BORIS (CTCFL) is not expressed in most human breast cell lines and high grade breast carcinomas

The function of brother of the regulator of imprinted sites in cancer development

As Douglas Hanahan and Robert Weinberg compiled, there are nine hallmarks of cancer that are conducive to cancer cell development and survival. Previous studies showed that brother of the regulator of imprinted sites (BORIS) might promote cancer progression through these aspects. The competition between BORIS and CCCTC-binding factor (CTCF), which is crucial in the formation of chromatin loops, affects the normal function of CTCF and leads to neoplasia and deformity. In addition, BORIS belongs to the cancer-testis antigen families, which are potential targets in cancer diagnosis and treatment. Herein, we discuss the function and mechanisms of BORIS, especially in cancer development.

Targeting CTCFL/BORIS for the immunotherapy of cancer

Cancer vaccines have great potential in the fight against metastatic malignancies. Current anti-tumor immunotherapy is hindered by existing tolerance to tumor-associated antigens (TAA) and tumor escape using various mechanisms, highlighting the need for improved targets for immunotherapy. The cancer-testis antigen CTCFL/BORIS was discovered 16 years ago and possesses all features necessary for an ideal TAA. Recently CTCFL/BORIS has received additional attention as a target expressed in cancer stem cells (CSC). These cells drive tumor growth recurrence, metastasis, and treatment resistance. CTCFL/BORIS silencing leads to senescence and death of CSC. Therefore, an immunotherapeutic strategy that targets CTCFL/BORIS may lead to the selective destruction of CSC and potential eradication of metastatic disease. The high immunotherapeutic potential of CTCFL/BORIS antigen was shown in a stringent 4T1 mouse model of breast cancer. Using these highly metastatic, poorly immunogenic carcinoma cells inoculated into T-helper2 prone mice, we showed that DC fed with recombinant CTCFL/BORIS as an immunogen inhibited tumor growth and reduced the number of metastases in distant organs. About 20% of CTCFL/BORIS immunized animals were tumor free. 50% of animals remained metastasis free. Those having metastasis showed at least tenfold fewer metastases compared to controls. In a rat model of breast cancer, we showed that alphavirus-based CTCFL/BORIS immunotherapy was capable of cancer elimination as we were able to cure 50% of animals. Based on the above data, we believe that translation of CTCFL/BORIS-targeting immunotherapeutic strategies to the clinic will provide new avenues for improving survival of breast cancer patients with advanced metastatic disease.

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.

Molecular Lesions of Insulator CTCF and Its Paralogue CTCFL (BORIS) in Cancer: An Analysis from Published Genomic Studies

CTCF (CCCTC-binding factor) is a transcription regulator with hundreds of binding sites in the human genome. It has a main function as an insulator protein, defining together with cohesins the boundaries of areas of the genome called topologically associating domains (TADs). TADs contain regulatory elements such as enhancers which function as regulators of the transcription of genes inside the boundaries of the TAD while they are restricted from regulating genes outside these boundaries. This paper will examine the most common genetic lesions of CTCF as well as its related protein CTCFL (CTCF-like also called BORIS) in cancer using publicly available data from published genomic studies. Cancer types where abnormalities in the two genes are more common will be examined for possible associations with underlying repair defects or other prevalent genetic lesions. The putative functional effects in CTCF and CTCFL lesions will also be explored.

A map of human PRDM9 binding provides evidence for novel behaviors of PRDM9 and other zinc-finger proteins in meiosis

PRDM9 binding localizes almost all meiotic recombination sites in humans and mice. However, most PRDM9-bound loci do not become recombination hotspots. To explore factors that affect binding and subsequent recombination outcomes, we mapped human PRDM9 binding sites in a transfected human cell line and measured PRDM9-induced histone modifications. These data reveal varied DNA-binding modalities of PRDM9. We also find that human PRDM9 frequently binds promoters, despite their low recombination rates, and it can activate expression of a small number of genes including CTCFL and VCX. Furthermore, we identify specific sequence motifs that predict consistent, localized meiotic recombination suppression around a subset of PRDM9 binding sites. These motifs strongly associate with KRAB-ZNF protein binding, TRIM28 recruitment, and specific histone modifications. Finally, we demonstrate that, in addition to binding DNA, PRDM9's zinc fingers also mediate its multimerization, and we show that a pair of highly diverged alleles preferentially form homo-multimers.

