PXN/Paxillin Phase Separation Promotes Focal Adhesion Assembly and Integrin Signaling

Focal adhesions (FAs) are transmembrane protein assemblies mediating cell-matrix connection. Tools to manipulate the compositionally intricate and dynamic FAs are currently limited, rendering many fundamental hypotheses untestable. Although protein liquid-liquid phase separation (LLPS) has been tied to the organization and dynamics of FAs, the underlying mechanisms remain unclear. Here, we experimentally tune the LLPS of PXN/Paxillin, an essential scaffold protein of FAs, by utilizing light-inducible Cry2 system. In addition to nucleating FA components, light-triggered PXN LLPS potently activates integrin signaling and subsequently accelerates cell spreading. PXN favors homotypic interaction-driven LLPS in vitro. In cells, PXN condensates are associated with plasma membrane, and modulated by actomyosin contraction and client proteins of FAs. Interestingly, non-specific weak inter-molecular interactions, together with specific molecular interactions, underlie the multicomponent condensation of PXN, and are efficient to promote FA assembly and integrin signaling. Thus, our data establish an active role of PXN phase transition into a condensed membrane-associated compartment in promoting assembly/maturation of FAs.