title: FXR silencing in human colon cancer by DNA methylation and KRAS signaling.
abstract: Farnesoid X receptor (FXR) is a bile acid nuclear receptor described through mouse knockout studies as a tumor suppressor for the development of colon adenocarcinomas. This study investigates the regulation of FXR in the development of human colon cancer. We used immunohistochemistry of FXR in normal tissue (n = 238), polyps (n = 32), and adenocarcinomas, staged I-IV (n = 43, 39, 68, and 9), of the colon; RT-quantitative PCR, reverse-phase protein array, and Western blot analysis in 15 colon cancer cell lines; NR1H4 promoter methylation and mRNA expression in colon cancer samples from The Cancer Genome Atlas; DNA methyltransferase inhibition; methyl-DNA immunoprecipitation (MeDIP); bisulfite sequencing; and V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) knockdown assessment to investigate FXR regulation in colon cancer development. Immunohistochemistry and quantitative RT-PCR revealed that expression and function of FXR was reduced in precancerous lesions and silenced in a majority of stage I-IV tumors. FXR expression negatively correlated with phosphatidylinositol-4, 5-bisphosphate 3 kinase signaling and the epithelial-to-mesenchymal transition. The NR1H4 promoter is methylated in ~12% colon cancer The Cancer Genome Atlas samples, and methylation patterns segregate with tumor subtypes. Inhibition of DNA methylation and KRAS silencing both increased FXR expression. FXR expression is decreased early in human colon cancer progression, and both DNA methylation and KRAS signaling may be contributing factors to FXR silencing. FXR potentially suppresses epithelial-to-mesenchymal transition and other oncogenic signaling cascades, and restoration of FXR activity, by blocking silencing mechanisms or increasing residual FXR activity, represents promising therapeutic options for the treatment of colon cancer.
authors.affiliation: Dept. of Pharmacology and Toxicology, School of Pharmacy, Rutgers Univ., Piscataway, NJ 08854. guo@eohsi.rutgers.edu.
authors.forename: Ann M
authors.initials: AM
authors.lastname: Bailey
authors.forename: Le
authors.initials: L
authors.lastname: Zhan
authors.forename: Dipen
authors.initials: D
authors.lastname: Maru
authors.forename: Imad
authors.initials: I
authors.lastname: Shureiqi
authors.forename: Curtis R
authors.initials: CR
authors.lastname: Pickering
authors.forename: Galina
authors.initials: G
authors.lastname: Kiriakova
authors.forename: Julie
authors.initials: J
authors.lastname: Izzo
authors.forename: Nan
authors.initials: N
authors.lastname: He
authors.forename: Caimiao
authors.initials: C
authors.lastname: Wei
authors.forename: Veerabhadran
authors.initials: V
authors.lastname: Baladandayuthapani
authors.forename: Han
authors.initials: H
authors.lastname: Liang
authors.forename: Scott
authors.initials: S
authors.lastname: Kopetz
authors.forename: Garth
authors.initials: G
authors.lastname: Powis
authors.forename: Grace L
authors.initials: GL
authors.lastname: Guo
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology; D001647:Bile Acids and Salts / Q000378:metabolism; D063646:Carcinogenesis / Q000378:metabolism; D045744:Cell Line, Tumor; D003106:Colon / Q000378:metabolism / Q000473:pathology; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D003111:Colonic Polyps / Q000378:metabolism / Q000473:pathology; D019175:DNA Methylation; D058750:Epithelial-Mesenchymal Transition; D020868:Gene Silencing; D006801:Humans; D009367:Neoplasm Staging; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras); D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D001647:Bile Acids and Salts; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D018160:Receptors, Cytoplasmic and Nuclear; D018631:ras Proteins; D000099150:Receptor, Farnesoid X-Activated; C117307:KRAS protein, human
keywords: bile acids; colon cancer; farnesoid X receptor; nuclear receptor; promoter methylation