The cancer-testis antigen BORIS phenocopies the tumor suppressor CTCF in normal and neoplastic cells

Cancer stem cells: The important role of CD markers, Signaling pathways, and MicroRNAs

For the first time, a subset of small cancer cells identified in acute myeloid leukemia has been termed Cancer Stem Cells (CSCs). These cells are notorious for their robust proliferation, self-renewal abilities, significant tumor-forming potential, spread, and resistance to treatments. CSCs are a global concern, as it found in numerous types of cancer, posing a real-world challenge today. Our review encompasses research on key CSC markers, signaling pathways, and MicroRNA in three types of cancer: breast, colon, and liver. These factors play a critical role in either promoting or inhibiting cancer cell growth. The reviewed studies have shown that as cells undergo malignant transformation, there can be an increase or decrease in the expression of different Cluster of Differentiation (CD) markers on their surface. Furthermore, alterations in essential signaling pathways, such as Wnt and Notch1, may impact CSC proliferation, survival, and movement, while also providing potential targets for cancer therapies. Additionally, some research has focused on MicroRNAs due to their dual role as potential therapeutic biomarkers and their ability to enhance CSCs' response to anti-cancer drugs. MicroRNAs also regulate a wide array of cellular processes, including the self-renewal and pluripotency of CSCs, and influence gene transcription. Thus, these studies indicate that MicroRNAs play a significant role in the malignancy of various tumors. Although the gathered information suggests that specific CSC markers, signaling pathways, and MicroRNAs are influential in determining the destiny of cancer cells and could be advantageous for therapeutic strategies, their precise roles and impacts remain incompletely defined, necessitating further investigation.

BORIS/CTCFL epigenetically reprograms clustered CTCF binding sites into alternative transcriptional start sites

BACKGROUND

Pervasive usage of alternative promoters leads to the deregulation of gene expression in carcinogenesis and may drive the emergence of new genes in spermatogenesis. However, little is known regarding the mechanisms underpinning the activation of alternative promoters.

RESULTS

Here we describe how alternative cancer-testis-specific transcription is activated. We show that intergenic and intronic CTCF binding sites, which are transcriptionally inert in normal somatic cells, could be epigenetically reprogrammed into active de novo promoters in germ and cancer cells. BORIS/CTCFL, the testis-specific paralog of the ubiquitously expressed CTCF, triggers the epigenetic reprogramming of CTCF sites into units of active transcription. BORIS binding initiates the recruitment of the chromatin remodeling factor, SRCAP, followed by the replacement of H2A histone with H2A.Z, resulting in a more relaxed chromatin state in the nucleosomes flanking the CTCF binding sites. The relaxation of chromatin around CTCF binding sites facilitates the recruitment of multiple additional transcription factors, thereby activating transcription from a given binding site. We demonstrate that the epigenetically reprogrammed CTCF binding sites can drive the expression of cancer-testis genes, long noncoding RNAs, retro-pseudogenes, and dormant transposable elements.

CONCLUSIONS

Thus, BORIS functions as a transcription factor that epigenetically reprograms clustered CTCF binding sites into transcriptional start sites, promoting transcription from alternative promoters in both germ cells and cancer cells.

Association of mutation and expression of the brother of the regulator of imprinted sites (BORIS) gene with breast cancer progression

INTRODUCTION

The BORIS, 11 zinc-finger transcription factors, is a member of the cancer-testis antigen (CTA) family. It is mapped to chromosome number 20q13.2 and this region is genetically linked to the early onset of breast cancer. The current study analyzed the correlation between BORIS mutations and the expression of the protein in breast cancer cases.

MATERIALS AND METHODS

A population-based study including a total of 155 breast cancer tissue samples and an equal number of normal adjacent tissues from Indian female breast cancer patients was carried out. Mutations of the BORIS gene were detected by polymerase chain reaction-single standard confirmation polymorphisms (PCR-SSCP) and automated DNA sequencing and by immunohistochemistry for BORIS protein expression were performed. The observed findings were correlated with several clinicopathological parameters to find out the clinical relevance of associations.

RESULTS

Of all the cases 16.12% (25/155) showed mutations in the BORIS gene. The observed mutations present on codon 329 are missense, leading to Val> Ile (G>A) change on exon 5 of the BORIS gene. A significant association was observed between mutations of the BORIS gene and some clinicopathological features like nodal status (p = 0.013), estrogen receptor (ER) expression (p = 0.008), progesterone receptor (PR) expression (p = 0.039), clinical stage (p = 0.010) and menopausal status (p = 0.023). The protein expression analysis showed 20.64% (32/155) samples showing low or no expression (+), 34.19% (53/155) with moderate expression (++), and 45.17% (70/155) showing high expression (+++) of BORIS protein. A significant association was observed between the expression of BORIS protein and clinicopathological features like clinical stage (p = 0.013), nodal status (p = 0.049), ER expression (p = 0.039), and PR expression (p = 0.027). When mutation and protein expression were correlated in combination with clinicopathological parameters a significant association was observed in the category of high (+++) level of BORIS protein expression (p = 0.017).

CONCLUSION

The BORIS mutations and high protein expression occur frequently in carcinoma of the breast suggesting their association with the onset and progression of breast carcinoma. Further, the BORIS has the potential to be used as a biomarker.

CTCF: a misguided jack-of-all-trades in cancer cells

The emergence and progression of cancers is accompanied by a dysregulation of transcriptional programs. The three-dimensional (3D) organization of the human genome has emerged as an important multi-level mediator of gene transcription and regulation. In cancer cells, this organization can be restructured, providing a framework for the deregulation of gene activity. The CTCF protein, initially identified as the product from a tumor suppressor gene, is a jack-of-all-trades for the formation of 3D genome organization in normal cells. Here, we summarize how CTCF is involved in the multi-level organization of the human genome and we discuss emerging insights into how perturbed CTCF function and DNA binding causes the activation of oncogenes in cancer cells, mostly through a process of enhancer hijacking. Moreover, we highlight non-canonical functions of CTCF that can be relevant for the emergence of cancers as well. Finally, we provide guidelines for the computational identification of perturbed CTCF binding and reorganized 3D genome structure in cancer cells.

Key roles of CCCTC-binding factor in cancer evolution and development

The processes of cancer and embryonic development have a partially overlapping effect. Several transcription factor families, which are highly conserved in the evolutionary history of biology, play a key role in the development of cancer and are often responsible for the pivotal developmental processes such as cell survival, expansion, senescence, and differentiation. As an evolutionary conserved and ubiquitously expression protein, CCCTC-binding factor (CTCF) has diverse regulatory functions, including gene regulation, imprinting, insulation, X chromosome inactivation, and the establishment of three-dimensional (3D) chromatin structure during human embryogenesis. In various cancers, CTCF is considered as a tumor suppressor gene and plays homeostatic roles in maintaining genome function and integrity. However, the mechanisms of CTCF in tumor development have not been fully elucidated. Here, this review will focus on the key roles of CTCF in cancer evolution and development (Cancer Evo-Dev) and embryogenesis.

