Transcriptional activator involved in T-cell lymphocyte differentiation. Necessary for the survival of CD4(+) CD8(+) immature thymocytes. Isoforms lacking the N-terminal CTNNB1 binding domain cannot fulfill this role. Binds to the T-lymphocyte-specific enhancer element (5'-WWCAAAG-3') found in the promoter of the CD3E gene. Represses expression of the T-cell receptor gamma gene in alpha-beta T-cell lineages (By similarity). Required for the development of natural killer receptor-positive lymphoid tissue inducer T-cells (By similarity). TLE1, TLE2, TLE3 and TLE4 repress transactivation mediated by TCF7 and CTNNB1.May also act as feedback transcriptional repressor of CTNNB1 and TCF7L2 target genes. Binds the armadillo repeat of CTNNB1 and forms a stable complex (PubMed:9488439 PubMed:9783587). Interacts with TLE5, TLE1, TLE2, TLE3 and TLE4 (PubMed:9783587, PubMed:11266540). Interacts with MLLT11 (PubMed:26079538). Long isoform interacts (via N-terminus) with SOX13; inhibits WNT-mediated transcriptional activity (PubMed:17218525, PubMed:20028982). 2 series of isoforms, L and S, are produced by alternative promoter usage. Additional isoforms seem to exist. Predominantly expressed in T-cells. Also detected in proliferating intestinal epithelial cells and in the basal epithelial cells of mammary gland epithelium. By TCF7L2 and CTNNB1. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Produced by alternative splicing of isoform 4L. Produced by alternative splicing of isoform 4S. Belongs to the TCF/LEF family. Wrong choice of frame.