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.
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.
Vatolin
Sergei
S
Laboratory of Immunopathology, National Institutes of Allergy and Infectious Disease, NIH, Bethesda, Maryland, USA.
Abdullaev
Ziedulla
Z
Pack
Svetlana D
SD
Flanagan
Patrick T
PT
Custer
Mary
M
Loukinov
Dmitri I
DI
Pugacheva
Elena
E
Hong
Julie A
JA
Morse
Herbert
H
Schrump
David S
DS
Risinger
John I
JI
Barrett
J Carl
JC
Lobanenkov
Victor V
VV
D000818:Animals; D000951:Antigens, Neoplasm; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D001483:Base Sequence; D045744:Cell Line, Tumor; D019175:DNA Methylation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000077209:Decitabine; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D058950:Melanoma-Specific Antigens; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D012190:Retroviridae / Q000235:genetics; D015533:Transcriptional Activation; D014162:Transfection
D000951:Antigens, Neoplasm; C456540:CTCFL protein, human; D004268:DNA-Binding Proteins; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D000077209:Decitabine; D001374:Azacitidine