['Wildtype p53 and Smad4 are important suppressor genes in tumor genesis and development. The mutation in p53 gene is closely related to the early formation of breast cancer. In this research, we try to explore the status of Smad4 in breast cancer cell line MCF7 after knocking down p53.', "MCF-7 was bought from American Type Culture Collection (ATCC). Cells were cultured in Dulbecco's Modified Eagle Medium (DMEM) with 10% fetal bovine serum (FBS) in incubator containing 5% CO2 at 37°C. In this study we apply to analytical methods such as growth ratio analysis in vitro, immunoblot analysis, flow cytometry for cell cycle analysis, RNA extraction and Real-Time PCR and data analysis.", 'The results indicated that specific down regulating of p53 can significantly increase the expression of Smad4 in cancer cell line MCF7 and promote cell apoptosis. In MCF7 cell line p53 gene is negatively related to Smad4 in great extent.'] Does down-regulated P53 by siRNA increase Smad4 's activity in promoting cell apoptosis in MCF-7 cells?