He et al. Journal of Experimental & Clinical Cancer Research 2011, 30:109 http://www.jeccr.com/content/30/1/109 Page 7 of 9 Figure 6 CDK8 and b-catenin mRNA expression in colon tumor and adjacent normal tissues detected by real-time PCR. Fresh tumor and corresponding adjacent tissues from 12 patients were resected under sterile conditions and then snapfrozen in liquid nitrogen immediately. 200 mg tissue was taken out from liquid nitrogen and plused 1 ml Trizol when RNA was extaracted. Real-time PCR is performed for the expression levels of CDK8 (A) and b-catenin (B). Results are given as means ± SD from three independent experiments. P < 0.05. could induce proto-oncogene activation [19]. Addition- ally, Morris and colleagues screened E2F1-dependent apoptotic genes and found that E2F1 could inhibit Wnt/ b-catenin activity and CDK8 was the most potential inhibitor of E2F1 [9,19]. Furthermore, CDK8 may also be involved in other signaling pathways. It is reported that CDK8 is a positive co-stimulatory regulator of the expression of p53 gene [20] and p53’s downstream gene p21 since the binding of CDK8 to the p53 gene can increase its transcription activity. Furthermore, CDK8 could regulate the Notch signaling pathway [21] and exerted positive regulatory effects on the tumorigenicity related mRNA prolongation [22]. Therefore, CDK8 may be considered to be a proto-oncogene based on the above observations. To investigate the effects of the activity of b-catenin on colon cancer through CDK8, CDK8 interference was constructed and transfected in colon cancer cells CT116 by the application of siRNA in our study. The alteration of the expression of b-catenin, proliferation, cell apopto- sis and cell cycle distribution in HCT116 cells were determined. After silencing CDK8 by siRNA, our results showed that b-catenin expression was markedly lower at the mRNA and protein level, and it is considered that there was a significant association between CDK8 and b-catenin expression. Such results support the claim of Ron Firestein et al [8] that only CDK8 play a central role of post-translational modulator of b-catenin in colon cancer. Additionally, it was showed that cell pro- liferation was reduced after CDK8 blocking using MTT assay. Flow cytometry analysis revealed that the rate of cell apoptosis in the CDK8-siRNA group was markedly higher compared to the control groups, and the majority of cells was in the G0/G1 phase in the CDK8-siRNA group. We suggest that CDK8-siRNA transfection may decrease cell proliferation and facilitate apoptosis of colon cancer cells. Furthermore, the cell cycle arrest after CDK8-siRNA transfection may be related to the reduced transcription activity of b-catenin, since b-cate- nin can regulate the expression of certain cell cycle- related genes, including survivin and c-myc. However, the exact effect and mechanism on these downstream genes of b-catenin followed with marked reduction of CDK8 needs to be elucidated in future studies. Accord- ing to our results, it was speculated that the possibility of the regulation of colon cancer through control of CDK8 is theoretically applicable. To confirm the expression and relationship of CDK8 and b-catenin based on colon cancer tissues, real-time PCR and IHC were performed in our study. As pre- dicted, both CDK8 and b-catenin expression level were markedly higher in tumor compared to adjacent normal tissues. Furthermore, the expression of b-catenin showed positively related to CDK8 expression. Mean- while, it is reported that the expression of b-catenin was still positive or high in some colon cancer cell lines that have negative expression of CDK8. It is suggested that there might be other factors for regulating the activity of b-catenin such as pancreatic adenocarcinoma up- regulated factor (PAUF) [23] and Delta-like4 (DLL4) [24] expect CDK8. Neverthless, our observations sug- gested that CDK8-siRNA can effectively inhibit the tran- scription activity of the b-catenin signaling pathway in colon cancer cells HCT116, thereby resulting in the