Promoter hypermethylation of DNA repair gene MGMT in laryngeal squamous cell carcinoma

Abstract

The relationship between hypermethylation of CpG islands in the promoter regions of O⁶-methylguanine DNA methyltransferase (MGMT) genes and laryngeal squamous cell carcinoma was explored. Methylation-specific PCR and semi-quantitative RT-PCR were used to study the promoter methylation and mRNA expression of the MGMT gene in laryngeal carcinoma tissues, tissues adjacent to the tumor and normal laryngeal tissues. Hypermethylation of MGMT gene was detected in 16 samples of 46 (34.8%) laryngeal squamous cell carcinoma samples. However, the MGMT hypermethylation was not detected in all tissues adjacent to the tumors and normal tissues. No significant difference in MGMT gene hypermethylation was found in samples with different histological grades (χ³=3.130,P=0.077) or in samples from patients with different TNM status (χ²=3.957,P=0.138). No expression of MGMT mRNA was detected in all hypermethylated laryngeal carcinoma tissues. The expression of MGMT mRNA was detected in all unmethylated laryngeal carcinoma tissues, tissues adjacent to the tumors and normal tissues. It suggests that MGMT gene promoter hypermethylation is associated with MGMT gene transcription loss in laryngeal carcinoma tissues and possibly plays an important role in carcinogenesis of laryngeal tissues.

Keywords

laryngeal carcinoma / O⁶-methylguanine DNA methyltransferase gene / hypermethylation / methylation-specific PCR

References

[1] EadieJ S, ConradM, ToorchenD, et al.. Mechanism of mutagenesis by O⁶-methylguanine. Nature, 1984, 308: 201-203

[2] PetersonL A, ThomsonN M, CrankshawD L, et al.. Interactions between methylating and pyridyloxobutylating agents in A/J mouse lungs: Implications for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone induced lung tumorigenesis. Cancer Res, 2001, 61(15): 5757-5763

[3] HermanJ G, GraffJ R, MyohanenS, et al.. Methylation-specific PCR assay for methylation status of CpG island. Proc Natl Acad Sci USA, 1996, 93: 9821-9826

[4] WongH, AndersonW D, ChengT, et al.. Monitoring mRNA expression by polymerase chain reaction: the primer-dropping' method. Anal Biochem, 1994, 233: 251-258

[5] KongW J, ZhangS, GuoC, et al.. Methylation-associated silencing of death-associated protein kinase gene in laryngeal squamous cell cancer. Laryngoscope, 2005, 115: 1395-1401

[6] BaylinS B, HermanJ G, GraffJ R, et al.. Alterations in DNA methylation: a fundamental aspect of neoplasia. Adv Cancer Res, 1998, 72: 141-196

[7] MatternJ, KoomagiR, VolmM. Smoking-related increase of O⁶-methylguanine-DNA methyltransferase expression in human lung carcinomas. Carcinogenesis, 1998, 19(7): 1247-1250

[8] EstellerM, HamiltonS R, BurgerP C, et al.. Inactivation of the DNA repair gene O⁶-methylgunine-DNA methyltransferase by promoter hypermethylation is a common event in primary human neoplasia. Cancer Res, 1999, 59: 793-797

[9] DayR S, ZiolkowskiC H, ScudieroD A, et al.. Defective repair of alkylated DNA by human tumor and SV40-transformed human cell strains. Nature (Lond), 1980, 288: 724-727

[10] FornaceA J, PapathanasiouM A, HollanderM C, et al.. Expression of the O⁶-methylguanine DNA methyltransferase gene MGMT in MER+ and MER− human tumor cells. Cancer Res, 1990, 50: 7908-7911

[11] PieperR O, FutscherB W, DongQ, et al.. Comparison of O⁶-methylguanine-DNA methyltransferase gene (MGMT) MRNA levels in MER+ and MER− human tumor cell lines containing the MGMT gene by the polymerase chain reaction technique. Cancer Commun, 1990, 2: 13-20

[12] KroesR A, EricksonL C. The role of mRNA stability and transcription in O⁶-methylguanine-DNA methyltransferase (MGMT) expression in Mer- human tumor cell lines. Carcinogenesis (Lond), 1995, 16: 2255-2257

[13] BelinskyS A, DevereuxT R, MaronpotR R, et al.. Relationship between the formation of promutagenic adducts and the activation of the K-ras protooncogene in lung tumors from A/J mice treated with nitrosamines. Cancer Res, 1989, 49: 5305-5311

[14] ZaidiN H, PretlowT P, O'RiordanM A, et al.. Transgenic expression of human MGMT protects against azoxymethane-induced aberrant crypt foci and G to A mutations in the K-ras oncogene of mouse colon. Carcinogenesis (Lond), 1995, 16: 451-456

[15] EstellerM, RisquesR A, ToyotaM, et al.. Promoter hypermethylation of the DNA repair gene O⁶-methyl-guanine-DNA methyltransferase is associated with the presence of G:C to A:T transition mutations in p53 in human colorectal tumorigenesis. Cancer Res, 2001, 61: 4689-4692

[16] WolfP, HuY C, DoffekK, et al.. O⁶-methylguanine-DNA methyltransferase promoter hypermethylation shifts the p53 mutational spectrum in non-small cell lung cancer. Cancer Res, 2001, 61: 8113-8117