In Vitro Assessment of the Expression and T Cell Immunogenicity of the Tumor-Associated Antigens BORIS, MUC1, hTERT, MAGE-A3 and Sp17 in Uterine Cancer

Background: While immunotherapy moved to the forefront of treatment of various cancers, it remains underexplored for uterine cancer. This might be due to the small patient population with advanced endometrial carcinoma and uterine sarcoma. Data about immunotherapeutic targets are scarce in endometrial carcinoma and lacking in uterine sarcoma. Methods: Expression of five tumor-associated antigens (TAA) (BORIS, MUC1, hTERT, MAGE-A3 and Sp17) was validated in uterine tumor samples by immunohistochemistry (IHC) and/or quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). TAA immunogenicity was analyzed by determining spontaneous T cell responses towards overlapping peptide pools covering the whole TAA in patient blood. Results: At mRNA level, MAGE-A3 and Sp17 were overexpressed in a minority of patients and BORIS was moderately overexpressed (26% in endometrial carcinoma and 62% in uterine sarcoma). hTERT was overexpressed in the vast majority of tumors. On protein level, MUC1 was upregulated in primary, recurrent and metastatic EMCAR and in metastatic US tumors. hTERT protein was highly expressed in both normal and malignant tissue. Spontaneous TAA-specific T cell responses were detected in a minority of patients, except for hTERT to which T cell responses occurred more frequently. Conclusions: These data point to MUC1 and hTERT as most suitable targets based on expression levels and T cell immunogenicity for use in immunotherapeutic regimens.

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.

Possible prognostic value of BORIS transcript variants ratio in laryngeal squamous cell carcinomas - a pilot study

BORIS is a paralog of a highly conserved, multi-functional chromatin factor CTCF. Unlike CTCF, which has been shown to possess tumor-suppressive properties, BORIS belongs to the "cancer/testis antigen" family normally expressed only in germ cells and aberrantly activated in a variety of tumors. The consequences of BORIS expression, relative abundance of its isoforms, and its role in carcinogenesis have not been completely elucidated. It activates transcription of hTERT and MYC, genes relevant for laryngeal carcinoma progression. In this study, BORIS expression has been analyzed at the transcriptional level by RT-PCR and protein level by semi-quantitative immunohistochemistry in 32 laryngeal squamous cell carcinomas and adjacent non-tumorous tissue. BORIS was detected in 44 % (14/32) laryngeal squamous cell carcinoma samples, while it was detected only in one normal, tumor-adjacent tissue sample. Tree based survival analysis, using the recursive partitioning algorithm mvpart, extracted the ratio of relative abundance of BORIS transcript variants containing exon 7 (BORIS 7+) and those lacking exon 7 (BORIS 7-) as an independent prognostic factor associated with disease relapse during a 5-year follow-up period. Patients having BORIS 7+/BORIS 7- ratio ≥1 had a higher rate of disease relapse than patients with BORIS 7+/BORIS 7- ratio <1. Hazard ratio for that group, based on Cox Proportional Hazard Regression, was 3.53. This is the first study analyzing expression of BORIS protein and transcript variants in laryngeal squamous cell carcinoma relative to its possible prognostic value for recurrence and overall survival.

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.

