Integrin-based adhesions are central to the functions of blood and vascular cells. The heterogeneity of adhesions and their dynamic evolution has complicated efforts to study their fine composition, assembly, and disassembly. Our studies have shown that a transition between two adhesion archetypes is controlled by a simple binary molecular switch of vinculin competition with and displacement of RIAM or lamellipodin(Lpd), members of the MRL family, from binding sites on talin's rod domain. Furthermore, we developed methods to image the complex of MRL proteins with integrins and talin (MIT complex) and showed that it formed the tips of ?sticky fingers,? cellular protrusions that sense the density of matrix proteins and physical state of the substrate during mesenchymal cell migration. mesenchymal cell migration. We hypothesize that the MIT complex represents one among many distinct modules that contribute to the overall structure and function of integrin- based adhesions. This suggests the paradigm that the integrin adhesome can be analyzed as a dynamic assembly of these modules, which form prior to entry into the adhesions. This concept has enabled us to propose a new approach to studying adhesions by developing methods to purify each module formed prior to integrin ligation. To test this paradigm, we propose to purify 4 such modules and to characterize each for a) the presence of talin-activated integrins b) characterize its protein composition. c) establish its biochemical topology and regulation d) visualize it in living cells and e) evaluate its functions The proposed experiments will generate foundational data for the adhesion field in three ways: a) the integrin adhesome will be re- interpreted as a compendium of modular components; each with its own specific composition. b) The functional studies will identify new regulators of blood and vascular cell adhesion and signaling that may be exploitable as therapeutic targets c) A complete definition of the protein composition of each module will serve as a public resource for the analysis of integrin-based adhesions and will be hypothesis-generating for future studies to understand the regulation of assembly of each module and its functional outputs.
We propose a new paradigm to understand how cells assemble cytoplasmic anchoring and signaling complexes at sites in the body to which they adhere. Our newly developed methods will enable us to obtain a complete accounting of the contents of the modular building blocks of these adhesions and to use that information to understand how these adhesions can control processes such as the passage of white blood cells through the body, the clumping of platelets that leads to heart attack and stroke, and the health and behavior of the endothelial cells that line our blood vessels.