CECR2 is involved in spermatogenesis and forms a complex with SNF2H in the testis

Double whammy: the genetic variants in CECR2 and high Hcy on the development of neural tube defects

Introduction: Neural tube defects (NTDs) are serious congenital malformations. The etiology of NTDs involves both genetic and environmental factors. Loss of CECR2 in mice has been shown to result in NTDs. Our previous study indicated that high homocysteine (HHcy) levels could further reduced the expression level of CECR2. This investigation aims to explore the genetic influence of the chromatin remodeling gene, CECR2, in humans and determine if HHcy can have a synergistic effect on protein expression. Methods: We conducted Next-Generation Sequencing (NGS) of the CECR2 gene in 373 NTD cases and 222 healthy controls, followed by functional assay application to select and evaluate CECR2 missense variants and subsequent Western blotting to identify protein expression levels. Results: From the analysis, we identified nine rare, NTD-specific mutations within the CECR2 gene. Significantly, four missense variants (p.E327V, p.T521S, p.G701R, and p.G868R) were selected via functional screening. The E9.5 mouse ectodermal stem cell line NE-4C, transfected with plasmids expressing p.E327V, p.T521S, p.G868R variants or a recombinant harboring all four (named as 4Mut), exhibited notable reductions in CECR2 protein expression. Furthermore, exposure to homocysteine thiolactone (HTL), an extremely reactive homocysteine metabolite, amplified the reduction in CECR2 expression, accompanied by a significant increase in the apoptotic molecule Caspase3 activity, a potential NTD inducer. Importantly, folic acid (FA) supplementation effectively counteracted the CECR2 expression decline induced by CECR2 mutation and HTL treatment, leading to reduced apoptosis. Discussion: Our observations underscore a synergistic relationship between HHcy and genetic variations in CECR2 concerning NTDs, thereby reinforcing the concept of gene-environment interaction phenomena in NTD etiology.

Genome-Wide Identification and Characterization of the BRD Family in Nile Tilapia (Oreochromis niloticus)

Simple Summary

Nile tilapia is a good model for genome-wide identification and examination of the expression and role of gene families. In this study, we identified 54 bromodomain genes (BRDs) divided into eight subfamilies in Nile tilapia. Phylogenetic analysis revealed a high conservation of the BRDs family in vertebrates, with BRDs expansion due to fish-specific duplications. Most of the BRDs displayed sexually dimorphic expression in the gonads at 90 and 180 dah (days after hatching), including 21 testis-dominated genes (brdt, brd4a and brd2b, etc.), and 9 ovary-dominated genes (brd3b, brd2a and kat2a, etc.). Male fish treated with JQ1 (BET subfamily inhibitor) displayed abnormal spermatogenesis. The numbers of germ cells were reduced and the expression of steroidogenic enzyme genes was downregulated, while the expression of apoptosis-promoting genes was elevated in the testes of treated fish.

Abstract

The bromodomain (BRD) proteins specifically recognize the N-acetyllysine motifs, which is a key event in the reading process of epigenetic marks. BRDs are evolutionarily highly conserved. Over recent years, BRDs attracted great interest because of their important roles in biological processes. However, the genome-wide identification of this family was not carried out in many animal groups, in particular, in teleosts. Moreover, the expression patterns were not reported for any of the members in this family, and the role of the BRD family was not extensively studied in fish reproduction. In this study, we identified 16 to 120 BRD genes in 24 representative species. BRDs expanded significantly in vertebrates. Phylogenetic analysis showed that the BRD family was divided into eight subfamilies (I–VIII). Transcriptome analysis showed that BRDs in Nile tilapia (Oreochromis niloticus) exhibited different expression patterns in different tissues, suggesting that these genes may play different roles in growth and development. Gonadal transcriptome analysis showed that most of the BRDs display sexually dimorphic expression in the gonads at 90 and 180 dah (days after hatching), including 21 testis-dominated genes (brdt, brd4a and brd2b, etc.), and nine ovary-dominated genes (brd3b, brd2a and kat2a, etc.). Consistent with transcriptomic data, the results of qRT-PCR and fluorescence in situ hybridization showed that brdt expression was higher in the testis than in the ovary, suggesting its critical role in the spermatogenesis of the tilapia. Male fish treated with JQ1 (BET subfamily inhibitor) displayed abnormal spermatogenesis. The numbers of germ cells were reduced, and the expression of steroidogenic enzyme genes was downregulated, while the expression of apoptosis-promoting genes was elevated in the testis tissue of treated fish. Our data provide insights into the evolution and expression of BRD genes, which is helpful for understanding their critical roles in sex differentiation and gonadal development in teleosts.

