The Regulation of Hedgehog Signaling by Smoothened and Its Binding Partners

Transfer proposal - Cellular signal transduction refers to the movement of signals from outside the cell to inside. Complex signal transduction involves the coupling of ligand-receptor interactions to many intracellular events. These events include protein interaction and phosphorylation. Eventual outcome of the signal transduction is switching specific genes on or off in a regulated manner. Cancer cells arise when such signal transduction goes awry, and this is often due to incorrect responses to the signals that should normally regulate cell growth and differentiation. The Hedgehog (Hh) pathway is one of the major cell-signaling pathways in animal development, controlling cell growth, proliferation, and differentiation. Aberrant Hh signaling induces numerous types of cancer. Recent studies indicate that hyperactive Hh signaling occurs in almost all basal cell carcinomas (BCCs) and in nearly 30% of extracutaneous cancers, including medulloblastomas, prostate, gastrointestinal and small cell lung cancers. The emerging role of Hh signaling in different cancer types further emphasizes the relevance of studying this pathway to human health. The Hh pathway is highly conserved from insect to human, so both vertebrate and invertebrate model systems can be used to study its mechanisms. In Hh pathway, Smoothened (Smo) acts as a signal transducer and plays an essential role in the Hh signal transduction. Smo has been a major therapeutic target because mutations that lead to Smo activation induce BCC and medulloblastoma. We have recently identified a novel mechanism of Smo regulation. In this project, we will elucidate the molecular basis of Hh signal transduction at the cell membrane, mainly involved by Smo and its binding partners, such as Cos2, Fu, Ci, Mts, and Wdb. The functional significance of Smo activation in response to Hh signal and the mechanism of Smo transducing Hh signal to downstream will be delineated in this project by genetic and biochemical studies. Understanding Smo activation, the focus of our project, should thus not only provide insights into fundamental developmental processes, but may also lead to new diagnostic tools and therapeutic treatments for cancers caused by dysregulation of Hh signaling. To accomplish the goals of this project, chimeric Smo proteins will be constructed by tagging them with fluorescent proteins, permitting us to visualize their distribution and uptake. The chimeric constructs will be tested both in Drosophila tissue culture cells and in transgenic Drosophila.