CTCF as a regulator of alternative splicing: new tricks for an old player

Three decades of research have established the CCCTC-binding factor (CTCF) as a ubiquitously expressed chromatin organizing factor and master regulator of gene expression. A new role for CTCF as a regulator of alternative splicing (AS) has now emerged. CTCF has been directly and indirectly linked to the modulation of AS at the individual transcript and at the transcriptome-wide level. The emerging role of CTCF-mediated regulation of AS involves diverse mechanisms; including transcriptional elongation, DNA methylation, chromatin architecture, histone modifications, and regulation of splicing factor expression and assembly. CTCF thereby appears to not only co-ordinate gene expression regulation but contributes to the modulation of transcriptomic complexity. In this review, we highlight previous discoveries regarding the role of CTCF in AS. In addition, we summarize detailed mechanisms by which CTCF mediates AS regulation. We propose opportunities for further research designed to examine the possible fate of CTCF-mediated alternatively spliced genes and associated biological consequences. CTCF has been widely acknowledged as the 'master weaver of the genome'. Given its multiple connections, further characterization of CTCF's emerging role in splicing regulation might extend its functional repertoire towards a 'conductor of the splicing orchestra'.

The Mutational Landscape of Myeloid Leukaemia in Down Syndrome

Children with Down syndrome (DS) are particularly prone to haematopoietic disorders. Paediatric myeloid malignancies in DS occur at an unusually high frequency and generally follow a well-defined stepwise clinical evolution. First, the acquisition of mutations in the GATA1 transcription factor gives rise to a transient myeloproliferative disorder (TMD) in DS newborns. While this condition spontaneously resolves in most cases, some clones can acquire additional mutations, which trigger myeloid leukaemia of Down syndrome (ML-DS). These secondary mutations are predominantly found in chromatin and epigenetic regulators-such as cohesin, CTCF or EZH2-and in signalling mediators of the JAK/STAT and RAS pathways. Most of them are also found in non-DS myeloid malignancies, albeit at extremely different frequencies. Intriguingly, mutations in proteins involved in the three-dimensional organization of the genome are found in nearly 50% of cases. How the resulting mutant proteins cooperate with trisomy 21 and mutant GATA1 to promote ML-DS is not fully understood. In this review, we summarize and discuss current knowledge about the sequential acquisition of genomic alterations in ML-DS.

Structure-function relationships explain CTCF zinc finger mutation phenotypes in cancer

CCCTC-binding factor (CTCF) plays fundamental roles in transcriptional regulation and chromatin architecture maintenance. CTCF is also a tumour suppressor frequently mutated in cancer, however, the structural and functional impact of mutations have not been examined. We performed molecular and structural characterisation of five cancer-specific CTCF missense zinc finger (ZF) mutations occurring within key intra- and inter-ZF residues. Functional characterisation of CTCF ZF mutations revealed a complete (L309P, R339W, R377H) or intermediate (R339Q) abrogation as well as an enhancement (G420D) of the anti-proliferative effects of CTCF. DNA binding at select sites was disrupted and transcriptional regulatory activities abrogated. Molecular docking and molecular dynamics confirmed that mutations in residues specifically contacting DNA bases or backbone exhibited loss of DNA binding. However, R339Q and G420D were stabilised by the formation of new primary DNA bonds, contributing to gain-of-function. Our data confirm that a spectrum of loss-, change- and gain-of-function impacts on CTCF zinc fingers are observed in cell growth regulation and gene regulatory activities. Hence, diverse cellular phenotypes of mutant CTCF are clearly explained by examining structure-function relationships.

Ctcf haploinsufficiency mediates intron retention in a tissue-specific manner

CTCF is a master regulator of gene transcription and chromatin organisation with occupancy at thousands of DNA target sites genome-wide. While CTCF is essential for cell survival, CTCF haploinsufficiency is associated with tumour development and hypermethylation. Increasing evidence demonstrates CTCF as a key player in several mechanisms regulating alternative splicing (AS), however, the genome-wide impact of Ctcf dosage on AS has not been investigated.

We examined the effect of Ctcf haploinsufficiency on gene expression and AS in five tissues from Ctcf hemizygous (Ctcf^+/-) mice. Reduced Ctcf levels caused distinct tissue-specific differences in gene expression and AS in all tissues. An increase in intron retention (IR) was observed in Ctcf^+/- liver and kidney. In liver, this specifically impacted genes associated with cytoskeletal organisation, splicing and metabolism. Strikingly, most differentially retained introns were short, with a high GC content and enriched in Ctcf binding sites in their proximal upstream genomic region. This study provides new insights into the effects of CTCF haploinsufficiency on organ transcriptomes and the role of CTCF in AS regulation.

Association of mutation and low expression of the CTCF gene with breast cancer progression

Background

CTCF encodes 11-zinc finger protein which is implicated in multiple tumors including the carcinoma of the breast. The Present study investigates the association of CTCF mutations and their expression in breast cancer cases.

Methods

A total of 155 breast cancer and an equal number of adjacent normal tissue samples from 155 breast cancer patients were examined for CTCF mutation(s) by PCR-SSCP and automated DNA sequencing. Immunohistochemistry (IHC) method was used to analyze CTCF expression. Molecular findings were statistically analyzed with various clinicopathological features to identify associations of clinical relevance.

Results

Of the total, 16.1% (25/155) cases exhibited mutation in the CTCF gene. Missense mutations Gln > His (G > T) in exon 1 and silent mutations Ser > Ser (C > T) in exon 4 of CTCF gene were analyzed. A significant association was observed between CTCF mutations and some clinicopathological parameters namely menopausal status (p = 0.02) tumor stage (p = 0.03) nodal status (p = 0.03) and ER expression (p = 0.04). Protein expression analysis showed 42.58% samples having low or no expression (+), 38.0% with moderate (++) expression and 19.35% having high (+++) expression for CTCF. A significant association was found between CTCF protein expression and clinicopathological parameters include histological grade (p = 0.04), tumor stage (p = 0.04), nodal status (p = 0.03) and ER status (p = 0.04).

Conclusions

The data suggest that CTCF mutations leading to its inactivation significantly contribute to the progression of breast cancer.

