Role of the α1 integrin cytoplasmic tail in the formation of focal complexes, actin organization, and in the control of cell migration

Integrins play a key role in cellular motility; an essential process for embryonic development and tissue morphogenesis, and also for pathological processes such as tumor cell invasion and metastasis. Recently, we showed that the cytoplasmic tail of integrin α1 regulates the formation of focal complexes, F-actin cytoskeleton reorganization, and migration. We now report that the α1 tail directly engages in collagen IV-mediated migration by regulation of the small GTPase Rac1. Deletion variants of the α1 integrin differ in their ability to activate Rac1. Constitutively active Rac1 rescues motility in otherwise immotile cells expressing a truncated α1 integrin without any cytoplasmic tail. In these cells, levels of GTP-Rac1 are constitutively elevated, but kept non-functional in the cytoplasm. The conserved GFFKR motif is sufficient to convey Rac1 activation, but downregulates the amount of GTP-Rac1 in the absence of the α1-specific sequence PLKKKMEK. This sequence is also required for the recruitment of PI3K to focal adhesions following Rac1 activation. Our results demonstrate that the short α1 cytoplasmic tail is crucial for Rac1 activation and PI3K localization, which in turn results in cytoskeletal rearrangement and subsequent migration.