for Breast Cancer Management: A Preliminary Study Based on Bioinformatics Analysis and qRT-PCR Validation

Background

Epigenetic modification of chromatin is an important step in the regulation of gene expression. The chromobox family proteins (CBXs), as epigenetic modifier, may play a vital role in tumorigenesis and cancer progression. Herein we explored the correlation between CBXs and breast cancer (BC) via the bioinformatics approach and qRT-PCR validation.

Methods

Several databases, including GEPIA, TCGA, GEO, K-M plotter, STRING, DAVID, cBioPortal, CIBERSORT, and HPA were employed to analyze the expression levels of CBXs and the correlations between CBXs and prognosis (overall and recurrence-free survival) in BC. We analyzed molecular functions, genetic variations, transcription factors of CBXs, and immune cell infiltration status. ROC curve analysis was performed to determine the predictive value of CBXs. RNA extracted from 11 human BC and paired adjacent normal tissues were subjected to qRT-PCR.

Results

The mRNA expression level of CBX1-5 was significantly upregulated, while that of CBX7 was significantly downregulated in BC; no expression disparities were observed in CBX6/8 expression. Further, high mRNA expression of CBX1/2/3/4/8 correlated with advanced BC, whereas high mRNA expression of CBX6/7 correlated with early BC. High mRNA expressions of CBX1/2/3/5 predict poor OS and RFS, while higher mRNA expressions of CBX6/7 predict better OS and RFS in patients with BC. ROC curve analysis revealed that CBX3 showed excellent discriminatory ability. Gene ontology enrichment analysis showed that CBXs primarily participated in SUMOylation and post-/transcriptional regulation. Moreover, they presented varying degrees of amplification in BC tissues and were related to the infiltration of various immune cells.

Conclusion

CBXs can serve as putative biomarkers for BC. Further studies are warranted to determine the exact molecular mechanisms underlying the action of CBXs in BC, particularly CBX1/2/3/5/7.

CBX Family Members in Two Major Subtypes of Renal Cell Carcinoma: A Comparative Bioinformatic Analysis

The biological function and clinical values of Chromobox (CBX) family proteins in renal cell carcinoma (RCC) are still poorly investigated. This study aimed to compare the expression profiles and clinical relevance of CBXs between the two most frequent subtypes of RCC, clear cell renal cell carcinomas (ccRCC) and papillary renal cell carcinomas (pRCC), and to investigate whether CBXs would play a more or less similar role in the pathogenesis and progression of these RCC subtypes. Considering these two RCC populations in the TCGA database, we built a bioinformatics framework by integrating a computational pipeline with several online tools. CBXs showed a similar trend in ccRCC and pRCC tissues but with some features specific for each subtype. Specifically, the relative expressions of CBX3 and CBX2 were, respectively, the highest and lowest among all CBXs in both RCC subtypes. These data also found confirmation in cellular validation. Except for CBX4 and CBX8, all others were deregulated in the ccRCC subtype. CBX1, CBX6, and CBX7 were also significantly associated with the tumor stage. Further, low expression levels of CBX1, CBX5, CBX6, CBX7, and high expression of CBX8 were associated with poor prognosis. Otherwise, in the pRCC subtype, CBX2, CBX3, CBX7, and CBX8 were deregulated, and CBX2, CBX6, and CBX7 were associated with the tumor stage. In addition, in pRCC patients, low expression levels of CBX2, CBX4, and CBX7 were associated with an unfavorable prognosis. Similarly, CBX3, CBX6, and CBX7 presented the highest alteration rate in both subtypes and were found to be functionally related to histone binding, nuclear chromosomes, and heterochromatin. Furthermore, CBX gene expression levels correlated with immune cell infiltration, suggesting that CBXs might reflect the immune status of RCC subtypes. Our results highlight similarities and differences of CBXs within the two major RCC subtypes, providing new insights for future eligible biomarkers or possible molecular therapeutic targets for these diseases.

CBXs-related prognostic gene signature correlates with immune microenvironment in gastric cancer

Background: Chromobox (CBX) proteins are important Polycomb family proteins in the development of gastric cancer. Nonetheless, the relationship between CBXs and gastric cancer microenvironment remains unclear.

Methods: Multiple databases were used for the analysis of CBXs expression and clinical value in gastric cancer patients. A Cox regression analysis was used to evaluate the prognostic importance of CBXs. Thereafter, regression analysis of LASSO Cox was used to construct the prognostic model. Spearman's correlation between risk score and immune infiltration was analyzed using the McP-counter algorithm. A predicted nomogram was developed to predict the overall survival of gastric cancer patients after 1, 2, and 3 years.

Results: In contrast with normal tissues, mRNA and protein expression levels of CBX2/3 were significantly high in gastric cancer tissues, whereas those of CBX6/7 were low. CBXs significantly correlated with immune subtypes and molecular subtypes. A prognostic gene model based on five CBX genes (CBX1, CBX2, CBX3, CBX7, and CBX8) predicted the overall survival of gastric cancer patients. A significant correlation was noted between the risk score of the CBXs-related prognostic gene model and immune-cell infiltration. Low risk patients could achieve a better response to immune checkpoint inhibitors. A predictive nomogram constructed using the above five CBX genes revealed that overall survival rates over 1, 2, and 3 years could be reasonably predicted. Therefore, the roles of CBXs were associated with chromatin modifications and histone methylation, etc.

