Gene dysregulation by histone variant H2A.Z in bladder cancer

The Clonal Hematopoiesis-associated Gene Srcap Plays an Essential Role in Hematopoiesis

Somatic mutations arising in hematopoietic stem cells (HSCs) may provide the latter with a fitness advantage, allowing the mutant HSC to clonally expand. Such mutations have been recurrently identified in the chromatin modifier, SRCAP, in both non-malignant and leukemic clones, suggesting that this gene plays a significant role in hematopoiesis. We generated a conditional Srcap loss of function murine model and determined the consequences of hematopoietic-specific loss of this gene. We show that Srcap is essential for normal fetal liver erythropoiesis and monocytopoiesis. In Srcap deficient fetal livers, the number of phenotypic HSCs is similar to that of controls, but these HSCs exhibit a profound repopulating defect. Likewise, conditional deletion of Srcap during adult hematopoiesis results in a rapid loss of HSCs. Loss of Srcap is associated with evidence of increased DNA damage in HSCs and lineage-restricted progenitors as assessed by y-H2AX expression. Consistent with this finding, we observed strong transcriptional upregulation of the p53 pathway in Srcap deficient erythroid precursors. Collectively our data highlight the importance of Srcap in maintaining HSC function and supporting hematopoietic differentiation and suggests that it plays an essential role in maintaining genomic integrity.

Navigating glioblastoma complexity: the interplay of neurotransmitters and chromatin

Glioblastoma is the most aggressive brain cancer with an unfavorable prognosis for patient survival. Glioma stem cells, a subpopulation of cancer cells, drive tumor initiation, self-renewal, and resistance to therapy and, together with the microenvironment, play a crucial role in glioblastoma maintenance and progression. Neurotransmitters such as noradrenaline, dopamine, and serotonin have contrasting effects on glioblastoma development, stimulating or inhibiting its progression depending on the cellular context and through their action on glioma stem cells, perhaps changing the epigenetic landscape. Recent studies have revealed that serotonin and dopamine induce chromatin modifications related to transcriptional plasticity in the mammalian brain and possibly in glioblastoma; however, this topic still needs to be explored because of its potential implications for glioblastoma treatment. Also, it is essential to consider that neurotransmitters' effects depend on the tumor's microenvironment since it can significantly influence the response and behavior of cancer cells. This review examines the possible role of neurotransmitters as regulators of glioblastoma development, focusing on their impact on the chromatin of glioma stem cells.

The Function of H2A Histone Variants and Their Roles in Diseases

Epigenetic regulation, which is characterized by reversible and heritable genetic alterations without changing DNA sequences, has recently been increasingly studied in diseases. Histone variant regulation is an essential component of epigenetic regulation. The substitution of canonical histones by histone variants profoundly alters the local chromatin structure and modulates DNA accessibility to regulatory factors, thereby exerting a pivotal influence on gene regulation and DNA damage repair. Histone H2A variants, mainly including H2A.Z, H2A.B, macroH2A, and H2A.X, are the most abundant identified variants among all histone variants with the greatest sequence diversity. Harboring varied chromatin occupancy and structures, histone H2A variants perform distinct functions in gene transcription and DNA damage repair. They are implicated in multiple pathophysiological mechanisms and the emergence of different illnesses. Cancer, embryonic development abnormalities, neurological diseases, metabolic diseases, and heart diseases have all been linked to histone H2A variant alterations. This review focuses on the functions of H2A histone variants in mammals, including H2A.Z, H2A.B, macroH2A, and H2A.X, and their current roles in various diseases.

Integration of single-cell RNA-seq and bulk RNA-seq to construct liver hepatocellular carcinoma stem cell signatures to explore their impact on patient prognosis and treatment

BACKGROUND

Liver hepatocellular carcinoma (LIHC) is a prevalent form of primary liver cancer. Research has demonstrated the contribution of tumor stem cells in facilitating tumor recurrence, metastasis, and treatment resistance. Despite this, there remains a lack of established cancer stem cells (CSCs)-associated genes signatures for effectively predicting the prognosis and guiding the treatment strategies for patients diagnosed with LIHC.

METHODS

The single-cell RNA sequencing (scRNA-seq) and bulk RNA transcriptome data were obtained based on public datasets and computerized firstly using CytoTRACE package and One Class Linear Regression (OCLR) algorithm to evaluate stemness level, respectively. Then, we explored the association of stemness indicators (CytoTRACE score and stemness index, mRNAsi) with survival outcomes and clinical characteristics by combining clinical information and survival analyses. Subsequently, weighted co-expression network analysis (WGCNA) and Cox were applied to assess mRNAsi-related genes in bulk LIHC data and construct a prognostic model for LIHC patients. Single-sample gene-set enrichment analysis (ssGSEA), Cell-type Identification By Estimating Relative Subsets Of RNA Transcripts (CIBERSORT) and Tumor Immune Estimation Resource (TIMER) analysis were employed for immune infiltration assessment. Finally, the potential immunotherapeutic response was predicted by the Tumor Immune Dysfunction and Exclusion (TIDE), and the tumor mutation burden (TMB). Additionally, pRRophetic package was applied to evaluate the sensitivity of high and low-risk groups to common chemotherapeutic drugs.

RESULTS

A total of four genes (including STIP1, H2AFZ, BRIX1, and TUBB) associated with stemness score (CytoTRACE score and mRNAsi) were identified and constructed a risk model that could predict prognosis in LIHC patients. It was observed that high stemness cells occurred predominantly in the late stages of LIHC and that poor overall survival in LIHC patients was also associated with high mRNAsi scores. In addition, pathway analysis confirmed the biological uniqueness of the two risk groups. Personalized treatment predictions suggest that patients with a low risk benefited more from immunotherapy, while those with a high risk group may be conducive to chemotherapeutic drugs.

CONCLUSION

The current study developed a novel prognostic risk signature with genes related to CSCs, which provides novel ideas for the diagnosis, prognosis and treatment of LIHC.

Roles of Histone H2A Variants in Cancer Development, Prognosis, and Treatment

Histones are nuclear proteins essential for packaging genomic DNA and epigenetic gene regulation. Paralogs that can substitute core histones (H2A, H2B, H3, and H4), named histone variants, are constitutively expressed in a replication-independent manner throughout the cell cycle. With specific chaperones, they can be incorporated to chromatin to modify nucleosome stability by modulating interactions with nucleosomal DNA. This allows the regulation of essential fundamental cellular processes for instance, DNA damage repair, chromosomal segregation, and transcriptional regulation. Among all the histone families, histone H2A family has the largest number of histone variants reported to date. Each H2A variant has multiple functions apart from their primary role and some, even be further specialized to perform additional tasks in distinct lineages, such as testis specific shortH2A (sH2A). In the past decades, the discoveries of genetic alterations and mutations in genes encoding H2A variants in cancer had revealed variants' potentiality in driving carcinogenesis. In addition, there is growing evidence that H2A variants may act as novel prognostic indicators or biomarkers for both early cancer detection and therapeutic treatments. Nevertheless, no studies have ever concluded all identified variants in a single report. Here, in this review, we summarize the respective functions for all the 19 mammalian H2A variants and their roles in cancer biology whilst potentiality being used in clinical setting.

