In conclusion, our experiments showed that the shRNA targeted against MTA1 could specifically mediate the MTA1 gene silence and consequentially recover the protein expression of ER alpha, resulting in increase sensitivity of antiestrogens, as well as suppress the protein expression of MMP-9 and cyclinD1 in ER-negative human breast cancer cell lines MDA-MB-231. The gene discussed is MMP9; the disease is breast cancer.