Conclusion: In summary, we identified a prognostic CBXs model comprising five genes (CBX1, CBX2, CBX3, CBX7, and CBX8) for gastric cancer patients through bioinformatics analysis.

Chromobox 7/8 serve as independent indicators for glioblastoma via promoting proliferation and invasion of glioma cells

Background

The chromobox family, a critical component of epigenetic regulators, participates in the tumorigenesis and progression of many malignancies. However, the roles of the CBX family members (CBXs) in glioblastoma (GBM) remain unclear.

Methods

The mRNA expression of CBXs was analyzed in tissues and cell lines by Oncomine and Cancer Cell Line Encyclopedia (CCLE). The differential expression of CBXs at the mRNA level was explored in The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases with the “beeswarm” R package. The protein expression of CBXs in GBM was further examined on Human Protein Atlas (HPA). The correlations between CBXs and IDH mutation and between CBXs and GBM subtypes were investigated in the TCGA portal and CGGA database with the “survminer” R package. The alteration of CBXs and their prognostic value were further determined via the cBioPortal and CGGA database with the “survival” R package. The univariate and multivariate analyses were performed to screen out the independent prognostic roles of CBXs in the CGGA database. Cytoscape was used to visualize the functions and related pathways of CBXs in GBM. U251 and U87 glioma cells with gene intervention were used to validate the role of CBX7/8 in tumor proliferation and invasion. Proliferation/invasion-related markers were conducted by Western blot and immunostaining.

Results

CBXs presented significantly differential expressions in pan-cancers. CBX2/3/5/8 were upregulated, whereas CBX6/7 were downregulated at mRNA level in GBM of TCGA and CGGA databases. Similarly, high expression of CBX2/3/5 and low expression of CBX6/8 were further confirmed at the protein level in the HPA. CBX2/6/7 were positively correlated with IDH mutation and CBX1/2/4/5/8 were closely related to GBM subtypes. CBX7 and CBX8 presented the independent prognostic factors for GBM patient survival. GO and KEGG analyses indicated that CBXs were closely related to the histone H3-K36, PcG protein complex, ATPase, and Wnt pathway. The overexpression of CBX7 and underexpression of CBX8 significantly inhibited the proliferation and invasion of glioma cells in vivo and in vitro.

Conclusion

Our results suggested that CBX7 and CBX8 served as independent prognostic indicators that promoted the proliferation and invasion of glioma cells, providing a promising strategy for diagnosing and treating GBM.

Mechanisms of Polycomb group protein function in cancer

Cancer arises from a multitude of disorders resulting in loss of differentiation and a stem cell-like phenotype characterized by uncontrolled growth. Polycomb Group (PcG) proteins are members of multiprotein complexes that are highly conserved throughout evolution. Historically, they have been described as essential for maintaining epigenetic cellular memory by locking homeotic genes in a transcriptionally repressed state. What was initially thought to be a function restricted to a few target genes, subsequently turned out to be of much broader relevance, since the main role of PcG complexes is to ensure a dynamically choregraphed spatio-temporal regulation of their numerous target genes during development. Their ability to modify chromatin landscapes and refine the expression of master genes controlling major switches in cellular decisions under physiological conditions is often misregulated in tumors. Surprisingly, their functional implication in the initiation and progression of cancer may be either dependent on Polycomb complexes, or specific for a subunit that acts independently of other PcG members. In this review, we describe how misregulated Polycomb proteins play a pleiotropic role in cancer by altering a broad spectrum of biological processes such as the proliferation-differentiation balance, metabolism and the immune response, all of which are crucial in tumor progression. We also illustrate how interfering with PcG functions can provide a powerful strategy to counter tumor progression.

Prognostic Value and Therapeutic Potential of CBX Family Members in Ovarian Cancer

Background: Ovarian cancer (OV) is one of the common malignant tumors and has a poor prognosis. Chromobox (CBX) family proteins are critical components of epigenetic regulation complexes that repress target genes transcriptionally via chromatin modification. Some studies have investigated the function specifications among several CBXs members in multiple cancer types, however, little is known about the functions and prognostic roles of distinct CBXs family proteins in ovarian cancer. Methods: In this study, several bioinformatics databases and in vitro experiments were used to analyze the expression profiles, prognostic values, and therapeutic potential of the CBXs family (CBX1-8) in ovarian cancer. Results: It was found that higher expression of CBX3/8 and lower expression of CBX1/6/7 were detected in OV tissues. CBX2/4/5/8 were significantly correlated with individual cancer stages of OV. The expression of CBX1/2/3 were all significantly associated with worse overall survival (OS) and progression-free survival (PFS) for OV patients, whereas the expression of other five CBXs members showed either irrelevant (CBX5 and CBX8) or inconsistent (CBX4, CBX6, and CBX7) results for both OS and PFS in OV. These results showed that only CBX3 had consistent results in expression and prognosis. Further cell experiments also showed that CBX3 promoted the proliferation of ovarian cancer cells. CBX3 was highly expressed in chemoresistant OV tissues. These results indicated that CBX3 was the most likely prognostic indicator and new therapeutic target in OV. Furthermore, gene enrichment analysis suggests that the CBXs family was primarily involved in mast cell activation and mast cell mediated immunity. Individual CBXs members were associated with varying degrees of the infiltration of immune cells, especially B cells. Finally, a high genetic alteration rate of CBXs family (39%) was observed in OV. The low methylation status of CBX3/8 in OV may be associated with their high expression levels. Conclusions: Taken together, these findings exhibited the pivotal value of CBXs family members (especially CBX3) in the prognosis and chemoresistance of ovarian cancer. Our results may provide new insight to explore new prognostic biomarkers and therapeutic targets for ovarian cancer.