BORIS/CTCFL promotes a switch from a proliferative towards an invasive phenotype in melanoma cells

Melanoma is among the most aggressive cancers due to its tendency to metastasize early. Phenotype switching between a proliferative and an invasive state has been suggested as a critical process for metastasis, though the mechanisms that regulate state transitions are complex and remain poorly understood. Brother of Regulator of Imprinted Sites (BORIS), also known as CCCTC binding factor-Like (CTCFL), is a transcriptional modulator that becomes aberrantly expressed in melanoma. Yet, the role of BORIS in melanoma remains elusive. Here, we show that BORIS is involved in melanoma phenotype switching. Genetic modification of BORIS expression in melanoma cells combined with whole-transcriptome analysis indicated that BORIS expression contributes to an invasion-associated transcriptome. In line with these findings, inducible BORIS overexpression in melanoma cells reduced proliferation and increased migration and invasion, demonstrating that the transcriptional switch is accompanied by a phenotypic switch. Mechanistically, we reveal that BORIS binds near the promoter of transforming growth factor-beta 1 (TFGB1), a well-recognized factor involved in the transition towards an invasive state, which coincided with increased expression of TGFB1. Overall, our study indicates a pro-invasive role for BORIS in melanoma via transcriptional reprogramming.

Choice of binding sites for CTCFL compared to CTCF is driven by chromatin and by sequence preference

The two paralogous zinc finger factors CTCF and CTCFL differ in expression such that CTCF is ubiquitously expressed, whereas CTCFL is found during spermatogenesis and in some cancer types in addition to other cell types. Both factors share the highly conserved DNA binding domain and are bound to DNA sequences with an identical consensus. In contrast, both factors differ substantially in the number of bound sites in the genome. Here, we addressed the molecular features for this binding specificity. In contrast to CTCF we found CTCFL highly enriched at ‘open’ chromatin marked by H3K27 acetylation, H3K4 di- and trimethylation, H3K79 dimethylation and H3K9 acetylation plus the histone variant H2A.Z. CTCFL is enriched at transcriptional start sites and regions bound by transcription factors. Consequently, genes deregulated by CTCFL are highly cell specific. In addition to a chromatin-driven choice of binding sites, we determined nucleotide positions critical for DNA binding by CTCFL, but not by CTCF.

CTCF Expression is Essential for Somatic Cell Viability and Protection Against Cancer

CCCTC-binding factor (CTCF) is a conserved transcription factor that performs diverse roles in transcriptional regulation and chromatin architecture. Cancer genome sequencing reveals diverse acquired mutations in CTCF, which we have shown functions as a tumour suppressor gene. While CTCF is essential for embryonic development, little is known of its absolute requirement in somatic cells and the consequences of CTCF haploinsufficiency. We examined the consequences of CTCF depletion in immortalised human and mouse cells using shRNA knockdown and CRISPR/Cas9 genome editing as well as examined the growth and development of heterozygous Ctcf (Ctcf^+/-) mice. We also analysed the impact of CTCF haploinsufficiency by examining gene expression changes in CTCF-altered endometrial carcinoma. Knockdown and CRISPR/Cas9-mediated editing of CTCF reduced the cellular growth and colony-forming ability of K562 cells. CTCF knockdown also induced cell cycle arrest and a pro-survival response to apoptotic insult. However, in p53 shRNA-immortalised Ctcf^+/- MEFs we observed the opposite: increased cellular proliferation, colony formation, cell cycle progression, and decreased survival after apoptotic insult compared to wild-type MEFs. CRISPR/Cas9-mediated targeting in Ctcf^+/- MEFs revealed a predominance of in-frame microdeletions in Ctcf in surviving clones, however protein expression could not be ablated. Examination of CTCF mutations in endometrial cancers showed locus-specific alterations in gene expression due to CTCF haploinsufficiency, in concert with downregulation of tumour suppressor genes and upregulation of estrogen-responsive genes. Depletion of CTCF expression imparts a dramatic negative effect on normal cell function. However, CTCF haploinsufficiency can have growth-promoting effects consistent with known cancer hallmarks in the presence of additional genetic hits. Our results confirm the absolute requirement for CTCF expression in somatic cells and provide definitive evidence of CTCF's role as a haploinsufficient tumour suppressor gene. CTCF genetic alterations in endometrial cancer indicate that gene dysregulation is a likely consequence of CTCF loss, contributing to, but not solely driving cancer growth.

BORIS: a key regulator of cancer stemness

BORIS (CTCFL) is a DNA binding protein which is involved in tumorigenesis. Although, there are different opinions on the level of gene expression and function of BORIS in normal and cancer tissues, the results of many studies have classified BORIS as a protein belonging to cancer/testis (CT) genes, which are identified as a group of genes that are expressed normally in testis, and abnormally in various types of cancers. In testis, BORIS induces the expression of some male germ cell/testis specific genes, and plays crucial roles during spermatogenesis and production of sperm. In tumorigenesis, the role of BORIS in the expression induction of some CT genes and oncogenes, as well as increasing proliferation/viability of cancer cells has been demonstrated in many researches. In addition to cancer cells, some believe that BORIS is also expressed in normal conditions and plays a universal function in cell division and regulation of genes. The following is a comprehensive review on contradictory views on the expression pattern and biological function of BORIS in normal, as well as cancer cells/tissues, and presents some evidence that support the expression of BORIS in cancer stem cells (CSCs) and advanced stage/poorer differentiation grade of cancers. Boris is involved in the regulation of CSC cellular and molecular features such as self-renewal, chemo-resistance, tumorigenicity, sphere-forming ability, and migration capacity. Finally, the role of BORIS in regulating two important signaling pathways including Wnt/β-catenin and Notch in CSCs, and its ability in recruiting transcription factors or chromatin-remodeling proteins to induce tumorigenesis is discussed.

Direct and rapid identification of T315I-Mutated BCR-ABL expressing leukemic cells using infrared microspectroscopy

Despite the major success obtained by the use of tyrosine kinase inhibitors (TKI) in chronic myeloid leukemia (CML), resistances to therapies occur due to mutations in the ABL-kinase domain of the BCR-ABL oncogene. Amongst these mutations, the "gatekeeper" T315I is a major concern as it renders leukemic cells resistant to all licenced TKI except Ponatinib. We report here that Fourier transform infrared (FTIR) microspectroscopy is a powerful methodology allowing rapid and direct identification of a spectral signature in single cells expressing T315I-mutated BCR-ABL. The specificity of this spectral signature is confirmed using a Dox-inducible T315I-mutated BCR-ABL-expressing human UT-7 cells as well as in murine embryonic stem cells. Transcriptome analysis of UT-7 cells expressing BCR-ABL as compared to BCR-ABL T315I clearly identified a molecular signature which could be at the origin of the generation of metabolic changes giving rise to the spectral signature. Thus, these results suggest that this new methodology can be applied to the identification of leukemic cells harbouring the T315I mutation at the single cell level and could represent a novel early detection tool of mutant clones. It could also be applied to drug screening strategies to target T315I-mutated leukemic cells.

