title: Decoupling of DNA methylation and activity of intergenic LINE-1 promoters in colorectal cancer.
abstract: Hypomethylation of LINE-1 repeats in cancer has been proposed as the main mechanism behind their activation; this assumption, however, was based on findings from early studies that were biased toward young and transpositionally active elements. Here, we investigate the relationship between methylation of 2 intergenic, transpositionally inactive LINE-1 elements and expression of the LINE-1 chimeric transcript (LCT) 13 and LCT14 driven by their antisense promoters (L1-ASP). Our data from DNA modification, expression, and 5'RACE analyses suggest that colorectal cancer methylation in the regions analyzed is not always associated with LCT repression. Consistent with this, in HCT116 colorectal cancer cells lacking DNA methyltransferases DNMT1 or DNMT3B, LCT13 expression decreases, while cells lacking both DNMTs or treated with the DNMT inhibitor 5-azacytidine (5-aza) show no change in LCT13 expression. Interestingly, levels of the H4K20me3 histone modification are inversely associated with LCT13 and LCT14 expression. Moreover, at these LINE-1s, H4K20me3 levels rather than DNA methylation seem to be good predictor of their sensitivity to 5-aza treatment. Therefore, by studying individual LINE-1 promoters we have shown that in some cases these promoters can be active without losing methylation; in addition, we provide evidence that other factors (e.g., H4K20me3 levels) play prominent roles in their regulation.
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Natasha
authors.initials: N
authors.lastname: Vafadar-Isfahani
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Christina
authors.initials: C
authors.lastname: Parr
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Lara E
authors.initials: LE
authors.lastname: McMillan
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Juliane
authors.initials: J
authors.lastname: Sanner
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Yeo
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Saddington
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Oliver
authors.initials: O
authors.lastname: Peacock
authors.affiliation: b School of Biological Sciences , University of Edinburgh , Edinburgh , UK.
authors.forename: Hazel A
authors.initials: HA
authors.lastname: Cruickshanks
authors.affiliation: c MRC Human Genetics Unit , Institute of Genetics and Molecular Medicine, University of Edinburgh , Edinburgh , UK.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Meehan
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Lund
authors.affiliation: a School of Medicine, Royal Derby Hospital , University of Nottingham , Derby , UK.
authors.forename: Cristina
authors.identifier: 0000-0002-1053-4618
authors.initials: C
authors.lastname: Tufarelli
mesh_terms: D001374:Azacitidine / Q000008:administration & dosage; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000096:biosynthesis / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics; D011401:Promoter Regions, Genetic; D000097584:DNA Methyltransferase 3B
chemical_list: D001374:Azacitidine; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000097584:DNA Methyltransferase 3B; C000619380:DNMT1 protein, human
keywords: CRC; H4K20me3; L1-ASP; L1PA2; LCT; LINE-1; chromatin; colorectal cancer; methylation; retrotransposons