Significance of chromobox protein (CBX) expression in diffuse LBCL

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is the main pathological type of non-Hodgkin lymphoma (NHL). Chromobox (CBX) family proteins are classical components of polycomb group (PcG) complexes in many cancer types, resulting in accelerated carcinogenesis. Nevertheless, the prognostic, functional and expression significance of these CBX family members in DLBCL remain unclear and elusive.

METHODS

CBX transcriptional levels were confirmed using Oncomine, Gene Expression Profiling Interactive Analysis (GEPIA) and Cancer Cell Line Encyclopedia (CCLE) databases. The protein levels of CBX family members were analysed using The Human Protein Atlas (HPA) database. Information on the PPI network, functional enrichment, drug sensitivity, prognostic value, miRNA network, protein structure, genetic alteration and immune cell infiltration were generated using the GeneMANIA, Metascape, GSCALite, GEPIA, PDB, cBioPortal, and TIMER databases, and the correlation of these factors with CBX expression levels in DLBCL was assessed.

RESULTS

CBX1/2/3/5/6/8 mRNA levels were significantly enhanced in DLBCL tissues compared to corresponding normal tissues. CBX1/3/4/5/8 protein expression levels were obviously increased, whereas CBX7 was obviously decreased. This difference might be attributed to miRNA regulation based on the miRNA network. Overall survival (OS) analysis showed that CBX levels were not correlated with prognosis in DLBCL patients, indicating that CBXs are not good biomarkers for DLBCL patients. Furthermore, functional enrichment analyses indicated that CBXs were closely related to DNA duplex unwinding, covalent chromatin modification, and histone lysine methylation. The levels of CBXs were also significantly associated with diverse immune cell infiltration in DLBCL.

CONCLUSIONS

This study reveals that dysregulated CBXs are involved in DLBCL development and might represent potential therapeutic targets for DLBCL.

Polycomb group proteins in cancer: multifaceted functions and strategies for modulation

Polycomb repressive complexes (PRCs) are a heterogenous collection of dozens, if not hundreds, of protein complexes composed of various combinations of subunits. PRCs are transcriptional repressors important for cell-type specificity during development, and as such, are commonly mis-regulated in cancer. PRCs are broadly characterized as PRC1 with histone ubiquitin ligase activity, or PRC2 with histone methyltransferase activity; however, the mechanism by which individual PRCs, particularly the highly diverse set of PRC1s, alter gene expression has not always been clear. Here we review the current understanding of how PRCs act, both individually and together, to establish and maintain gene repression, the biochemical contribution of individual PRC subunits, the mis-regulation of PRC function in different cancers, and the current strategies for modulating PRC activity. Increased mechanistic understanding of PRC function, as well as cancer-specific roles for individual PRC subunits, will uncover better targets and strategies for cancer therapies.

Polycomb Paralog Chromodomain Inhibitors Active against Both CBX6 and CBX8*

Methyllysine reader proteins bind to methylated lysine residues and alter gene transcription by changing either the compaction state of chromatin or by the recruitment of other multiprotein complexes. The polycomb paralog family of methyllysine readers bind to trimethylated lysine on the tail of histone 3 (H3) via a highly conserved aromatic cage located in their chromodomains. Each of the polycomb paralogs are implicated in several disease states. CBX6 and CBX8 are members of the polycomb paralog family with two structurally similar chromodomains. By exploring the structure-activity relationships of a previously reported CBX6 inhibitor we have discovered more potent and cell permeable analogs. Our current report includes potent, dual-selective inhibitors of CBX6 and CBX8. We have shown that the -2 position in our scaffold is an important residue for selectivity amongst the polycomb paralogs. Preliminary cell-based studies show that the new inhibitors impact cell proliferation in a rhabdoid tumor cell line.

Long Noncoding RNA MIR100HG Knockdown Attenuates Hepatocellular Carcinoma Progression by Regulating MicroRNA-146b-5p/Chromobox 6

PURPOSE

Hepatocellular carcinoma (HCC) accounts for approximately ninety percent of primary liver cancer. This study attempted to investigate the effects of the long noncoding RNA MIR100HG (MIR100HG) in HCC and the underlying molecular mechanism.

MATERIALS AND METHODS

qRT-PCR was implemented to analyze the expression of MIR100HG, microRNA-146b-5p (miR-146b-5p), and Chromobox 6 (CBX6). The correlation between MIR100HG and clinicopathological features of HCC patients was assessed. Additionally, the effects of MIR100HG knockdown on HCC cell viability, migration, and invasion were explored. The interactions among MIR100HG, miR-146b-5p, and CBX6 were confirmed. Furthermore, rescue experiments were conducted to investigate whether MIR100HG knockdown modulates HCC cell behaviors through modulating the miR-146b-5p/CBX6 axis.

