title: Promoter hypermethylation and downregulation of the FAS gene may be involved in colorectal carcinogenesis.
abstract: Aberrant DNA methylation has been investigated in carcinogenesis and as biomarker for the early detection of colorectal cancer (CRC). The present study aimed to define the methylation status in the regulatory elements of two proapoptotic genes, Fas cell surface death receptor (FAS) and BCL2-associated X protein (BAX). DNA methylation analysis was performed in tumor and adjacent normal tissue usingHpaII/MspI restriction digestion and methylation-specific polymerase chain reaction (PCR). The results observed downregulation of the FAS and BAX genes in the CRC tissues compared with the adjacent normal samples. Furthermore, demethylation using 5-aza-2'-deoxycytidine treatment followed by reverse-transcription quantitative PCR were performed on the HT-29 cell line to measure BAX and FAS mRNA expression following demethylation. The 5-aza-2'-deoxycytidine treatment resulted in significant FAS gene upregulation in the HT-29 cell line, but no significant difference in BAX expression. Furthermore, analysis of CpG islands in the FAS gene promoter revealed that the FAS promoter was significantly hypermethylated in 53.3% of tumor tissues compared with adjacent normal samples. Taken together, the results indicate that decreased expression of the FAS gene due to hypermethylation of its promoter may lead to apoptotic resistance, and acts as an important step during colorectal carcinogenesis.
authors.affiliation: Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran 19857-17453, Iran; School of Medicine, Shahroud University of Medical Sciences, Shahroud 36247-73955, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Manoochehri
authors.affiliation: School of Medicine, Shahroud University of Medical Sciences, Shahroud 36247-73955, Iran.
authors.forename: Nasim
authors.initials: N
authors.lastname: Borhani
authors.affiliation: Gastroenterology and Hepatology Department, Baqiyatallah Research Center for Gastroenterology and Liver Diseases, Baqiyatallah University of Medical Sciences, Tehran 14359-15371, Iran.
authors.forename: Ashraf
authors.initials: A
authors.lastname: Karbasi
authors.affiliation: Cell and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran 19857-17453, Iran.
authors.forename: Ameneh
authors.initials: A
authors.lastname: Koochaki
authors.affiliation: Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran 19857-17453, Iran; Cell and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran 19857-17453, Iran.
authors.forename: Bahram
authors.initials: B
authors.lastname: Kazemi
keywords: Fas cell surface death receptor; apoptosis; colorectal cancer; gene expression; methylation