Activation of β-catenin signaling pathways by classical G-protein-coupled receptors:: Mechanisms and consequences in cycling and non-cycling cells

Wnt signaling pathways are some of the most intensely studies in all of biology. Recently, a number of classical heterotrimeric G protein coupled receptors (GPCRs) have been shown to activate the canonical Wnt pathway, culminating in the stabilization of beta-catenin and induction of transcription of genes regulated by the Tcf/Lef family of transactivators. However, mechanisms by which these GPCRs accomplish this differ in key ways, and in some circumstances, the phenotypes produced are novel. Herein, we will examine mechanisms by which classical GPCRs interact with the canonical Wnt pathway, culminating in its activation, and describe the consequences of this activation, focusing on the heart. In the heart, the contractile cells, or cardiomyocytes, are terminally differentiated and virtually exclusively grow by increasing cell size (hypertrophy) rather than cell number, and we will describe how GPCR-mediated activation of the canonical pathway can drive this process.