Identification and validation of an H2AZ1-based index model: a novel prognostic tool for hepatocellular carcinoma

The H2A.Z variant histone 1 (H2AZ1) is aberrantly expressed in various tumors, correlating with an unfavorable prognosis. However, its role in hepatocellular carcinoma (HCC) remains unclear. We aimed to elucidate the pathways affected by H2AZ1 and identify promising therapeutic targets for HCC. Following bioinformatic analysis of gene expression and clinical data from The Cancer Genome Atlas and Gene Expression Omnibus database, we found 6,344 dysregulated genes related to H2AZ1 overexpression in HCC tissues (P < 0.05). We performed weighted gene co-expression network analysis to identify the gene module most related to H2AZ1. The H2AZ1-based index was further developed using Cox regression analysis, which revealed that the poor prognosis in the high H2AZ1-based index group could be attributed to elevated tumor stemness (P < 0.05). Moreover, the clinical model showed good prognostic potential (AUC > 0.7). We found that H2AZ1 knockdown led to reduced superoxide dismutase (SOD) activity, elevated malondialdehyde (MDA) levels, and increased apoptosis rate in tumor cells (P < 0.001). Thus, we developed an H2AZ1-based index model with the potential to predict the prognosis of patients with HCC. Our findings provide initial evidence that H2AZ1 overexpression plays a pivotal role in HCC initiation and progression.

Competition for H2A.Z underlies the developmental impacts of repetitive element de-repression

The histone variant H2A.Z is central to early embryonic development, determining transcriptional competency through chromatin regulation of gene promoters and enhancers. In addition to genic loci, we find that H2A.Z resides at a subset of evolutionarily young repetitive elements, including DNA transposons, long interspersed nuclear elements and long terminal repeats, during early zebrafish development. Moreover, increases in H2A.Z occur when repetitive elements become transcriptionally active. Acquisition of H2A.Z corresponds with a reduction in the levels of the repressive histone modification H3K9me3 and a moderate increase in chromatin accessibility. Notably, however, de-repression of repetitive elements also leads to a significant reduction in H2A.Z over non-repetitive genic loci. Genic loss of H2A.Z is accompanied by transcriptional silencing at adjacent coding sequences, but remarkably, these impacts are mitigated by augmentation of total H2A.Z protein via transgenic overexpression. Our study reveals that levels of H2A.Z protein determine embryonic sensitivity to de-repression of repetitive elements, that repetitive elements can function as a nuclear sink for epigenetic factors and that competition for H2A.Z greatly influences overall transcriptional output during development. These findings uncover general mechanisms in which counteractive biological processes underlie phenotypic outcomes.

Primary Hepatic Neuroendocrine Carcinoma with Metastasis to the Mesentery: A Case Report

Primary hepatic neuroendocrine carcinomas (PHNECs) are extremely rare, with only about 90 cases having been reported in the English-language literature. Among all neuroendocrine neoplasms, primary hepatic neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs) are extremely rare, accounting for 0.3% of NETs and 0.28-0.46% of malignant liver tumors. Additionally, primary hepatic NECs occur infrequently. The clinical diagnosis of primary hepatic NEC remains challenging because of its rarity and the lack of information about its characteristic appearance on images. Consequently, pathological examination through the performance of a preoperative liver tumor biopsy is essential for diagnosis. Due to the lack of availability of substantial high-quality data, there is no standard therapy for primary hepatic NEC. We present the first case of PHNEC metastasized to the mesentery reported in the English-language literature.

Interplay Between the Histone Variant H2A.Z and the Epigenome in Pancreatic Cancer

BACKGROUND

The oncogenic process is orchestrated by a complex network of chromatin remodeling elements that shape the cancer epigenome. Histone variant H2A.Z regulates DNA control elements such as promoters and enhancers in different types of cancer; however, the interplay between H2A.Z and the pancreatic cancer epigenome is unknown.

OBJECTIVE

This study analyzed the role of H2A.Z in different DNA regulatory elements.

METHODS

We performed Chromatin Immunoprecipitation Sequencing assays (ChiP-seq) with total H2A.Z and acetylated H2A.Z (acH2A.Z) antibodies and analyzed published data from ChIP-seq, RNA-seq, bromouridine labeling-UV and sequencing (BruUV-seq), Hi-C and ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) in the pancreatic cancer cell line PANC-1.

RESULTS

The results indicate that total H2A.Z facilitates the recruitment of RNA polymerase II and transcription factors at promoters and enhancers allowing the expression of pro-oncogenic genes. Interestingly, we demonstrated that H2A.Z is enriched in super-enhancers (SEs) contributing to the transcriptional activation of key genes implicated in tumor development. Importantly, we established that H2A.Z contributes to the three-dimensional (3D) genome organization of pancreatic cancer and that it is a component of the Topological Associated Domains (TADs) boundaries in PANC-1 and that total H2A.Z and acH2A.Z are associated with A and B compartments, respectively.

CONCLUSIONS

H2A.Z participates in the biology and development of pancreatic cancer by generating a pro-oncogenic transcriptome through its posttranslational modifications, interactions with different partners, and regulatory elements, contributing to the oncogenic 3D genome organization. These data allow us to understand the molecular mechanisms that promote an oncogenic transcriptome in pancreatic cancer mediated by H2A.Z.

BPTF inhibition antagonizes colorectal cancer progression by transcriptionally inactivating Cdc25A

As the largest subunit of the nuclear remodeling factor complex, Bromodomain PHD Finger Transcription Factor (BPTF) has been reported to be involved in tumorigenesis and development in several cancers. However, to date, its functions and related molecular mechanisms in colorectal cancer (CRC) are still poorly defined and deserve to be revealed. In this study, we uncovered that, under the expression regulation of c-Myc, BPTF promoted CRC progression by targeting Cdc25A. BPTF was found to be highly expressed in CRC and promoted the proliferation and metastasis of CRC cells through BPTF specific siRNAs, shRNAs or inhibitors. Based on RNA-seq, combined with DNA-pulldown, ChIP and luciferase reporter assay, we proved that, by binding to -178/+107 region within Cdc25A promoter, BPTF transcriptionally activated Cdc25A, thus accelerating the cell cycle process of CRC cells. Meanwhile, BPTF itself was found to be transcriptionally regulated by c-Myc. Moreover, BPTF knockdown or inactivation was verified to sensitize CRC cells to chemotherapeutics, 5-Fluorouracil (5FU) and Oxaliplatin (Oxa), c-Myc inhibitor and cell cycle inhibitor not just at the cellular level in vitro, but in subcutaneous xenografts or AOM/DSS-induced in situ models of CRC in mice, while Cdc25A overexpression partially reversed BPTF silencing-caused tumor growth inhibition. Clinically, BPTF, c-Myc and Cdc25A were highly expressed in CRC tissues simultaneously, the expression of any two of the three was positively correlated, and their expressions were highly relevant to tumor differentiation, TNM staging and poor prognosis of CRC patients. Thus, our study indicated that the targeted inhibition of BPTF alone, or together with chemotherapy and/or cell cycle-targeted therapy, might act as a promising new strategy for CRC treatment, while c-Myc/BPTF/Cdc25A signaling axis is expected to be developed as an associated set of candidate biomarkers for CRC diagnosis and prognosis prediction.

The role of histone modifications: from neurodevelopment to neurodiseases

Epigenetic regulatory mechanisms, including DNA methylation, histone modification, chromatin remodeling, and microRNA expression, play critical roles in cell differentiation and organ development through spatial and temporal gene regulation. Neurogenesis is a sophisticated and complex process by which neural stem cells differentiate into specialized brain cell types at specific times and regions of the brain. A growing body of evidence suggests that epigenetic mechanisms, such as histone modifications, allow the fine-tuning and coordination of spatiotemporal gene expressions during neurogenesis. Aberrant histone modifications contribute to the development of neurodegenerative and neuropsychiatric diseases. Herein, recent progress in understanding histone modifications in regulating embryonic and adult neurogenesis is comprehensively reviewed. The histone modifications implicated in neurodegenerative and neuropsychiatric diseases are also covered, and future directions in this area are provided.

GAS41 mediates proliferation and GEM chemoresistance via H2A.Z.2 and Notch1 in pancreatic cancer

PURPOSE

GAS41 is a YEATS domain protein that binds to acetylated histone H3 to promote the chromatin deposition of H2A.Z in non-small cell lung cancer. The role of GAS41 in pancreatic cancer is still unknown. Here, we aimed to reveal this role.

