This Unit studies the spatial and temporal organization of intracellular signals that are initiated by stimulation of cell surface receptors by hormones and neurotransmitters. Eukaryotic cells contain a great variety of cell surface receptors through which they receive signals from their environment or from other cells. Transmission of extracellular signals to the cell interior is based on receptor-induced recruitment and assembly of proteins into signaling complexes at the inner leaflet of the plasma membrane. It is being increasingly recognized that cells impose temporal and spatial constraints on the various signaling cascades to ensure signal specificity. Mutations that affect the cellular distribution of regulatory molecules can lead to loss of function, as well as to the development of malignancies.

Our research addresses the nature of the molecular determinants which underlie important protein-protein and protein-lipid interactions that are critical for proper localization of signaling molecules. Most signaling proteins have a modular structure
in which each module confers interaction with binding modules of other molecules. One of the goals of the group is to define minimal protein motifs that have the ability to recognize conformation-specific features of their natural binding partners in order to
create GFP-tagged protein chimeras that can track molecular interactions in live cells.

Using this approach, we have utilized GFP fusion proteins that specifically recognize the various forms of inositol phosholipids to study the cellular compartments in which changes in these lipids take place, and to investigate the manner in which such inositide lipid changes regulate specific cellular processes.

Other work in the Unit has been focused on the role of phosphatidylinositol (PI) 4-kinase enzymes in cellular signaling, following the isolation and molecular cloning of two of these proteins from bovine adrenal and brain in this laboartory. These enzymes are type-III PI 4-kinases, and although both catalyze the same reaction, namely the synthesis of phosphatidylinositol (PI) 4-phosphate, they show distinct subcellular distributions and assume non-redundant functions. Phosphoinositides are involved in almost all aspects of cellular functions in which cellular membranes are remodeled, such as exocytosis, endocytosis, and vesicular trafficking. A combination of research tools to follow inositide dynamics and those that alter the function(s) of the distinct PI 4-kinases will help to define the role of these enzymes at specific signaling steps within the cell. It is also the aim of this laboratory to design methods for the screening of small molecules that would interrupt protein-inositide interactions and could be used as specific inhibitors of inositide-regulated signaling steps.