He et al. Journal of Experimental & Clinical Cancer Research 2011, 30:109 http://www.jeccr.com/content/30/1/109 Page 6 of 9 Figure 5 Effect of CDK8-siRNA transfection on the apoptosis and cell cycle of HCT116 cells. 48 h after transfection, cell apoptosis (A) and cell cycle (B) were determined by flow cytometry. Quadrants D2-D4 represent necrotic/late apoptotic cells, viable cells, and early apoptotic cells, respectively. Results are given as means ± SD from three independent experiments. scrambled siRNA (50.20 ± 2.43%) and non-siRNA group (54.33 ± 2.55%) (P < 0.01) (Figure 5B). CDK8 and b-catenin expression in fresh colon tumor and adjacent normal tissues To further confirm the expression of CDK8 and b-cate- nin in colon cancer, we detected the expression of CDK8 and b-catenin in fresh colon cancer tissues and adjacent normal tissues of the same patient. Real-time PCR was adopted to detect the mRNA levels. Results showed that mRNA expression levels of CDK8 and b- catenin in tumor tissues was significantly higher than in adjacent normal tissues (P < 0.05) (Figure 6). In addi- tion, the expression of CDK8 was correlated with the expression of b-catenin in both tumor tissues (r = 0.744, P < 0.01) and adjacent normal tissues (r = 0.650, P < 0.05). Shown by IHC, the positive cells were expressed as brown particles distributed in the cytoplasm of tumor cells (Figure 7). Of the 47 colon tumors, the positive rate of CDK8 and b-catenin was 76.6% (36/47) and 95.7% (45/47). However, in adjacent normal tissues, the positive rate was 21.3% (10/47) and 88.9% (40/47), respectively. The difference between them was statistically significant (P < 0.05). As predicted, the expression of CDK8 was also correlated with the expres- sion of b-catenin in both tumor tissues (r = 0.485, P < 0.05) and adjacent normal tissues (r = 0.346, P < 0.05). Discussion Aberrant activation of the Wnt/b-catenin pathway has been shown to be associated with numerous human cancers [1,2,16]. Previous studies revealed that an abnormality in b-catenin signaling pathway may be responsible for almost all types of colon cancers [4,17]. It has been reported that CDK8 plays a central role in the regulation of b-catenin activation [3,18]. Based on such a background, further exploring of the role of CDK8 and b-catenin in the oncogenesis and progression of colon cancer as well as their correlation, not only provides a broad understanding of the etiology of colon cancer, but also may provide an intervention stategy with CDK8 and b-catenin as a target. Ron Firestein et al [8] found that CDK8 was necessary for the b-catenin-mediated activation of proto-onco- genes. They noted that, in the absence of CDK8, the activity of b-catenin-mediated transcription was signifi- cantly decreased, whereas an overexpression of CDK8