METHODS

GAS41 expression in pancreatic cancer tissues and cell lines was examined using qRT-PCR, Western blotting and immunohistochemistry. MTT, colony formation, spheroid formation and in vivo tumorigenesis assays were performed to assess the proliferation, tumorigenesis, stemness and gemcitabine (GEM) resistance of pancreatic cancer cells. Mechanistically, co-immunoprecipitation (co-IP) and chromatin immunoprecipitation (ChIP) assays were used to evaluate the roles of GAS41, H2A.Z.2 and Notch1 in pancreatic cancer.

RESULTS

We found that GAS41 is overexpressed in human pancreatic cancer tissues and cell lines, and that its expression increases following the acquisition of GEM resistance. We also found that GAS41 up-regulates Notch, as well as pancreatic cancer cell stemness and GEM resistance in vitro and in vivo. We show that GAS41 binds to H2A.Z.2 and activates Notch and its downstream mediators, thereby regulating stemness and drug resistance. Depletion of GAS41 or H2A.Z.2 was found to down-regulate Notch and to sensitize pancreatic cancer cells to GEM.

CONCLUSION

Our data indicate that GAS41 mediates proliferation and GEM resistance in pancreatic cancer cells via H2A.Z.2 and Notch1.

H2A.Z's 'social' network: functional partners of an enigmatic histone variant

The histone variant H2A.Z has been extensively studied to understand its manifold DNA-based functions. In the past years, researchers identified its specific binding partners, the 'H2A.Z interactome', that convey H2A.Z-dependent chromatin changes. Here, we summarize the latest findings regarding vertebrate H2A.Z-associated factors and focus on their roles in gene activation and repression, cell cycle regulation, (neuro)development, and tumorigenesis. Additionally, we demonstrate how protein-protein interactions and post-translational histone modifications can fine-tune the complex interplay of H2A.Z-regulated gene expression. Last, we review the most recent results on interactors of the two isoforms H2A.Z.1 and H2A.Z.2.1, which differ in only three amino acids, and focus on cancer-associated mutations of H2A and H2A.Z, which reveal fascinating insights into the functional importance of such minuscule changes.

Spotlight on histone H2A variants: From B to X to Z

Chromatin, the functional organization of DNA with histone proteins in eukaryotic nuclei, is the tightly-regulated template for several biological processes, such as transcription, replication, DNA damage repair, chromosome stability and sister chromatid segregation. In order to achieve a reversible control of local chromatin structure and DNA accessibility, various interconnected mechanisms have evolved. One of such processes includes the deposition of functionally-diverse variants of histone proteins into nucleosomes, the building blocks of chromatin. Among core histones, the family of H2A histone variants exhibits the largest number of members and highest sequence-divergence. In this short review, we report and discuss recent discoveries concerning the biological functions of the animal histone variants H2A.B, H2A.X and H2A.Z and how dysregulation or mutation of the latter impacts the development of disease.

H2A Histone Family Member Z (H2AFZ) Serves as a Prognostic Biomarker in Lung Adenocarcinoma: Bioinformatic Analysis and Experimental Validation

Background

H2A histone family member Z (H2AFZ) is a special subtype in the H2A histone family, which participates in the regulation of gene transcription. Nevertheless, little is known about the role of H2AFZ in the tumor microenvironment and genetic factors associated with lung cancer.

Material/Methods

The expression of H2AFZ in LUAD was analyzed via Tumor Immune Estimation Resource (TIMER), the Cancer Genome Atlas (TCGA), and Gene Expression Omnibus (GEO) databases at the mRNA level. To detect the protein expression level of H2AFZ, immunohistochemistry (IHC) was performed using LUAD tissues and non-tumor lung tissues. Kaplan-Meier survival analysis and Cox regression analysis were conducted to identify the effect of H2AFZ expression on overall survival (OS) based on TCGA-LUAD and the GEO dataset GSE68465 cohorts, and our LUAD patient cohort was used for validation. Identification of signaling pathways associated with the expression of H2AFZ was performed using Gene Set Enrichment Analysis (GSEA). The influences of expression of H2AFZ on tumor immune-infiltrating cell (TIICs) were assessed via TIMER and CIBERSORT.

Results

The expression of H2AFZ was increased in LUAD tissues at both mRNA and protein levels. In addition, high expression of H2AFZ predicted poor OS and might be an independent prognostic predictor in LUAD patients. Moreover, H2AFZ affected the relative proportion of TIICs and was positively associated with Myeloid-derived suppressor cells (MDSC) infiltration level in LUAD.

Conclusions

H2AFZ was upregulated in LUAD and related to poor prognosis of LUAD patients; thus, it could be an underlying prognostic biomarker correlated with immune infiltration in LUAD.

Alterations of Chromatin Regulators in the Pathogenesis of Urinary Bladder Urothelial Carcinoma

Simple Summary

Urinary bladder cancer is one of the ten major cancers worldwide, with higher incidences in males, in smokers, and in highly industrialized countries. New therapies beyond cytotoxic chemotherapy are urgently needed to improve treatment of these tumors. A better understanding of the mechanisms underlying their development may help in this regard. Recently, it was discovered that a group of proteins regulating the state of chromatin and thus gene expression is exceptionally and frequently affected by gene mutations in bladder cancers. Altered function of these mutated chromatin regulators must therefore be fundamental in their development, but how and why is poorly understood. Here we review the current knowledge on changes in chromatin regulators and discuss their possible consequences for bladder cancer development and options for new therapies.

Abstract

Urothelial carcinoma (UC) is the most frequent histological type of cancer in the urinary bladder. Genomic changes in UC activate MAPK and PI3K/AKT signal transduction pathways, which increase cell proliferation and survival, interfere with cell cycle and checkpoint control, and prevent senescence. A more recently discovered additional category of genetic changes in UC affects chromatin regulators, including histone-modifying enzymes (KMT2C, KMT2D, KDM6A, EZH2), transcription cofactors (CREBBP, EP300), and components of the chromatin remodeling complex SWI/SNF (ARID1A, SMARCA4). It is not yet well understood how these changes contribute to the development and progression of UC. Therefore, we review here the emerging knowledge on genomic and gene expression alterations of chromatin regulators and their consequences for cell differentiation, cellular plasticity, and clonal expansion during UC pathogenesis. Our analysis identifies additional relevant chromatin regulators and suggests a model for urothelial carcinogenesis as a basis for further mechanistic studies and targeted therapy development.

H2AFZ Is a Prognostic Biomarker Correlated to TP53 Mutation and Immune Infiltration in Hepatocellular Carcinoma

H2A family member Z (H2AFZ) is a highly conserved gene encoding H2A.Z.1, an isoform of histone variant H2A.Z, and is implicated in cancer. In this study, we report that overexpression of H2AFZ is associated with tumor malignancy and poor prognosis in HCC patients. Functional network analysis suggested that H2AFZ mainly regulates cell cycle signaling and DNA replication via pathways involving several cancer-related kinases and transcription factor E2F1. Further studies revealed that H2AFZ overexpression is regulated by TP53 mutation and led to an attenuation of rapid proliferation phenotype and aggressive behavior in HCC cells. Moreover, we found that H2AFZ was related to immune infiltrations and was co-expressed with immune checkpoint genes, including CD274 (PD-L1), CTLA-4, HAVCR2 (TIM3), LAG3, PDCD1 (PD-1), and TIGIT (VSIG9) in HCC, indicating that H2AFZ-overexpressed HCC patients may be sensitive to immune checkpoint blockades (ICBs). Integrated analysis suggested that H2AFZ^high/TP53^mut patients had the shortest OS and PFS time, but most likely to respond to ICBs. These findings indicate that the H2AFZ possesses potential value as a novel prognostic indicator for HCC patients and is correlated with immune infiltration in HCC, laying a foundation for future study of HCC investigation and intervention.

