He et al. Journal of Experimental & Clinical Cancer Research 2011, 30:109 http://www.jeccr.com/content/30/1/109 Page 5 of 9 Figure 3 Representative Western blots of CDK8 and b-catenin expression level in CDK-siRNA transfected HCT116 cells. 72 h later of CDK8-siRNA transfection of HCT116 cells, protein expression of CDK8 (A) and b-catenin (B) was determined by western blot assay. a: non-siRNA group; b: scrambled siRNA group; c: CDK-siRNA group. Results are given as average value of the gray in three target genes and interal controls from three independent experiments. other two groups (P < 0.01). Similarly, there was no sig- nificant difference between the scrambled siRNA group and non-siRNA group. Effect of CDK8-siRNA transfection on the growth of HCT116 cells The cell proliferation of HCT116 cells following 24, 48 and 72 h of transfection was detected by MTT assay. Results showed that the number of viable cells in the CDK8- siRNA group was significantly lower compared to that of the scrambled siRNA and non-siRNA groups 48 and 72 h after CDK8-siRNA transfection (P < 0.05) (Figure 4). Effect of CDK8-siRNA transfection on the apoptosis and cell cycle of HCT116 cells We performed experiments to evaluate the apoptosis and cell cycle of HCT116 cells by CDK8-siRNA. As shown in figure 5, following 48 h transfection, it was indicated that the rate of apoptosis in the CDK8-siRNA group (23.50 ± 1.20%) was significantly higher than that of the scrambled siRNA (4.87 ± 1.48%) and non-siRNA groups (4.77 ± 1.42%) (P < 0.01) (Figure 5A). On the other hand, the cell cycle analysis showed that G0/G1 phase of CDK8-siRNA transfected group in a ratio of 65.77 ± 1.17%, was significantly higher than that of Figure 4 Cell proliferation activity after transfection of CDK8-siRNA assessed by MTT assay. Curves of cell growth after transfection for 24, 48 and 72 h by MTT assay. Results are given as means ± SD from three independent experiments. P < 0.05.