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      Role of epigenetics in transformation of inflammation into colorectal cancer

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          Abstract

          Molecular mechanisms associated with inflammation-promoted tumorigenesis have become an important topic in cancer research. Various abnormal epigenetic changes, including DNA methylation, histone modification, chromatin remodeling, and noncoding RNA regulation, occur during the transformation of chronic inflammation into colorectal cancer (CRC). These changes not only accelerate transformation but also lead to cancer progression and metastasis by activating carcinogenic signaling pathways. The NF-κB and STAT3 signaling pathways play a particularly important role in the transformation of inflammation into CRC, and both are critical to cellular signal transduction and constantly activated in cancer by various abnormal changes including epigenetics. The NF-κB and STAT3 signals contribute to the microenvironment for tumorigenesis through secretion of a large number of pro-inflammatory cytokines and their crosstalk in the nucleus makes it even more difficult to treat CRC. Compared with gene mutation that is irreversible, epigenetic inheritance is reversible or can be altered by the intervention. Therefore, understanding the role of epigenetic inheritance in the inflammation-cancer transformation may elucidate the pathogenesis of CRC and promote the development of innovative drugs targeting transformation to prevent and treat this malignancy. This review summarizes the literature on the roles of epigenetic mechanisms in the occurrence and development of inflammation-induced CRC. Exploring the role of epigenetics in the transformation of inflammation into CRC may help stimulate futures studies on the role of molecular therapy in CRC.

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          Most cited references86

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          CpG islands in vertebrate genomes.

          Although vertebrate DNA is generally depleted in the dinucleotide CpG, it has recently been shown that some vertebrate genes contain CpG islands, regions of DNA with a high G+C content and a high frequency of CpG dinucleotides relative to the bulk genome. In this study, a large number of sequences of vertebrate genes were screened for the presence of CpG islands. Each CpG island was then analysed in terms of length, nucleotide composition, frequency of CpG dinucleotides, and location relative to the transcription unit of the associated gene. CpG islands were associated with the 5' ends of all housekeeping genes and many tissue-specific genes, and with the 3' ends of some tissue-specific genes. A few genes contained both 5' and 3' CpG islands, separated by several thousand base-pairs of CpG-depleted DNA. The 5' CpG islands extended through 5'-flanking DNA, exons and introns, whereas most of the 3' CpG islands appeared to be associated with exons. CpG islands were generally found in the same position relative to the transcription unit of equivalent genes in different species, with some notable exceptions. The locations of G/C boxes, composed of the sequence GGGCGG or its reverse complement CCGCCC, were investigated relative to the location of CpG islands. G/C boxes were found to be rare in CpG-depleted DNA and plentiful in CpG islands, where they occurred in 3' CpG islands, as well as in 5' CpG islands associated with tissue-specific and housekeeping genes. G/C boxes were located both upstream and downstream from the transcription start site of genes with 5' CpG islands. Thus, G/C boxes appeared to be a feature of CpG islands in general, rather than a feature of the promoter region of housekeeping genes. Two theories for the maintenance of a high frequency of CpG dinucleotides in CpG islands were tested: that CpG islands in methylated genomes are maintained, despite a tendency for 5mCpG to mutate by deamination to TpG+CpA, by the structural stability of a high G+C content alone, and that CpG islands associated with exons result from some selective importance of the arginine codon CGX. Neither of these theories could account for the distribution of CpG dinucleotides in the sequences analysed. Possible functions of CpG islands in transcriptional and post-transcriptional regulation of gene expression were discussed, and were related to theories for the maintenance of CpG islands as "methylation-free zones" in germline DNA.
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            Clinical impact of different classes of infiltrating T cytotoxic and helper cells (Th1, th2, treg, th17) in patients with colorectal cancer.

            The tumor microenvironment includes a complex network of immune T-cell subpopulations. In this study, we systematically analyzed the balance between cytotoxic T cells and different subsets of helper T cells in human colorectal cancers and we correlated their impact on disease-free survival. A panel of immune related genes were analyzed in 125 frozen colorectal tumor specimens. Infiltrating cytotoxic T cells, Treg, Th1, and Th17 cells were also quantified in the center and the invasive margin of the tumors. By hierarchical clustering of a correlation matrix we identified functional clusters of genes associated with Th17 (RORC, IL17A), Th2 (IL4, IL5, IL13), Th1 (Tbet, IRF1, IL12Rb2, STAT4), and cytotoxicity (GNLY, GZMB, PRF1). Patients with high expression of the Th17 cluster had a poor prognosis, whereas patients with high expression of the Th1 cluster had prolonged disease-free survival. In contrast, none of the Th2 clusters were predictive of prognosis. Combined analysis of cytotoxic/Th1 and Th17 clusters improved the ability to discriminate relapse. In situ analysis of the density of IL17+ cells and CD8+ cells in tumor tissues confirmed the results. Our findings argue that functional Th1 and Th17 clusters yield opposite effects on patient survival in colorectal cancer, and they provide complementary information that may improve prognosis. ©2011 AACR.
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              Polycomb silencers control cell fate, development and cancer.

              Polycomb group (PcG) proteins are epigenetic gene silencers that are implicated in neoplastic development. Their oncogenic function might be associated with their well-established role in the maintenance of embryonic and adult stem cells. In this review, we discuss new insights into the possible mechanisms by which PcGs regulate cellular identity, and speculate how these functions might be relevant during tumorigenesis.
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                Author and article information

                Contributors
                Journal
                World J Gastroenterol
                World J. Gastroenterol
                WJG
                World Journal of Gastroenterology
                Baishideng Publishing Group Inc
                1007-9327
                2219-2840
                21 June 2019
                21 June 2019
                : 25
                : 23
                : 2863-2877
                Affiliations
                Institute of Digestive Diseases, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200032, China
                Digestive Endoscopy Department, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200032, China
                Institute of Digestive Diseases, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200032, China
                Institute of Digestive Diseases, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200032, China. jiliver@ 123456vip.sina.com
                Author notes

                Author contributions: All authors contributed equally to this paper with regard to conception and design of the research, literature review and analysis, manuscript critical revision and editing, and final approval of the final version.

                Corresponding author: Guang Ji, MD, PhD, Chief Physician, Director, Doctor, Full Professor, Occupational Physician, Professor, Research Scientist, Teacher, Institute of Digestive Diseases, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, 725 South Wanping Road, Shanghai 200032, China. jiliver@ 123456vip.sina.com

                Telephone: +86-21-64385700 Fax: +86-21-64398310

                Article
                jWJG.v25.i23.pg2863
                10.3748/wjg.v25.i23.2863
                6589733
                31249445
                8c7e14e4-4f4d-46cb-b82c-3fffb8142974
                ©The Author(s) 2019. Published by Baishideng Publishing Group Inc. All rights reserved.

                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.

                History
                : 2 March 2019
                : 24 April 2019
                : 8 May 2019
                Categories
                Review

                colorectal cancer,inflammation,dna methylation,histone modification,lncrna,micrornas,epigenetics

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