Cancer testis antigens as immunogenic and oncogenic targets in breast cancer

Breast cancer cells frequently express tumor-associated antigens that can elicit immune responses to eradicate cancer. Cancer-testis antigens (CTAs) are a group of tumor-associated antigens that might serve as ideal targets for cancer immunotherapy because of their cancer-restricted expression and robust immunogenicity. Previous clinical studies reported that CTAs are associated with negative hormonal status, aggressive tumor behavior and poor survival. Furthermore, experimental studies have shown the ability of CTAs to induce both cellular and humoral immune responses. They also demonstrated the implication of CTAs in promoting cancer cell growth, inhibiting apoptosis and inducing cancer cell invasion and migration. In the current review, we attempt to address the immunogenic and oncogenic potential of CTAs and their current utilization in therapeutic interventions for breast cancer.

Functional roles of CTCF in breast cancer

CTCF, Zinc-finger protein, has been identified as a multifunctional transcription factor that regulates gene expression through various mechanisms, including recruitment of other co-activators and binding to promoter regions of target genes. Furthermore, it has been proposed to be an insulator protein that contributes to the establishment of functional three-dimensional chromatin structures. It can disrupt transcription through blocking the connection between an enhancer and a promoter. Previous studies revealed that the onset of various diseases, including breast cancer, could be attributed to the aberrant expression of CTCF itself or one or more of its target genes. In this review, we will describe molecular dysfunction involving CTCF that induces tumorigenesis and summarize the functional roles of CTCF in breast cancer.

MAGEA1 inhibits the expression of BORIS via increased promoter methylation

Melanoma-associated antigen A1 (MAGEA1) and BORIS are members of the cancer testis antigens (CTA) family. Their functions and expression regulation mechanisms are not fully understood. In this study, we revealed new functions and regulatory mechanisms of MAGEA1 and BORIS in breast cancer cells, which were investigated in parental and genetically manipulated breast cancer cells via gene overexpression or siRNA interference-mediated down-regulation. We identified the interaction between MAGEA1 and CTCF, which was required for the binding of MAGEA1 to BORIS promoter and critical for the recruitment of DNMT3a. A protein complex containing MAGEA1, CTCF and DNMT3a will be formed before or after the conjunction with BORIS promoter. The binding of this complex to the BORIS promoter accounts for the hypermethylation and repression of BORIS expression, which results in cell death in the breast cancer cell lines tested. Multiple approaches are employed, including co-IP, GST-pull down, co-localization, cell death analyses using the Annexin V-FITC/PI double staining and caspase3 activation assays, ChIP and bisulfite sequencing PCR assays for methylation. These results have implications in the development of strategies in CTA-based immune therapeutics.

ASCT2 regulates glutamine uptake and cell growth in endometrial carcinoma

Glutamine commonly becomes a conditionally essential amino acid in cancer. Glutamine is supplied to the cell by transporters such as ASCT2 (SLC1A5), which is frequently upregulated in multiple cancers. Here we investigated the expression of ASCT2 in endometrial carcinoma, and evaluated the contribution of ASCT2 to glutamine uptake and endometrial cancer cell growth. Analysis of human gene expression data showed that ASCT2 was significantly upregulated in both endometrioid and serous subtypes of endometrial carcinoma, compared to normal, age-matched endometrium. Furthermore, immunohistochemical staining of primary human endometrioid adenocarcinomas showed that tumours stain positive for ASCT2 in either a uniform or mosaic expression pattern, while normal adjacent glands appeared predominantly negative for ASCT2 staining. Chemical inhibition of glutamine transport by benzylserine or GPNA led to a significant decrease in endometrial cancer cell growth and spheroid cross-sectional area. ASCT2 knockdown recapitulated the decrease of cell growth and spheroid cross-sectional area in HEC1A cells, suggesting a reliance on ASCT2-mediated glutamine uptake. ASCT2 knockdown in Ishikawa cells led to lower glutamine uptake and cell growth, but did not affect spheroid area. Ishikawa cells express higher levels of the glutamine transporter SNAT1 compared to HEC1A cells, suggesting these cells may rely on both ASCT2 and SNAT1 for glutamine uptake. Since SNAT1 is also significantly upregulated in the endometrioid and serous subtypes, these data indicate that ASCT2 and SNAT1 could be used as markers of malignancy, and/or potential therapeutic targets in patients with endometrial carcinoma.

ASCT2 regulates glutamine uptake and cell growth in endometrial carcinoma

Glutamine commonly becomes a conditionally essential amino acid in cancer. Glutamine is supplied to the cell by transporters such as ASCT2 (SLC1A5), which is frequently upregulated in multiple cancers. Here we investigated the expression of ASCT2 in endometrial carcinoma, and evaluated the contribution of ASCT2 to glutamine uptake and endometrial cancer cell growth. Analysis of human gene expression data showed that ASCT2 was significantly upregulated in both endometrioid and serous subtypes of endometrial carcinoma, compared to normal, age-matched endometrium. Furthermore, immunohistochemical staining of primary human endometrioid adenocarcinomas showed that tumours stain positive for ASCT2 in either a uniform or mosaic expression pattern, while normal adjacent glands appeared predominantly negative for ASCT2 staining. Chemical inhibition of glutamine transport by benzylserine or GPNA led to a significant decrease in endometrial cancer cell growth and spheroid cross-sectional area. ASCT2 knockdown recapitulated the decrease of cell growth and spheroid cross-sectional area in HEC1A cells, suggesting a reliance on ASCT2-mediated glutamine uptake. ASCT2 knockdown in Ishikawa cells led to lower glutamine uptake and cell growth, but did not affect spheroid area. Ishikawa cells express higher levels of the glutamine transporter SNAT1 compared to HEC1A cells, suggesting these cells may rely on both ASCT2 and SNAT1 for glutamine uptake. Since SNAT1 is also significantly upregulated in the endometrioid and serous subtypes, these data indicate that ASCT2 and SNAT1 could be used as markers of malignancy, and/or potential therapeutic targets in patients with endometrial carcinoma.

