Carcinogenesis Advance Access published online on July 9, 2007
Carcinogenesis, doi:10.1093/carcin/bgm160
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MGMT germline polymorphism is associated with somatic MGMT promoter methylation and gene silencing in colorectal cancer
1 Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
2 Department of Pathology, Brigham and Women's Hospital, Boston, MA 02115, USA
3 Department of Pathology, Harvard Medical School, Boston, MA 02115, USA
4 Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA
5 California Pacific Medical Center, San Francisco, CA 94107, USA
6 Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School, Boston, MA 02115, USA
* Corresponding Author: Shuji Ogino, M.D., Ph.D. Department of Medical Oncology Dana-Farber Cancer Institute Harvard Medical School 75 Francis St., BWH Pathology Boston, MA 02115 USA Telephone: 617-632-3978 Fax: 617-277-9015 Email: shuji_ogino{at}dfci.harvard.edu
O-6-methylguanine-DNA methyltransferase (MGMT) repairs inappropriately methylated guanine residues in DNA. MGMT promoter methylation and gene silencing are common events in colorectal cancer, and may or may not coexist with the CpG island methylator phenotype (CIMP). To date, no study has examined the relationship between MGMT promoter methylation and common MGMT single nucleotide polymorphisms (SNP), which have been associated with colorectal cancer risk. Utilizing real-time PCR (MethyLight technology), we quantified DNA methylation in MGMT and 8 other markers (a CIMP-diagnostic panel, including CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1) in 182 colorectal cancers collected from two prospective cohorts, the Nurses’ Health Study and the Health Professionals Follow-up Study. We genotyped 4 MGMT germline SNPs in normal DNA, and assessed microsatellite instability (MSI), 18q loss of heterozygosity, KRAS and BRAF status in tumors. The presence of a common MGMT promoter SNP (NM_002412.2:c.-56C>T) was strongly associated with MGMT methylation (multivariate odds ratio 18.0; 95% confidence interval (CI), 6.2-52.1, p<0.0001). The presence of the c.-56C>T SNP was also associated with loss of MGMT expression in tumors (assessed by immunohistochemistry) (p=0.009). This promoter SNP was not correlated with KRAS, BRAF, CIMP or MSI status. None of the other 3 non-promoter SNPs was significantly associated with any molecular changes tested. In conclusion, we have found a strong association between the germline polymorphism (c.-56C>T) of the MGMT promoter and promoter methylation/silencing of MGMT in colorectal cancer. Our data provide compelling evidence for common susceptibility for MGMT promoter CpG island methylation.
Key Words: colon cancer • MGMT • SNP • promoter • methylation
Received May 16, 2007; revised June 19, 2007; accepted July 3, 2007.