CECR2 drives breast cancer metastasis by promoting NF-κB signaling and macrophage-mediated immune suppression

Metastasis is the major cause of cancer-related deaths due to the lack of effective therapies. Emerging evidence suggests that certain epigenetic and transcriptional regulators drive cancer metastasis and could be targeted for metastasis treatment. To identify epigenetic regulators of breast cancer metastasis, we profiled the transcriptomes of matched pairs of primary breast tumors and metastases from human patients. We found that distant metastases are more immune inert with increased M2 macrophages compared to their matched primary tumors. The acetyl-lysine reader, cat eye syndrome chromosome region candidate 2 (CECR2), was the top up-regulated epigenetic regulator in metastases associated with an increased abundance of M2 macrophages and worse metastasis-free survival. CECR2 was required for breast cancer metastasis in multiple mouse models, with more profound effect in the immunocompetent setting. Mechanistically, the nuclear factor κB (NF-κB) family member v-rel avian reticuloendotheliosis viral oncogene homolog A (RELA) recruits CECR2 to increase chromatin accessibility and activate the expression of their target genes. These target genes include multiple metastasis-promoting genes, such as TNC, MMP2, and VEGFA, and cytokine genes CSF1 and CXCL1, which are critical for immunosuppression at metastatic sites. Consistent with these results, pharmacological inhibition of CECR2 bromodomain impeded NF-κB-mediated immune suppression by macrophages and inhibited breast cancer metastasis. These results reveal that targeting CECR2 may be a strategy to treat metastatic breast cancer.

Chromatin remodeling factor CECR2 forms tissue-specific complexes with CCAR2 and LUZP1

Chromatin remodeling complexes alter chromatin structure to control access to DNA and therefore control cellular processes such as transcription, DNA replication, and DNA repair. CECR2 is a chromatin remodeling factor that plays an important role in neural tube closure and reproduction. Loss-of-function mutations in Cecr2 result primarily in the perinatal lethal neural tube defect exencephaly, with non-penetrant mice that survive to adulthood exhibiting subfertility. CECR2 forms a complex with ISWI proteins SMARCA5 and/or SMARCA1, but further information on the structure and function of the complex is not known. We therefore have identified candidate components of the CECR2-containing remodeling factor (CERF) complex in embryonic stem (ES) cells through mass spectroscopy. Both SMARCA5 and SMARCA1 were confirmed to be present in CERF complexes in ES cells and testis. However, novel proteins CCAR2 and LUZP1 are CERF components in ES cells but not testis. This tissue specificity in mice suggests these complexes may also have functional differences. Furthermore, LUZP1, loss of which is also associated with exencephaly, appears to play a role in stabilizing the CERF complex in ES cells. Keywords: CECR2, LUZP1, CCAR2, Chromatin remodeling factor, Neural tube defects.

A novel tumor suppressor CECR2 down regulation links glutamine metabolism contributes tumor growth in laryngeal squamous cell carcinoma

PURPOSE

Glutamine plays an important role in tumor metabolism and progression. This research aimed to find out how Gln exert their effects on laryngeal squamous cell carcinoma (LSCC).

METHODS

Cell proliferation was measured by CCK8 and EdU assay, mitochondrial bioenergetic activity was measured by mitochondrial stress tests. Gene expression profiling was revealed by RNA sequencing and validated by RT-qPCR. In LSCC patients, protein expression in tumor and adjacent tissues was examined and scored by IHC staining. RNAi was performed by stably expressed shRNA in TU177 cells. In vivo tumor growth analysis was performed using a nude mouse tumorigenicity model.

RESULTS

Gln deprivation suppressed TU177 cell proliferation, which was restored by αKG supplementation. By transcriptomic analysis, we identified CECR2, which encodes a histone acetyl-lysine reader, as the downstream target gene for Gln and αKG. In LSCC patients, the expression of CECR2 in tumors was lower than adjacent tissues. Furthermore, deficiency of CECR2 promoted tumor cell growth both in vitro and in vivo, suggesting it has tumor suppressor effects. Besides, cell proliferation inhibited by Gln withdrawal could be restored by CECR2 depletion, and the proliferation boosted by αKG supplementation could be magnified either, suggested that CECR2 feedback suppressed Gln and αKG's effect on tumor growth. Transcriptomic profiling revealed CECR2 regulated the expression of a series of genes involved in tumor progression.

