β1D-integrin splice variant stabilizes integrin dynamics and reduces integrin signaling by limiting paxillin recruitment

Abstract

Heterodimeric integrin receptors control cell adhesion, migration and extracellular matrix assembly. While the β-subunit determines extracellular ligand specificity, the β-integrin chain binds to an acidic residue of the ligand, and cytoplasmic adapter proteins like talin, kindlin and paxillin, to form mechanosensing cell-matrix adhesions. Alternative splicing of the β1-integrin cytoplasmic tail creates ubiquitously expressed β1A and the heart and skeletal muscle specific β1D-form. To study the physiological difference between these forms, we developed fluorescent β1-integrins and analyzed their dynamics, localization, and cytoplasmic adapter recruitment and effects on cell proliferation. On fibronectin, GFP-β1A-integrin showed dynamic exchange in peripheral focal adhesions, and long, central fibrillar adhesions. In contrast, GFP-β1D-integrins exchanged slowly, forming immobile and short central adhesions. While adhesion-recruitment of GFP-β1A-integrin was sensitive to C-terminal tail mutagenesis, GFP-β1D-integrin was recruited independently of the distal NPXY-motif. In addition, the P786A mutation in the proximal, talin-binding NPXY783-motif, switched β1D to a highly dynamic integrin. In contrast, the inverse A786P mutation in β1A-integrin interfered with paxillin recruitment and proliferation. Thus, differential β1-integrin splicing controls integrin-dependent adhesion-signaling, to adapt to specific physiological needs of differentiated muscle cells.