Wnt3a regulates Lef-1 expression during airway submucosal gland morphogenesis

Regulation of the lymphoid enhancer factor 1 (Lef-1) transcription factor is important for the inductive formation of many epithelial-derived appendages including airway submucosal glands (SMGs). Although Wnts have been linked to developmental processes involving transcriptional activation of the Lef-1 protein, there is little in vivo information directly linking Wnts with the transcriptional regulation of the Lef-1 promoter. In the present study, we hypothesized that Wnt3a directly regulates Lef-1 gene expression required for SMG morphogenesis in mice. In support of this hypothesis, TOPGAL reporter mice demonstrated activation of β-catenin/Tcf complexes during early phases of SMG development and immunolocalization studies confirmed abundant expression of Tcf4, but not Tcf1 or Tcf3, at this stage. ChIP analysis in primary airway epithelial cells revealed that Tcf4 associates with a known Wnt Responsive Region in the Lef-1 promoter and transfection of Cos-1 cells with dominant active β-catenin and Tcf4 synergistically activated the Lef-1 promoter. Using Wnt3a deficient and Lef-1 promoter-GFP reporter mice, we also demonstrate that Wnt3a induces Lef-1 gene expression in newly forming SMG buds of mice and is required for the maintenance of gland bud growth. These findings provide the first in vivo evidence that Wnt3a can transcriptionally regulate the Lef-1 gene.