Conditional Expression of the CTCF-Paralogous Transcriptional Factor BORIS in Normal Cells Results in Demethylation and Derepression of MAGE-A1 and Reactivation of Other Cancer-Testis Genes

Abstract

Brother of the Regulator of Imprinted Sites (BORIS) is a mammalian CTCF paralog with the same central 11Zn fingers (11ZF) that mediate specific interactions with varying f50-bp target sites. Regulated in vivo occupancy of such sites may yield structurally and functionally distinct CTCF/DNA complexes involved in various aspects of gene regulation, including epigenetic control of gene imprinting and X chromosome inactivation. The latter functions are mediated by meCpGsensitive 11ZF binding. Because CTCF is normally present in all somatic cells, whereas BORIS is active only in CTCF-and 5-methylcytosine-deficient adult male germ cells, switching DNA occupancy from CTCF to BORIS was suggested to regulate site specificity and timing of epigenetic reprogramming. In addition to 11ZF-binding paternal imprinting control regions, cancer-testis gene promoters also undergo remethylation during CTCF/BORIS switching in germ cells. Only promoters of cancer testis genes are normally silenced in all somatic cells but activated during spermatogenesis when demethylated in BORIS-positive germ cells and are found aberrantly derepressed in various tumors. We show here that BORIS is also expressed in multiple cancers and is thus itself a cancer-testis gene and that conditional expression of BORIS in normal fibroblasts activates cancer-testis genes selectively. We tested if replacement of CTCF by BORIS on regulatory DNA occurs in vivo on activation of a prototype cancer-testis gene, MAGE-A1. Transition from a hypermethylated/silenced to a hypomethylated/activated status induced in normal cells by 5-aza-2V -deoxycytidine (5-azadC) was mimicked by conditional input of BORIS and is associated with complete switching from CTCF to BORIS occupancy at a single 11ZF target. This site manifested a novel type of CTCF/BORIS 11ZF binding insensitive to CpG methylation. Whereas 5-azadC induction of BORIS takes only few hours, derepression of MAGE-A1 occurred 1 to 2 days later, suggesting that BORIS mediates cancer-testis gene activation by 5-azadC. Indeed, infection of normal fibroblasts with anti-BORIS short hairpin RNA retroviruses before treatment with 5-azadC blocked reactivation of MAGE-A1. We suggest that BORIS is likely tethering epigenetic machinery to a novel class of CTCF/BORIS 11ZF target sequences that mediate induction of cancer-testis genes. (Cancer Res 2005; 65(17): 7751-62)

Dynamic transcriptional regulatory complexes including BORIS, CTCF and Sp1 modulate NY-ESO-1 expression in lung cancer cells

“…In addition, we have demonstrated that BORIS as well as NY-ESO-1 expression can be induced in cultured lung cancer cells (but not normal human bronchial epithelial (NHBE) cells) following exposure to the DNA-demethylating agent 5-aza-2 0 deoxycytidine (DAC), the histone deacetylase (HDAC) inhibitor Depsipeptide FK228 (DP), or sequential DAC/DP. Furthermore, we have shown that a CTCF-to-BORISshift in occupancy of the NY-ESO-1 promoter coincides with de-repression of this CT gene in lung cancer cells (Hong et al, 2005); a similar phenomenon was observed for activation of MAGE-A1 in these cells (Vatolin et al, 2005).…”

BORIS, a paralogue of the transcription factor, CTCF, is aberrantly expressed in breast tumours

“…The appearance of common CTA (including BORIS) during gametogenesis and tumorigenesis prompts the hypothesis that induction of the gametogenetic programme in somatic cells may be associated with tumour development (Old, 2001;Kalejs and Erenpreisa, 2005). As BORIS seems to function as an upstream regulator for several CTA Vatolin et al, 2005), it is tempting to speculate that BORIS could be the 'master switch' in the process of cell reprogramming, which can guide the epigenetic machinery to a set of target genes eventually leading to their activation. It is important to note that BORIS may also act as an activator of genes responsible for proliferation in particular tissues, such as ER and PR genes in mammary glands.…”

“…This chromosome region is often amplified in many cancers and is believed to contain a dominant immortalising or transforming gene(s) (Tanner et al, 1994;Cuthill et al, 1999). Recent reports show that BORIS is a downstream regulator of cancer -testis genes: expression of BORIS in normal cells leads to derepression of cancer -testis genes MAGE-A1, NY-ESO-1 and others Vatolin et al, 2005).…”

L’intrusion des régulateurs de l’épigénome mâle dans les cellules somatiques cancéreuses

“…Bien que l'on ne connaisse pas précisément le rôle de BORIS au cours de la spermatogenèse, il est probable qu'il soit impliqué dans la régulation de l'expression d'autres gènes spécifiquement impliqués dans les voies de signalisation propres à la spermatogenèse, qui normalement sont aussi réprimés dans les cellules somatiques. L'expression illégitime de BORIS a été détectée dans un nombre significatif de cancers [7][8][9][10][11]. De manière intéressante, l'activation de BORIS dans les cellules somatiques induit l'expression d'autres facteurs C/T (pour cancer/testis), plus particulièrement celle des gènes MAGE-A [7] et de CTAG1/NY-ESO1 [12].…”

“…L'expression illégitime de BORIS a été détectée dans un nombre significatif de cancers [7][8][9][10][11]. De manière intéressante, l'activation de BORIS dans les cellules somatiques induit l'expression d'autres facteurs C/T (pour cancer/testis), plus particulièrement celle des gènes MAGE-A [7] et de CTAG1/NY-ESO1 [12]. Dans ce dernier cas, BORIS recrute le facteur de transcription SP1 au promoteur de CTAG1 pour déréprimer sa transcription [13].…”