title: Epigenetic silencing of miR-137 is an early event in colorectal carcinogenesis.
abstract: Global downregulation of microRNAs (miRNA) is a common feature in colorectal cancer (CRC). Whereas CpG island hypermethylation constitutes a mechanism for miRNA silencing, this field largely remains unexplored. Herein, we describe the epigenetic regulation of miR-137 and its contribution to colorectal carcinogenesis. We determined the methylation status of miR-137 CpG island in a panel of six CRC cell lines and 409 colorectal tissues [21 normal colonic mucosa from healthy individuals (N-N), 160 primary CRC tissues and their corresponding normal mucosa (N-C), and 68 adenomas]. TaqMan reverse transcription-PCR and in situ hybridization were used to analyze miR-137 expression. In vitro functional analysis of miR-137 was performed. Gene targets of miR-137 were identified using a combination of bioinformatic and transcriptomic approaches. We experimentally validated the miRNA:mRNA interactions. Methylation of the miR-137 CpG island was a cancer-specific event and was frequently observed in CRC cell lines (100%), adenomas (82.3%), and CRC (81.4%), but not in N-C (14.4%; P < 0.0001 for CRC) and N-N (4.7%; P < 0.0001 for CRC). Expression of miR-137 was restricted to the colonocytes in normal mucosa and inversely correlated with the level of methylation. Transfection of miR-137 precursor in CRC cells significantly inhibited cell proliferation. Gene expression profiling after miR-137 transfection discovered novel potential mRNA targets. We validated the interaction between miR-137 and LSD-1. Our data indicate that miR-137 acts as a tumor suppressor in the colon and is frequently silenced by promoter hypermethylation. Methylation silencing of miR-137 in colorectal adenomas suggests it to be an early event, which has prognostic and therapeutic implications.
authors.affiliation: Department of Internal Medicine, Division of Gastroenterology, Charles A Sammons Cancer Center and Baylor Research Institute, Baylor University Medical Center, Dallas, Texas 75246, USA.
authors.forename: Francesc
authors.initials: F
authors.lastname: Balaguer
authors.forename: Alexander
authors.initials: A
authors.lastname: Link
authors.forename: Juan Jose
authors.initials: JJ
authors.lastname: Lozano
authors.forename: Miriam
authors.initials: M
authors.lastname: Cuatrecasas
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nagasaka
authors.forename: C Richard
authors.initials: CR
authors.lastname: Boland
authors.forename: Ajay
authors.initials: A
authors.lastname: Goel
mesh_terms: D000368:Aged; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015536:Down-Regulation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D045325:HCT116 Cells; D019073:HT29 Cells; D056466:Histone Demethylases / Q000235:genetics; D006801:Humans; D008297:Male; D035683:MicroRNAs / Q000096:biosynthesis / Q000235:genetics*; D008875:Middle Aged; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D014162:Transfection
chemical_list: C545567:MIRN137 microRNA, human; D035683:MicroRNAs; D012333:RNA, Messenger; D056466:Histone Demethylases; C495195:KDM1A protein, human