Non-redundant functions of H2A.Z.1 and H2A.Z.2 in chromosome segregation and cell cycle progression

H2A.Z is a H2A‐type histone variant essential for many aspects of cell biology, ranging from gene expression to genome stability. From deuterostomes, H2A.Z evolved into two paralogues, H2A.Z.1 and H2A.Z.2, that differ by only three amino acids and are encoded by different genes (H2AFZ and H2AFV, respectively). Despite the importance of this histone variant in development and cellular homeostasis, very little is known about the individual functions of each paralogue in mammals. Here, we have investigated the distinct roles of the two paralogues in cell cycle regulation and unveiled non‐redundant functions for H2A.Z.1 and H2A.Z.2 in cell division. Our findings show that H2A.Z.1 regulates the expression of cell cycle genes such as Myc and Ki‐67 and its depletion leads to a G1 arrest and cellular senescence. On the contrary, H2A.Z.2, in a transcription‐independent manner, is essential for centromere integrity and sister chromatid cohesion regulation, thus playing a key role in chromosome segregation.

The emerging role of ISWI chromatin remodeling complexes in cancer

Disordered chromatin remodeling regulation has emerged as an essential driving factor for cancers. Imitation switch (ISWI) family are evolutionarily conserved ATP-dependent chromatin remodeling complexes, which are essential for cellular survival and function through multiple genetic and epigenetic mechanisms. Omics sequencing and a growing number of basic and clinical studies found that ISWI family members displayed widespread gene expression and genetic status abnormalities in human cancer. Their aberrant expression is closely linked to patient outcome and drug response. Functional or componential alteration in ISWI-containing complexes is critical for tumor initiation and development. Furthermore, ISWI-non-coding RNA regulatory networks and some non-coding RNAs derived from exons of ISWI member genes play important roles in tumor progression. Therefore, unveiling the transcriptional regulation mechanism underlying ISWI family sparked a booming interest in finding ISWI-based therapies in cancer. This review aims at describing the current state-of-the-art in the role of ISWI subunits and complexes in tumorigenesis, tumor progression, immunity and drug response, and presenting deep insight into the physiological and pathological implications of the ISWI transcription machinery in cancers.

Comprehensive bioinformatic analysis reveals oncogenic role of H2A.Z isoforms in cervical cancer progression

Objectives

Cervical cancer ranks as the fourth most common neoplasia in women worldwide in which epigenetic alterations play an important role. Several studies have reported pro-oncogenic role of the histone variant H2A.Z in different types of cancer; however, the role of H2A.Z in cervical cancer remains poorly studied. This study aimed to determine the potential role of H2A.Z in cervical cancer through a bioinformatic approach.

Materials and Methods

H2A.Z expression was analyzed in The Human Protein Atlas, The Cancer Genome Atlas, and Gene Expression Omnibus datasets. The promoter regions of H2AZ1 and H2AZ2 genes were downloaded from Expasy, and the prediction of transcription factor binding motifs was performed using CONSITE, Alibaba, and ALGGEN. ChIP-seq and RNA-seq data from HeLa-S3 cells were downloaded from ENCODE. The discovery motif was investigated using MEME-ChIP. The functional annotation was examined in Enrich.

Results

The expression of H2A.Z is elevated in cervical cancer. Interestingly, DNA methylation, copy number, and transcription factors AP2α and ELK1 are involved in H2A.Z overexpression. Additionally, H2A.Z is enriched on promoter and enhancer regions of genes involved in pathways associated with cancer development. In these regions, H2A.Z enables the recruitment of transcription factors such as NRF1, NFYA, and RNA Pol II. Finally, H2A.Z allows the expression of genes associated with proliferation in patients with cervical cancer.

Conclusion

Our findings suggest that H2A.Z overexpression and its presence in promoters and enhancers could be regulating the transcription of genes involved in cervical carcinogenesis.

The H2A.Z-nuclesome code in mammals: emerging functions

H2A.Z is a histone variant that provides specific structural and docking-side properties to the nucleosome, resulting in diverse and specialised molecular and cellular functions. In this review, we discuss the latest studies uncovering new functional aspects of mammalian H2A.Z in gene transcription, including pausing and elongation of RNA polymerase II (RNAPII) and enhancer activity; DNA repair; DNA replication; and 3D chromatin structure. We also review the recently described role of H2A.Z in embryonic development, cell differentiation, neurodevelopment, and brain function. In conclusion, our cumulative knowledge of H2A.Z over the past 40 years, in combination with the implementation of novel molecular technologies, is unravelling an unexpected and complex role of histone variants in gene regulation and disease.

H2AFZ: A Novel Prognostic Marker in Canine Melanoma and a Predictive Marker for Resistance to CDK4/6 Inhibitor Treatment

Uncontrolled proliferation is a key feature of tumor progression and malignancy. This suggests that cell-cycle related factors could be exploited as cancer biomarkers and that pathways specifically involved in the cell cycle, such as the Rb-E2F pathway, could be targeted as an effective anti-tumor therapy. We investigated 34 formalin-fixed paraffin-embedded (FFPE) tissue samples of canine cutaneous melanocytoma, cutaneous melanoma, and oral melanoma. Corresponding clinical follow-up data were used to determine the prognostic value of the mRNA expression levels of several cell cycle regulated E2F target genes (E2F1, DHFR, CDC6, ATAD2, MCM2, H2AFZ, GINS2, and survivin/BIRC5). Moreover, using four canine melanoma cell lines, we explored the possibility of blocking the Rb-E2F pathway by using a CDK4/6 inhibitor (Palbociclib) as a potential anti-cancer therapy. We investigated the expression levels of the same E2F target gene transcripts before and after treatment to determine the potential utility of these molecules as predictive markers. The E2F target gene H2AFZ was expressed in 91.43% of the primary tumors and H2AFZ expression was significantly higher in cases with unfavorable clinical outcome. Among the other tested genes, survivin/BIRC5 showed as well-promising results as a prognostic marker in canine melanoma. Three of the four tested melanoma cell lines were sensitive to the CDK4/6 inhibitor. The resistant cell line displayed higher expression levels of H2AFZ before treatment compared to the CDK4/6 inhibitor-sensitive cell lines. The present results suggest that CDK4/6 inhibitors could potentially be used as a new anti-cancer treatment for canine melanoma and that H2AFZ could serve as a prognostic and predictive marker for patient selection.

Discovery of High-Affinity Inhibitors of the BPTF Bromodomain

The dysfunctional bromodomain PHD finger transcription factor (BPTF) exerts a pivotal influence in the occurrence and development of many human diseases, particularly cancers. Herein, through the structural decomposition of the reported BPTF inhibitor TP-238, the effective structural fragments were synthetically modified to obtain our lead compound DC-BPi-03. DC-BPi-03 was identified as a novel BPTF-BRD inhibitor with a moderate potency (IC₅₀ = 698.3 ± 21.0 nM). A structure-guided structure-activity relationship exploration gave rise to two BPTF inhibitors with much higher affinities, DC-BPi-07 and DC-BPi-11. Notably, DC-BPi-07 and DC-BPi-11 show selectivities 100-fold higher than those of other BRD targets. The cocrystal structures of BPTF in complex with DC-BPi-07 and DC-BPi-11 demonstrate the rationale of chemical efforts from the atomic level. Further study showed that DC-BPi-11 significantly inhibited leukemia cell proliferation.

Opportunity knocks for uncovering the new function of an understudied nucleosome remodeling complex member, the bromodomain PHD finger transcription factor, BPTF

Nucleosome remodeling provides access to genomic DNA for recruitment of the transcriptional machinery to mediate gene expression. The aberrant function of nucleosome remodeling complexes has been correlated to human cancer, making them emerging therapeutic targets. The bromodomain PHD finger transcription factor, BPTF, is the largest member of the human nucleosome remodeling factor NURF. Over the last five years, BPTF has become increasingly identified as a protumorigenic factor, prompting investigations into the molecular mechanisms associated with BPTF function. Despite a druggable bromodomain, small molecule discovery is at an early stage. Here we highlight recent investigations into the biology being discovered for BPTF, chemical biology approaches used to study its function, and small molecule inhibitors being designed as future chemical probes and therapeutics.

