Abstract: Objective: To study the effects of down-regulated Smad4 expression on the proliferation and apoptosis of breast carcinoma MCF-7 cells, and to explore their mechanisms. Methods: The human breast carcinoma MCF-7 cells and MDA-MB-231cells were cultured in vitro. RT-PCR method was used to detect the expression levels of Smad4 mRNA in MCF-7 cells and MDA-MB-231 cells. The Smad4-shRNA plasmid and Scramble-shRNA plasmid were respectively stably transfected into the MCF-7 cells with high expression of Smad4. The experiment was divided into non-transfected MCF-7 cells (normal control) group,Smad4 gene silencing group, Scramble (negative control)group.The proliferation abilities of the cells in various groups were detected by CCK-8 method. The apoptotic rates of the cells in various groups were detected by flow cytometry. Real-time PCR method was used to detect the mRNA expression levels of the proliferation-related genes CDKN1A, CDK1 and CDK2 and the apoptosis-related genes Suvivin, bcl-2, caspase 3 and caspase 9. Results: The proliferation abilities of cells had no statistical significance between various groups(P>0.05). The mRNA expression levels of CDKN1A, CDK1 and CDK2 in the cells had no statistical significance between various groups (P>0.05).Compared with normal control group and negative control group, the apoptotic rate of the cells in Smad4 gene silencing group was significantly decreased(P<0.01), the expression levels of Suvivin and bcl-2 mRNA in Smad4 gene silencing group were significantly increased(P<0.01), and the mRNA expression levels of caspase 3 and caspase 9 in Smad4 gene silencing group were significantly decreased(P<0.05). Conclusion: Smad4 could induce the apoptosis of MCF-7 cells by down-regulating the expressions of Suvivin and bcl-2 and up-regulating the expressions of caspase 3 and caspase 9.

Key words: Smad4, MCF-7 cells, cell proliferation, apoptosis