OBJECTIVETo investigate the relationship between hypermethylation of Runx3 gene promoter and estrogen receptor (ER) and the implications of Runx3 gene promoter hypermethylation in ER positive breast cancer.

METHODSWestern blot and RT-PCR were used to detect the protein and mRNA expression of Runx3 gene in breast cancer cell lines (MCF7 and SKBR3) and normal breast epithelium cell line (MCF10A). Immunohistochemical SP method was used to detect the expression of ER and Runx3 proteins in 113 tissue samples of breast cancer. Moreover, methylation specific PCR was used to detect RUN3 promoter methylation in cell lines MCF7, SKBR3, MCF10A and 113 tissue samples of breast cancer.

RESULTSOf the 3 cell lines, Runx3 protein and mRNA were detectable in MCF10A, but were absent in MCF7 and SKBR3. MCF7 had a high methylation status at Runx3 promoter, in contrast, MCF10A and SKBR3 showed unmethylated RUN3 promoter. Among the 113 cases of breast cancer, 68 cases were ER positive and 45 were negative. The positive rates of Runx3 protein expression in ER positive and negative tumors were 26.5% (18/68) and 66.7% (30/45), respectively (P<0.05). Runx3 promoter hypermethylation was seen in 82.4% (56/68) of ER positive breast cancer cases and 22.2% (10/45) of ER negative ones (P<0.05). Among 68 cases of ER positive cases, Runx3 promoter hypermethylation was positively correlated with the clinical tumor stage (OR=5.84, P<0.05).

CONCLUSIONSRunx3 gene promoter hypermethylation is present mainly in the ER positive breast cancers. Testing of Runx3 promoter methylation may provide additional reference for clinical stage and prognosis of breast cancer patients, especially in those with ER positive tumors.