CTCF and CTCFL mRNA expression in 17β-estradiol-treated MCF7 cells

Estrogens play a key role in breast cancer, with 60-70% of the cases expressing estrogen receptors (ERs), which are encoded by the ESR1 gene. CTCFL, a paralogue of the chromatin organizer CTCF, is a potential biomarker of breast cancer, but its expression in this disease is currently controversial. A positive correlation has been reported between CTCFL and ERs in breast tumors and there also exists a coordinated interaction between CTCF and ERs in breast cancer cells. Therefore, there appears to be an association between CTCF, CTCFL and estrogens in breast cancer; however, there has been no report on the effects of estrogens on CTCF and CTCFL expression. The aim of this study was to determine the effect of 17β-estradiol (E2) on the CTCF and CTCFL mRNA expression in the MCF7 breast cancer cell line. The promoter methylation status of CTCFL and data mining for estrogen response elements in promoters of the CTCF and CTCFL genes were also determined. The transcription of CTCF and CTCFL was performed by quantitative polymerase chain reaction (qPCR) and the promoter methylation status of CTCFL was determined by methylation-specific PCR. The MCF7 cells exhibited basal transcription of CTCF, which was significantly downregulated to 0.68 by 1 μM E2; basal or E2-regulated transcription of CTCFL was not detected. Under basal conditions, the CTCFL promoter was methylated. Through data mining, an estrogen response element was identified in the CTCF promoter, but no such element was found in CTCFL. These results suggested that estrogens may modulate CTCF expression, although there was no apparent association between ERs and CTCFL.

Apicidin and docetaxel combination treatment drives CTCFL expression and HMGB1 release acting as potential antitumor immune response inducers in metastatic breast cancer cells

Currently approved combination regimens available for the treatment of metastatic tumors, such as breast cancer, have been shown to increase response rates, often at the cost of a substantial increase in toxicity. An ideal combination strategy may consist of agents with different mechanisms of action leading to complementary antitumor activities and safety profiles. In the present study, we investigated the effects of the epigenetic modulator apicidin in combination with the cytotoxic agent docetaxel in tumor breast cell lines characterized by different grades of invasiveness. We report that combined treatment of apicidin and docetaxel, at low toxicity doses, stimulates in metastatic breast cancer cells the expression of CTCF-like protein and other cancer antigens, thus potentially favoring an antitumor immune response. In addition, apicidin and docetaxel co-treatment specifically stimulates apoptosis, characterized by an increased Bax/Bcl-2 ratio and caspase-8 activation. Importantly, following combined exposure to these agents, metastatic cells were also found to induce signals of immunogenic apoptosis such as cell surface expression of calreticulin and release of considerable amounts of high-mobility group box 1 protein, thus potentially promoting the translation of induced cell death into antitumor immune response. Altogether, our results indicate that the combined use of apicidin and docetaxel, at a low toxicity profile, may represent a potential innovative strategy able to activate complementary antitumor pathways in metastatic breast cancer cells, associated with a potential control of metastatic growth and possible induction of antitumor immunity.

Dose-dependent activation of putative oncogene SBSN by BORIS

Testis-specific transcription factor BORIS (Brother of the Regulator of Imprinted Sites), a paralog and proposed functional antagonist of the widely expressed CTCF, is abnormally expressed in multiple tumor types and has been implicated in the epigenetic activation of cancer-testis antigens (CTAs). We have reported previously that suprabasin (SBSN), whose expression is restricted to the epidermis, is epigenetically derepressed in lung cancer. In this work, we establish that SBSN is a novel non-CTA target of BORIS epigenetic regulation. With the use of a doxycycline-inducible BORIS expressing vector, we demonstrate that relative BORIS dosage is critical for SBSN activation. At lower concentrations, BORIS induces demethylation of the SBSN CpG island and disruption and activation of chromatin around the SBSN transcription start site (TSS), resulting in a 35-fold increase in SBSN expression in the H358 human lung cancer cell line. Interestingly, increasing BORIS concentrations leads to a subsequent reduction in SBSN expression via chromatin repression. In a similar manner, increase in BORIS concentrations leads to eventual decrease of cell growth and colony formation. This is the first report demonstrating that different amount of BORIS defines its varied effects on the expression of a target gene via chromatin structure reorganization.

