Regulation of Polarized Traffic by PI-Metabolizing Enz.

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DESCRIPTION (provided by applicant): The local generation of distinct phosphatidylinositol (PI) lipid species has been implicated in the regulation of numerous membrane trafficking events and in the control of cytoskeletal dynamics. The compartmentalized synthesis of noninterchangeable pools of PIs by PI-metabolizing enzymes is critical to the cell's ability to control these multiple PI-dependent functions independently. We are interested in the role of phosphatidylinositol kinases and inositol polyphosphate phosphatases in polarized membrane traffic in renal epithelial cells, and have found that apical and basolateral biosynthetic pathways are differentially sensitive to overexpression of the PI metabolizing enzymes PI-4 kinase beta and PI-5 kinase alpha. Moreover, the observation that Lowe Syndrome (a disease with severe renal manifestations) is caused by molecular defects in a Golgi-tocalized PI-catabolizing enzyme suggests a role for inositol polyphosphate 5-phosphatase activity in biosynthetic transport. In this proposal, we will correlate the effects of expressing individual PI-metabolizing enzymes on transport with actual changes in PI lipid composition across the Golgi complex and test hypotheses to explain the mechanisms by which distinct PI species regulate membrane traffic. These experiments will significantly enhance our understanding of how localized PI synthesis operates at a molecular level to regulate polarized biosynthetic traffic in normal and disease states.