Journal Article

Epigenetic alterations in <i>RASSF1A</i> in human aberrant crypt foci

Emily J. Greenspan, Melissa A. Jablonski, Thiruchandurai V. Rajan, Joel Levine, Glenn S. Belinsky and Daniel W. Rosenberg

in Carcinogenesis

Volume 27, issue 7, pages 1316-1322
Published in print July 2006 | ISSN: 0143-3334
Published online March 2006 | e-ISSN: 1460-2180 | DOI:
Epigenetic alterations in RASSF1A in human aberrant crypt foci

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CpG island methylation (CIM) is an epigenetic mechanism for transcriptional silencing that occurs at various stages of colon tumorigenesis. CIM has been found in serrated adenomas and hyperplastic polyps. There is also evidence for hypermethylation in aberrant crypt foci (ACF) that are found in resected colons from cancer patients. Our study addresses promoter methylation of a tumor suppressor gene, RASSF1A, within the colonic epithelium of subjects undergoing screening colonoscopies in the absence of synchronous tumors. Patients included in this study were at elevated risk for colorectal cancer (CRC) based on family history, but without a previously occurring or synchronous colon carcinoma. ACF were identified using close-focus magnifying chromendoscopy and collected by biopsy in situ. We isolated ACF and adjacent normal colonic epithelium by laser capture microdissection (LCM) and studied methylation of the RASSF1A promoter region in ACF and in adjacent normal mucosa. Expression of RASSF1A was verified using quantitative real-time polymerase chain reaction (QRT–PCR). We found that 8.6% (3 out of 35) of ACF had K-ras mutations and 24% (6 out of 25) had RASSF1A hypermethylation. Our results demonstrate that RASSF1A hypermethylation and K-ras mutations are not mutually exclusive and are present in patients at elevated risk of CRC. Importantly, CIM of RASSF1A is an early epigenetic aberration, occurring in the absence of synchronous colon tumors and is not accompanied by field effects into the surrounding epithelium.

Keywords: ACF, aberrant crypt foci; ANM, adjacent normal mucosa; CIM, CpG island methylation; CRC, colorectal cancer; FBS, fetal bovine serum; H&E, hematoxylin and eosin; LCM, laser capture microdissection; MMR, mismatch repair; MSI, microsatellite instability; MSP, methylation-specific PCR; PCR, polymerase chain reaction; QRT–PCR, quantitative real-time PCR

Journal Article.  4963 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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