Protein expression and methylation of MGMT, a DNA repair gene and their correlation with clinicopathological parameters in invasive ductal carcinoma of the breast
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Epigenetic mechanisms such as DNA methylation are being increasingly recognized to play an important role in cancer and may serve as a cancer biomarker. The aim of this study was to evaluate the promoter methylation status of MGMT (O6-methylguanine-DNA methyltransferase) and a possible correlation with the expression of MGMT and standard clinicopathological parameters in invasive ductal breast carcinoma patients (IDC) of Kashmir. Methylation-specific PCR was carried out to investigate the promoter methylation status of MGMT in breast tumors paired with the corresponding normal tissue samples from 128 breast cancer patients. The effect of promoter methylation on protein expression in the primary breast cancer and adjacent normal tissues was evaluated by immunohistochemistry (n = 128) and western blotting (n = 30). The frequency of tumor hypermethylation was 39.8 % and a significant difference in methylation frequency among breast tumors were found (p < 0.001) when compared with the corresponding normal tissue. Immunohistochemical analysis showed no detectable expression of MGMT in 68/128 (53.1 %) tumors. MGMT promoter methylation mediated gene silencing was associated with loss of its protein expression (rs = −0.285, p = 0.001, OR = 3.38, 95 % CI = 1.59–7.17). A significant correlation was seen between loss of MGMT and lymph node involvement (p = 0.030), tumor grade (p < 0.0001), loss of estrogen receptors (ER; p = 0.021) and progesterone receptors (PR) (p = 0.016). Also, MGMT methylation was found to be associated with tumor grade (p = 0.011), tumor stage (p = 0.009), and loss of ER (p = 0.003) and PR receptors (p = 0.009). To our knowledge, our findings, for the first time, in Kashmiri population, indicate that MGMT is aberrantly methylated in breast cancer and promoter hypermethylation could be attributed to silencing of MGMT gene expression in breast cancer. Our data suggests that MGMT promoter hypermethylation could have a potential function as molecular biomarker of breast oncogenesis. Also, based on their predictive value of response to therapy, the immunohistochemical evaluation and interpretation of MGMT may also help in future to establish therapeutic strategies for patients with breast cancer.
KeywordsBreast cancer Promoter methylation MGMT MSP Kashmir
The authors are thankful to the University Grants Commission (UGC), New Delhi, India, for providing the funds that allowed us to carry out this research.
Conflicts of interest
The contributing authors declare that they have no competing interests.
- 1.Ferlay J, Soerjomataram I, Ervik M, Dikshit R, Eser S, Mathers C, Rebelo M, Parkin D, Forman D, Bray F: GLOBOCAN 2012 v1.0, Cancer Incidence and Mortality Worldwide: IARC CancerBase No. 11 [Internet]. Lyon, France: International Agency for Research on Cancer; 2013. Available from: http://globocan.iarc.fr, accessed on 13/February/2014. In, 2013.
- 2.Indian Council of Medical Research ND, 2013.: National Cancer registry Programme: Consolidated Report of the Population Based Cancer Registries (PBCR) 2007–2011. In, 2013.Google Scholar
- 4.RCC: Sheri-Kashmir Institute of Medical Sciences. Retreived on 04/07/2014 2013.Google Scholar
- 5.Dworkin AM, Huang THM, Toland AE: Epigenetic alterations in the breast: Implications for breast cancer detection, prognosis and treatment. In Seminars in Cancer Biology. Elsevier, 2009:165–171.Google Scholar
- 15.Mehrotra J, Ganpat MM, Kanaan Y, Fackler MJ, McVeigh M, Lahti-Domenici J, et al. Estrogen receptor/progesterone receptor-negative breast cancers of young African-American women have a higher frequency of methylation of multiple genes than those of Caucasian women1. Clin Cancer Res. 2004;10:2052–7.CrossRefPubMedGoogle Scholar
- 19.Alkam Y, Mitomi H, Nakai K, Himuro T, Saito T, Takahashi M, et al. Protein expression and methylation of DNA repair genes hMLH1, hMSH2, MGMT and BRCA1 and their correlation with clinicopathological parameters and prognosis in basal-like breast cancer. Histopathology. 2013;63:713–25.PubMedGoogle Scholar
- 22.Esteller M, Toyota M, Sanchez-Cespedes M, Capella G, Peinado MA, Watkins DN, et al. Inactivation of the DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation is associated with G to A mutations in K-ras in colorectal tumorigenesis. Cancer Res. 2000;60:2368–71.PubMedGoogle Scholar
- 23.Pertschuk LP, Kim DS, Nayer K, Feldman JG, Eisenberg KB, Carter AC, et al. Immunocytochemical estrogen and progestin receptor assays in breast cancer with monoclonal antibodies. Histopathologic, demographic, and biochemical correlations and relationship to endocrine response and survival. Cancer. 1990;66:1663–70.CrossRefPubMedGoogle Scholar
- 27.Rhodes A, Jasani B, Anderson E, Dodson AR, Balaton AJ. Evaluation of HER-2/neu immunohistochemical assay sensitivity and scoring on formalin-fixed and paraffin-processed cell lines and breast tumors a comparative study involving results from laboratories in 21 countries. Am J Clin Pathol. 2002;118:408–17.CrossRefPubMedGoogle Scholar
- 38.Kaina B, Christmann M, Naumann S, Roos WP. MGMT: key node in the battle against genotoxicity, carcinogenicity and apoptosis induced by alkylating agents. DNA Repair. 2007;6:1079–1099.Google Scholar