Christopher E. Turner - US grants

I have recently identified a novel vinculin-binding protein, paxillin. This proposal is aimed at further characterizing paxillin, its interaction with vinculin and at identifying other paxillin-binding proteins. These data are expected to contribute to our understanding of cytoskeletal- membrane interactions. The nucleotide sequence of paxillin will be obtained from paxillin cDNA. The resulting predicted amino acid sequence will be analyzed for potential homologies with other proteins and for suggestions of possible enzymatic or structural function. Appropriate biochemical assays will be performed on the purified protein to confirm/disprove such indications. The paxillin cDNA will be transfected in whole or in part into mammalian cells to determine which regions of the protein are required for focal adhesion localization. In parallel, partial or full length fusion proteins of paxillin and vinculin will be used in in vitro assays to map their binding sites. The interaction of these two proteins will also be examined at the electron microscope level. Following transformation by Rous sarcoma virus, paxillin contains high levels of phosphotyrosine. The role of paxillin phosphorylation in the loss of focal adhesion integrity during viral or chemically induced transformation will be investigated. The effects of paxillin phosphorylation on vinculin binding will be determined in vitro. In an attempt to identify novel paxillin-binding proteins I will isolate protein complexes containing paxillin from cells grown in culture possessing focal adhesions at their interface with the substratum. Cells will be gently permeabilized and, in some cases, the actin cytoskeleton stabilized with phalloidin. Proteins will be differentially extracted from these cells using changes in ionic strength, pH and divalent cation concentrations. Proteins released in conjunction with paxillin will be co-isolated by immunoprecipitation of paxillin under non-denaturing conditions. Where appropriate, experiments will be performed in the presence of chemical cross-linkers to stabilize interactions between paxillin and its associated proteins. Antibodies will be generated against any novel paxillin-binding proteins and these will be used to study further the proteins regarding their role in cytoskeletal membrane organization.

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.

DESCRIPTION (provided by applicant): Integrin-mediated interaction of cells with the extracellular matrix control a diverse set of physiologic processes including cell migration during embryogenesis and metastasis, cell proliferation, tissue maintenance, differentiation and repair. Protein complexes associated with the integrin cytoplasmic domains facilitate integrin signaling and interactions with the actin cytoskeleton. This proposal will focus on the importance of recently identified interactions between the integrin-linked kinase ILK, the actin binding protein actopaxin and the molecular adapter protein paxillin in the regulation of cell adhesion, motility, proliferation and differentiation. In Aim 1 epitope-tagged mutant cDNAs of ILK and actopaxin will be transfected into fibroblasts followed by co-precipitation experiments to further characterize the ILK and actopaxin binding domains. The importance of these domains for subcellular localization will be assessed by immunofluorescence microscopy. We have recently demonstrated that actopaxin mutants perturb cell adhesion/spreading on collagen. Experiments proposed in Aim 2 will identify the molecular basis for this defect by assaying for changes in integrin function as well as effect on downstream signaling events. The role of ILK and actopaxin in mediating cell motility will be addressed using time-lapse microscopy, Boyden chamber and wound assays. In Aim 3 we will investigate the importance of ILK-actopaxin associations in regulating cell proliferation and differentiation. Sites of actopaxin phosphorylation resulting from associated cyclinB/cdc2 kinase activity will be delineated. The role of phosphorylation of these sites in regulating protein-protein interactions and cytoskeleton changes associated with transition through mitosis will be examined by co-precipitation analysis and immunofluorescence microscopy. Potential effects on proliferation and cell survival will be examined. The involvement of ILK and actopaxin interactions in regulating cell differentiation will be examined in the context of skeletal muscle myoblast differentiation. Together these experiments will address evolutionarily conserved mechanisms of protein linkages between the extracellular matrix and the actin cytoskeleton that are of importance to the understanding of cardiovascular and musculoskeletal defects and metastatic transformation.

DESCRIPTION (provided by applicant): The migration of cancer cells away from the primary tumor mass and their subsequent metastasis to distant organs is regarded as a fatal step in cancer progression and is associated with the majority of cancer mortalities. Furthermore, individual cancer cells appear to be able to evade current pharmacologic intervention of invasion and metastasis by switching between mesenchymal and amoeboid modes of motility. The cellular mechanisms controlling this phenotypic plasticity are poorly understood. We have recently identified distinct functions for the closely related adhesion-associated scaffold proteins paxillin and Hic-5 in the regulation of tumor cell plasticity, invasion and metastasis. In this proposal, using established cancer cell lines, as well as cells isolated from primary tumors, we will apply state-of-the art real-time imaging techniques to track tumor cell morphology and migration as well as adhesion and cytoskeletal dynamics in 3D-extracellular matrix in vitro model systems. Xenograft studies in mice will be used to evaluate the relative impact of paxillin and Hic-5 signaling on tumor progression and metastasis in vivo. We will use RNA interference and mutant protein expression to dissect the respective roles for paxillin and Hic-5 in controlling the mode of tumor cell invasion and identify the pertinent functional domains and signaling pathways. We will use similar approaches to study a role for paxillin in the regulation of matrix metalloproteinase-2 (MMP-2) trafficking and secretion to control mesenchymal tumor invasion strategies. Hic-5 is upregulated during TGF-¿-induced epithelial mesenchymal transition. The role of Hic-5 in TGF-¿-dependent cell invasion, through the formation and function of matrix-degrading invadopodia, will also be examined. The proposed studies will provide insight into the underlying cellular mechanisms controlling tumor cell migration and invasion and the coordination of their phenotypic plasticity and may in the future suggest novel strategies for detection or treatment of metastatic cancers.

The goal of this research project is to employ programmable materials from the field of biomaterials science, particle-tracking algorithms from the fields of biomechanics and biophysics, and molecular probes from the fields of cell and molecular biology to track and model the interaction of multiple intracellular components and the resultant large-scale cellular behaviors. A grand challenge in biomechanics and mechanobiology is that of understanding the complex interactions that occur between intracellular structures and how those interactions produce function at the cell and tissue levels. Through three objectives, this project will yield a method for quantitatively characterizing interactions between intracellular components and linking those patterns with large-scale behaviors such as cell polarization. First, the biomechanical sequence of cell polarization at the intracellular level will be elucidated via automated, synchronized tracking of multiple components in single cells in highly constrained environments. Second, cell polarization will be induced in individual cells using smart substrates and patterns in intracellular components will be linked to this large-scale cell behavior. Third, cell polarization will be studied and modeled, from the intracellular to multicellular levels, in a model of contact inhibition release/localized epithelial-mesenchymal transition with high cell densities. Coordinated cell movements are critical to biological processes such as embryonic development, cancer progression, and wound healing. Although cell movement is generated by structures inside cells, it is not known how interactions of those structures produce cell movement and resulting organization within groups of cells. This project will answer that question. A new computational approach will quantify the simultaneously interactions of several different important structures inside cells. New smart material will be used to trigger changes to cell movement, and the computational approach will determine how interactions of structures inside cells also change. Both low cell densities, where cells interact rarely, and high cell densities, where cells are always touching as happens in living organisms, will be studied. A model for collective movement of large groups of cells that can make predictions about tissues formation and disease will be developed.

Society will benefit from the technical and professional development of the individuals involved, important advances in the fields of biomechanics, biophysics, and biology, and breakthroughs that can be anticipated in healthcare fields. Research, education, and diversity at both collaborating institutions will be further integrated through a yearly summer research program that will recruit exceptional Hampton University students as undergraduate researchers.