RESULTS

The expression of MIR100HG and CBX6 was enhanced, while miR-146b-5p was inhibited in HCC cells. High MIR100HG expression was positively associated with the TNM tumor stage and Edmondson-Steiner grading in HCC patients. MIR100HG knockdown considerably reduced the HCC cell viability, migration, and invasion. In addition, MIR100HG directly targeted miR-146b-5p, and miR-146b-5p directly targeted CBX6 in HCC cells. Moreover, miR-146b-5p suppression or CBX6 elevation evidently rescued the suppressed viability, migration, and invasion of HCC cells caused by MIR100HG knockdown.

CONCLUSIONS

Knockdown of MIR100HG inhibited the viability, migration, and invasion of HCC cells by targeting the miR-146b-5p/CBX6 axis, offering a potential therapeutic target for HCC therapy.

Comprehensive Analysis of the Expression and Prognosis Value of Chromobox Family Members in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) accounts for 80% of all renal cancers and has a poor prognosis. Chromobox (CBX) family protein expression has been reported in a variety of human malignancies, but the roles of CBXs in ccRCC remain unclear. In this study, by using ONCOMINE, UALCAN, GEPIA, Kaplan-Meier Plotter, cBioPortal, and TIMER, we found the transcriptional levels of CBX3 and CBX4 in ccRCC tissues were significantly higher than those in normal kidney tissues, whereas the transcriptional levels of CBX1, CBX5, CBX6, and CBX7 were significantly reduced in ccRCC tissues. The promoters of CBX2, CBX3, CBX4, CBX5, CBX6, CBX7, and CBX8 were hypermethylated, whereas the CBX1 promoter was hypomethylated in ccRCC. The expression of CBX1, CBX3, CBX4, CBX5, CBX6, and CBX7 was significantly associated with clinicopathological parameters in ccRCC patients. ccRCC patients with high expression levels of CBX3, CBX4, and CBX8 and low expression levels of CBX1, CBX5, CBX6, and CBX7 showed a strong association with poor overall survival. Genetic alterations in CBXs were correlated with poor overall survival and disease-free survival in patients with ccRCC. Moreover, we found significant associations between the expression of CBXs and infiltration of immune cells (B cells, CD8+ T cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells). Our results provide novel insights into the development of CBX-based biomarkers and therapeutic targets for ccRCC.

Expression and prognostic significance of CBX2 in colorectal cancer: database mining for CBX family members in malignancies and vitro analyses

Background

The Chromobox (CBX) domain protein family, a core component of polycomb repressive complexes 1, is involved in transcriptional repression, cell differentiation, and program development by binding to methylated histone tails. Each CBX family member plays a distinct role in various biological processes through their own specific chromatin domains, due to differences in conserved sequences of the CBX proteins. It has been demonstrated that colorectal cancer (CRC) is a multiple-step biological evolutionary process, whereas the roles of the CBX family in CRC remain largely unclear.

Methods

In the present study, the expression and prognostic significance of the CBX family in CRC were systematically analyzed through a series of online databases, including Cancer Cell Line Encyclopedia (CCLE), Oncomine, Human Protein Atlas (HPA), and Gene Expression Profiling Interactive Analysis (GEPIA). For in vitro verification, we performed cell cloning, flow cytometry and transwell experiments to verify the proliferation and invasion ability of CRC cells after knocking down CBX2.

Results

Most CBX proteins were found to be highly expressed in CRC, but only the elevated expression of CBX2 could be associated with poor prognosis in patients with CRC. Further examination of the role of CBX2 in CRC was performed through several in vitro experiments. CBX2 was overexpressed in CRC cell lines via the CCLE database and the results were verified by RT-qPCR. Moreover, the knockdown of CBX2 significantly suppressed CRC cell proliferation and invasion. Furthermore, the downregulation of CBX2 was found to promote CRC cell apoptosis.

Conclusions

Based on these findings, CBX2 may function as an oncogene and potential prognostic biomarker. Thus, the association between the abnormal expression of CBX2 and the initiation of CRC deserves further exploration.

Prognosis and Immune Infiltration of Chromobox Family Genes in Sarcoma

Background

Chromobox family genes (CBXs) are known to play roles in numerous modifications of the chromatin in order to inhibit the transcription of target genes. CBXs have been shown to be expressed at high levels in many types of cancer and can also serve as a target gene for therapeutic purposes. However, little is known about the expression and prognostic value of CBXs in human sarcomas.

Methods

The transcription level of CBXs was analyzed using the Oncomine dataset, and the differential expression of CBXs in sarcoma was reported by the Gene Expression Profiling Interactive Analysis (GEPIA) dataset. We also used the CCLE dataset to evaluate the expression of CBXs in a sarcoma cell line. The prognostic value of CBXs was analyzed using GEPIA and Kaplan–Meier analysis. In addition, the corrections between CBXs and their co-expressed genes were reported using Oncomine and GEPIA datasets. DAVID was used to perform GO function enrichment analysis for the CBXs and their co-expression genes. Finally, TIMER was used to analyze the immune cell infiltration of CBXs in patients with sarcoma.

Results

HP1-α/β/γ (CBX1/3/5) and CBX4/6/8 were found to be overexpressed in human sarcoma, and CBXs were upregulated in almost all the sarcoma cell line. The expression levels of HP1-α/β/γ (CBX1/3/5) and CBX7 were associated with overall survival (OS) in patients with sarcoma, while high expression levels of CBX7 were related to disease-free survival (DFS). In addition, the expression levels of CBX2/6/7 were related to recurrence-free survival (RFS). We also found that the CBX family was positively correlated with the infiltration of immune cells, including CD8⁺ T cells, CD4⁺ T cells, B cells, macrophages, neutrophils, and dendritic cells, in sarcoma.

