G protein signaling from activated rat frizzled-1 to the beta-catenin-Lef-Tcf pathway.

The frizzled receptors, which mediate development and display seven hydrophobic, membrane-spanning segments, are cell membrane-localized. We constructed a chimeric receptor with the ligand-binding and transmembrane segments from the beta2-adrenergic receptor (beta2AR) and the cytoplasmic domains from rat Frizzled-1 (Rfz1). Stimulation of mouse F9 clones expressing the chimera (beta2AR-Rfz1) with the beta-adrenergic agonist isoproterenol stimulated stabilization of beta-catenin, activation of a beta-catenin-sensitive promoter, and formation of primitive endoderm. The response was blocked by inactivation of pertussis toxin-sensitive, heterotrimeric guanine nucleotide-binding proteins (G proteins) and by depletion of Galphaq and Galphao. Thus, G proteins are elements of Wnt/Frizzled-1 signaling to the beta-catenin-lymphoid-enhancer factor (LEF)-T cell factor (Tcf) pathway.