Signaling through the Leukocyte Integrin LFA-1 in T Cells Induces a Transient Activation of Rac-1 That Is Regulated by Vav and PI3K/Akt-1

Abstract

Integrin LFA-1 is a receptor that is able to transmit multiple intracellular signals in leukocytes. Herein we show that LFA-1 induces a potent and transient increase in the activity of the small GTPase Rac-1 in T cells. Maximal Rac-1 activity peaked 10 -15 min after LFA-1 stimulation and rapidly declined to basal levels at longer times. We have identified Vav, a guanine nucleotide exchange factor for Rac-1, and PI3K/Akt, as regulators of the activation and inactivation phases of the activity of Rac-1, respectively, in the context of LFA-1 signaling based on the following experimental evidence: (i) LFA-1 induced activation of Vav and PI3K/Akt with kinetics consistent with a regulatory role for these molecules on Rac-1, (ii) overexpression of a constitutively active Vav mutant induces activation of Rac independently of LFA-1 stimulation whereas overexpression of a dominant-negative Vav mutant blocks LFA-1-mediated Rac activation, (iii) pharmacological inhibition of PI3K/Akt prevented the fall in the activity of Rac-1 after its initial activation but had no effect on Vav activity, and (iv) overexpression of a dominant-negative or a constitutively active Akt-1 induced or inhibited, respectively, Rac-1 activity. Finally, we show that T cells with a sustained Rac activity have impaired capacity to elongate onto ICAM-1. These results demonstrate that down-regulation of the activity of this GTPase is a requirement for the regulation of T cell morphology and motility and highlight the importance of temporal regulation of the signaling triggered from this integrin.

The Rac activator Tiam1 controls efficient T-cell trafficking and route of transendothelial migration

“…44 Likely candidates are Rac activators of the Vav family. Vav1 activates Rac upon LFA-1 stimulation 45 and has been implicated in T-cell adhesion mediated by the integrin ␣4␤1. 16 Together these data suggest that different activators of Rac have specific functions in the various steps of T-cell trafficking.…”

An LFA-1 (αLβ2) Small-Molecule Antagonist Reduces Inflammation and Joint Destruction in Murine Models of Arthritis

“…The IL-2 mRNA was quantified by real-time PCR using SYBR Green I reagent (Applied Biosystems) (26), and GAPDH mRNA as an internal standard. Specifically, 500 ng RNA was used to make cDNA using SuperScript II RNAse H (Invitrogen, Carlsbad, CA) reverse transcriptase with oligo(dT) [12][13][14][15][16][17][18] primer (Invitrogen). IL-2 message was detected with the forward primer 59-CTGCTGGATTTACAGATGATTTTGA-39 and the reverse primer 59-TTGGGCATGTAAAACTTAAATGTGA-39.…”

“…The importance of LFA-1 in cell trafficking is not restricted to lymphocytes, and it appears to play an equally important role in the migration of other leukocytes (12). Engagement of LFA-1 on the surface of these cells induces a potent and transient increase in the activity of the small GTPase Rac-1, leading to cell polarization and motility (13). Thus, LFA-1 is capable of transducing signals that influence lymphocyte activation, the formation of the immunological synapse, as well as signals involved in extravasation and migration.…”

Phosphorylation of the LFA-1 Integrin β2-Chain on Thr-758 Leads to Adhesion, Rac-1/Cdc42 Activation, and Stimulation of CD69 Expression in Human T Cells

“…LFA-1 has been intimately linked to T cell costimulation, whereby ligation of the integrin together with TCR recognition of cognate antigen leads to full T cell activation. Many signaling pathways are activated after LFA-1 ligation, including phospholipase C␥ (15), mitogen-activated protein kinase pathways (16,17), phosphatidylinositol 3-kinase (17), and Rac-1 (18).…”