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. May also act as feedback transcriptional repressor of CTNNB1 and TCF7L2 target genes. TLE1, TLE2, TLE3 and TLE4 repress transactivation mediated by TCF7 and CTNNB1. Binds the armadillo repeat of CTNNB1 and forms a stable complex. Interacts with AES, TLE1, TLE2, TLE3 and TLE4. By TCF7L2 and CTNNB1. Predominantly expressed in T-cells. Also detected in proliferating intestinal epithelial cells and in the basal epithelial cells of mammary gland epithelium. Belongs to the TCF/LEF family. 16 isoforms of the human protein are produced by alternative promoter. Note: This description may include information from UniProtKB.