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 CCTTTGATC 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 (By similarity). Necessary for the maintenance of the epithelial stem-cell compartment of the small intestine. Interacts with TGFB1I1 (PubMed:16291758). Interacts with SPIN1 (By similarity). Interacts with CTNNB1 (via the armadillo repeat); forms stable transcription complex (PubMed:19816403). Interacts with EP300. Interacts with NLK. Interacts with CCDC85B (probably through the HMG box); prevents interaction with CTNNB1 (By similarity). Interacts with TNIK (PubMed:19816403). 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 C11orf84/SPINDOC in a SPIN1-dependent manner (By similarity). Diffuse pattern. Colocalizes with SUMO1 and PIAS4 in a subset of PML (promyelocytic leukemia) nuclear bodies (By similarity). Detected in adult brain and liver, and at lower levels in intestine, with a clear increase from the distal colon to the duodenum. Detected at low levels in heart, lung, kidney, pituitary and testis. First detected at 10.5 dpc. Highly expressed at 13.5 dpc-16.5 dpc in the central nervous system, in particular in the roof of the mesencephalon, at the ditelencephalic junction and in dorsal thalamus. At 13.5 dpc, detected at low levels in gastrointestinal epithelia. Phosphorylated at Thr-178 and/or Thr-189 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 (By similarity). 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 (By similarity). 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). May result from the retention of an intron in the cDNA. Dominant negative form which cannot bind CTNNB1. Expression is VAX2-dependent. Belongs to the TCF/LEF family.