Epigenetic Deregulation of Apoptosis in Cancers

Cancer cells possess the ability to evade apoptosis. Genetic alterations through mutations in key genes of the apoptotic signaling pathway represent a major adaptive mechanism of apoptosis evasion. In parallel, epigenetic changes via aberrant modifications of DNA and histones to regulate the expression of pro- and antiapoptotic signal mediators represent a major complementary mechanism in apoptosis regulation and therapy response. Most epigenetic changes are governed by the activity of chromatin modifying enzymes that add, remove, or recognize different marks on histones and DNA. Here, we discuss how apoptosis signaling components are deregulated at epigenetic levels, particularly focusing on the roles of chromatin-modifying enzymes in this process. We also review the advances in cancer therapies with epigenetic drugs such as DNMT, HMT, HDAC, and BET inhibitors, as well as their effects on apoptosis modulation in cancer cells. Rewiring the epigenome by drug interventions can provide therapeutic advantage for various cancers by reverting therapy resistance and leading cancer cells to undergo apoptotic cell death.

Molecular Mechanisms of Oncogenesis through the Lens of Nucleosomes and Histones

At the cellular level, cancer is the disease of both the genome and the epigenome, and the interplay between genetic mutations and epigenetic states may occur at the level of elementary chromatin units, the nucleosomes. They are formed by a segment of DNA wrapped around an octamer of histone proteins. In this review, we survey various mechanisms of cancer etiology and progression mediated by histones and nucleosomes. In particular, we discuss the effects of mutations in histones, changes in their expression and slicing on epigenetic dysregulation and carcinogenesis. The links between cancer phenotypes and differential expression of histone variants and isoforms are summarized. Finally, we discourse the geometric and steric effects of DNA compaction in nucleosomes on DNA mutation rate, interactions with transcription factors, including pioneer transcription factors, and prospects of cancer cells' genome and epigenome editing.

JAZF1, A Novel p400/TIP60/NuA4 Complex Member, Regulates H2A.Z Acetylation at Regulatory Regions

Histone variants differ in amino acid sequence, expression timing and genomic localization sites from canonical histones and convey unique functions to eukaryotic cells. Their tightly controlled spatial and temporal deposition into specific chromatin regions is accomplished by dedicated chaperone and/or remodeling complexes. While quantitatively identifying the chaperone complexes of many human H2A variants by using mass spectrometry, we also found additional members of the known H2A.Z chaperone complexes p400/TIP60/NuA4 and SRCAP. We discovered JAZF1, a nuclear/nucleolar protein, as a member of a p400 sub-complex containing MBTD1 but excluding ANP32E. Depletion of JAZF1 results in transcriptome changes that affect, among other pathways, ribosome biogenesis. To identify the underlying molecular mechanism contributing to JAZF1's function in gene regulation, we performed genome-wide ChIP-seq analyses. Interestingly, depletion of JAZF1 leads to reduced H2A.Z acetylation levels at > 1000 regulatory sites without affecting H2A.Z nucleosome positioning. Since JAZF1 associates with the histone acetyltransferase TIP60, whose depletion causes a correlated H2A.Z deacetylation of several JAZF1-targeted enhancer regions, we speculate that JAZF1 acts as chromatin modulator by recruiting TIP60's enzymatic activity. Altogether, this study uncovers JAZF1 as a member of a TIP60-containing p400 chaperone complex orchestrating H2A.Z acetylation at regulatory regions controlling the expression of genes, many of which are involved in ribosome biogenesis.

H2A.Z overexpression suppresses senescence and chemosensitivity in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most intractable and devastating malignant tumors. Epigenetic modifications such as DNA methylation and histone modification regulate tumor initiation and progression. However, the contribution of histone variants in PDAC is unknown. Here, we demonstrated that the histone variant H2A.Z is highly expressed in PDAC cell lines and PDAC patients and that its overexpression correlates with poor prognosis. Moreover, all three H2A.Z isoforms (H2A.Z.1, H2A.Z.2.1, and H2A.Z.2.2) are highly expressed in PDAC cell lines and PDAC patients. Knockdown of these H2A.Z isoforms in PDAC cell lines induces a senescent phenotype, cell cycle arrest in phase G2/M, increased expression of cyclin-dependent kinase inhibitor CDKN2A/p16, SA-β-galactosidase activity and interleukin 8 production. Transcriptome analysis of H2A.Z-depleted PDAC cells showed altered gene expression in fatty acid biosynthesis pathways and those that regulate cell cycle and DNA damage repair. Importantly, depletion of H2A.Z isoforms reduces the tumor size in a mouse xenograft model in vivo and sensitizes PDAC cells to gemcitabine. Overexpression of H2A.Z.1 and H2A.Z.2.1 more than H2A.Z.2.2 partially restores the oncogenic phenotype. Therefore, our data suggest that overexpression of H2A.Z isoforms enables cells to overcome the oncoprotective barrier associated with senescence, favoring PDAC tumor grow and chemoresistance. These results make H2A.Z a potential candidate as a diagnostic biomarker and therapeutic target for PDAC.

Histone Variants: Guardians of Genome Integrity

Chromatin integrity is key for cell homeostasis and for preventing pathological development. Alterations in core chromatin components, histone proteins, recently came into the spotlight through the discovery of their driving role in cancer. Building on these findings, in this review, we discuss how histone variants and their associated chaperones safeguard genome stability and protect against tumorigenesis. Accumulating evidence supports the contribution of histone variants and their chaperones to the maintenance of chromosomal integrity and to various steps of the DNA damage response, including damaged chromatin dynamics, DNA damage repair, and damage-dependent transcription regulation. We present our current knowledge on these topics and review recent advances in deciphering how alterations in histone variant sequence, expression, and deposition into chromatin fuel oncogenic transformation by impacting cell proliferation and cell fate transitions. We also highlight open questions and upcoming challenges in this rapidly growing field.

Normal Patterns of Histone H3K27 Methylation Require the Histone Variant H2A.Z in Neurospora crassa

Neurospora crassa contains a minimal Polycomb repression system, which provides rich opportunities to explore Polycomb-mediated repression across eukaryotes and enables genetic studies that can be difficult in plant and animal systems. Polycomb Repressive Complex 2 is a multi-subunit complex that deposits mono-, di-, and trimethyl groups on lysine 27 of histone H3, and trimethyl H3K27 is a molecular marker of transcriptionally repressed facultative heterochromatin. In mouse embryonic stem cells and multiple plant species, H2A.Z has been found to be colocalized with H3K27 methylation. H2A.Z is required for normal H3K27 methylation in these experimental systems, though the regulatory mechanisms are not well understood. We report here that Neurospora crassa mutants lacking H2A.Z or SWR-1, the ATP-dependent histone variant exchanger, exhibit a striking reduction in levels of H3K27 methylation. RNA-sequencing revealed downregulation of eed, encoding a subunit of PRC2, in an hH2Az mutant compared to wild type, and overexpression of EED in a ΔhH2Az;Δeed background restored most H3K27 methylation. Reduced eed expression leads to region-specific losses of H3K27 methylation, suggesting that differential dependence on EED concentration is critical for normal H3K27 methylation at certain regions in the genome.

