Lymphocyte enhancer factor 1 (LEF1) is a member of the TCF/LEF1 family of HMG transcription factors, which also includes three other members, TCF1, TCF3, and TCF4. They have been implicated in Wnt signaling and tumorigenesis. LEF1 was originally identified in pre-B and T cells. LEF1 is expressed in developing B and T cells and at multiple sites of organogenesis during embryonic development.
LEF1 deficient mice exhibit defects in pro-B cell proliferation and survival in vitro and in vivo .
LEF1 has no transcriptional activation potential by itself, but it can act as an architectural protein in the assembly of multiprotein enhancer complexes. In the T cell receptor α enhancer, for example, LEF1 regulates transcription in association with ALY and in collaboration with other enhancer binding proteins. In addition, TCF/LEF1 proteins have been shown to interact with β -catenin, an important effector in the Wnt signalling pathway. TCF/LEF1 proteins associate with β -catenin through amino-terminal sequences, and together these proteins mediate a transcriptional response to Wnt signalling.
Targeted inactivation of both LEF1 and TCF1 genes results in an early block in T cell differentiation. In addition, TCF1-/- mice show a defect in the function of dendritic cells. (for detailed references, see  ).