Conclusions

The results from the present study indicated that CBXs were significantly associated with prognosis and immunological status in sarcoma. These data suggest that CBXs could serve as potential biomarkers for prognosis and immune infiltration in human sarcoma.

CBX6 Promotes HCC Metastasis Via Transcription Factors Snail/Zeb1-Mediated EMT Mechanism

PURPOSE

Hepatocellular carcinoma (HCC) is the most common malignant tumor worldwide with high morbidity and mortality rates. We aimed to examine the expression of chromobox 6 (CBX6) in HCC and analyze its correlation with clinicopathological features of HCC patients. Moreover, the role of CBX6 in the HCC cell proliferation, invasion and metastasis and the potential mechanism underlying HCC metastasis were also investigated.

METHODS

We used quantitative polymerase chain reaction (qRT-PCR) and Western blot to evaluate the expression levels of CBX6 in HCC cell lines. Furthermore, the expression of CBX6 in HCC and the adjacent non-tumor tissues was assessed by immunohistochemistry (IHC). Cell proliferation was evaluated using MTT assay, cell migration and invasion were measured using wound healing and transwell assays. Finally, we detected the expression of target proteins in HCC cell lines transfected with CBX6 overexpression plasmid or CBX6 shRNA plasmid by Western blot.

RESULTS

We found that the expression of CBX6 was increased in 280 cases of HCC tissues compared that in adjacent non-tumor tissues. HCC patients with high CBX6 expression had a higher tendency to have high growth rate, strong invasion ability, high clinical stage and poor tumor differentiation. Functional study demonstrated that the upregulation of CBX6 promotes proliferation, migration and invasion of HCC cells while silencing CBX6 in HCC cells significantly inhibited cell proliferation, migration and invasion. Furthermore, CBX6 could accelerate the EMT process in HCC cells by upregulating the expression of snail and zeb1.

CONCLUSION

CBX6 played an important role in the process of tumorigenesis and progression in HCC and enhanced the invasion and metastasis ability of HCC cells through regulating transcription factors snail/zeb1-mediated EMT mechanism, which indicated that the protein could serve as a novel therapeutic target for the treatment of HCC.

Identification of the Roles of Chromobox Family Members in Gastric Cancer: A Study Based on Multiple Datasets

Background

As the important components in polycomb repressive complexes 1 (PRC1) and heterochromatin protein 1 (HP1), Chromobox (CBX) family members are involved in epigenetic regulatory function, transcriptional repression, and other cellular metabolisms. Increasing studies have indicated significant associations between CBX and tumorigenesis, which is a progression in different types of cancers. However, the information about the roles of each CBX in gastric cancer is extremely limited.

Methods

We explored CBX mRNA expression, corrections with clinicopathological parameters, protein expression, prognostic values, enrichment analysis with several databases including Oncomine, Human Protein Atlas, UALCAN, Kaplan-Meier plotter, cBioPortal, GeneMANIA, and Enrichr.

Results

In our study, comparing to the normal tissues, higher mRNA expression of CBX1/2/3/4/5/8 and lower mRNA expression of CBX7 were found in GC tissues while upregulations of CBX1/2/3/4/5/8 and downregulations of CBX7 were indicated to be significantly correlated to the nodal metastasis status and individual cancer stages in GC patients. As for protein level, the expression of CBX2/3/4/5/6 was higher and the expression of CBX7 was lower in the GC tissues than those in the normal. What is more, higher mRNA expression of CBX1/5/6/8 and lower mRNA expression of CBX7 were markedly correlated to poor outcomes of OS and FP in GC patients. Besides, high mutation rate of CBXs (42%) was observed in GC patients.

Conclusions

We suggest that CBX5/7 may serve as potential therapeutic targets for GC while CBX1/8 may serve as potential prognostic indicators for GC.

Comprehensive analysis of the prognosis for chromobox family in gastric cancer

Background

Chromobox (CBX) family proteins are a class of transcriptional repressors involved in epigenetic regulation and developmental processes of various tumors, including gastric cancer. However, the function and prognosis of different CBXs in gastric cancer remain unknown.

Methods

This study addresses this issue by synthesizing several mainstream databases (Oncomine, GEPIA2, cBioportal, and Kaplan-Meier plotter, among others) that currently contain many tumor samples and provide very reliable analysis results, investigating the role of CBXs in the prognosis of gastric cancer.

Results

The mRNA of CBX1/2/3/4/5/8 was highly expressed in gastric cancer, the mRNA of CBX7 was lowly expressed in gastric cancer, and the mRNA expression of CBX6 was not significantly different in CRC. Besides, high and low CBXs mRNA expression correlated with cancer stage, node metastasis status, H. pylori infection status, and tumor grade in CRC patients. We found that high mRNA expression of CBX4/5/6/7/8 was significantly associated with worse overall survival (OS), progression-free survival (FP), and post-progression survival (PPS) in a large number of CRC patients. High mRNA expression of CBX3 was significantly associated with better OS and FP. We also found that none of the eight CBXs family genes had a mutation rate of less than 5% in gastric cancer, and the highest mutation rate was in CBX3 (14%).

Conclusions

These results suggest that CBX3/4/5/6/7/8 could be a prognostic biomarker in gastric cancer patients.