New inhibitors for the BPTF bromodomain enabled by structural biology and biophysical assay development

Bromodomain-containing proteins regulate transcription through protein-protein interactions with chromatin and serve as scaffolding proteins for recruiting essential members of the transcriptional machinery. One such protein is the bromodomain and PHD-containing transcription factor (BPTF), the largest member of the nucleosome remodeling complex, NURF. Despite an emerging role for BPTF in regulating a diverse set of cancers, small molecule development for inhibiting the BPTF bromodomain has been lacking. Here we cross-validate three complementary biophysical assays to further the discovery of BPTF bromodomain inhibitors for chemical probe development: two direct binding assays (protein-observed 19F (PrOF) NMR and surface plasmon resonance (SPR)) and a competitive inhibition assay (AlphaScreen). We first compare the assays using three small molecules and acetylated histone peptides with reported affinity for the BPTF bromodomain. Using SPR with both unlabeled and fluorinated BPTF, we further determine that there is a minimal effect of 19F incorporation on ligand binding for future PrOF NMR experiments. To guide medicinal chemistry efforts towards chemical probe development, we subsequently evaluate two new BPTF inhibitor scaffolds with our suite of biophysical assays and rank-order compound affinities which could not otherwise be determined by PrOF NMR. Finally, we cocrystallize a subset of small molecule inhibitors and present the first published small molecule-protein structures with the BPTF bromodomain. We envision the biophysical assays described here and the structural insights from the crystallography will guide researchers towards developing selective and potent BPTF bromodomain inhibitors.

The Use of Mononucleosome Immunoprecipitation for Analysis of Combinatorial Histone Post-translational Modifications and Purification of Nucleosome-Interacting Proteins

The nucleosome is the principal structural unit of chromatin. Although many studies focus on individual histone post-translational modifications (PTMs) in isolation, it is important to recognize that multiple histone PTMs can function together or cross-regulate one another within the nucleosome context. In addition, different modifications or histone-binding surfaces can synergize to stabilize the binding of nuclear factors to nucleosomes. To facilitate these types of studies, we present here a step-by-step protocol for isolating high yields of mononucleosomes for biochemical analyses. Furthermore, we discuss differences and variations of the basic protocol used in different publications and characterize the relative abundance of selected histone PTMs and chromatin-binding proteins in the different chromatin fractions obtained by this method.

Vital and Distinct Roles of H2A.Z Isoforms in Hepatocellular Carcinoma

Purpose

H2A.Z is an oncogenic histone variant that is overexpressed in cancers. Two isoforms of H2A.Z, H2AFZ and H2AFV, are identical except for a three-amino acid difference. However, their isoform-specific functions remain unclear in cancer development. Thereby, this study aimed to investigate whether the two isoforms play distinct functions in hepatocarcinogenesis.

Materials and Methods

Expressions of H2A.Z isoforms in 116 paired hepatocellular cancerous and para-cancerous tissues were detected by employing qPCR. GEO and TCGA databases were used to probe expressions and prognostic value of the two H2A.Z isoforms. A comprehensive meta-analysis was conducted. Furthermore, co-expressed analysis of H2AFZ and H2AFV was performed by using cBioPortal database. H2A.Z binding genes from Chip-seq were intersected with H2A.Z isoforms co-expressed genes to perform functional annotations. Cell proliferation experiments from H2AFZ knockout HepG2 and BEL-7402 cells were implemented. Finally, RNA-seq was applied to analyse alternative splicing in H2AFZ knockout and wild-type cells.

Results

H2AFZ and H2AFV were both significantly upregulated (P < 0.01) in hepatocellular carcinoma and related to poor prognosis (P < 0.01). The two H2A.Z isoforms played vital roles in cell proliferation. It is also predicted that unique functions of H2AFV contain spindle midzone and microtubule, while H2AFZ is especially associated with RNA export and spliceosome. Further, devoid H2AFZ may restrain liver cancer cell proliferation and cause many alternative splicing events.

Conclusion

Both H2A.Z isoforms play vital and distinct roles in the occurrence and progression of liver cancer, which may pave a way for novel therapeutic applications for cancers in the future.

NMR Analyses of Acetylated H2A.Z Isoforms Identify Differential Binding Interactions with the Bromodomain of the NURF Nucleosome Remodeling Complex

Gene specific recruitment of bromodomain-containing proteins to chromatin is affected by post-translational acetylation of lysine on histones. Whereas interactions of the bromodomain with acetylation patterns of native histones (H2A, H2B, H3, and H4) have been well characterized, the motif for recognition for histone variants H2A.Z I and H2A.Z II by bromodomains has yet to be fully investigated. Elucidating these molecular mechanisms is crucial for understanding transcriptional regulation in cellular processes involved in both development and disease. Here, we have used protein-observed fluorine NMR to fully characterize the affinities of H2A.Z I and II acetylation patterns for BPTF's bromodomain and found the diacetylated mark of lysine 7 and 13 on H2A.Z II to have the strongest interaction with K7ac preferentially engaging the binding site. We further examined the selectivity of H2A.Z histones against a variety of bromodomains, revealing that the bromodomain of CECR2 binds with the highest affinity and specificity for acetylated H2A.Z I over isoform II. These results support a possible role for different H2A.Z transcriptional activation mechanisms that involve recruitment of chromatin remodeling complexes.

Gene Expression Analyses in Non Muscle Invasive Bladder Cancer Reveals a Role for Alternative Splicing and Tp53 Status

Non-muscle invasive bladder cancer (NMIBC) represents a crucial problem for the national health care systems due to its high rates of recurrence and the consequent need of frequent follow-ups. Here, gene expression analyses in patients diagnosed as NMIBC were performed to determine those molecular pathways involved in tumor initiation, finding that both MYC and E2F are up regulated and helps to tumor initiation and progression. Our results also support an important involvement of alternative splicing events, modifying key pathways to favour bladder tumor evolution. Finally, since MDM2 showed differential exon usage, mutations in TP53 and its protein expression have been also studied in the same patients. Our data support that recurrence is epigenetically mediated and favoured by an increase protein expression of TP53, which appears more frequently mutated in advanced stages and grades, being associated to a worse prognosis. Therefore, TP53 mutational status could be used as a potential biomarker in the first stages of NMIBC to predict recurrence and prognosis.

The histone variant H2A.Z in gene regulation

The histone variant H2A.Z is involved in several processes such as transcriptional control, DNA repair, regulation of centromeric heterochromatin and, not surprisingly, is implicated in diseases such as cancer. Here, we review the recent developments on H2A.Z focusing on its role in transcriptional activation and repression. H2A.Z, as a replication-independent histone, has been studied in several model organisms and inducible mammalian model systems. Its loading machinery and several modifying enzymes have been recently identified, and some of the long-standing discrepancies in transcriptional activation and/or repression are about to be resolved. The buffering functions of H2A.Z, as supported by genome-wide localization and analyzed in several dynamic systems, are an excellent example of transcriptional control. Posttranslational modifications such as acetylation and ubiquitination of H2A.Z, as well as its specific binding partners, are in our view central players in the control of gene expression. Understanding the key-mechanisms in either turnover or stabilization of H2A.Z-containing nucleosomes as well as defining the H2A.Z interactome will pave the way for therapeutic applications in the future.

Compound C620-0696, a new potent inhibitor targeting BPTF, the chromatin-remodeling factor in non-small-cell lung cancer

Bromodomain PHD-finger transcription factor (BPTF) is the largest subunit of the nucleosome remodeling factor and plays an important role in chromatin remodeling for gene activation through its association with histone acetylation or methylation. BPTF is also involved in oncogene transcription in diverse progressions of cancers. Despite clinical trials for inhibitors of bromodomain and extra-terminal family proteins in human cancers, no potent and selective inhibitor targeting the BPTF bromodomain has been discovered. In this study, we identified a potential inhibitor, namely, C620-0696, by computational docking modeling to target bromodomain. Results of biolayer interferometry revealed that compound C620-0696 exhibited high binding affinity to the BPTF bromodomain. Moreover, C620-0696 was cytotoxic in BPTF with a high expression of non-small-cell lung cancer (NSCLC) cells. It suppressed the expression of the BPTF target gene c-MYC, which is known as an oncogenic transcriptional regulator in various cancers. C620-0696 also partially inhibited the migration and colony formation of NSCLC cells owing to apoptosis induction and cell cycle blockage. Thus, our study presents an effective strategy to target a bromodomain factor-mediated tumorigenesis in cancers with small molecules, supporting further exploration of the use of these inhibitors in oncology.