Depletion of CTCF in Breast Cancer Cells Selectively Induces Cancer Cell Death via p53

CCCTC-binding factor (CTCF), a ubiquitous 11-zinc finger multifunctional protein, has distinct molecular functions, such as transcriptional activation, repression, and chromatin barrier activity, in a locus-specific manner. Elevated CTCF levels in breast cancer cells are known to contribute to tumorigenesis; however, the underlying mechanism remains elusive. We investigated the effect of CTCF expression on breast cancer cell survival and elucidated its mechanism. CTCF depletion in MCF-7 cells led to a decreased cell growth and proliferation, surpassing the growth of normal cells under co-culture system of MCF-7-GFP and MCF10A. Here we propose that the phenotypes observed in CTCF-depleted MCF-7 cancer cells, such as reduced cell proliferation, increased apoptosis, and cell cycle arrest, are closely linked with the activation of p53. The consensus CTCF-binding site, located approximately 800 bp upstream of the first exon of TP53, was marked by H3K27me3, but not by the active mark H3K4me3, although CTCF is expressed. Knockdown of CTCF conversely led to the recruitment of H3K4me3 instead of H3K27me3, accompanying with the higher enrichment of PolII in the proximal promoter region of TP53. With the activation of p53, increased p21 and Bax expressions were observed in CTCF knockdown MCF-7 cells. Elucidating functional roles of CTCF and regulation mechanisms may help to guide CTCF and/or its related molecules as a therapeutic target to prevent cancer cell growth.

CCCTC-binding factor inhibits breast cancer cell proliferation and metastasis via inactivation of the nuclear factor-kappaB pathway

CCCTC-binding factor (CTCF) is an important epigenetic regulator implicated in multiple cellular processes, including growth, proliferation, differentiation, and apoptosis. Although CTCF deletion or mutation has been associated with human breast cancer, the role of CTCF in breast cancer is questionable. We investigated the biological functions of CTCF in breast cancer and the underlying mechanism. The results showed that CTCF expression in human breast cancer cells and tissues was significantly lower than that in normal breast cells and tissues. In addition, CTCF expression correlated significantly with cancer stage (P = 0.043) and pathological differentiation (P = 0.029). Furthermore, CTCF overexpression resulted in the inhibition of proliferation, migration, and invasion, while CTCF knockdown induced these processes in breast cancer cells. Transcriptome analysis and further experimental confirmation in MDA-MD-231 cells revealed that forced overexpression of CTCF might attenuate the DNA-binding ability of nuclear factor-kappaB (NF-κB) p65 subunit and inhibit activation of NF-κB and its target pro-oncogenes (tumor necrosis factor alpha-induced protein 3 [TNFAIP3]) and genes for growth-related proteins (early growth response protein 1 [EGR1] and growth arrest and DNA-damage-inducible alpha [GADD45a]). The present study provides a new insight into the tumor suppressor roles of CTCF in breast cancer development and suggests that the CTCF/NF-κB pathway is a potential target for breast cancer therapy.

The antiproliferative ELF2 isoform, ELF2B, induces apoptosis in vitro and perturbs early lymphocytic development in vivo

Background

ELF2 (E74-like factor 2) also known as NERF (new Ets-related factor), a member of the Ets family of transcription factors, regulates genes important in B and T cell development, cell cycle progression, and angiogenesis. Conserved ELF2 isoforms, ELF2A, and ELF2B, arising from alternative promoter usage can exert opposing effects on target gene expression. ELF2A activates, whilst ELF2B represses, gene expression, and the balance of expression between these isoforms may be important in maintaining normal cellular function.

Methods

We compared the function of ELF2 isoforms ELF2A and ELF2B with other ELF subfamily proteins ELF1 and ELF4 in primary and cancer cell lines using proliferation, colony-forming, cell cycle, and apoptosis assays. We further examined the role of ELF2 isoforms in haemopoietic development using a Rag1^-/-murine bone marrow reconstitution model.

Results

ELF2B overexpression significantly reduced cell proliferation and clonogenic capacity, minimally disrupted cell cycle kinetics, and induced apoptosis. In contrast, ELF2A overexpression only marginally reduced clonogenic capacity with little effect on proliferation, cell cycle progression, or apoptosis. Deletion of the N-terminal 19 amino acids unique to ELF2B abrogated the antiproliferative and proapoptotic functions of ELF2B thereby confirming its crucial role. Mice expressing Elf2a or Elf2b in haemopoietic cells variously displayed perturbations in the pre-B cell stage and multiple stages of T cell development. Mature B cells, T cells, and myeloid cells in steady state were unaffected, suggesting that the main role of ELF2 is restricted to the early development of B and T cells and that compensatory mechanisms exist. No differences in B and T cell development were observed between ELF2 isoforms.

Conclusions

We conclude that ELF2 isoforms are important regulators of cellular proliferation, cell cycle progression, and apoptosis. In respect to this, ELF2B acts in a dominant negative fashion compared to ELF2A and as a putative tumour suppressor gene. Given that these cellular processes are critical during haemopoiesis, we propose that the regulatory interplay between ELF2 isoforms contributes substantially to early B and T cell development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0446-7) contains supplementary material, which is available to authorized users.

CTCF genetic alterations in endometrial carcinoma are pro-tumorigenic

CTCF is a haploinsufficient tumour suppressor gene with diverse normal functions in genome structure and gene regulation. However the mechanism by which CTCF haploinsufficiency contributes to cancer development is not well understood. CTCF is frequently mutated in endometrial cancer. Here we show that most CTCF mutations effectively result in CTCF haploinsufficiency through nonsense-mediated decay of mutant transcripts, or loss-of-function missense mutation. Conversely, we identified a recurrent CTCF mutation K365T, which alters a DNA binding residue, and acts as a gain-of-function mutation enhancing cell survival. CTCF genetic deletion occurs predominantly in poor prognosis serous subtype tumours, and this genetic deletion is associated with poor overall survival. In addition, we have shown that CTCF haploinsufficiency also occurs in poor prognosis endometrial clear cell carcinomas and has some association with endometrial cancer relapse and metastasis. Using shRNA targeting CTCF to recapitulate CTCF haploinsufficiency, we have identified a novel role for CTCF in the regulation of cellular polarity of endometrial glandular epithelium. Overall, we have identified two novel pro-tumorigenic roles (promoting cell survival and altering cell polarity) for genetic alterations of CTCF in endometrial cancer.