Expression and prognostic value of Chromobox family members in gastric cancer

Background

The Chromobox (CBX) protein family, which is a crucial part of the epigenetic regulatory complex, plays an important role in the occurrence and development of cancer; however, the function and prognostic value of CBX family members in gastric cancer is not clear.

Methods

we investigated the relationship between CBX members and gastric cancer using a range of tools and databases: Oncomine, Kaplan-Meier plotter, cBioPortal, ULCAN, Metascape, and GEPIA.

Results

The results showed that, relative to normal gastric tissue, mRNA expression levels of CBX1-6 were significantly higher in gastric cancer tissue, whereas the level of CBX7 was significantly lower. Furthermore, overexpression of CBX3-6 and underexpression of CBX7 mRNAs was significantly related to the poor prognosis and survival of gastric cancer patients, making these CBX family members useful biomarkers. Finally, overexpression of CBX1 mRNA was significantly related to the poor prognosis of gastric cancer patients treated with adjuvant 5-fluorouracil-based chemotherapy.

Conclusions

The members of the CBX family can be used as prognosis and survival biomarkers for gastric cancer and CBX1 may be a biomarker for choosing the chemotherapy regimen of gastric cancer patients.

CBX4 transcriptionally suppresses KLF6 via interaction with HDAC1 to exert oncogenic activities in clear cell renal cell carcinoma

Background

Dysregulation of polycomb chromobox (CBX) proteins that mediate epigenetic gene silencing contributes to the progression of human cancers. Yet their roles in clear cell renal cell carcinoma (ccRCC) remain to be explored.

Methods

The expression of CBX4 and its clinical significance were determined by qRT-PCR, western blot, immunohistochemistry and statistical analyses. The biological function of CBX4 in ccRCC tumor growth and metastasis and the underlying mechanism were investigated using in vitro and in vivo models.

Findings

CBX4 exerts oncogenic activities in ccRCC via interaction with HDAC1 to transcriptionally suppress tumor suppressor KLF6. CBX4 expression is increased in ccRCC and correlated with poor prognosis in two independent cohorts containing 840 patients. High CBX4 expression is significantly associated with Fuhrman grade and tumor lymph node invasion. CBX4 overexpression promotes tumor growth and metastasis, whereas CBX4 knockdown results in the opposite phenotypes. Mechanistically, CBX4 downregulates KLF6 via repressing the transcriptional activity of its promoter. Further studies show that CBX4 physically binds to HDAC1 to maintain its localization on the KLF6 promoter. Ectopic expression of KLF6 or disruption of CBX4-HDAC1 interaction attenuates CBX4-mediated cell growth and migration. Furthermore, CBX4 depletion markedly enhances the histone deacetylase inhibitor (HDACi)-induced cell apoptosis and suppression of tumor growth.

Interpretation

Our data suggest CBX4 as an oncogene with prognostic potential in ccRCC. The newly identified CBX4/HDAC1/KLF6 axis may represent a potential therapeutic target for the clinical intervention of ccRCC.

Classification of early and late stage liver hepatocellular carcinoma patients from their genomics and epigenomics profiles

Background

Liver Hepatocellular Carcinoma (LIHC) is one of the major cancers worldwide, responsible for millions of premature deaths every year. Prediction of clinical staging is vital to implement optimal therapeutic strategy and prognostic prediction in cancer patients. However, to date, no method has been developed for predicting the stage of LIHC from the genomic profile of samples.

Methods

The Cancer Genome Atlas (TCGA) dataset of 173 early stage (stage-I), 177 late stage (stage-II, Stage-III and stage-IV) and 50 adjacent normal tissue samples for 60,483 RNA transcripts and 485,577 methylation CpG sites, was extensively analyzed to identify the key transcriptomic expression and methylation-based features using different feature selection techniques. Further, different classification models were developed based on selected key features to categorize different classes of samples implementing different machine learning algorithms.

Results

In the current study, in silico models have been developed for classifying LIHC patients in the early vs. late stage and cancerous vs. normal samples using RNA expression and DNA methylation data. TCGA datasets were extensively analyzed to identify differentially expressed RNA transcripts and methylated CpG sites that can discriminate early vs. late stages and cancer vs. normal samples of LIHC with high precision. Naive Bayes model developed using 51 features that combine 21 CpG methylation sites and 30 RNA transcripts achieved maximum MCC (Matthew’s correlation coefficient) 0.58 with an accuracy of 78.87% on the validation dataset in discrimination of early and late stage. Additionally, the prediction models developed based on 5 RNA transcripts and 5 CpG sites classify LIHC and normal samples with an accuracy of 96–98% and AUC (Area Under the Receiver Operating Characteristic curve) 0.99. Besides, multiclass models also developed for classifying samples in the normal, early and late stage of cancer and achieved an accuracy of 76.54% and AUC of 0.86.

Conclusion

Our study reveals stage prediction of LIHC samples with high accuracy based on the genomics and epigenomics profiling is a challenging task in comparison to the classification of cancerous and normal samples. Comprehensive analysis, differentially expressed RNA transcripts, methylated CpG sites in LIHC samples and prediction models are available from CancerLSP (http://webs.iiitd.edu.in/raghava/cancerlsp/).

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.

