Involvement of SET in the Wnt signaling pathway and the development of human colorectal cancer

The SET oncoprotein is involved in cancer progression by modulating multiple cellular processes, including the inhibition of the tumor suppressor, protein phosphatase 2 (PP2A). Based upon these multiple activities, we hypothesized that targeted inhibition of SET is likely to have multiple discrete and measurable effects on cancer cells. In the present study, the mRNA expression levels of SET, PP2A and beta-catenin were examined in 31 pairs of human colorectal adenocarcinoma tissues and corresponding adjacent normal colorectal tissues by quantitative real-time polymerase chain reaction (qPCR). A small interfering RNA targeting SET was transfected into the human colon carcinoma cell lines, LS174T and SW480. The mRNA levels of SET, PP2A, beta-catenin, c-Myc, E-cadherin and p53 were determined by qPCR analysis and the protein levels of SET, c-Myc, PP2A and beta-catenin were examined by western blot analysis. mRNA expression levels of SET and beta-catenin were found to be elevated in 22 (70.9%) samples, while PP2A expression levels were upregulated in eight (25.8%) samples. In addition, the knockdown of SET mRNA expression caused the upregulation of PP2A and c-Myc in the two cell lines, whereas beta-catenin, E-cadherin and p53 mRNA expression was downregulated. Consistent with these results, the protein expression of beta-catenin and c-Myc was found to be downregulated, whereas PP2A was upregulated at the protein level. Based on these results, we proposed that SET is essential in the carcinogenesis of human colorectal adenocarcinoma. In addition, it is suggested that SET promotes carcinogenesis through regulation of the Wnt signaling pathway.