A cell cycle role for the epigenetic factor CTCF-L/BORIS

CTCF is a ubiquitous epigenetic regulator that has been proposed as a master keeper of chromatin organisation. CTCF-like, or BORIS, is thought to antagonise CTCF and has been found in normal testis, ovary and a large variety of tumour cells. The cellular function of BORIS remains intriguing although it might be involved in developmental reprogramming of gene expression patterns. We here unravel the expression of CTCF and BORIS proteins throughout human epidermis. While CTCF is widely distributed within the nucleus, BORIS is confined to the nucleolus and other euchromatin domains. Nascent RNA experiments in primary keratinocytes revealed that endogenous BORIS is present in active transcription sites. Interestingly, BORIS also localises to interphase centrosomes suggesting a role in the cell cycle. Blocking the cell cycle at S phase or mitosis, or causing DNA damage, produced a striking accumulation of BORIS. Consistently, ectopic expression of wild type or GFP- BORIS provoked a higher rate of S phase cells as well as genomic instability by mitosis failure. Furthermore, down-regulation of endogenous BORIS by specific shRNAs inhibited both RNA transcription and cell cycle progression. The results altogether suggest a role for BORIS in coordinating S phase events with mitosis.

Expression of the epigenetic factor BORIS (CTCFL) in the human genome

BORIS, or CTCFL, the so called Brother of the Regulator of Imprinted Sites because of the extensive homology in the central DNA binding region of the protein to the related regulator, CTCF, is expressed in early gametogenesis and in multiple cancers but not in differentiated somatic cells. Thus it is a member of the cancer testes antigen group (CTAs). Since BORIS and CTCF target common DNA binding sites, these proteins function on two levels, the first level is their regulation via the methylation context of the DNA target site and the second level is their distinct and different epigenetic associations due to differences in the non-homologous termini of the proteins. The regulation on both of these levels is extensive and complex and the sphere of influence of each of these proteins is associated with vastly different cellular signaling processes. On the level of gene expression, BORIS has three known promoters and multiple spliced mRNAs which adds another level of complexity to this intriguing regulator. BORIS expression is observed in the majority of cancer tissues and cell lines analyzed up to today. The expression profile and essential role of BORIS in cancer make this molecule very attractive target for cancer immunotherapy. This review summarizes what is known about BORIS regarding its expression, structure, and function and then presents some theoretical considerations with respect to its genome wide influence and its potential for use as a vaccine for cancer immunotherapy.

BORIS in human cancers -- a review

Brother of the regulator of the imprinted site (BORIS) or CTCFL is an 11 zinc finger (ZF) protein, which is considered to be a new oncogene. It is a paralogue of CCCTC-binding factor (CTCF), generated by a duplication event. BORIS is highly expressed in primary spermatocytes, although it is silenced at later stages of spermatogenesis. BORIS has either not been found in normal human tissues or cells or has been detected at very low levels. The expression of the BORIS gene is predominantly controlled by DNA-methylation, while its activation requires the demethylation of its promoter. Re-expression of BORIS in cancers is due to the hypomethylation of its promoter. High expression of BORIS protein and RNA correlates with the tumour size and grade in cancer patients. High percentages of BORIS transcripts were detected in breast, endometrial, prostatic and colon cancer patients. Lower percentages of BORIS were found in patients with melanoma and cancers of the head and neck. The expression of BORIS varied from low to high in lung, colon and ovarian cancer, melanoma and leukaemic cell lines. Lower expressions of BORIS were found in head and neck, breast, kidney, bladder, testicular and prostate carcinoma cell lines. An inhibitor of DNA methylation, 5-aza-2'deoxy-cytidine (5-azadC), and histone deacetylase inhibitors induced or enhanced the expression of BORIS in various carcinoma cell lines. The silencing of BORIS induced apoptosis in tumorous cell lines. BORIS antitumor vaccines have been tested in mice with several cancers, based on the deletion of the DNA-binding ZF-region of the BORIS.

