ADERACTIN

Cell-matrix adhesion plays a major role during cell migration. Proteins from adhesion structures connect the extra-cellular matrix to the actin cytoskeleton. This connection allows the growing actin network to push the plasma membrane and the contractile cables (stress fibers) to draw the cell body. This mechanical coupling is dynamic and highly regulated. The transmission of force to the substrate depends on the regulation of actin dynamics associated with adhesion structures. In addition, nascent focal complexes mature into larger focal adhesions in response to the traction force applied by stress fibers. This project aims to understand two important aspects of focal adhesions: 1, the coordinated regulation of actin dynamics in focal adhesions that controls the transmission of force to the substrate. 2, the molecular mechanisms underlying the mechano-sensitivity of focal adhesion. As a model system we will study one of the major pathway that connects the trans-membrane adhesion receptors integrins to the actin cytoskeleton: integrin beta1-talin-alpha-actinin-vinculin-VASP .The first objective is to understand the detailed molecular mechanisms by which the binding and the dynamics of the actin filaments are regulated in adhesion structures by these proteins. This first step will be completed by structural studies of the focal adhesion proteins in complex with actin filament-like complexes in collaboration with Louis Renault. The second objective is to integrate the knowledge that we will acquire into a biomimetic system to understand how these activities are coordinated to produce a coherent regulation of actin dynamics. The third objective is to understand the molecular basis of the mechano-sensitivity of focal adhesions. In order to reach this last objective, we will study the modifications in protein composition and actin dynamics in the biomimetic system upon the application of an acto-myosin traction force on the actin network. Although the acto-myosin contraction is physiologically relevant, the activity of myosin is difficult to control and to quantify. Therefore we will collaborate with a physicist in the laboratory (Guillaume Romet-Lemonne) who will use optical tweezers to apply forces on the biomimetic assay to reveal the mechano-sensitivity of individual proteins. To understand the relative contributions of the proteins in the force transmission to the substrate, we will also use optical tweezers to measure the strength of the bonds between the individual proteins and the actin filaments.