Brother of Regulator of Imprinted Sites (BORIS) suppresses apoptosis in colorectal cancer

Identifying oncogenes that promote cancer cell proliferation or survival is critical for treatment of colorectal cancer. The Brother of Regulator of Imprinted Sites (BORIS) is frequently expressed in most types of cancer, but rarely in normal tissues. Aberrantly expressed BORIS relates to colorectal cancer, but its function in colorectal cancer cells remains unclear. In addition, previous studies indicated the significance of cytoplasm-localized BORIS in cancer cells. However, none of them investigated its function. Herein, we investigated the functions of BORIS in cancer cell proliferation and apoptosis and the role of cytoplasm-localized BORIS in colorectal cancer. BORIS expression correlated with colorectal cancer proliferation. BORIS overexpression promoted colorectal cancer cell growth, whereas BORIS knockdown suppressed cell proliferation. Sensitivity of colorectal cancer cells to 5-fluorouracil (5-FU) was inversely correlated with BORIS expression. These data suggest that BORIS functions as an oncogene in colorectal cancer. BORIS silencing induced reactive oxygen species (ROS) production and apoptosis, whereas BORIS supplementation inhibited apoptosis induced by BORIS short interfering RNA (siRNA), hydrogen peroxide (H₂O₂) or 5-FU. Introduction of BORIS-ZFdel showed that cytoplasmic localization of BORIS inhibited apoptosis but not ROS production. Our study highlights the anti-apoptotic function of BORIS in colorectal cancer.

LAT1 is a putative therapeutic target in endometrioid endometrial carcinoma

l-type amino acid transporters (LAT1-4) are expressed in various cancer types and are involved in the uptake of essential amino acids such as leucine. Here we investigated the expression of LAT1-4 in endometrial adenocarcinoma and evaluated the contribution of LATs to endometrial cancer cell growth. Analysis of human gene expression data showed that all four LAT family members are expressed in endometrial adenocarcinomas. LAT1 was the most highly expressed, and showed a significant increase in both serous and endometrioid subtypes compared to normal endometrium. Endometrioid patients with the highest LAT1 levels exhibited the lowest disease-free survival. The pan-LAT inhibitor BCH led to a significant decrease in cell growth and spheroid area in four endometrial cancer cell lines tested in vitro. Knockdown of LAT1 by shRNA inhibited cell growth in HEC1A and Ishikawa cells, as well as inhibiting spheroid area in HEC1A cells. These data show that LAT1 plays an important role in regulating the uptake of essential amino acids such as leucine into endometrial cancer cells. Increased ability of BCH compared to LAT1 shRNA at inhibiting Ishikawa spheroid area suggests that other LAT family members may also contribute to cell growth. LAT1 inhibition may offer an effective therapeutic strategy in endometrial cancer patients whose tumours exhibit high LAT1 expression.

Increased expression of brother of the regulator of imprinted sites in peripheral blood neutrophils is associated with both benign and malignant breast lesions

BACKGROUND

BORIS, a paralog of the multifunctional CCCTC-binding factor (CTCF) gene is restricted to testis and normally not present in females. It is aberrantly activated in various human cancers including cancer breast. Using immunohistochemistry, western blot and/or RT-PCR, significantly higher levels of BORIS expression were reported in the neutrophils of cancer breast patients. We hypothesized that Flow Cytometry might be a better technique for objective quantitative evaluation of BORIS in neutrophils and we wanted to investigate if BORIS would discriminate between benign and malignant breast lesions.

METHODS

The study included 85 females; 52 breast cancer, 13 benign breast lesions and 20 age-matched healthy controls. BORIS expression in the neutrophils was detected by Flow Cytometry.

RESULTS

High level of BORIS was detected in all malignant (64.4 ± 16.6%) and benign cases (67 ± 12.3), mean florescent intensity ratio (MFIR) of 7.2 ± 4.1 and 7 ± 3.5, median 5.8 and 6.6%; and staining index (SI) 8.3 ± 3.9 and 8.2 ± 3.4, median 7.6 and 7.9 respectively vs.13.4 ± 11.5% MFI 1.8 ± 0.7, median1.6 and SI 2.6 ± 0.69, median 2.5 for the control. BORIS level was comparable in the malignant and benign group (P = 0.934) and significantly higher than control (P = 0.0001). There was no correlation between neutrophil BORIS expression and ER/PR status, HER-2/neu expression or tumor stage or size.

CONCLUSIONS

Increased BORIS expression in peripheral blood neutrophils is associated with both benign and malignant breast lesions; apparently, increased proliferation of breast tissue is the determining factor. This excludes BORIS as a tumor marker but it does not jeopardize its value as a potential therapeutic target. © 2016 International Clinical Cytometry Society.

Epigenetic silencing of miR-181c by DNA methylation in glioblastoma cell lines

Background

Post-transcriptional regulation by microRNAs is recognized as one of the major pathways for the control of cellular homeostasis. Less well understood is the transcriptional and epigenetic regulation of genes encoding microRNAs. In the present study we addressed the epigenetic regulation of the miR-181c in normal and malignant brain cells.

Methods

To explore the epigenetic regulation of the miR-181c we evaluated its expression using RT-qPCR and the in vivo binding of the CCCTC-binding factor (CTCF) to its regulatory region in different glioblastoma cell lines. DNA methylation survey, chromatin immunoprecipitation and RNA interference assays were used to assess the role of CTCF in the miR-181c epigenetic silencing.

Results

We found that miR-181c is downregulated in glioblastoma cell lines, as compared to normal brain tissues. Loss of expression correlated with a notorious gain of DNA methylation at the miR-181c promoter region and the dissociation of the multifunctional nuclear factor CTCF. Taking advantage of the genomic distribution of CTCF in different cell types we propose that CTCF has a local and cell type specific regulatory role over the miR-181c and not an architectural one through chromatin loop formation. This is supported by the depletion of CTCF in glioblastoma cells affecting the expression levels of NOTCH2 as a target of miR-181c.

Conclusion

Together, our results point to the epigenetic role of CTCF in the regulation of microRNAs implicated in tumorigenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2273-6) contains supplementary material, which is available to authorized users.

The dual specificity phosphatase 2 gene is hypermethylated in human cancer and regulated by epigenetic mechanisms

Background

Dual specificity phosphatases are a class of tumor-associated proteins involved in the negative regulation of the MAP kinase pathway. Downregulation of the dual specificity phosphatase 2 (DUSP2) has been reported in cancer. Epigenetic silencing of tumor suppressor genes by abnormal promoter methylation is a frequent mechanism in oncogenesis. It has been shown that the epigenetic factor CTCF is involved in the regulation of tumor suppressor genes.

Methods

We analyzed the promoter hypermethylation of DUSP2 in human cancer, including primary Merkel cell carcinoma by bisulfite restriction analysis and pyrosequencing. Moreover we analyzed the impact of a DNA methyltransferase inhibitor (5-Aza-dC) and CTCF on the epigenetic regulation of DUSP2 by qRT-PCR, promoter assay, chromatin immuno-precipitation and methylation analysis.