Widespread expression of BORIS/CTCFL in normal and cancer cells

BORIS (CTCFL) is the paralog of CTCF (CCCTC-binding factor; NM_006565), a ubiquitously expressed DNA-binding protein with diverse roles in gene expression and chromatin organisation. BORIS and CTCF have virtually identical zinc finger domains, yet display major differences in their respective C- and N-terminal regions. Unlike CTCF, BORIS expression has been reported only in the testis and certain malignancies, leading to its classification as a “cancer-testis” antigen. However, the expression pattern of BORIS is both a significant and unresolved question in the field of DNA binding proteins. Here, we identify BORIS in the cytoplasm and nucleus of a wide range of normal and cancer cells. We compare the localization of CTCF and BORIS in the nucleus and demonstrate enrichment of BORIS within the nucleolus, inside the nucleolin core structure and adjacent to fibrillarin in the dense fibrillar component. In contrast, CTCF is not enriched in the nucleolus. Live imaging of cells transiently transfected with GFP tagged BORIS confirmed the nucleolar accumulation of BORIS. While BORIS transcript levels are low compared to CTCF, its protein levels are readily detectable. These findings show that BORIS expression is more widespread than previously believed, and suggest a role for BORIS in nucleolar function.

Integrated genomic analysis of nodular tissue in macronodular adrenocortical hyperplasia: progression of tumorigenesis in a disorder associated with multiple benign lesions

CONTEXT

Massive macronodular adrenocortical disease or ACTH-independent macronodular adrenal hyperplasia (AIMAH) is a clinically and genetically heterogeneous disorder.

OBJECTIVE AND DESIGN

Whole-genome expression profiling and oligonucleotide array comparative genomic hybridization changes were analyzed in samples of different nodules from the same patients with AIMAH. Quantitative RT-PCR and staining were employed to validate the mRNA array data.

RESULTS

Chromosomal gains were more frequent in larger nodules when compared with smaller nodules from the same patients. Among the 50 most overexpressed genes, 50% had a chromosomal locus that was amplified in the comparative genomic hybridization data. Although the list of most over- and underexpressed genes was similar between the nodules of different size, the gene set enrichment analysis identified different pathways associated with AIMAH that corresponded to the size; the smaller nodules were mainly enriched for metabolic pathways, whereas p53 signaling and cancer genes were enriched in larger nodules. Confirmatory studies demonstrated that BCL2, E2F1, EGF, c-KIT, MYB, PRKCA, and CTNNB1 were overexpressed in the larger nodules at messenger and/or protein levels. Chromosomal enrichment analysis showed that chromosomes 20q13 and 14q23 might be involved in progression of AIMAH from smaller to larger tumors.

CONCLUSION

Integrated transcriptomic and genomic data for AIMAH provides supporting evidence to the hypothesis that larger adrenal lesions, in the context of this chronic, polyclonal hyperplasia, accumulate an increased number of genomic and, subsequently, transcript abnormalities. The latter shows that the disease appears to start with mainly tissue metabolic derangements, as suggested by the study of the smaller nodules, but larger lesions showed aberrant expression of oncogenic pathways.

BORIS/CTCFL expression is insufficient for cancer-germline antigen gene expression and DNA hypomethylation in ovarian cell lines

Expression of the cancer-germline (CG) (or cancer-testis) antigen gene BORIS/CTCFL has been proposed to mediate activation of CG antigen genes in cancer. Consistent with this idea, we have observed that BORIS is frequently expressed in ovarian cancer, often in conjunction with other CG genes. Here we assessed the role of BORIS in CG antigen gene regulation and DNA methylation using normal and cancerous ovarian cell lines, and the CG genes MAGE-A1, NY-ESO-1, and XAGE-1 as models. Adenoviral vectored BORIS was expressed at robust levels and exhibited predominant nuclear localization in ovarian cells. However, BORIS expression in immortalized ovarian surface epithelial cells or ovarian cancer cell lines did not induce CG antigen gene expression or lead to CG antigen promoter DNA hypomethylation. BORIS overexpression also did not alter global DNA methylation, as assessed by genomic 5-methyl-deoxycytidine levels and LINE-1 methylation. We used decitabine to further assess the role of BORIS in CG gene activation and found that decitabine treatment induced BORIS and other CG genes with similar kinetics, suggesting that BORIS induction does not account for the induction of other CG genes by decitabine in ovarian cancer cells. In agreement, siRNA knockdown of BORIS did not block decitabine-mediated induction of CG genes or DNA hypomethylation in ovarian cancer cells treated with this agent. We conclude that BORIS is insufficient for CG antigen gene expression and DNA hypomethylation in ovarian cell lines, and that additional factors are likely required for CG antigen expression in ovarian cancer.