CONCLUSION

We confirmed the Gln-αKG-CECR2 axis contributes to tumor growth in LSCC. This finding provided a potential therapeutic opportunity for the use of associated metabolites as a potential treatment for LSCC.

Implantation failure and embryo loss contribute to subfertility in female mice mutant for chromatin remodeler Cecr2†

Defects in the maternal reproductive system that result in early pregnancy loss are important causes of human female infertility. A wide variety of biological processes are involved in implantation and establishment of a successful pregnancy. Although chromatin remodelers have been shown to play an important role in many biological processes, our understanding of the role of chromatin remodelers in female reproduction remains limited. Here, we demonstrate that female mice mutant for chromatin remodeler Cecr2 are subfertile, with defects detected at the peri-implantation stage or early pregnancy. Using both a less severe hypomorphic mutation (Cecr2GT) and a more severe presumptive null mutation (Cecr2Del), we demonstrate a clear difference in the severity of the phenotype depending on the mutation. Although neither strain shows detectable defects in folliculogenesis, both Cecr2GT/GT and Cecr2GT/Del dams show defects in pregnancy. Cecr2GT/GT females have a normal number of implantation sites at embryonic day 5.5 (E5.5), but significant embryo loss by E10.5 accompanied by the presence of vaginal blood. Cecr2GT/Del females show a more severe phenotype, with significantly fewer detectable implantation sites than wild type at E5.5. Some Cecr2GT/Del females also show premature loss of decidual tissue after artificial decidualization. Together, these results suggest a role for Cecr2 in the establishment of a successful pregnancy.

The nuclear factor CECR2 promotes somatic cell reprogramming by reorganizing the chromatin structure

Somatic cells can be reprogrammed into pluripotent stem cells with a minimal set of defined factors, Oct3/4, Sox2, Klf4, and c-Myc, also known as OKSM, although this reprogramming is somewhat inefficient. Recent work has identified other nuclear factors, including SALL4, that can synergize with the OSK factors to improve reprogramming dynamics, but the specific role of each of these factors remains poorly understood. In this study, we sought to learn more about the role of SALL4. We observed that SALL4 was the most significant factor in promoting OKS-induced reprogramming. To look for molecules downstream of SALL4, we screened a set of putative targets to determine whether they could promote OKS-induced reprogramming. We identified CECR2, a multidomain nuclear factor and histone acetyl-lysine reader, as a SALL4 effector. Mechanistically, we determined that SALL4 activates Cecr2 expression by directly binding to its promotor region. CECR2 in turn promotes reprogramming by forming a chromatin remodeling complex; this complex contained the SWI/SNF family member SMARCA1 and was dependent on CECR2’s DTT domain. In combination, our findings suggest that CECR2 is a novel reprogramming factor and works through a protein network to overcome epigenetic barriers during reprogramming.

Cytotoxic activity of bromodomain inhibitor NVS-CECR2-1 on human cancer cells

Bromodomain (BRD), a protein module that recognizes acetylated lysine residues on histones and other proteins, has recently emerged as a promising therapeutic target for human diseases such as cancer. While most of the studies have been focused on inhibitors against BRDs of the bromo- and extra-terminal domain (BET) family proteins, non-BET family BRD inhibitors remain largely unexplored. Here, we investigated a potential anticancer activity of the recently developed non-BET family BRD inhibitor NVS-CECR2-1 that targets the cat eye syndrome chromosome region, candidate 2 (CECR2). We show that NVS-CECR2-1 inhibits chromatin binding of CECR2 BRD and displaces CECR2 from chromatin within cells. NVS-CECR2-1 exhibits cytotoxic activity against various human cancer cells, killing SW48 colon cancer cells in particular with a submicromolar half maximum inhibition value mainly by inducing apoptosis. The sensitivity of the cancer cells to NVS-CECR2-1 is reduced by CECR2 depletion, suggesting that NVS-CECR2-1 exerts its activity by targeting CECR2. Interestingly, our data show that NVS-CECR2-1 also kills cancer cells by CECR2-independent mechanism. This study reports for the first time the cancer cell cytotoxic activity for NVS-CECR2-1 and provides a possibility of this BRD inhibitor to be developed as an anticancer therapeutic agent.

