Mechanotransduction associated with integrin-mediated phagocytosis – PHAGOMECANO

Phagocytosis is the mechanism of internalization of large particles of several microns in size and therefore, as other cellular functions dealing with large scales, it involves important mechanical constraints that have been poorly investigated. Phagocytosis is an ideal cellular function to understand how cells adapt to the mechanical properties of their environment because it is a local and inducible process that internalizes particles of variable mechanical properties.

Many surface receptors capable to mediate phagocytosis belong to the integrins family of cell adhesion receptors that bind to extracellular matrix ligands, cell surface ligands and soluble ligands. Integrins signal through the plasma membrane in both directions. An “inside-out” signal induces a conformational change of the integrin that is necessary to activate its binding to extracellular ligands while the “outside-in” signal couples the ligand binding adhesion sites to the cytoplasmic tail, which links to the cytoskeleton and downstream signaling pathways.

Our working hypothesis is that actin-binding proteins (ABPs), and their associated regulators, are mechanoensitive hubs at the center of feedback loops that control anchoring to the actin cytoskeleton and activation of the integrins during phagocytosis.

Our proposal aims at understanding how these actin-associated mechanosensitive machineries, involved in particle adhesion to the CR3 receptor (CD11b/CD18 or integrin aMß2) and the subsequent anchoring of the actin cytoskeleton, sense and respond to mechanical parameters.
The objectives of this project are the following:
(i) to dissect the mechanisms by which mechanosensitive protein machineries sense force and modulate actin dynamics and anchoring during phagocytosis
(ii) to determine the importance of the same protein machineries in the regulation of the adhesive properties of CR3.

To this end, the complementary expertise of two groups, who have separately made important contributions in their fields and have already collaborated, will be brought together. They will combine investigation of actin remodeling downstream of integrins during phagocytosis using experimental models to follow phagosome completion with improved resolution and in vitro reconstitution with pure proteins of the dynamics of mechanosensitive protein machineries associated with integrin-mediated adhesion. The sequential recruitment of the proteins at phagocytic sites in living macrophages will be used to refine the in vitro system, while the interactions between molecular partners characterized in vitro will be used to generate mutants and analyze their functions in living cells.

This work will bring new insight into the overlooked force-dependent CR3/integrin-mediated actin dynamics and adhesion associated with phagocytosis. Our project will contribute to expand scientific knowledge and could provide therapeutic strategies, because integrin-mediated phagocytosis is important in a variety of normal and pathological contexts such as the turnover and remodelling of tissues, disposal of dead cells and bacteria clearance. Integrin-mediated phagocytosis could also serve as a reference model to reveal new concepts associated with the regulation of integrins in other mechnanosensitive processes like cell adhesion or migration. Therefore this work will contribute to bring knowledge and approaches to the emerging field of mechanobiology.