Based on these computational predictions, we confirm experimentally that miR-503 suppresses proliferation in MCF-7 cells, and we identify a new target of miR-503, the oncogene ZNF217. These results provide a quantitative understanding of the temporal response of mRNAs and miRNAs to estrogen stimulation, and suggest that miR-503 is a candidate therapeutic target for treatment of breast cancer. Here, ZNF217 is linked to breast carcinoma.