One of our major interests is in understanding the mechanisms of signaling and protein targeting during membrane trafficking. Specifically, we are charting novel G-protein mediated signaling pathways on intracellular membranes. During the last few years we have discovered a number of new proteins that are located on intracellular membranes and are involved in G-protein signaling. One of these proteins, GAIP, is the charter member of a new family of proteins, the RGS proteins, which share a common core domain and act as regulators of G protein signaling for members of the G?i subfamily of G proteins. GAIP is located on clathrin-coated vesicles and is believed to be involved in regulating endocytosis. Another of these proteins,CALNUC, is an EF-hand, Ca2+-binding protein that is located both in the Golgi as well as in the cytoplasm where it binds G?i3. We are now investigating the functions of these proteins in signal transduction during membrane trafficking using biochemical, molecular biological and morphological approaches. Another long-standing interest of our laboratory is in understanding the cellular and molecular basis of diseases of the kidney glomerulus, especially autoimmune diseases. We have identified and cloned a protein called megalin (or gp330) that serves as a target antigen for a rat experimental autoimmune disease model. This protein proved to be an endocytosis receptor with unique properties and is a member of the LDL receptor gene family. It is the main endocytic receptor in the kidney. We are now studying its functions and trafficking. Most recently we have mapped its binding sites for antibodies and ligands and shown that it is an endocytic receptor for insulin in the kidney.