Colorectal neoplasia results from a progressive process of gene mutation and epigenetic alterations that drive the initiation and progression of normal colon to benign adenomas to malignant adenocarcinomas (paralleling histological changes) because these mutations affect signaling pathways that deregulate hallmark behaviors of normal colon stem cells. DNA mismatch repair (MMR), an evolutionary-conserved system that repairs polymerase mistakes after DNA synthesis and corrects insertion/deletion (I/D) loops at microsatellite sequences throughout the genome, is disrupted in the germline of familial colon cancer (Lynch syndrome) as well as inactivated in up to 20% of sporadic colorectal neoplasms due to hypermethylation of one of the components of DNA MMR. The genetic consequences of disrupted DNA MMR is non-repair of the polymerase mistakes and insertion/deletion loops that occur in non-coding as well as coding microsatellite regions after DNA heteroduplexes form first, causing neoplasia to commence that defines the clinical syndromes. We hypothesize that human DNA MMR has specific recognition fidelity in targeting repair of I/D loops, but the fundamentals of how heteroduplex DNA forms are independent of DNA MMR. Our preliminary data using novel constructs in which to measure human DNA MMR mutation indicate that (a) heteroduplex DNA forms prior to mutation and appears independent of the DNA MMR status, and that full mutation is only seen with defective DNA MMR, and (b) the ability of microsatellites to form I/D loops and subsequent mutation is influenced by flanking DNA sequences that surround the microsatellite. Additionally, there is growing evidence that elevated microsatellite instability at selected tetranucleotide repeats (EMAST), seen is 60% of colon cancer specimens, may be associated inflammation-induced reduction of the DNA MMR protein hMSH3, causing this genetic signature. How EMAST fits into the pathogenesis of colon neoplasia is not defined. In this continuation proposal, we will focus on hMSH3 and how deficiency causes EMAST, and determine the biological consequences of EMAST. More specifically, we hypothesize that hMSH3 prevents tetranucleotide frameshifts, and this will be examined in Specific Aim 1. We further aim to understand the role of hMSH3 on influencing potential target genes for mutation (Specific Aim 2). We will also define EMAST by hMSH3 expression, and examine the link of inflammation with hMSH3 and EMAST (Specific Aim 3). The impact of this proposal lies in understanding the fundamentals of how DNA is altered to drive a common cancer, and our ability to potentially intervene ultimately by pharmacologic or direct intervention to prevent occurrence or death from colorectal cancer.

Public Health Relevance

Colorectal cancer is among the most common cancers afflicting Americans. This cancer is derived and driven by conditions, some within DNA, that allow for mutation of key growth regulatory genes that then abrogates their normal regulatory function. This proposal aims to understand how DNA becomes mutated, as well how inflammation may influence this mutation. Ultimately, interfering with this process through pharmacologic or direct intervention should prevent or reduce colorectal cancer deaths.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Clinical, Integrative and Molecular Gastroenterology Study Section (CIMG)
Program Officer
Hamilton, Frank A
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University of Michigan Ann Arbor
Internal Medicine/Medicine
Schools of Medicine
Ann Arbor
United States
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Carethers, John M (2016) GRG Profiles: John M. Carethers. Dig Dis Sci 61:1429-35
Koi, Minoru; Garcia, Melissa; Choi, Chan et al. (2016) Microsatellite Alterations With Allelic Loss at 9p24.2 Signify Less-Aggressive Colorectal Cancer Metastasis. Gastroenterology 150:944-55
Basa, Ranor C B; Davies, Vince; Li, Xiaoxiao et al. (2016) Decreased Anti-Tumor Cytotoxic Immunity among Microsatellite-Stable Colon Cancers from African Americans. PLoS One 11:e0156660
Carethers, John M; Goel, Ajay (2016) Presentation of the Julius M. Friedenwald Medal to C. Richard Boland, MD, AGAF. Gastroenterology 150:1673-7
Suzuki, Satoshi; Iwaizumi, Moriya; Tseng-Rogenski, Stephanie et al. (2016) Production of truncated MBD4 protein by frameshift mutation in DNA mismatch repair-deficient cells enhances 5-fluorouracil sensitivity that is independent of hMLH1 status. Cancer Biol Ther 17:760-8
Carethers, John M (2016) Facilitating Minority Medical Education, Research, and Faculty. Dig Dis Sci 61:1436-9
Fearon, Eric R; Carethers, John M (2015) Molecular subtyping of colorectal cancer: time to explore both intertumoral and intratumoral heterogeneity to evaluate patient outcome. Gastroenterology 148:10-3
Carethers, John M (2015) Screening for colorectal cancer in African Americans: determinants and rationale for an earlier age to commence screening. Dig Dis Sci 60:711-21
Carethers, John M; Braun, Jonathan; Sands, Bruce E (2015) Genetics, Genetic Testing, and Biomarkers of Digestive Diseases. Gastroenterology 149:1131-3
Carethers, John M; Koi, Minoru; Tseng-Rogenski, Stephanie S (2015) EMAST is a Form of Microsatellite Instability That is Initiated by Inflammation and Modulates Colorectal Cancer Progression. Genes (Basel) 6:185-205

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