Regulation of Frizzled receptor aktivity at the plasma membrane: an interplay of the receptor, the trimeric G protein Go, an RGS protein and a scaffolding protein Kermit
Final Report Abstract
G protein-coupled receptors (GPCR) constitute the biggest receptor family and are the target of more than 50% of all drugs on the market. Heterotrimeric G proteins are the key transducers of these receptors, with the α-subunit playing the function of the molecular switch in the signaling. Gαo is a major G protein in the brain, heart, and breast epithelia, and can promote oncogenic transformation if overactivated. Using human cells and Drosophila fruit flies as the experimental models, we investigated two signaling partners of Gαo – the RGS protein Dhit (RGS19 in mammals) and the scaffolding protein Kermit. We discover that Dhit and RGS19 possess a unique double inhibitory activity towards Gαo and Gαi in flies and humans, slowing down the rate of activation of the G proteins and speeding up the rate of their deactivation. Through protein crystallography, structure analysis, mutagenesis, and protein biochemistry, we pinpointed the molecular mechanism of this unusual activity. We find that this double negative activity has important implications in signaling in human cells and developing Drosophila nervous system, and may possibly prevent oncogenic transformation in the breast. The other signaling partner of Gαo discovered in the course of this project, Kermit, is shown to regulate another epithelial phenomenon – planar cell polarity (PCP). In PCP, epithelia become polarized in the plane of the tissue, and the PCP signaling pathway regulates both normal development and pathogenic situations, such as cancer cell metastasis. We find that the Gαo-Kermit interactions are important for the intracellular trafficking of the key PCP regulator Vang, conserved in fruit flies and mammals. Overall, our studies provide important clues into the GPCR-mediated signaling mechanisms and may have implications for the understanding of the mechanisms of disease.