Selectivity, ligand deconstruction, and cellular activity analysis of a BPTF bromodomain inhibitor

Bromodomain and PHD finger containing protein transcription factor (BPTF) is an epigenetic protein involved in chromatin remodelling and is a potential anticancer target. The BPTF bromodomain has one reported small molecule inhibitor (AU1, rac-1). Here, advances made on the structure-activity relationship of a BPTF bromodomain ligand are reported using a combination of experimental and molecular dynamics simulations leading to the active enatiomer (S)-1. Additionally, a ligand deconstruction analysis was conducted to characterize important pharmacophores for engaging the BPTF bromodomain. These studies have been enabled by a protein-based fluorine NMR approach, highlighting the versatility of the method for selectivity, ligand deconstruction, and ligand binding. To enable future analysis of biological activity, cell growth analyses in a panel of cancer cell lines were carried out using CRISPR-Cas9 and (S)-1 to identify cell-based model systems that are sensitive to BPTF inhibition.

Advancements in the Development of non-BET Bromodomain Chemical Probes

The bromodomain and extra terminal (BET) family of bromodomain-containing proteins (BCPs) have been the subject of extensive research over the past decade, resulting in a plethora of high-quality chemical probes for their tandem bromodomains. In turn, these chemical probes have helped reveal the profound biological role of the BET bromodomains and their role in disease, ultimately leading to a number of molecules in active clinical development. However, the BET subfamily represents just 8/61 of the known human bromodomains, and attention has now expanded to the biological role of the remaining 53 non-BET bromodomains. Rapid growth of this research area has been accompanied by a greater understanding of the requirements for an effective bromodomain chemical probe and has led to a number of new non-BET bromodomain chemical probes being developed. Advances since December 2015 are discussed, highlighting the strengths/caveats of each molecule, and the value they add toward validating the non-BET bromodomains as tractable therapeutic targets.

WDR5 supports colon cancer cells by promoting methylation of H3K4 and suppressing DNA damage

BACKGROUND

KMT2/MLL proteins are commonly overexpressed or mutated in cancer and have been shown to support cancer maintenance. These proteins are responsible for methylating histone 3 at lysine 4 and promoting transcription and DNA synthesis; however, they are inactive outside of a multi-protein complex that requires WDR5. WDR5 has been implicated in cancer for its role in the COMPASS complex and its interaction with Myc; however, the role of WDR5 in colon cancer has not yet been elucidated.

METHODS

WDR5 expression was evaluated using RT-qPCR and western blot analysis. Cell viability and colony forming assays were utilized to evaluate the effects of WDR5 depletion or inhibition in colon cancer cells. Downstream effects of WDR5 depletion and inhibition were observed by western blot.

RESULTS

WDR5 is overexpressed in colon tumors and colon cancer cell lines at the mRNA and protein level. WDR5 depletion reduces cell viability in HCT116, LoVo, RKO, HCT15, SW480, SW620, and T84 colon cancer cells. Inhibition of the WDR5:KMT2/MLL interaction using OICR-9429 reduces cell viability in the same panel of cell lines albeit not to the same extent as RNAi-mediated WDR5 depletion. WDR5 depletion reduced H3K4Me3 and increased phosphorylation of H2AX in HCT116, SW620, and RKO colon cancer cells; however, OICR-9429 treatment did not recapitulate these effects in all cell lines potentially explaining the reduced toxicity of OICR-9429 treatment as compared to WDR5 depletion. WDR5 depletion also sensitized colon cancer cells to radiation-induced DNA damage.

CONCLUSIONS

These data demonstrate a clear role for WDR5 in colon cancer and future studies should examine its potential to serve as a therapeutic target in cancer. Additional studies are needed to fully elucidate if the requirement for WDR5 is independent of or consistent with its role within the COMPASS complex. OICR-9429 treatment was particularly toxic to SW620 and T84 colon cancer cells, two cell lines without mutations in WDR5 and KMT2/MLL proteins suggesting COMPASS complex inhibition may be particularly effective in tumors lacking KMT2 mutations. Additionally, the ability of WDR5 depletion to amplify the toxic effects of radiation presents the possibility of targeting WDR5 to sensitize cells to DNA-damaging therapies.

Functional analysis of gene expression profiling-based prediction in bladder cancer

The present study aimed to analyze the modification of gene expression in bladder cancer (BC) by identifying significant differentially expressed genes (DEGs) and functionally assess them using bioinformatics analysis. To achieve this, two microarray datasets, GSE24152 (which included 10 fresh tumor tissue samples from urothelial bladder carcinoma patients and 7 benign mucosa samples from the bladder), and GSE42089 (which included 10 tissues samples from urothelial cell carcinoma patients and 8 tissues samples from the normal bladder), were downloaded from the Gene Expression Omnibus database for further analysis. Differentially expressed genes (DEGs) were screened between benign the mucosa and control groups in GSE24152 and GSE42089 datasets. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analysis were performed on overlapping DEGs identified in GSE24152 and GSE42089. Protein-protein interaction (PPI) networks and sub-networks were then constructed to identify key genes and main pathways. GO terms analysis was also performed for the selected clusters. In total, 1,325 DEGs in GSE24152 and 647 DEGs in GSE42089 were screened, in which 619 common DEGs were identified. The DEGs were mainly enriched in pathways and GO terms associated with mitotic and chromosome assembly, including nucleosome assembly, spindle checkpoint and DNA replication. In the interaction network, progesterone receptor (PGR), MAF bZIP transcription factor G (MAFG), cell division cycle 6 (CDC6) and members of the minichromosome maintenance family (MCMs) were identified as key genes. Histones were also considered to be significant factors in BC. Nucleosome assembly and sequence-specific DNA binding were the most significant clustered GO terms. In conclusion, the DEGs, including PGR, MAFG, CDC6 and MCMs, and those encoding the core histone family were closely associated with the development of BC via pathways associated with mitotic and chromosome assembly.

Transcriptional regulation mediated by H2A.Z via ANP32e-dependent inhibition of protein phosphatase 2A

The mechanisms that regulate H2A.Z and its requirement for transcription in differentiated mammalian cells remains ambiguous. In this study, we identified the interaction between the C-terminus of ANP32e and N-terminus of H2A.Z in a yeast two-hybrid screen. Knockdown of ANP32e resulted in proteasomal degradation and nuclear depletion of H2A.Z or of a chimeric green florescence protein fused to its N-terminus. This effect was reversed by inhibition of protein phosphatase 2A (PP2A) and, conversely, reproduced by overexpression of its catalytic subunit. Accordingly, knockdown of ANP32e inhibited phosphorylation of H2A.Z, whereas a mutation of serine-9 proved its requirement for both the protein's stability and nuclear localization, as did knockdown of the nuclear mitogen and stress-induced kinase 1. Moreover, ANP32e's knockdown also revealed its differential requirement for cell signaling and gene expression, whereas, genome-wide binding analysis confirmed its co-localization with H2A.Z at transcription start sites, as well as, gene bodies of inducible and tissue-specific genes. The data also suggest that H2A.Z restricts transcription, which is moderated by ANP32e at the promoter and gene bodies of expressed genes. Thus, ANP32e, through inhibition of PP2A, is required for nucleosomal inclusion of H2A.Z and the regulation of gene expression.

