Objective   To explore the effects of Smad4 gene silencing by small interfering RNA (siRNA) on the proliferation of prostate cancer cells in vitro.     Methods   Expression of Smad4 gene in several prostate cancer cell lines (LNCaP

PC-3

DU145

IF11

and IA8) was detected by semi-quantitative reverse transcription-PCR (RT-PCR) and Western blotting for the screening of the positive cells. Three siRNA targeting three d

ifferent domains of Smad4 gene were designed

synthesized

and transfected into Smad4-positive cells by Lipofectamine

TM

2000. After transfection for 48 h

expression of Smad4 gene in Smad4-positive cells was detected by RT-PCR and Western blotting again

and the proliferative potency was also analyzed by MTT assay at the same time.     Results   There was a remarkable difference in the expressions of Smad4 mRNA and protein between these cells. Smad4 was highly expressed in LNCaP

PC-3

and DU145 cells

but not in IF11 and IA8 cells. Compared with the negative control (siRNA-NC) groups

transfection of three targeting siRNA in PC-3 cells knocked down the expression of Smad4 mRNA significantly

but only siRNA3 silenced the expression of Smad4 protein. Smad4 gene silencing enhanced the proliferative capacity of PC-3 cells after transfection.     Conclusion   There is difference in the expression of Smad4 gene in prostate cancer cell lines. The chemically synthesized specific siRNA targeting Smad4 could effectively reduce the expression of Smad4 gene

and enhance the proliferative capacity of PC-3 cells in vitro.