Participates in the Wnt signaling pathway and modulates MYC expression by binding to its promoter in a sequence-specific manner. Acts as repressor in the absence of CTNNB1, and as activator in its presence. Activates transcription from promoters with several copies of the Tcf motif 5'-CCTTTGATC-3' in the presence of CTNNB1. TLE1, TLE2, TLE3 and TLE4 repress transactivation mediated by TCF7L2/TCF4 and CTNNB1. Expression of dominant-negative mutants results in cell-cycle arrest in G1. Necessary for the maintenance of the epithelial stem-cell compartment of the small intestine. Interacts with TGFB1I1 (By similarity). Interacts with CTNNB1 (via the armadillo repeat); forms stable transcription complex (PubMed:9065401, PubMed:9916915, PubMed:10080941, PubMed:19816403, PubMed:28829046, PubMed:29739711, PubMed:17052462). Interacts with EP300. Interacts with NLK. Interacts with CCDC85B (probably through the HMG box); prevents interaction with CTNNB1. Interacts with TNIK. Interacts with MAD2L2; prevents TCF7L2/TCF4 binding to promZIPK/DAPK3oters, negatively modulating its transcriptional activity. Interacts with ZIPK/DAPK3. Interacts with XIAP/BIRC4 and TLE3. Interacts with DDIT3/CHOP. The CTNNB1 and TCF7L2/TCF4 complex interacts with PML (isoform PML-4). Identified in a complex with CTNNB1 and FERMT2. Interacts with SPIN1 (PubMed:22258766, PubMed:24589551, PubMed:29061846). Interacts with C11orf84/SPINDOC in a SPIN1-dependent manner (PubMed:29061846). Diffuse pattern. Colocalizes with SUMO1 and PIAS4 in a subset of PML (promyelocytic leukemia) nuclear bodies. Detected in epithelium from small intestine, with the highest expression at the top of the crypts and a gradient of expression from crypt to villus. Detected in colon epithelium and colon cancer, and in epithelium from mammary gland and carcinomas derived therefrom. Highly expressed in crypt regions and barely detectable in villi in epithelium from fetal small intestine at week 16. At week 22 expression in villi had increased strongly. The promoter-specific activation domain interacts with the transcriptional coactivator EP300. In vitro, phosphorylated by TNIK. Phosphorylated at Thr-201 and/or Thr-212 by NLK. Phosphorylation by NLK at these sites inhibits DNA-binding by TCF7L2/TCF4, thereby preventing transcriptional activation of target genes of the canonical Wnt/beta-catenin signaling pathway. Polysumoylated. Sumoylation is enhanced by PIAS family members and desumoylation is enhanced by SENP2. Sumoylation/desumoylation regulates TCF7L2/TCF4 transcription activity in the Wnt/beta-catenin signaling pathway without altering interaction with CTNNB1 nor binding to DNA. Constitutive activation and subsequent transactivation of target genes may lead to the maintenance of stem-cell characteristics (cycling and longevity) in cells that should normally undergo terminal differentiation and constitute the primary transforming event in colorectal cancer (CRC). Disease susceptibility is associated with variants affecting the gene represented in this entry. Low expression in pancreas and colon. Common splicing form, lowest expression in skeletal muscle. High transcriptional activity. Major isoform in liver. Belongs to the TCF/LEF family.