CHORD

Our two groups share interest in the function of the Hedgehog protein as a central regulator of metazoan development. Hedgehog signaling has adapted the molecular functions of several molecules already established in earlier life forms. For example, Hedgehog maturation uses a unique intein-like mechanism from viruses that links Hedgehog covalently to a cholesterol moiety. In addition, Hedgehog receptor Patched is a member of the cholesterol transporter family that regulates membrane cholesterol levels in eucaryotes and related molecules (hopanoids) in procaryotes. Our joint proposal is based on our unique observations that the transmembrane protein Dispatched – a Hedgehog-release regulator- removes plasma membrane cholesterol from cells, consistent with Dispatched belonging to the family of transmembrane efflux pumps that contains a sterol sensing domain. Deletion of Dispatched in mammalian cells increased cellular cholesterol levels, and showed a strong decrease of expression of genes required for cholesterol biosynthesis and uptake, consistent with cholesterol overload in these cells. Together with the fact that Dispatched is expressed in almost all cell types, both in vertebrates et invertebrates, we propose that the fundamental function of Dispatched is to transport cholesterol out of the cell to maintain cholesterol homeostasis, with important pathophysiological implications. Based on our seminal findings on Dispatched, fly genetics (Thérond) will be combined with advanced biochemistry/cell biology analysis (Grobe) to study cholesterol-related Dispatched function in physiological and pathological contexts. We will characterize Dispatched-dependent cell mechanism of action and decipher the underlying network of cholesterol-regulated gene expression. The information obtained will be integrated with the in vivo analysis in Drosophila model system of Dispatched regulation on cholesterol homeostasis in different tissues, bypassing its role for Hedgehog function.