Results

Here we report a significant tumor-specific hypermethylation of DUSP2 in primary Merkel cell carcinoma (p = 0.05). An increase in methylation of DUSP2 was also found in 17 out of 24 (71 %) cancer cell lines, including skin and lung cancer. Treatment of cancer cells with 5-Aza-dC induced DUSP2 expression by its promoter demethylation, Additionally we observed that CTCF induces DUSP2 expression in cell lines that exhibit silencing of DUSP2. This reactivation was accompanied by increased CTCF binding and demethylation of the DUSP2 promoter.

Conclusions

Our data show that aberrant epigenetic inactivation of DUSP2 occurs in carcinogenesis and that CTCF is involved in the epigenetic regulation of DUSP2 expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2087-6) contains supplementary material, which is available to authorized users.

Long Noncoding RNA CUDR Regulates HULC and β-Catenin to Govern Human Liver Stem Cell Malignant Differentiation

Long noncoding RNA cancer upregulated drug resistant (CUDR) is overexpressed in many tumors and promotes tumorigenesis. Herein, we demonstrate CUDR could enhance the human embryonic stem cells (ESC) differentiation into hepatocyte-like cells by reducing trimethylation on histone H3 twenty-seventh lysine (H3K27me3). On the other hand, excessive CUDR triggers hepatocyte-like cells malignant transformation. Mechanistically, we identify CUDR causes highly upregulated in liver cancer (HULC) and β-catenin abnormal expression by inhibiting HULC promoter methylation and promoting β-catenin promoter-enhancer chromatin looping formation mediated by CUDR-ccctc-binding factor (CTCF) complex, which recruits more RNA polII and P300. Strikingly, HULC and β-catenin activity are crucial for CUDR oncogenic function. These findings provide the first demonstration that CUDR plays a positive potential role in liver cancer stem cell through the cascade of CUDR-HULC/CUDR-β-catenin signaling, and offer insights into a novel link between long noncoding RNA (lncRNA) and the epigenetic modification in cancer stem cells.

Different Effects of BORIS/CTCFL on Stemness Gene Expression, Sphere Formation and Cell Survival in Epithelial Cancer Stem Cells

Cancer stem cells are cancer cells characterized by stem cell properties and represent a small population of tumor cells that drives tumor development, progression, metastasis and drug resistance. To date, the molecular mechanisms that generate and regulate cancer stem cells are not well defined. BORIS (Brother of Regulator of Imprinted Sites) or CTCFL (CTCF-like) is a DNA-binding protein that is expressed in normal tissues only in germ cells and is re-activated in tumors. Recent evidences have highlighted the correlation of BORIS/CTCFL expression with poor overall survival of different cancer patients. We have previously shown an association of BORIS-expressing cells with stemness gene expression in embryonic cancer cells. Here, we studied the role of BORIS in epithelial tumor cells. Using BORIS-molecular beacon that was already validated, we were able to show the presence of BORIS mRNA in cancer stem cell-enriched populations (side population and spheres) of cervical, colon and breast tumor cells. BORIS silencing studies showed a decrease of sphere formation capacity in breast and colon tumor cells. Importantly, BORIS-silencing led to down-regulation of hTERT, stem cell (NANOG, OCT4, SOX2 and BMI1) and cancer stem cell markers (ABCG2, CD44 and ALDH1) genes. Conversely, BORIS-induction led to up-regulation of the same genes. These phenotypes were observed in cervical, colon and invasive breast tumor cells. However, a completely different behavior was observed in the non-invasive breast tumor cells (MCF7). Indeed, these cells acquired an epithelial mesenchymal transition phenotype after BORIS silencing. Our results demonstrate that BORIS is associated with cancer stem cell-enriched populations of several epithelial tumor cells and the different phenotypes depend on the origin of tumor cells.

Age- and pregnancy-associated DNA methylation changes in mammary epithelial cells

Postnatal mammary gland development and differentiation occur during puberty and pregnancy. To explore the role of DNA methylation in these processes, we determined the genome-wide DNA methylation and gene expression profiles of CD24(+)CD61(+)CD29(hi), CD24(+)CD61(+)CD29(lo), and CD24(+)CD61(-)CD29(lo) cell populations that were previously associated with distinct biological properties at different ages and reproductive stages. We found that pregnancy had the most significant effects on CD24(+)CD61(+)CD29(hi) and CD24(+)CD61(+)CD29(lo) cells, inducing distinct epigenetic states that were maintained through life. Integrated analysis of gene expression, DNA methylation, and histone modification profiles revealed cell-type- and reproductive-stage-specific changes. We identified p27 and TGFβ signaling as key regulators of CD24(+)CD61(+)CD29(lo) cell proliferation, based on their expression patterns and results from mammary gland explant cultures. Our results suggest that relatively minor changes in DNA methylation occur during luminal differentiation compared with the effects of pregnancy on CD24(+)CD61(+)CD29(hi) and CD24(+)CD61(+)CD29(lo) cells.

The apoptosis associated tyrosine kinase gene is frequently hypermethylated in human cancer and is regulated by epigenetic mechanisms

Epigenetic gene inactivation through promoter hypermethylation is an important aberration involved in the silencing of tumor-associated genes in cancer. Here we identified the apoptosis associated tyrosine kinase (AATK) as an epigenetically downregulated tumor related gene. We analyzed the epigenetic regulation of AATK in several human cancer cell lines and normal tissues by methylation and expression analysis. Hypermethylation of AATK was also analyzed in 25 primary lung tumors, 30 breast cancers and 24 matching breast tissues. In normal tissues the AATK CpG island promoter was unmethylated and AATK was expressed. Hypermethylation of AATK occurred frequently in 13 out of 14 (93%) human cancer cell lines. Methylation was reversed by 5-aza-2′-deoxycytidine treatment leading to re-expression of AATK in cancer cell lines. Aberrant methylation of AATK was also revealed in primary lung (40%) and breast (53%) cancers, but was found to be significantly less methylated in matching normal breast tissues (17%; p<0.01). In addition, we observed that AATK is epigenetically reactivated through the chromatin regulator CTCF. We further show that overexpression of Aatk significantly suppresses colony formation in cancer cell lines. Our findings suggest that the apoptosis associated tyrosine kinase is frequently inactivated in human cancers and acts as a tumor suppressive gene.

