Structure and Function of cell adhesion sites

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Integrin-dependent adhesion and signaling are required for cell motility, survival, and responsiveness to mechanical cues. Cells of the respiratory, cardiovascular, musculoskeletal, and urogenital systems are exposed to physical tension as part of their normal physiology. Cells respond and adapt to mechanical stress by remodeling their actin cytoskeletons and adopting new gene expression programs. Despite the critical importance of mechanical signals for embryonic development, wound healing, and tissue homeostasis, little is understood about how physical force influences cell behavior. This proposal builds on a recent discovery of my lab that the LIM protein, zyxin, is rapidly mobilized from fibroblast focal adhesions to actin stress fibers in response to externally applied, uniaxial, cyclic stretch. The mobilization of zyxin in response to physical tension depends on integrin-based adhesion. Exposure of cells to mechanical stimulation results in actin stress fiber reinforcement and cytoskeletal alignment perpendicular to the stretch vector. By comparing wild-type and zyxin-null fibroblasts, we determined that zyxin is essential for the thickening of actin stress fibers that occurs in response to mechanical tension. The proposed research will define the molecular mechanism by which zyxin contributes to the cellular responsiveness to physical stress. First, we will explore the signals that stimulate changes in zyxin localization and function in response to mechanical stress. Second, we will explore how integrin activation and signaling are regulated in response to mechanical stress. Third, we will define the molecular mechanism by which stress fibers are reinforced in response to stretch. Fourth, we will interrogate the mechanism of stretch-modulated gene expression. These studies provide a framework for understanding cell signaling in response to mechanical cues. A molecular understanding of how cells respond to mechanical stress may ultimately suggest strategies for therapeutic intervention in cardiomyopathy, osteoporosis, and fibrotic disorders, all pathological conditions driven by signaling in response to mechanical cues.