The promoter methylation and expression of the O6-methylguanine-DNA methyltransferase gene in uterine sarcoma and carcinosarcoma

Abstract

O6-methylguanine-DNA methyltransferase (MGMT) gene promoter hypermethylation is observed in a number of solid tumors and is correlated with the silencing of MGMT expression. In glioblastoma patients treated with the alkylating agent temozolomide, MGMT gene methylation status was shown to have predictive value in terms of prolonged overall survival. Recently, temozolomide has demonstrated promising activity in the treatment of soft tissue sarcomas, including those of the uterus. The tissue specimens involving tumor samples and normal uterine fragments were obtained from nine patients with smooth muscle uterine sarcoma, 11 with stromal uterine sarcoma and 17 with mixed uterine tumors. MGMT gene promoter methylation was analyzed by combined bisulfite restriction analysis (COBRA) while its expression levels were assessed using the real-time reverse transcription polymerase chain reaction (qRT-PCR). MGMT promoter methylation was observed in 27% of all tumor samples analyzed. When stratified by the disease type, 55.5% (5/9) of smooth muscle sarcomas, 23.5% (4/17) of mixed uterine tumor tissues and 9% (1/11) of stromal sarcomas showed MGMT methylation. The MGMT promoter methylation was associated with lower levels of gene expression in tumors when compared with those with an unmethylated promoter (P=0.0232) or normal tissues (P=0.0141). To conclude, MGMT promoter methylation and downregulation of gene expression is observed in a fraction of carcinosarcomas and non-epithelial malignant tumors of corpus uteri. The assessment of MGMT promoter methylation status may potentially identify patients who would benefit from temozolomide treatment.

Figure 1

The representative results of MGMT promoter methylation analysis. Lanes 12–71, tumor samples; -, negative control (whole genome amplified DNA from the blood sample of a healthy donor); +, positive control (in vitro methylated DNA from the blood sample of a healthy donor); M, molecular weight marker; MGMT, O6-methylguanine-DNA methyltransferase.

Figure 2

The MGMT expression levels in tumors with methylated or unmethylated MGMT and normal uterine tissues; MGMT, O6-methylguanine-DNA methyltransferase. Horizontal lines indicate standard error of the mean (SEM).