Wnt-3A/β-catenin signaling induces transcription from the LEF-1 promoter

Abstract

Members of the Wnt family of secreted molecules have been established as key factors in determining cell fate and morphogenic signaling. It has long been recognized that Wnt induces morphogenic signaling through the Tcf/LEF-1 cascade by regulating free intracellular levels of β-catenin, a co-factor for Tcf/LEF-1 transcription factors. In the present study, we have demonstrated that Wnt-3A can also directly induce transcription from the LEF-1 promoter. This induction was dependent on glycogen synthase kinase 3β inactivation, a rise in free intracellular β-catenin, and a short 110-bp Wnt-responsive element (WRE) in the LEF-1 promoter. Linear and internal deletion of this WRE led to a dramatic increase in constitutive LEF-1 promoter activity and loss of Wnt-3A responsiveness. In isolation, the 110-bp WRE conferred context-independent Wnt-3A or β-catenin(S37A) responsiveness to a heterologous SV40 promoter. Studies expressing dominant active and negative forms of LEF-1, β-catenin, GSK-3β, and β-catenin/ LEF-1 fusions suggest that Wnt-3A activates the LEF-1 promoter through a β-catenin-dependent and LEF-1-independent process. Wnt-3A expression also induced multiple changes in the binding of factors to the WRE and suggests that regulatory mechanisms may involve modulation of a multiprotein complex. In summary, these results provide evidence for transcriptional regulation of the LEF-1 promoter by Wnt and enhance the mechanistic understanding of Wnt/β-catenin signaling in the regulation of LEF-1-dependent developmental processes.