RESUMEN
Heterodimeric integrin receptors control cell adhesion, migration and extracellular matrix assembly. While the α integrin subunit determines extracellular ligand specificity, the ß integrin chain binds to an acidic residue of the ligand, and cytoplasmic adapter protein families such as talins, kindlins and paxillin, to form mechanosensing cell matrix adhesions. Alternative splicing of the ß1 integrin cytoplasmic tail creates ubiquitously expressed ß1A, and the heart and skeletal muscle-specific ß1D form. To study the physiological difference between these forms, we developed fluorescent ß1 integrins and analyzed their dynamics, localization, and cytoplasmic adapter recruitment and effects on cell proliferation. On fibronectin, GFP-tagged ß1A integrin showed dynamic exchange in peripheral focal adhesions, and long, central fibrillar adhesions. In contrast, GFP-ß1D integrins exchanged slowly, forming immobile and short central adhesions. While adhesion recruitment of GFP-ß1A integrin was sensitive to C-terminal tail mutagenesis, GFP-ß1D integrin was recruited independently of the distal NPXY motif. In addition, a P786A mutation in the proximal, talin-binding NPXY783 motif switched ß1D to a highly dynamic integrin. In contrast, the inverse A786P mutation in ß1A integrin interfered with paxillin recruitment and proliferation. Thus, differential ß1 integrin splicing controls integrin-dependent adhesion signaling, to adapt to the specific physiological needs of differentiated muscle cells.
