| Summary: | We have shown that LEF-1 protein is expressed in both HCT116 and SW480 colorectal cancer cell lines, consistent with its expression in colorectal cancer tissue, and, using PCR, have examined the expression of specific Tcf-1, Lef-1, Tcf-3 and Tcf-4 isoforms in these cells. this analysis showed that repressive Tcf-1 isoforms are expressed in colorectal cancer cells, whilst extensive alternative splicing produces a variety of Lef-1 and Tcf-4 isoforms. To assess the role that Tcf-4 and Lef-1 were playing in colorectal cancer, siRNA mediated knockdown of these genes was used in colorectal cancer cells to investigate effects on cell proliferation, cell morphology and downstream target genes. To reduce total Wnt signalling, beta-catenin siRNA was used, and the effects compared with specific Tcf-4 and Lef-1 siRNAs. Our results showed that Tcf-4 siRNA reduced cell proliferation, halting cells in G2 phase of the cell cycle, and reducing the expression of genes involved in the cell cycle. In contrast, Lef-1 siRNA hardly affected cell proliferation, but did affect cell morphology, causing cells to become larger and more spread out. Consistent with this finding, Lef-1 siRNA also reduced the expression of genes possibly involved in cell morphology, whilst Tcf-4 siRNA did not. In addition, it seems that alternative Lef/Tcf isoforms have varying effects on target genes, since siRNA that targeted specific isoforms had different effects on Wnt target gene expression. These results suggest that Lef-1 and Tcf-4 mediate different events in colorectal cancer, a difference which may be important for the progression of the cancer.
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