Identification of T-cell factor-4 isoforms that contribute to the malignant phenotype of hepatocellular carcinoma cells.

The Wnt/β-catenin signaling pathway is frequently activated in hepatocellular carcinoma (HCC). Downstream signaling events involving the Wnt/β-catenin cascade occur through T-cell factor (TCF) proteins. The human TCF-4 gene is composed of 17 exons with multiple alternative splicing sites. However, the role of different TCF-4 isoforms in the pathogenesis of HCC is unknown. The purpose of this study was to identify and characterize TCF-4 isoforms in HCC. We identified 14 novel TCF-4 isoforms from four HCC cell lines. Functional analysis following transfection and expression in HCC cells revealed distinct effects on the phenotype. The TCF-4J isoform expression produced striking features of malignant transformation characterized by high cell proliferation rate, migration and colony formation even though its transcriptional activity was low. In contrast, the TCF-4K isoform displayed low TCF transcriptional activity; cell proliferation rate and colony formation were reduced as well. Interestingly, TCF-4J and TCF-4K differed by only five amino acids (the SxxSS motif). Thus, these studies suggest that conserved splicing motifs may have a major influence on the transcriptional activity and functional properties of TCF-4 isoforms and alter the characteristics of the malignant phenotype.