Structure and Function of Paxillin

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DESCRIPTION (provided by applicant): Cell migration is essential for normal embryonic development, tissue repair and immune surveillance, but is also a contributing factor in mental retardation, developmental defects, tumor cell invasion and tissue fibrosis. It is a highly dynamic process requiring exquisite spatial and temporal control of cell adhesion to the extracellular matrix (ECM) in coordination with remodeling of the actin cytoskeleton. The Rho family GTPases play a central role in this regulation but the mechanisms controlling the activity of their key regulators, the guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs) remain poorly understood. Paxillin is a multi-domain scaffold/adapter protein, which recruits numerous structural and signaling molecules to cell adhesion sites and thereby functions as a central hub in the regulation cell migration. Aim 1 of this proposal will test the hypothesis that paxillin coordinates the spatial-temporal regulation of Rho family GTPase signaling and focal adhesion dynamics by establishing a local signaling network comprising the ARF GAP PKL/GIT2, the guanine nucleotide exchange factor Vav2 and the tyrosine phosphatase PTP-PEST. Hic-5, a close relative of paxillin is upregulated during epithelial-mesenchymal transition to promote cell migration via Rho-ROCK signaling and is an important regulator of cell motility, as well as patho-physiologic matrix remodeling in myofibroblasts. In Aim 2, using 2D- and 3D-matrix model systems, we will dissect the mechanism through which Hic-5 controls cell migration and contractility and test the hypothesis that Hic-5 functions both independently and in conjunction with paxillin to regulate these processes. To accomplish these goals, we will suppress endogenous protein expression by RNA interference or express mutant proteins in fibroblasts and utilize confocal fluorescence time-lapse microscopy, combined with Fluorescence Recovery after Photobleaching (FRAP) and Fluorescence Resonance Energy Transfer (FRET) analysis to evaluate cell morphology, polarity and migration as well focal adhesion dynamics and spatial- temporal changes in protein- protein interactions and Rho family GTPase activity. This will be combined with biochemical analysis of changes in intracellular signaling to include GEF activity assays, protein phosphorylation profiling and protein- protein interactions. Completion of these Aims will elucidate the roles of paxillin and Hic-5 and their potential interactions in regulating cell migration vi modulation of the Rho GTPase system. PUBLIC HEALTH RELEVANCE: ll movement is essential for normal processes such as embryonic development and tissue repair but it is also a key factor in cancer progression, tissue fibrosis and several cardiovascular and neurodegenerative disorders. Information gained from the proposed study will contribute to our understanding of how the cell migration machinery is regulated and thereby will potentially identify novel targets for corrective therapies for migration-associated disorders.