CBX2 Regulates Proliferation and Apoptosis via the Phosphorylation of YAP in Hepatocellular Carcinoma

Chromobox 2 (CBX2), a chromobox family protein, is a crucial component of the polycomb group complex: polycomb repressive complex 1 (PRC1). Research on CBX2 as an oncogene has been published in recent years. However, the connection between CBX2 and hepatocellular carcinoma (HCC) has not been studied. In this article, based on the results of immunohistochemical (IHC) staining of HCC and adjacent liver tissue microarrays, we found that high CBX2 expression is associated with poor prognosis in HCC patients. The results of a CCK8 assay, a clonogenic survival assay and a nude mouse tumorigenicity assay showed that knockdown of CBX2 inhibited the proliferation of HCC cells. According to the results of Annexin V-FITC/propidium iodide (PI) staining-based fluorescence activated cell sorting (FACS) analysis, knockdown of CBX2 increased HCC cell apoptosis. Furthermore, the RNA-seq results revealed that knockdown of CBX2 inhibited the expression of WTIP, which is an inhibitor of the Hippo pathway. We used western blotting to validate the mechanism and discovered that knockdown of CBX2 increased the phosphorylation of YAP, which explains why knockdown of CBX2 inhibits proliferation and increases apoptosis in HCC cells. In conclusion, CBX2 could be a potential target for HCC anticancer treatment.

Single Nucleotide Polymorphisms of CBX4 and CBX7 Decrease the Risk of Hepatocellular Carcinoma

Background

The chromobox (CBX) proteins CBX2, CBX4, CBX6, CBX7, and CBX8, also known as Polycomb (Pc) proteins, are canonical components of the Polycomb repressive complex 1 (PRC1). Abundant evidence indicates that abnormal expression of Pc proteins is associated with a variety of tumors, but their role in the pathogenesis of hepatocellular carcinoma (HCC) has not been fully elucidated. In the present study, we performed a case-control study to investigate the relationship between single nucleotide polymorphisms (SNPs) of CBX genes and HCC.

Methods

Nine SNPs on CBX genes (rs7217395, rs2036316 of CBX2; rs3764374, rs1285251, rs2289728 of CBX4; rs7292074 of CBX6; and rs710190, rs139394, rs5750753 of CBX7) were screened and genotyped using MassARRAY technology in 334 HCC cases and 321 controls. The association between SNPs and their corresponding gene expressions was analyzed through bioinformatics methods using the Ensembl database and Blood eQTL browser online tools.

Results

The results indicated that rs2289728 (G>A) of CBX4 (P = 0.03, OR = 0.56, 95% CI: 0.33-0.94) and rs139394 (C>A) of CBX7 (P = 0.02, OR = 0.55, 95% CI: 0.33-0.90) decreased the risk of HCC. Interaction between rs2036316 and HBsAg increased the risk of HCC (P = 0.02, OR = 6.88, 95% CI: 5.20-9.11), whereas SNP-SNP interaction between rs710190 and rs139394 reduced the risk of HCC (P = 0.03, OR = 0.33, 95% CI: 0.12-0.91). Gene expression analyses showed that the rs2289728 A allele and the rs139394 A allele significantly reduced CBX4 and CBX7 expression, respectively.

Conclusion

Our findings suggest that CBX4 rs2289728 and CBX7 rs139394 are protective SNPs against HCC. The two SNPs may reduce the risk of HCC while suppressing the expression of CBX4 and CBX7.

Downregulated Expression of Chromobox Homolog 7 in Hepatocellular Carcinoma

Background: As an essential member of the Polycomb group (PcG) proteins, chromobox homolog 7 (CBX7) is found deregulated in some human cancers, and is thought to be a contributing factor in carcinogenesis. However, the expression and role of CBX7 in hepatocellular carcinoma (HCC) is still not well characterized. Materials and Methods: The levels of the CBX7 protein were quantified in 75 paired HCC and adjacent nontumor tissues by immunohistochemistry; comparisons were made using McNemar's chi-square test. The Kaplan-Meier estimate was used for survival analysis. Results: We found that the expression of CBX7 in HCC tissues was significantly lower than that of adjacent nontumor tissues. In addition, decreased CBX7 expression levels were correlated with liver cirrhosis in HCC patients. Furthermore, the survival times of HCC patients who were CBX7-expression-negative were shorter than HCC patients who were CBX7-expression-positive. Conclusion: Our results show that downregulation of CBX7 is related to HCC progression and a poor prognosis in HCC patients.

Overexpression of CBX2 in breast cancer promotes tumor progression through the PI3K/AKT signaling pathway

Breast cancer is the second leading cause of cancer-related death among women worldwide. Emerging evidence suggests that chromobox homolog 2 (CBX2) is overexpressed in breast cancer and plays an essential role in tumor progression. However, its expression and functional roles in breast cancer development and progression require further exploration. Here, we evaluated CBX2 expression in breast cancer using mRNA expression data from the TCGA database; CBX2 expression was upregulated in breast cancer. Furthermore, upregulated CBX2 expression was significantly associated with poorer overall survival (OS) and progression-free survival (PFS) of breast cancer patients. Immunohistochemical analysis of CBX2 expression in a tissue microarray (TMA) cohort yielded concordant results. Univariate and multivariate analyses showed that elevated CBX2 expression was significantly and independently associated with poorer OS of patients in this TMA cohort. Additionally, we performed in vitro functional assays to evaluate the proliferation, migration, and invasion abilities of breast cancer cell lines wherein CBX2 was knocked down using short hairpin RNA (shRNA). CBX2 silencing inhibited cell proliferation, migration, and invasion in vitro. Furthermore, knockdown of CBX2 markedly reduced breast tumorigenesis in xenograft mouse models. Functional and pathway enrichment analyses indicated a positive correlation between high CBX2 expression and activation of the PI3K/AKT pathway, which were further confirmed by western blot and immunohistochemical analyses of mouse tumors. Our findings indicate that CBX2 is a potential prognostic biomarker and therapeutic target for breast cancer.

