The hypermethylation of CpG island in promoter regions and protein expression of O~6-methylguanine-DNA methyltransferase gene in colorectal tumor / 中华消化杂志

ABSTRACT

Objective To investigate the effect of promoter hypermethylation of O 6 methylguanine DNA methyltransferase (MGMT) gene on colorectal tumorigenesis and progression. Methods The promoter hypermethylation of O 6 methylguanine DNA methyltransferase gene was assayed in 27 sporadic colorectal adenomas, 62 sporadic colorectal carcinomas and 20 normal colorectal mucosa tissues by methylation specific PCR. At the same time, the expression of MGMT protein was studied in the same samples using immunohistochemistry. Results None of the normal colorectal mucosa tissues showed methylated bands. Promoter hypermethylation was detected in 40.7%(11/27) of adenomas and 43.5% (27/62) of carcinomas, respectively. MGMT proteins were expressed in nucleus and cytoplasm of normal colorectal mucosa tissues. Loss of MGMT expression was found in 22.2% (6/27) of adenomas and 45.2% (28/62) of carcinomas, respectively. There were significant difference among them ( P =0.041). Methylation was detected in 5 of the 6 adenomas( P =0.027) and 24 of the 28 carcinomas( P