Mutations ofO6-methylguanine-DNA methyltransferase gene in esophageal cancer tissues from Northern China

Abstract

Epidemiologic studies have implicated the involvement of environmental factors in the etiology of esophageal cancer (EC). Our previous data have indicated that EC patients and their blood relatives show genomic instability and are deficient in repair of DNA damage induced by N-nitrosocompounds and related genotoxic agents. Thus, exposure to high levels of N-alkylnitrosamines, which are known animal carcinogens and which induce alkyl adducts in DNA, may be causally linked to EC. Among the alkyl adducts, O 6 -alkylguanine was shown to be the critical one related to carcinogenic lesions; its repair varies widely in a tissue-specific fashion. O 6 -methylguanine-DNA methyltransferase (MGMT) is responsible for its repair. Hence, inactivating mutations in this protein would impair the efficiency of the repair process. To screen for possible mutations in the MGMT polypeptide in EC patients, we analyzed a highly conserved region of the MGMT gene in 40 EC tissues and lymphocytes of 6 high-risk EC family members from high EC areas of Northern China by polymerase chain reaction single-strand conformation polymorphism and by direct sequencing of PCR products. Ten base substitutions (point mutations) within 8 codons of 7 EC samples were identified. However, no germline mutation was found in the high EC families studied so far. Concurrent study in 30 pairs of fresh EC tissues and their adjacent normal mucosa by Southern blot and Western blot analyses showed deletion of the MGMT gene in 2 samples. Thus, the high frequency of mutations (7/40) and deletions (2/30) of the MGMT gene may be partially responsible for the overall high mutation rate observed in EC tissues. Int.

Generating mutations but providing chemosensitivity: the role of O6-methylguanine DNA methyltransferase in human cancer

“…The levels and activity of MGMT in healthy cells are regulated by its protein phosphorylation status (Srivenugopal et al, 2000), the binding of the E6 papillomavirus oncoprotein (Srivenugopal and Ali-Osman, 2002) and the action of p53 (Harris et al, 1996), glucocorticoid hormone (Biswas et al, 1999) and other transcription factors over its 5 0 -CpG island, which includes a classical promoter without TATA and CAAT boxes and a 59 bp enhancer element located at the first exon-intron boundary (Harris et al, 1991) (Figure 1). A single report has described mutations in the MGMT gene (Wang et al, 1997). However, there are many reports of individual differences in MGMT activity in tumors.…”

O6-methylguanine-DNA-methyltransferase expression and gene polymorphisms in relation to chemotherapeutic response in metastatic melanoma

“…The MGMT coding regions, exons 2 -5, were amplified by PCR with exon-specific PCR primers (Otsuka et al, 1996;Wang et al, 1997). PCR reactions were performed on a Perkin-Elmer 9600 thermal cycler (Applied Biosystems, Foster City, CA, USA) under the following amplification conditions: denaturation at 941C for 4 min, followed by 30 cycles at 941C for 30 s (35 cycles 40 s for exon 4), annealing for exons 2, 3 and 5 at 66, 60, and 67 for 30 s, respectively (exon 4 at 551C for 50 s), and 721C for 30 s (exon 4 for 60 s), and then a 7-min extension.…”

Lack of association between Caucasian lung cancer risk and O6-methylguanine-DNA methyltransferase-codon 178 genetic polymorphism

“…Several genetic polymorphisms in the MGMT have been reported [10][11][12][13][14][15][16]. Of these, a single nucleotide polymorphism (SNP) at codon 143 (exon 5) of MGMT, Ile (ATC) to Val (GTC), has been reported to be associated with susceptibility to esophageal and lung cancer [15,16].…”