Cellular Target Engagement Approaches to Monitor Epigenetic Reader Domain Interactions

Malfunctions in the basic epigenetic mechanisms such as histone modifications, DNA methylation, and chromatin remodeling are implicated in a number of cancers and immunological and neurodegenerative conditions. Within GlaxoSmithKline (GSK) we have utilized a number of variations of the NanoBRET technology for the direct measurement of compound-target engagement within native cellular environments to drive high-throughput, routine structure-activity relationship (SAR) profiling across differing epigenetic targets. NanoBRET is a variation of the bioluminescence resonance energy transfer (BRET) methodology utilizing proteins of interest fused to either NanoLuc, a small, high-emission-intensity luciferase, or HaloTag, a modified dehalogenase enzyme that can be selectively labeled with a fluorophore. The combination of these two technologies has enabled the application of NanoBRET to biological systems such as epigenetic protein-protein interactions, which have previously been challenging. By synergizing target engagement assays with more complex primary cell phenotypic assays, we have been able to demonstrate compound-target selectivity profiles to enhance cellular potency and offset potential liability risks. Additionally, we have shown that in the absence of a robust, cell phenotypic assay, it is possible to utilize NanoBRET target engagement assays to aid chemistry in progressing at a higher scale than would have otherwise been achievable. The NanoBRET target engagement assays utilized have further shown an excellent correlation with more reductionist biochemical and biophysical assay systems, clearly demonstrating the possibility of using such assay systems at scale, in tandem with, or in preference to, lower-throughput cell phenotypic approaches.

Bromodomain biology and drug discovery

The bromodomain (BrD) is a conserved structural module found in chromatin- and transcription-associated proteins that acts as the primary reader for acetylated lysine residues. This basic activity endows BrD proteins with versatile functions in the regulation of protein-protein interactions mediating chromatin-templated gene transcription, DNA recombination, replication and repair. Consequently, BrD proteins are involved in the pathogenesis of numerous human diseases. In this Review, we highlight our current understanding of BrD biology, and discuss the latest development of small-molecule inhibitors targeting BrDs as emerging epigenetic therapies for cancer and inflammatory disorders.

The role of ISWI chromatin remodeling complexes in brain development and neurodevelopmental disorders

The mammalian ISWI (Imitation Switch) genes SMARCA1 and SMARCA5 encode the ATP-dependent chromatin remodeling proteins SNF2L and SNF2H. The ISWI proteins interact with BAZ (bromodomain adjacent to PHD zinc finger) domain containing proteins to generate eight distinct remodeling complexes. ISWI complex-mediated nucleosome positioning within genes and gene regulatory elements is proving important for the transition from a committed progenitor state to a differentiated cell state. Genetic studies have implicated the involvement of many ATP-dependent chromatin remodeling proteins in neurodevelopmental disorders (NDDs), including SMARCA1. Here we review the characterization of mice inactivated for ISWI and their interacting proteins, as it pertains to brain development and disease. A better understanding of chromatin dynamics during neural development is a prerequisite to understanding disease pathologies and the development of therapeutics for these complex disorders.

CHD3 and CHD4 form distinct NuRD complexes with different yet overlapping functionality

CHD3 and CHD4 (Chromodomain Helicase DNA binding protein), two highly similar representatives of the Mi-2 subfamily of SF2 helicases, are coexpressed in many cell lines and tissues and have been reported to act as the motor subunit of the NuRD complex (nucleosome remodeling and deacetylase activities). Besides CHD proteins, NuRD contains several repressors like HDAC1/2, MTA2/3 and MBD2/3, arguing for a role as a transcriptional repressor. However, the subunit composition varies among cell- and tissue types and physiological conditions. In particular, it is unclear if CHD3 and CHD4 coexist in the same NuRD complex or whether they form distinct NuRD complexes with specific functions. We mapped the CHD composition of NuRD complexes in mammalian cells and discovered that they are isoform-specific, containing either the monomeric CHD3 or CHD4 ATPase. Both types of complexes exhibit similar intranuclear mobility, interact with HP1 and rapidly accumulate at UV-induced DNA repair sites. But, CHD3 and CHD4 exhibit distinct nuclear localization patterns in unperturbed cells, revealing a subset of specific target genes. Furthermore, CHD3 and CHD4 differ in their nucleosome remodeling and positioning behaviour in vitro. The proteins form distinct CHD3- and CHD4-NuRD complexes that do not only repress, but can just as well activate gene transcription of overlapping and specific target genes.

