The role of Runt-related transcription factor 3 ( RUNX3) gene in breast cancer remains not fully understood. We studied the correlation between RUNX3 gene promoter methylation and estrogen receptor (ER) expression status in breast cancer. Three breast cancer cell lines and 113 formalin-fixed, paraffin-embedded breast cancer tissue samples were analyzed for RUNX3 expression. Methylation-specific polymerase chain reaction was used to analyze RUNX3 methylation on the samples. Migration and invasion ability were evaluated in MCF7 cell line (RUNX3 methylated) treated with methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR) to study the effect of RUNX3 methylation status. Our data showed that the expression of RUNX3 was high in MCF10A but not in MCF7 and SKBR3 cell lines, while the RUNX3 promoter showed hypermethylation in MCF7 but not in MCF10A and SKBR3. In tissues samples, Immunohistochemical (IHC) expression of RUNX3 protein was higher in ER-negative samples than in ER-positive cases, and it was negatively correlated with the methylation status of the RUNX3 gene promoter. Proliferation, migration, and invasion of MCF7 were suppressed when 5-Aza-CdR treated. Also, the hypermethylation status of RUNX3 gene promoter was reversed and RUNX3 expression was increased. In summary, our data suggest that hypermethylation of the RUNX3 gene promoter may play an important role in ER-positive breast tumor progression.
Keywords: RUNX3 methylation; breast cancer; estrogen receptor.