B-RAF mutation and accumulated gene methylation in aberrant crypt foci (ACF), sessile serrated adenoma/polyp (SSA/P) and cancer in SSA/P

Abstract

Background:Sessile serrated adenomas/polyps (SSA/Ps) are a putative precursor of colon cancer with microsatellite instability (MSI). However, the developmental mechanism of SSA/P remains unknown. We performed genetic analysis and genome-wide DNA methylation analysis in aberrant crypt foci (ACF), SSA/P, and cancer in SSA/P specimens to show a close association between ACF and the SSA/P-cancer sequence. We also evaluated the prevalence and number of ACF in SSA/P patients.Methods:ACF in the right-side colon were observed in 36 patients with SSA/Ps alone, 2 with cancers in SSA/P, and 20 normal subjects and biopsied under magnifying endoscopy. B-RAF mutation and MSI were analysed by PCR–restriction fragment length polymorphism (RFLP) and PCR–SSCP, respectively, in 15 ACF, 20 SSA/P, and 2 cancer specimens. DNA methylation array analysis of seven ACF, seven SSA/P, and two cancer in SSA/P specimens was performed using the microarray-based integrated analysis of methylation by isochizomers (MIAMI) method.Results:B-RAF mutations were frequently detected in ACF, SSA/P, and cancer in SSA/P tissues. The number of methylated genes increased significantly in the order of ACF<SSA/P<cancer. The most commonly methylated genes in SSA/P were PQLC1, HDHD3, RASL10B, FLI1, GJA3, and SLC26A2. Some of these genes were methylated in ACF, whereas all genes were methylated in cancers. Immunohistochemistry revealed their silenced expression. Microsatellite instability and MLH1 methylation were observed only in cancer. The prevalence and number of ACF were significantly higher in SSA/P patients than in normal subjects. A significant correlation was seen between the numbers of SSA/P and ACF in SSA/P patients.Conclusions:Our results suggest that ACF are precursor lesions of the SSA/P-cancer sequence in patients with SSA/P, where ACF arise by B-RAF mutation and methylation of some of the six identified genes and develop into SSA/Ps through accumulated methylation of these genes.

Protein expression of Fragile Histidine Triad and cyclooxgenase-2 in serrated neoplasia of the colorectum

“…The present results indicated that reduced FHIT expression was frequent in serrated neoplasias, particularly SSA/Ps, when compared with non-serrated neoplasias. Aberrant crypt foci in the right side of the colon, one of the characteristics of MVHP, is a precursor lesion for the SSA/P-cancer sequence (29) and shows reduced FHIT expression (13,30). In the present study, reduced or no FHIT expression was detected in 30.8% of MVHPs.…”

Distinguishable Prognostic Signatures of Left- and Right-Sided Colon Cancer: a Study Based on Sequencing Data

“…Lee MS et al found that there were noteworthy inverse correlations between EREG expression and methylation, as well as tumor position, BRAF mutation, and CIMP-high status [31]. Inoue A et al found that methylated RASL10B could be involved in the development from sessile serrated adenomas/polyps (SSA/Ps) to colon cancer [32]. Zou H et al demonstrated that profound down-regulation of RASL10B mRNA level could be observed in all breast cancer cell lines and suggested that RASL10B could act as a novel member of the Ras superfamily, which owns the potential to be a tumor suppressor [33].…”

The Molecular Pathogenesis of Colorectal Cancer and Its Potential Application to Colorectal Cancer Screening

“…31, 3231, 33 Inoue, 2014 It also appears that loss of MMR activity is not sufficient to induce polyp formation based on modeling studies and the lack of colon cancer seen in individuals with biallelic germline mutations in MMR genes. 34, 35 Of considerable importance regarding its clinical impact, there is substantial indirect data that polyps that arise in the setting of loss of MMR activity have a shortened polyp→CRC interval so that MSI CRCs can arise in as little as 2–3 years from a polyp.…”