The downregulation of putative anticancer target BORIS/CTCFL in an addicted myeloid cancer cell line modulates the expression of multiple protein coding and ncRNA genes

The BORIS/CTCFL gene, is a testis-specific CTCF paralog frequently erroneously activated in cancer, although its exact role in cancer remains unclear. BORIS is both a transcription factor and an architectural chromatin protein. BORIS' normal role is to establish a germline-like gene expression and remodel the epigenetic landscape in testis; it similarly remodels chromatin when activated in human cancer. Critically, at least one cancer cell line, K562, is dependent on BORIS for its self-renewal and survival. Here, we downregulate BORIS expression in the K562 cancer cell line to investigate downstream pathways regulated by BORIS. RNA-seq analyses of both mRNA and small ncRNAs, including miRNA and piRNA, in the knock-down cells revealed a set of differentially expressed genes and pathways, including both testis-specific and general proliferation factors, as well as proteins involved in transcription regulation and cell physiology. The differentially expressed genes included important transcriptional regulators such as SOX6 and LIN28A. Data indicate that both direct binding of BORIS to promoter regions and locus-control activity via long-distance chromatin domain regulation are involved. The sum of findings suggests that BORIS activation in leukemia does not just recapitulate the germline, but creates a unique regulatory network.

Expansion of the ISWI chromatin remodeler family with new active complexes

ISWI chromatin remodelers mobilize nucleosomes to control DNA accessibility. Complexes isolated to date pair one of six regulatory subunits with one of two highly similar ATPases. However, we find that each endogenously expressed ATPase co-purifies with every regulatory subunit, substantially increasing the diversity of ISWI complexes, and we additionally identify BAZ2B as a novel, seventh regulatory subunit. Through reconstitution of catalytically active human ISWI complexes, we demonstrate that the new interactions described here are stable and direct. Finally, we profile the nucleosome remodeling functions of the now expanded family of ISWI chromatin remodelers. By revealing the combinatorial nature of ISWI complexes, we provide a basis for better understanding ISWI function in normal settings and disease.

GNE-886: A Potent and Selective Inhibitor of the Cat Eye Syndrome Chromosome Region Candidate 2 Bromodomain (CECR2)

The biological function of bromodomains, epigenetic readers of acetylated lysine residues, remains largely unknown. Herein we report our efforts to discover a potent and selective inhibitor of the bromodomain of cat eye syndrome chromosome region candidate 2 (CECR2). Screening of our internal medicinal chemistry collection led to the identification of a pyrrolopyridone chemical lead, and subsequent structure-based drug design led to a potent and selective CECR2 bromodomain inhibitor (GNE-886) suitable for use as an in vitro tool compound.

The Mouse INO80 Chromatin-Remodeling Complex Is an Essential Meiotic Factor for Spermatogenesis

The ability to faithfully transmit genetic information across generations via the germ cells is a critical aspect of mammalian reproduction. The process of germ cell development requires a number of large-scale modulations of chromatin within the nucleus. One such occasion arises during meiotic recombination, when hundreds of DNA double-strand breaks are induced and subsequently repaired, enabling the transfer of genetic information between homologous chromosomes. The inability to properly repair DNA damage is known to lead to an arrest in the developing germ cells and sterility within the animal. Chromatin-remodeling activity, and in particular the BRG1 subunit of the SWI/SNF complex, has been shown to be required for successful completion of meiosis. In contrast, remodeling complexes of the ISWI and CHD families are required for postmeiotic processes. Little is known regarding the contribution of the INO80 family of chromatin-remodeling complexes, which is a particularly interesting candidate due to its well described functions during DNA double-strand break repair. Here we show that INO80 is expressed in developing spermatocytes during the early stages of meiotic prophase I. Based on this information, we used a conditional allele to delete the INO80 core ATPase subunit, thereby eliminating INO80 chromatin-remodeling activity in this lineage. The loss of INO80 resulted in an arrest during meiosis associated with a failure to repair DNA damage during meiotic recombination.

ISWI chromatin remodeling complexes in the DNA damage response

Regulation of chromatin structure is an essential component of the DNA damage response (DDR), which effectively preserves the integrity of DNA by a network of multiple DNA repair and associated signaling pathways. Within the DDR, chromatin is modified and remodeled to facilitate efficient DNA access, to control the activity of repair proteins and to mediate signaling. The mammalian ISWI family has recently emerged as one of the major ATP-dependent chromatin remodeling complex families that function in the DDR, as it is implicated in at least 3 major DNA repair pathways: homologous recombination, non-homologous end-joining and nucleotide excision repair. In this review, we discuss the various manners through which different ISWI complexes regulate DNA repair and how they are targeted to chromatin containing damaged DNA.