H2A.Z regulates tumorigenesis, metastasis and sensitivity to cisplatin in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is a fatal, malignant tumor of the liver; effective diagnostic biomarkers and therapeutic targets for ICC have not been identified yet. High expression of H2A histone family member Z (H2A.Z) is a high-risk factor for poor prognosis in patients with breast cancer and primary hepatocellular cancer. However, the significance of H2A.Z and its expression in ICC remains unknown. The present study demonstrated that H2A.Z is overexpressed in ICC and expression of H2A.Z correlated with poor prognosis in patients with ICC. H2A.Z regulated cell proliferation in vitro and in vivo via H2A.Z/S-phase kinase-associated protein 2/p27/p21 signaling. Inhibition of H2A.Z reduced cell proliferation and induced apoptosis in ICC. In addition, downregulation of H2AZ reduced tumor metastasis by repressing epithelial-mesenchymal transition and enhanced the antitumor effects of cisplatin in the treatment of ICC. Overall, H2A.Z promoted cell proliferation and epithelial-mesenchymal transition in ICC, suggesting that H2A.Z may be a novel biomarker and therapeutic target for ICC.

Post-Translational Modifications of H2A Histone Variants and Their Role in Cancer

Histone variants are chromatin components that replace replication-coupled histones in a fraction of nucleosomes and confer particular characteristics to chromatin. H2A variants represent the most numerous and diverse group among histone protein families. In the nucleosomal structure, H2A-H2B dimers can be removed and exchanged more easily than the stable H3-H4 core. The unstructured N-terminal histone tails of all histones, but also the C-terminal tails of H2A histones protrude out of the compact structure of the nucleosome core. These accessible tails are the preferential target sites for a large number of post-translational modifications (PTMs). While some PTMs are shared between replication-coupled H2A and H2A variants, many modifications are limited to a specific histone variant. The present review focuses on the H2A variants H2A.Z, H2A.X, and macroH2A, and summarizes their functions in chromatin and how these are linked to cancer development and progression. H2A.Z primarily acts as an oncogene and macroH2A and H2A.X as tumour suppressors. We further focus on the regulation by PTMs, which helps to understand a degree of context dependency.

Recognition of histone acetylation by the GAS41 YEATS domain promotes H2A.Z deposition in non-small cell lung cancer

Histone acetylation is associated with active transcription in eukaryotic cells. It helps to open up the chromatin by neutralizing the positive charge of histone lysine residues and providing binding platforms for "reader" proteins. The bromodomain (BRD) has long been thought to be the sole protein module that recognizes acetylated histones. Recently, we identified the YEATS domain of AF9 (ALL1 fused gene from chromosome 9) as a novel acetyl-lysine-binding module and showed that the ENL (eleven-nineteen leukemia) YEATS domain is an essential acetyl-histone reader in acute myeloid leukemias. The human genome encodes four YEATS domain proteins, including GAS41, a component of chromatin remodelers responsible for H2A.Z deposition onto chromatin; however, the importance of the GAS41 YEATS domain in human cancer remains largely unknown. Here we report that GAS41 is frequently amplified in human non-small cell lung cancer (NSCLC) and is required for cancer cell proliferation, survival, and transformation. Biochemical and crystal structural studies demonstrate that GAS41 binds to histone H3 acetylated on H3K27 and H3K14, a specificity that is distinct from that of AF9 or ENL. ChIP-seq (chromatin immunoprecipitation [ChIP] followed by high-throughput sequencing) analyses in lung cancer cells reveal that GAS41 colocalizes with H3K27ac and H3K14ac on the promoters of actively transcribed genes. Depletion of GAS41 or disruption of the interaction between its YEATS domain and acetylated histones impairs the association of histone variant H2A.Z with chromatin and consequently suppresses cancer cell growth and survival both in vitro and in vivo. Overall, our study identifies GAS41 as a histone acetylation reader that promotes histone H2A.Z deposition in NSCLC.

Oncogenic N-Ras Stimulates SRF-Mediated Transactivation via H3 Acetylation at Lysine 9

Signal transduction pathways regulate the gene expression by altering chromatin dynamics in response to mitogens. Ras proteins are key regulators linking extracellular stimuli to a diverse range of biological responses associated with gene regulation. In mammals, the three ras genes encode four Ras protein isoforms: H-Ras, K-Ras4A, K-Ras4B, and N-Ras. Although emerging evidence suggests that Ras isoforms differentially regulate gene expressions and are functionally nonredundant, the mechanisms underlying Ras specificity and Ras signaling effects on gene expression remain unclear. Here, we show that oncogenic N-Ras acts as the most potent regulator of SRF-, NF-κB-, and AP-1-dependent transcription. N-Ras-RGL2 axis is a distinct signaling pathway for SRF target gene expression such as Egr1 and JunB, as RGL2 Ras binding domain (RBD) significantly impaired oncogenic N-Ras-induced SRE activation. By monitoring the effect of Ras isoforms upon the change of global histone modifications in oncogenic Ras-overexpressed cells, we discovered that oncogenic N-Ras elevates H3K9ac/H3K23ac levels globally in the chromatin context. Importantly, chromatin immunoprecipitation (ChIP) assays revealed that H3K9ac is significantly enriched at the promoter and coding regions of Egr1 and JunB. Collectively, our findings define an undocumented role of N-Ras in modulating of H3 acetylation and in gene regulation.

SUMO modification system facilitates the exchange of histone variant H2A.Z-2 at DNA damage sites

Histone exchange and histone post-translational modifications play important roles in the regulation of DNA metabolism, by re-organizing the chromatin configuration. We previously demonstrated that the histone variant H2A.Z-2 is rapidly exchanged at damaged sites after DNA double strand break induction in human cells. In yeast, the small ubiquitin-like modifier (SUMO) modification of H2A.Z is involved in the DNA damage response. However, whether the SUMO modification regulates the exchange of human H2A.Z-2 at DNA damage sites remains unclear. Here, we show that H2A.Z-2 is SUMOylated in a damage-dependent manner, and the SUMOylation of H2A.Z-2 is suppressed by the depletion of the SUMO E3 ligase, PIAS4. Moreover, PIAS4 depletion represses the incorporation and eviction of H2A.Z-2 at damaged sites. These findings demonstrate that the PIAS4-mediated SUMOylation regulates the exchange of H2A.Z-2 at DNA damage sites.

Specific Acetylation Patterns of H2A.Z Form Transient Interactions with the BPTF Bromodomain

Post-translational lysine acetylation of histone tails affects both chromatin accessibility and recruitment of multifunctional bromodomain-containing proteins for modulating transcription. The bromodomain- and PHD finger-containing transcription factor (BPTF) regulates transcription but has also been implicated in high gene expression levels in a variety of cancers. In this report, the histone variant H2A.Z, which replaces H2A in chromatin, is evaluated for its affinity for BPTF with a specific recognition pattern of acetylated lysine residues of the N-terminal tail region. Although BPTF immunoprecipitates H2A.Z-containing nucleosomes, a direct interaction with its bromodomain has not been reported. Using protein-observed fluorine nuclear magnetic resonance (PrOF NMR) spectroscopy, we identified a diacetylation of H2A.Z on lysine residues 4 and 11, with the highest affinity for BPTF with a Kd of 780 μM. A combination of subsequent 1H NMR Carr-Purcell-Meiboom-Gill experiments and photo-cross-linking further confirmed the specificity of the diacetylation pattern at lysines 4 and 11. Because of an adjacent PHD domain, this transient interaction may contribute to a higher-affinity bivalent interaction. Further evaluation of specificity toward a set of bromodomains, including two BET bromodomains (Brd4 and BrdT) and two Plasmodium falciparum bromodomains, resulted in one midmicromolar affinity binder, PfGCN5 (Kd = 650 μM). With these biochemical experiments, we have identified a direct interaction of histone H2A.Z with bromodomains with a specific acetylation pattern that further supports the role of H2A.Z in epigenetic regulation.