MTA3 (metastasis-associated protein 3) is a component of the NuRD (nucleosome remodeling and histone deacetylation) complex. MTA3 is a member of a family of proteins (MTA1-3) differentially expressed in metastatic breast cancer cells. MTA3 functions as a repressor of the transcription factor Snail, a factor involved in epithelial to mesenchymal transitions. MTA3 expression is estrogen dependent in breast cancer cells. Studies show that ERalpha selectively bind the MTA3 promoter in an SP1-dependent fashion to stimulate MTA3 gene transcription.