Grant: Operating Grant

Hedgehog (Hh) family proteins are important growth factors that are secreted from specific groups of cells within tissues and convey information to neighbouring cells in a process known as cell-cell communication. These proteins play a critical role in controlling the growth and organization of embryonic and fetal tissues in species ranging from flies to man. They are also important for stem cell function, and consequently for maintenance of adult tissues. Due to their central role in these processes, misregulation of Hh activity can result in congenital birth defects and cancer. Much of our understanding of the mechanism of action of Hh proteins comes from studies in the fruit fly, Drosophila melanogaster. These studies have shown that binding of Hh to its receptor at the surface of a cell triggers an intracellular signal in that cell that is initiated by a protein called Smoothened (Smo). Upon exposure of cells to Hh, Smo becomes active, moves to the cell surface, and signals through a series of downstream proteins to regulate gene expression in the nucleus. We have been studying a protein called G-protein-coupled receptor kinase 2 (Gprk2) that is required for Smo to become fully active in flies and mammals. We have identified regions in fly Smo that become modified by Gprk2 through a process called phosphorylation. The same phosphorylated regions are found in Smoothened proteins in all animals, suggesting that Gprk2 phosphorylation represents an evolutionarily ancient mechanism for regulating Smoothened activity. We are proposing to define the molecular mechanisms by which Gprk2 promotes Smo activity. The results of this work will provide important new insights into how Hh signaling controls gene expression not just in flies but also in humans, with the goal of identifying potential therapeutic targets for the treatment of Hh-dependent cancers.