Expressions And Roles Of Smad4, Cdk4 And CyclinD1 In The Ventral Prostate Of Rats

Benign prostatic hyperplasia (BPH) and prostate cancer (CaP) often occur in old men. They are closely associated with cell proliferation and apoptosis. Overexpression of Smad4 has been shown to induce apoptosis of Madin - Darby canine kidney cells in vitro. But the mechanism about how Smad4 induce apoptosis is not clear now. It has been recognized that on the TGF - ?signaling pathway, Smad4 is in the downstream position. After it combines with receptor - specific Smads, they translocate from cytoplasm to nucleus. Where they can restrain activation of Cdk4 -CyclinDl complex and block G,/S transition.In this study, prostate proliferation and apoptosis model was built by castrated rats. Flow cytometry (FCM) was used to measure the rates of apoptosis and cell proliferation in the ventral prostate of intact rats and castrated rats. Western blot was used to evaluate the expressions of Smad4, Cdk4 and CyclinDl in the ventral prostate of intact and castrated rats . The correlation of these protein was analyzed in order to reveal the exact effect of Smad4 on prostate proliferation and apoptosis, and provide theory basis for studying molecule mechanism of BPH and CaP.MethodAdult Sprague - Dawley male rats were used for study. They were divided into two groups randomly. Total serum testosterone was assayed. One group was castrated through scrotum incision. Total serum testosterone was measured again 7 days after castration. The ventral prostates were harvested at same time .1. Total serum testosterone was assayed by Chemoluminescence immunoas-say.2. Rates of apoptosis and cell proliferation in the ventral prostate were examined by flow cytometry.3. Expressions of Smad4, Cdk4 and Cyclin Dl in prostate were analyzed by Western blot.4. Statistical analysis: all data were presented asx+s. t test was used to test the differences between two groups , and Pearson correlation analysis was used for the analysis of correlation. P <0. 05 was considered to be statistically significant.ResultThere are two groups of prostate samples: prostate of intact rats and of castrated rats. Total serum testosterone of intact rats was 2. 92 +2. 58nmol/L and that of castrated rats before castration was 2.98 +2. 66nmol/L. Total serum testosterone could not be detected ( <0. 69 nmol/L) after castration and the ventral prostate dramaticly shrinked.Rates of cell proliferation and apoptosis in the ventral prostate of intact rats were 8. 93 +2. 99% and 8. 98 +3. 57% , respectively. Those in castrated rats were 5.98 +2. 97% and 12.42 +4. 05% , respectively. The rates of cell proliferation decreased significantly and apoptosis increased significantly (P <0. 05) after castration.Western blot analysis: Expressions of Smad4, Cdk4 and Cyclin Dl were all detected in intact and castrated rats. Expressions of Smad4 and CycinDl increased significantly, and expression of Cdk4 decreased significantly ( P < 0.05) after castration.Correlation analysis: The expression of Smad4 positively correlated with the rate of apoptosis (r =0. 797 ,P <0.05) , but it had no correlation with the rate of proliferation. The expression of Smad4 negatively correlated with the expression of Cdk4 ( r = - 0. 804,P < 0. 05 ). The expression of Smad4 positively correlated with the expression of CyclinDl (r = 0. 829,P <0. 05). The expression of Cdk4 negatively correlated with the expression of CyclinDl (r = - 0. 852,P<0.05).Conclusion1. Both decrease of cell proliferation and increase of apoptosis take part in the atrophy of prostate in castrated rat.2. Overexpression of Smad4 can induce apoptosis of prostate.3. Cell proliferation transitorily appears in prostate after castration.4. Smad4 mainly influences cell proliferation and apoptosis in prostate through Cdk4/CyclinDl.