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Copyright ©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastrointest Oncol. Mar 15, 2017; 9(3): 105-120
Published online Mar 15, 2017. doi: 10.4251/wjgo.v9.i3.105
CpG island methylator phenotype in adenocarcinomas from the digestive tract: Methods, conclusions, and controversies
Francisco Sánchez-Vega, Valer Gotea, Yun-Ching Chen, Laura Elnitski
Francisco Sánchez-Vega, Valer Gotea, Yun-Ching Chen, Laura Elnitski, Genomic Functional Analysis Section, National Human Genome Research Institute, National Institutes of Health, Rockville, MD 20852, United States
Author contributions: Sánchez-Vega F, Gotea V, Chen YC and Elnitski L have all read and approved the final manuscript; Elnitski L developed the idea and supervised the research; Sánchez-Vega F, Gotea V and Chen YC generated and analyzed data; and all authors contributed to the writing and editing of the final manuscript; Sánchez-Vega F and Gotea V contributed equally to this work.
Conflict-of-interest statement: None.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Laura Elnitski, PhD, Senior Investigator, Head, Genomic Functional Analysis Section, National Human Genome Research Institute, National Institutes of Health, 5625 Fishers Lane, Rockville, MD 20852, United States. elnitski@mail.nih.gov
Telephone: +1-301-4510265 Fax: +1-301-4356170
Received: June 2, 2016
Peer-review started: June 6, 2016
First decision: September 2, 2016
Revised: November 3, 2016
Accepted: January 2, 2017
Article in press: January 3, 2017
Published online: March 15, 2017
Abstract

Over the last two decades, cancer-related alterations in DNA methylation that regulate transcription have been reported for a variety of tumors of the gastrointestinal tract. Due to its relevance for translational research, great emphasis has been placed on the analysis and molecular characterization of the CpG island methylator phenotype (CIMP), defined as widespread hypermethylation of CpG islands in clinically distinct subsets of cancer patients. Here, we present an overview of previous work in this field and also explore some open questions using cross-platform data for esophageal, gastric, and colorectal adenocarcinomas from The Cancer Genome Atlas. We provide a data-driven, pan-gastrointestinal stratification of individual samples based on CIMP status and we investigate correlations with oncogenic alterations, including somatic mutations and epigenetic silencing of tumor suppressor genes. Besides known events in CIMP such as BRAF V600E mutation, CDKN2A silencing or MLH1 inactivation, we discuss the potential role of emerging actors such as Wnt pathway deregulation through truncating mutations in RNF43 and epigenetic silencing of WIF1. Our results highlight the existence of molecular similarities that are superimposed over a larger backbone of tissue-specific features and can be exploited to reduce heterogeneity of response in clinical trials.

Keywords: CpG island methylator phenotype, CpG island, Promoter, DNA methylation, Hypermethylation, Gastrointestinal cancer

Core tip: Awareness of the CpG island methylator phenotype (CIMP) is growing for all adenocarcinomas. Here, we summarize previous work on the topic and discuss unanswered questions regarding commonalities and differences of CIMP tumors from esophageal, gastric, and colorectal adenocarcinomas, where data has been made available from the Cancer Genome Atlas. Our analysis includes a review of our pan-cancer method to stratify tumors based on CIMP and addresses the most frequent mutations found in those samples. We include new data implicating truncating mutations in RNF43 and silencing of WIF1I. We also describe in detail the methylation of CpG sites within the MLH1 promoter across these tumor types.