Triple-negative breast cancer is a highly aggressive tumor subtype that lacks effective therapeutic targets. Here, we show that ELK3 is overexpressed in a subset of breast cancers, in particular basal-like and normal-like/claudin-low cell lines. Suppression of ELK3 in MDA-MB-231 cells led to transdifferentiation from an invasive mesenchymal phenotype to a non-invasive epithelial phenotype both in vitro and in vivo. Suppression of ELK3 results in the extensive changes in genome expression profiles. Among these, GATA3, a master suppressor of metastasis, was epigenetically activated and we found that suppression of GATA3 led to the restoration of migration and invasion. These results suggest that the ELK3-GATA3 axis is a major pathway that promotes metastasis of MDA-MB-231 cells. Retrovirus expressing shRNA of ELK3 was transduced into MDA-MB-231 cell line and stable cell line of which ELK3 is suppressed more than 50% was selected by the drug selection (Puromycin).