FAK Modulates Cell Adhesion Strengthening Via Two Distinct Mechanisms: Integrin Binding and Vinculin Localization
Michael, Kristin E.
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Cell adhesion to the extracellular matrix (ECM) provides tissue structure and integrity as well as triggers signals that regulate complex biological processes such as cell cycle progression and tissue-specific cell differentiation. Hence, cell adhesion is critical to numerous physiological and pathological processes, including embryonic development, cancer metastasis, and wound healing, as well as biotechnological applications, such as host responses to implanted devices and integration of tissue-engineered constructs. During the adhesion process, integrin surface receptors bind ECM proteins, cluster, and associate with the actin cytoskeleton. Subsequent strengthening of the integrin/actin cytoskeleton interaction occurs via complexes of proteins known as focal adhesions. Due to the close association between biochemical and biophysical processes within adhesion complexes, mechanical analyses can provide important new insights into structure/function relationships involved in regulating the adhesion process. The objective of this project was to investigate the role of the protein tyrosine kinase FAK in cell adhesion strengthening. Our central hypothesis was that FAK regulates adhesion strengthening by modulating interactions between integrins and FA structural components. Using a novel combination of genetically engineered cells to control the interactions of FAK, a spinning disk adhesion assay with micropatterned substrates to obtain reproducible and sensitive measurements of adhesion strength, and quantitative biochemical assays for analyzing changes in adhesive complexes, we demonstrate that FAK modulates adhesion strengthening via two distinct mechanisms: (1) FAK expression results in elevated integrin activation leading to regulation of strengthening rate and (2) FAK regulates steady-state adhesion strength via vinculin recruitment to focal adhesions. We also show that the autophosphorylation and catalytic sites of FAK are critical to this regulation of adhesion strengthening. This work is significant because it both identifies functional mechanisms of FAK and provides the first evidence that focal adhesion signaling regulates the adhesion strengthening process. Furthermore, this research demonstrates that the dependency of migration on adhesion strength is highly complex and establishes a need for adhesion strengthening metrics in analyzing the functional mechanisms of molecules within adhesion complexes.