Rac1 is deactivated at integrin activation sites via an IQGAP1/filamin-A/RacGAP1 pathway

Abstract

SummaryCell migration makes a fundamental contribution to both normal physiology and disease pathogenesis. Integrin engagement with extracellular ligands spatially controls, via the cyclical activation and deactivation of the small GTPase Rac1, the dynamic membrane protrusion and cytoskeletal reorganization events that are required for directional migration. Although the pathways that control integrinmediated Rac1 activation are reasonably well defined, the mechanisms that are responsible for switching off activity are poorly understood. Here, proteomic analysis of activated integrin-associated complexes suggests filamin-A and IQ-motif-containing GTPase-activating protein 1 (IQGAP1) as candidates that link b1 integrin to Rac1. siRNA-mediated knockdown of either filamin-A or IQGAP1 induced high, dysregulated Rac1 activity during cell spreading on fibronectin. Using immunoprecipitation and immunocytochemistry, filamin-A and IQGAP1 were shown to be part of a complex that is recruited to active b1 integrin. Mass spectrometric analysis of individual filamin-A, IQGAP1 and Rac1 pull-downs and biochemical analysis, identified RacGAP1 as a novel IQGAP1 binding partner. Further immunoprecipitation and immunocytochemistry analyses demonstrated that RacGAP1 is recruited to IQGAP1 and active b1 integrin, and that suppression of RacGAP1 expression triggered elevated Rac1 activity during spreading on fibronectin. Consistent with these findings, reduced expression of filamin-A, IQGAP1 or RacGAP1 triggered unconstrained membrane protrusion and disrupted directional cell migration on fibrillar extracellular matrices. These findings suggest a model whereby integrin engagement, followed by filamin-A, IQGAP1 and RacGAP1 recruitment, deactivates Rac1 to constrain its activity spatially and thereby coordinate directional cell migration.

Rab7a regulates cell migration through Rac1 and vimentin

“…It has been demonstrated that active integrins, after initially activating Rac1 probably through a GEF (Guanine nucleotide Exchange Factor), subsequently recruit a complex involving a GAP (GTPase-activating protein) which down-regulates Rac1 activity in order to limit protrusive activity during cell migration [60,72]. Accordingly to these and also more recent findings [73], our data demonstrate that Rab7a depletion determines the accumulation of active β1-integrins at the leading edge of migrating cells (Fig.…”

“…Formation of filopodia is mediated by active Rac1 that controls actin cytoskeleton rearrangements and integrins, cell surface receptors involved in adhesion, spreading and migration, are transported to filopodia tips by myosin X, an unconventional myosin [45,60]. Interestingly, we established that Rab7a depletion strongly reduces formation of filopodia (Fig.…”

IQGAPs as Key Regulators of Actin-cytoskeleton Dynamics

“…Recent evidence clearly shows that, several integrin signals modulate the activity of Rho family GTPases through IQGAP1 (Wickstrom et al, 2010;Jacquemet et al, 2013aJacquemet et al, , 2013b, indicating IQGAP1 as a critical scaffold for signaling from transmembrane receptors.…”

p53 regulates cytoskeleton remodeling to suppress tumor progression

“…This resulted in the recruitment of IQGAP1 to the tips of pseudopods. The RacGAP1-IQGAP1 complex restricts Rac activity [146,147], and this permits RhoA activation as well as the formation of cellular protrusions and the invasion of 3D matrices [146].…”