Transcriptional expressions of Chromobox 1/2/3/6/8 as independent indicators for survivals in hepatocellular carcinoma patients

Chromobox (CBX) proteins are important components of epigenetic regulation complexes known to play key roles in hepatocellular carcinoma (HCC). Little is known about the function of distinct CBXs in HCC. To address this issue, the study investigated the roles of CBXs in the prognosis of HCC using ONCOMINE, UALCAN, Human Protein Atlas, Kaplan-Meier Plotter, c-BioPortal databases. Over expressions of 8 CBXs members were found to be significantly associated with clinical cancer stages and pathological tumor grades in HCC patients. Besides, higher mRNA expressions of CBX1/2/3/6/8 were found to be significantly associated with shorter overall survival (OS) in HCC patients, while higher mRNA expression of CBX7 was associated with favorable OS. Multivariate analysis also showed that high mRNA expressions of CBX1/2/3/6/8 were independent prognostic factors for shorter OS of HCC patients. Moreover, high mutation rate of CBXs (51%) was also observed in HCC patients, and genetic alteration in CBXs was associated with shorter OS and disease-free survival (DFS) in HCC patients. Taken together, these results indicated that CBX1/2/3/6/8 could be prognostic biomarkers for survivals of HCC patients.

Epigenetic small molecule modulators of histone and DNA methylation

DNA and histone methylation belong to the key regulatory components in the epigenetic machinery, and dysregulations of these processes have been associated with various human diseases. Small molecule modulators of these epigenetic targets are highly valuable both as chemical probes to study the biological roles of the target proteins, and as potential therapeutics. Indeed, recent years have seen the discovery of chemical modulators of several epigenetic targets, some of which are already marketed drugs or undergoing clinical trials. In this review, we will focus on small molecule modulators of DNA and histone methylation.

Polycomb protein RING1A limits hematopoietic differentiation in myelodysplastic syndromes

Genetic lesions affecting epigenetic regulators are frequent in myelodysplastic syndromes (MDS). Polycomb proteins are key epigenetic regulators of differentiation and stemness that act as two multimeric complexes termed polycomb repressive complexes 1 and 2, PRC1 and PRC2, respectively. While components and regulators of PRC2 such as ASXL1 and EZH2 are frequently mutated in MDS and AML, little is known about the role of PRC1.

To analyze the role of PRC1, we have taken a functional approach testing PRC1 components in loss- and gain-of-function experiments that we found overexpressed in advanced MDS patients or dynamically expressed during normal hematopoiesis.

This approach allowed us to identify the enzymatically active component RING1A as the key PRC1 component in hematopoietic stem cells and MDS. Specifically, we found that RING1A is expressed in CD34⁺ bone marrow progenitor cells and further overexpressed in high-risk MDS patients. Knockdown of RING1A in an MDS-derived AML cell line facilitated spontaneous and retinoic acid-induced differentiation. Similarly, inactivation of RING1A in primary CD34⁺ cells augmented erythroid differentiation. Treatment with a small compound RING1 inhibitor reduced the colony forming capacity of CD34⁺ cells from MDS patients and healthy controls. In MDS patients higher RING1A expression associated with an increased number of dysplastic lineages and blasts. Our data suggests that RING1A is deregulated in MDS and plays a role in the erythroid development defect.

Prognostic values of distinct CBX family members in breast cancer

Chromobox (CBX) family proteins are canonical components in polycomb repressive complexes 1 (PRC1), with epigenetic regulatory function and transcriptionally repressing target genes via chromatin modification. A plethora of studies have highlighted the function specifications among CBX family members in various cancer, including lung cancer, colon cancer and breast cancer. Nevertheless, the functions and prognostic roles of distinct CBX family members in breast cancer (BC) remain elusive. In this study, we reported the prognostic values of CBX family members in patients with BC through analysis of a series of databases, including CCLE, ONCOMINE, Xena Public Data Hubs, and Kaplan-Meier plotter. It was found that the mRNA expression of CBX family members were noticeably higher in BC than normal counterparts. CBX2 was highly expressed in Basal-like and HER-2 subtypes, while CBX4 and CBX7 expressions were enriched in Luminal A and Luminal B subtypes of BC. Survival analysis revealed that CBX1, CBX2 and CBX3 mRNA high expression was correlated to worsen relapse-free survival (RFS) for all BC patients, while CBX4, CBX5, CBX6 and CBX7 high expression was correlated to better RFS in this setting. Noteworthily, CBX1 and CBX2 were associated with chemoresistance whereas CBX7 was associated with tamoxifen sensitivity, as well as chemosensitivity in breast tumors. Therefore, we propose that CBX1, CBX2 and CBX7 are potential targets for BC treatment. The results might be beneficial for better understanding the complexity and heterogeneity in the molecular underpinning of BC, and to develop tools to more accurately predict the prognosis of patients with BC.