Tumor Progression Through Epigenetic Gene Silencing of O6−Methylguanine-DNA Methyltransferase in Human Biliary Tract Cancers
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We previously demonstrated in an immunohistochemical study that reduced expression of O6−methylguanine-DNA methyltransferase (MGMT) correlated with a poorer prognosis in patients with biliary tract cancers. The purpose of this study was to clarify how MGMT deficiency leads to a poor outcome in biliary tract cancer. Thus, we examined epigenetic (promoter methylation) and genetic (gene mutation) alterations in biliary tract cancer.
We examined 37 biliary tract cancer specimens from patients who underwent surgical resection. Promoter methylation was determined by one-step or two-step methylation-specific polymerase chain reaction. Gene mutation was identified by direct sequencing. The expression of MGMT protein in paraffin-embedded tissue was examined by immunohistochemistry.
Frequencies of promoter methylation were 70% for p16/INK4a, 49% for MGMT, 46% for hMLH1, 41% for E-cadherin, and 32% for DAPK genes. MGMT methylation status was closely correlated with the MGMT protein expression determined by immunohistochemistry (P < .001). Although this was not statistically significant, biliary tract cancer tumors with MGMT methylation expressed multigene methylation more frequently than tumors without MGMT methylation (P = .071). A total of 33 mutations were identified in 4 cancer-related genes: p53, K-ras, β-catenin, and p16/INK4a genes. The most common mutation was GC to AT transitions (58%), which were significantly associated with MGMT promoter methylation (P = .011). These findings suggest that loss of MGMT expression by promoter methylation results in accumulation of GC to AT gene mutations.
Reduced MGMT expression may increase the malignant potential of biliary tract cancer through both epigenetic and genetic mechanisms.
KeywordsDNA alkylation DNA repair gene MGMT Biliary tract cancer Multigene methylation Gene mutation
- 8.Sakumi, K, Shiraishi, A, Shimizu, S, Tsuzuki, T, Ishikawa, T, Sekiguchi, M 1997Methylnitrosourea-induced tumorigenesis in MGMT gene knockout miceCancer Res1524158Google Scholar
- 30.House, MG, Herman, JG, Guo, MZ, et al. 2003Aberrant hypermethylation of tumor suppressor genes in pancreatic endocrine neoplasmsAnn Surg Oncol23842332Google Scholar
- 32.Lee, S, Kim, WH, Jung, H-Y, Yang, MH, Kang, GH 2002Aberrant CpG island methylation of multiple genes in intrahepatic cholangiocarcinomaAm J Patho161101522Google Scholar
- 44.Wolf, P, Hu, YC, Doffek, K, Sidransky, D, Ahrendt, SA 2001O6-Methylguanine-DNA methyltransferase promoter hypermethylation shifts the p53 mutational spectrum in non-small cell lung cancerCancer Res6181127Google Scholar