Carcinogenesis Advance Access originally published online on July 9, 2007
Carcinogenesis 2007 28(9):1985-1990; 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, 75 Francis Street, 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, 75 Francis Street, Boston, MA 02115, USA
* To whom correspondence should be addressed. Tel: +1 617 632 3978; Fax: +1 617 277 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 co-exist 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 (SNPs), which have been associated with colorectal cancer risk. Utilizing real-time polymerase chain reaction (MethyLight technology), we quantified DNA methylation in MGMT and eight other markers (a CIMP diagnostic panel including CACNA1G, CDKN2A, 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 four MGMT germline SNPs in normal DNA and assessed microsatellite instability (MSI), 18q loss of heterozygosity and KRAS and BRAF status in tumors. The presence of a common MGMT promoter SNP (NM_002412.2:c.-56C>T) (rs16906252) was strongly associated with MGMT methylation (multivariate odds ratio 18.0; 95% confidence interval, 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 three 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.
Abbreviations: CACNA1 G, calcium channel, voltage-dependent, T type alpha-1 G subunit; CDKN2A, cyclin-dependent kinase inhibitor 2A (pl6/INK4A); CI, confidence interval; CIMP, CpG island methylator phenotype; CRABP1, cellular retinoic acid binding protein 1; IGF2, insulin-like growth factor 2; LOH, loss of heterozygosity; MGMT, O-6-methylguanine-DNA methyltransferase; MSI, microsatellite instability; MSS, microsatellite stable; NEUROG1, neurogenin 1; OR, odds ratio; PCR, polymerase chain reaction; PMR, percentage of methylated reference (degree of methylation); RUNX3, runt-related transcription factor 3; SNP, single nucleotide polymorphism; SOCS1, suppressor of cytokine signaling 1
Received May 16, 2007; revised June 19, 2007; accepted July 3, 2007.