Mouse BAZ1A (ACF1) is dispensable for double-strand break repair but is essential for averting improper gene expression during spermatogenesis

ATP-dependent chromatin remodelers control DNA access for transcription, recombination, and other processes. Acf1 (also known as BAZ1A in mammals) is a defining subunit of the conserved ISWI-family chromatin remodelers ACF and CHRAC, first purified over 15 years ago from Drosophila melanogaster embryos. Much is known about biochemical properties of ACF and CHRAC, which move nucleosomes in vitro and in vivo to establish ordered chromatin arrays. Genetic studies in yeast, flies and cultured human cells clearly implicate these complexes in transcriptional repression via control of chromatin structures. RNAi experiments in transformed mammalian cells in culture also implicate ACF and CHRAC in DNA damage checkpoints and double-strand break repair. However, their essential in vivo roles in mammals are unknown. Here, we show that Baz1a-knockout mice are viable and able to repair developmentally programmed DNA double-strand breaks in the immune system and germ line, I-SceI endonuclease-induced breaks in primary fibroblasts via homologous recombination, and DNA damage from mitomycin C exposure in vivo. However, Baz1a deficiency causes male-specific sterility in accord with its high expression in male germ cells, where it displays dynamic, stage-specific patterns of chromosomal localization. Sterility is caused by pronounced defects in sperm development, most likely a consequence of massively perturbed gene expression in spermatocytes and round spermatids in the absence of BAZ1A: the normal spermiogenic transcription program is largely intact but more than 900 other genes are mis-regulated, primarily reflecting inappropriate up-regulation. We propose that large-scale changes in chromatin composition that occur during spermatogenesis create a window of vulnerability to promiscuous transcription changes, with an essential function of ACF and/or CHRAC chromatin remodeling activities being to safeguard against these alterations.

The eukaryotic genome is packaged into a periodic nucleoprotein complex known as chromatin. Wrapping of DNA around nucleosomes, the basic repeat unit of chromatin, enables packing of long stretches of DNA into a compact nucleus but also impedes access by protein factors involved in essential cellular processes such as transcription, replication, recombination and repair. Chromatin remodeling factors are multi-protein complexes that utilize the energy released during ATP-hydrolysis to assemble, reposition, restructure and disassemble nucleosomes. These complexes disrupt histone-DNA contacts to ‘remodel’ the chromatin and grant access to the genome. Alternatively, access can also be denied to repress transcription, for example. Spermatogenesis, the developmental program that produces sperm, comprises a dramatic chromatin makeover and the induction of a transcriptional program that engages nearly one-third of the genome. Here we provide evidence suggesting that these large-scale alterations leave the genomic material vulnerable to spurious transcriptional changes which are normally repressed by ACF1 (BAZ1A in mammals), the defining member of the well-studied ACF/CHRAC chromatin remodeling complex. These findings indicate that Baz1a plays a previously unrealized role in male fertility and may represent a novel target for male contraceptive development.

Genome-wide screen of human bromodomain-containing proteins identifies Cecr2 as a novel DNA damage response protein

The formation of γ-H2AX foci after DNA double strand breaks (DSBs) is crucial for the cellular response to this lethal DNA damage. We previously have shown that BRG1, a chromatin remodeling enzyme, facilitates DSB repair by stimulating γ-H2AX formation, and this function of BRG1 requires the binding of BRGI to acetylated histone H3 on γ-H2AX-containing nucleosomes using its bromodomain (BRD), a protein module that specifically recognizes acetyl-Lys moieties. We also have shown that the BRD of BRG1, when ectopically expressed in cells, functions as a dominant negative inhibitor of the BRG1 activity to stimulate γ-H2AX and DSB repair. Here, we found that BRDs from a select group of proteins have no such activity, suggesting that the γ-H2AX inhibition activity of BRG1 BRD is specific. This finding led us to search for more BRDs that exhibit γ-H2AX inhibition activity in the hope of finding additional BRD-containing proteins involved in DNA damage responses. We screened a total of 52 individual BRDs present in 38 human BRD-containing proteins, comprising 93% of all human BRDs. We identified the BRD of cat eye syndrome chromosome region candidate 2 (Cecr2), which recently was shown to form a novel chromatin remodeling complex with unknown cellular functions, as having a strong γ-H2AX inhibition activity. This activity of Cecr2 BRD is specific because it depends on the chromatin binding affinity of Cecr2 BRD. Small interfering RNA knockdown experiments showed that Cecr2 is important for γ-H2AX formation and DSB repair. Therefore, our genomewide screen identifies Cecr2 as a novel DNA damage response protein.