Expression analysis of BORIS during pluripotent, differentiated, cancerous, and non-cancerous cell states

BORIS/CTCFL is an 11 zinc finger protein, which is the paralog of CTCF, a ubiquitously expressed protein with diverse roles in gene expression and chromatin organization. Several studies have shown that the expression of BORIS is restricted to normal adult testis, pluripotent cells, and diverse cancer cell lines. Thus, it is known as a cancer-testis (CT) gene that has been hypothesized to exhibit oncogenic properties and to be involved in cancer cell proliferation. On the contrary, other reports have shown that its expression is more widespread and can be detected in differentiated and normal somatic cells; hence, it might have roles in general cellular functions. The present study was aimed to analyze the expression of BORIS in different cell states of pluripotent, differentiated, cancerous and non-cancerous.We found that the two cell states of pluripotency and differentiation are not accompanied with significant variations of BORIS expression. Furthermore, Boris transcripts were detected at approximately the same level in cancer and non-cancer cell lines. These findings suggest that, in contrast to some previous reports, the expression of mouse BORIS is not limited to only cancerous cells or pluripotent cell states.

CTCFL (BORIS) mRNA Expression in a Peripheral Giant Cell Granuloma of the Oral Cavity

Peripheral giant cell granuloma (PGCG) is a relatively common benign reactive lesion of the oral cavity which can occur at any age. CTCFL/BORIS (CTCF like/Brother of the Regulator of Imprinted Sites) and CTCF (CCCTC-binding factor) are paralogous genes with an important role in the regulation of gene expression, genomic imprinting, and nuclear chromatin insulators regulation. BORIS expression promotes cell immortalization and growth while CTCF has tumor suppressor activity; the expression pattern may reflect the reverse transcription silencing of BORIS. The aim of this work was to describe a histopathological and molecular approach of an 8-year-old pediatric male patient with PGCG diagnosis. It was observed that the PGCG under study expressed CTCF as well as BORIS mRNAs alongside with the housekeeping gene GAPDH, which may be related to possible genetic and epigenetic changes in normal cells of oral cavity.

The promoter methylation status and mRNA expression levels of CTCF and SIRT6 in sporadic breast cancer

Promoter hypermethylation causes gene silencing and is thought to be an early event in carcinogenesis. This study was to detect promoter methylation status and mRNA expression levels of CCCTC-binding factor (CTCF) and sirtuin 6 (SIRT6), and to explore the relationship between methylation and mRNA expression in breast cancer patient samples. Promoter methylation analysis and expression profile analysis of two genes were performed by methylation-specific PCR, bisulfite sequencing PCR, and quantitative real-time PCR in cancer lesions and matched normal tissues. The promoter region of CTCF has not been hypermethylated in all patient samples. In contrast, methylation of SIRT6 gene was present in invasive cancers (93.5%) and matched normal tissues (96.8%) from 62 patients. Promoter hypermethylation of SIRT6 was also observed in ductal carcinoma in situ (three of three) and matched normal tissues (two of three). mRNA expression of CTCF and SIRT6 in invasive tumors showed a lower level than that in paired normal tissues (p=0.008 and p=0.030, respectively). The fold change values of CTCF expression were significantly lower in invasive ductal cancer lesions with Ki-67-positive status (p=0.042). In conclusion, our data showed that the methylation status of CTCF and SIRT6 promoter regions was not statistically different in cancer lesions compared with matched normal tissues. No significant association between promoter methylation status and expression profiles of CTCF and SIRT6 was found in invasive breast cancers.

Expression of the cancer-testis antigen BORIS correlates with prostate cancer

BACKGROUND

BORIS, a paralogue of the transcription factor CTCF, is a member of the cancer-testis antigen (CT) family. BORIS is normally present at high levels in the testis; however it is aberrantly expressed in various tumors and cancer cell lines. The main objectives of this study were to investigate BORIS expression together with sub-cellular localization in both prostate cell lines and tumor tissues, and assess correlations between BORIS and clinical/pathological characteristics.

METHODS

We examined BORIS mRNA expression, protein levels and cellular localization in a panel of human prostate tissues, cancer and benign, together with a panel prostate cell lines. We also compared BORIS levels and localization with clinical/pathological characteristics in prostate tumors.

RESULTS

BORIS was detected in all inspected prostate cancer cell lines and tumors, but was absent in benign prostatic hyperplasia. Increased levels of BORIS protein positively correlated with Gleason score, T-stage and androgen receptor (AR) protein levels in prostate tumors. The relationship between BORIS and AR was further highlighted in prostate cell lines by the ability of ectopically expressed BORIS to activate the endogenous AR mRNA and protein. BORIS localization in the nucleus plus cytoplasm was also associated with higher BORIS levels and Gleason score.

CONCLUSIONS

Detection of BORIS in prostate tumors suggests potential applications of BORIS as a biomarker for prostate cancer diagnosis, as an immunotherapy target and, potentially, a prognostic marker of more aggressive prostate cancer. The ability of BORIS to activate the AR gene indicates BORIS involvement in the growth and development of prostate tumors.

CTCF and BORIS in genome regulation and cancer

CTCF plays a vital role in chromatin structure and function. CTCF is ubiquitously expressed and plays diverse roles in gene regulation, imprinting, insulation, intra/interchromosomal interactions, nuclear compartmentalisation, and alternative splicing. CTCF has a single paralogue, the testes-specific CTCF-like gene (CTCFL)/BORIS. CTCF and BORIS can be deregulated in cancer. The tumour suppressor gene CTCF can be mutated or deleted in cancer, or CTCF DNA binding can be altered by epigenetic changes. BORIS is aberrantly expressed frequently in cancer, leading some to propose a pro-tumourigenic role for BORIS. However, BORIS can inhibit cell proliferation, and is mutated in cancer similarly to CTCF suggesting BORIS activation in cancer may be due to global genetic or epigenetic changes typical of malignant transformation.

BORIS/CTCFL is an RNA-binding protein that associates with polysomes

BACKGROUND

BORIS (CTCFL), a paralogue of the multifunctional and ubiquitously expressed transcription factor CTCF, is best known for its role in transcriptional regulation. In the nucleus, BORIS is particularly enriched in the nucleolus, a crucial compartment for ribosomal RNA and RNA metabolism. However, little is known about cytoplasmic BORIS, which represents the major pool of BORIS protein.

RESULTS

We show, firstly, that BORIS has a putative nuclear export signal in the C-terminal domain. Furthermore, BORIS associates with mRNA in both neural stem cells and young neurons. The majority of the BORIS-associated transcripts are different in the two cell types. Finally, by using polysome profiling we show that BORIS is associated with actively translating ribosomes.

CONCLUSION

We have demonstrated the RNA binding properties of cellular BORIS and its association with actively translating ribosomes. We suggest that BORIS is involved in gene expression at both the transcriptional and post-transcriptional levels.