Colorectal carcinoma (CRC) is the most common gastrointestinal malignancy, affecting about 160,000 individuals per year in the U.S. and the rate of CRC is 1.5 times higher in African Americans than in Caucasian. Several lines of evidence generated by epidemiological, animal and in vitro studies suggest a pathway in the development of colon cancer. The biomarkers of neoplastic transformation, which have a predictive value as antecedents of malignancy include: markers of cell cycle regulator p16 and gene mutations (p53, and DNA mismatch repair genes including hMHL1). Methylation of the DNA is part of the regulation of gene products in the CpG island. Genes can be turned off by methylation and in some cases turning off important genes (e.g. tumor suppressor genes) can be suicidal to cells. We postulate that micro- satellite instability (MSI) and/or silencing of p16 (tumor suppressor gene), which is known to modulate cellular proliferation in colonic mucosa, may alter chromosome behavior in the process of neoplastic transformation. The important role of methylation and MSI in the pathogenicity of colon cancer has been increasingly recognized. Identification of errors in DNA replication that can be detected by MSI is part of the neoplastic progression provides a unique opportunity to study the development of colonic neoplasia. In this proposal we plan to conduct experiments on normal and colon cancer tissues resected from subjects (n=120) over the past 3 to four years. Tissue will be obtained retrospectively from archival specimens of CRC patients diagnosed at Howard University and Johns Hopkins University to determine chromosome imbalance and gene alterations. Five microsatellite loci will be measured by MSI and, by immunohistochemistry in tissue samples. Non-parametric statistical tests will be applied to determine the correlation between histological changes (degree of dysplasia, expansion of the cryptal proliferative zone) and changes in the expression of biomarkers of neoplastic transformation (p16 methylation and MSI). There is anecdotal evidence that a higher percentage of colorectal cancers from African Americans have MSI. This has not yet been well studied, therefore we are carrying out this pilot project to better define the prevalence of MSI in cancers from African American persons. The purpose of this collaborative proposal is to examine the effect of gene methylation such as p16 and MSI in the pathway of neoplastic transformation in patients with a history of resected colon cancer compared with changes in similar markers in mucosal biopsies in normal controls.
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