PDZ Domains from the Junctional Proteins Afadin and ZO-1 Act as Mechanosensors

Abstract

Intercellular adhesion complexes must withstand mechanical forces to maintain tissue cohesion, while also retaining the capacity for dynamic remodeling during tissue morphogenesis and repair. Most cell-cell adhesion complexes contain at least one PSD95/Dlg/ZO-1 (PDZ) domain situated between the adhesion molecule and the actin cytoskeleton. However, PDZ-mediated interactions are characteristically nonspecific, weak, and transient, with several binding partners per PDZ domain, micromolar dissociation constants, and bond lifetimes of seconds or less. Here, we demonstrate that the bonds between the PDZ domain of the cytoskeletal adaptor protein afadin and the intracellular domains of the adhesion molecules nectin-1 and JAM-A form molecular catch bonds that reinforce in response to mechanical load. In contrast, the bond between the PDZ3-SH3-GUK (PSG) domain of the cytoskeletal adaptor ZO-1 and the JAM-A intracellular domain becomes dramatically weaker in response to ~2 pN of load, the amount generated by single molecules of the cytoskeletal motor protein myosin II. These results suggest that PDZ domains can serve as force-responsive mechanical anchors at cell-cell adhesion complexes, and that mechanical load can enhance the selectivity of PDZ-peptide interactions. PDZ mechanosensitivity may thus help to generate the intricate molecular organization of cell-cell junctions and allow junctional complexes to dynamically remodel in response to mechanical load.

Cell Adhesion at the Tight Junctions: New Aspects and New Functions

“…The direct application of pulling forces on JAM-A through trans-homophilic JAM-A interaction activates various RhoA GEFs and increases RhoA activity [83]. Also, recent experiments with recombinant proteins indicate that the strength of the JAM-A-ZO-1 interaction is modulated by mechanical forces that act on this binary interaction [84]. Besides ZO-1, JAM-A interacts with the AJ-localized protein afadin [80].…”

“…Besides ZO-1, JAM-A interacts with the AJ-localized protein afadin [80]. Despite comparable affinities, the interaction of JAM-A with the PDZ domain of afadin is reinforced in response to the mechanical load over a given force range, whereas, by contrast, the interaction of JAM-A with the PDZ3 of ZO-1 is destabilized in response to a mechanical load [84]. These observations thus indicate that the protein interaction networks at TJs dynamically change in the presence of mechanical forces.…”