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Abstract
Ligand binding to certain heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) stimulates the rapid synthesis of cyclic adenosine monophosphate (cAMP) through the G protein αs subunit, which activates adenylyl cyclase (AC). We found that the transmembrane receptor low-density lipoprotein receptor–related protein 6 (LRP6), a co-receptor for Wnt proteins, bound to the Gαsβγ heterotrimer and that knockdown of LRP6 attenuated cAMP production by various GPCRs, including parathyroid hormone receptor 1 (PTH1R). Knockdown of LRP6 disrupted the localization of Gαs to the plasma membrane, which led to a decrease in the extent of coupling of Gαs to PTH1R and inhibited the production of cAMP and the activation of cAMP-dependent protein kinase (PKA) in response to PTH. PKA phosphorylated LRP6, which enhanced the binding of Gαs to LRP6, its localization to the plasma membrane, and the production of cAMP in response to PTH. Decreased PTH-dependent cAMP production was observed in single cells in which LRP6 was knocked down or mutated at the PKA site by monitoring the cAMP kinetics. Thus, we suggest that the binding of Gαs to LRP6 is required to establish a functional GPCR-Gαs-AC signaling pathway for the production of cAMP, providing an additional regulatory component to the current GPCR-cAMP paradigm.
