Chemotaxis, the directed movement of cells along extracellular gradients, is an intriguing and vital process that guides cells in developing embryos. In the adult, chemotaxis is required for correct and immune responses and in tissue maintenance and repair. In addition to these roles in normal physiology, inappropriate cell migration is the basis for pathological conditions including cancer metastasis and chronic inflammatory diseases such as atherosclerosis, asthma and arthritis. In chemotaxing cells, although receptors and linked G-proteins remain uniformly distributed around the cell perimeter, signaling is highly polarized. PI3Ks and PTEN bind to the membrane at the front and back of the cell, respectively, and the resulting accumulation of PI(3,4,5)P3 promotes pseudopodia production at the front. These observations raise new questions. First, how does receptor/G-protein signaling localize these key enzymes? By randomly mutagenizing PI3K and PTEN, we will screen for versions that bind constitutively and use these reagents to identify the membrane binding sites biochemically. To find regulators of binding, we will screen for mutations in the genome that cause, or can reverse, constitutive membrane localization of each enzyme. Second, how does localized PI(3,4,5)P3 promote pseudopodia extension? We have recent evidence to suggest that elevated PI(3,4,5)P3 regulates the cytoskeleton by signaling through PKB. We will use cell-free systems to define the mechanisms by which receptor/G-protein signaling controls PKB activity and will identify PKB substrates by mass- spectrometry of proteins that immunoprecipitate with phosphospecific antibodies that recognize PKB targets. The role of each putative target in mediating chemoattractant-induced responses will be assessed by gene disruption and overexpression studies. We will also image PKB activation and kinase activity in living cells undergoing chemotaxis using validated FRET-based reporters. Third, what additional strongly polarized components contribute to the directional response? To identify more polarity proteins, we will express an arrayed library of cDNAs fused to GFP and visually inspect highly polarized cells for those that localize to the front or back. The function of these genes in chemotactic signaling will be assessed by both loss of function and gain of function studies. Finally, we will test whether these proteins have conserved functions in appropriate polarized mammalian cells. Relevance to public health: Our research focuses on the basic mechanisms that guide migrating cells, such as those closing a wound or gathering at the site of an infection. This cellular """"""""homing"""""""" response is critical for many normal functions and is often altered in diseases. Our studies will provide basic information and likely lead to new strategies for intervening in pathological conditions involving cell migration such as cancer metastasis, atherosclerosis, asthma, and arthritis.
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