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

• Published in: Cancer research (Chicago, Ill.) Ill.), 2005-09, Vol.65 (17), p.7751-7762
• Main Authors: VATOLIN, Sergei, ABDULLAEV, Ziedulla, RISINGER, John I, BARRETT, J. Carl, LOBANENKOV, Victor V, PACK, Svetlana D, FLANAGAN, Patrick T, CUSTER, Mary, LOUKINOV, Dmitri I, PUGACHEVA, Elena, HONG, Julie A, MORSE, Herbert III, SCHRUMP, David S
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Neoplasm; Azacitidine - analogs & derivatives; Azacitidine - pharmacology; Base Sequence; Biological and medical sciences; Cell Line, Tumor; DNA Methylation - drug effects; DNA-Binding Proteins - biosynthesis; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Fibroblasts - drug effects; Fibroblasts - metabolism; Fibroblasts - physiology; Gene Expression Regulation, Neoplastic - genetics; Genetic Vectors - genetics; Gynecology. Andrology. Obstetrics; Humans; Immunohistochemistry; Male genital diseases; Medical sciences; Melanoma-Specific Antigens; Molecular Sequence Data; Neoplasm Proteins - antagonists & inhibitors; Neoplasm Proteins - genetics; Nucleic Acid Conformation; Promoter Regions, Genetic; Protein Binding; Retroviridae - genetics; Retrovirus; RNA, Small Interfering - genetics; Transcriptional Activation; Transfection; Tumors
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-05-0858

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 approximately 50-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 meCpG-sensitive 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-2'-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.