Cytohesin-1 regulates beta-2 integrin-mediated adhesion through both ARF-GEF function and interaction with LFA-1

Abstract

Intracellular signaling pathways, which regulate the interactions of integrins with their ligands, affect a wide variety of biological functions. Here we provide evidence of how cytohesin-1, an integrin-binding protein and guanine-nucleotide exchange factor (GEF) for ARF GTPases, regulates cell adhesion. Mutational analyses of the b-2 cytoplasmic domain revealed that the adhesive function of LFA-1 depends on its interaction with cytohesin-1, unless the integrin is activated by exogenous divalent cations. Secondly, cytohesin-1 induces expression of an extracellular activation epitope of LFA-1, and the exchange factor function is not essential for this activity. In contrast, LFA-1-mediated cell adhesion and spreading on intercellular cell adhesion molecule 1 is strongly inhibited by a cytohesin-1 mutant, which fails to catalyze ARF GDP±GTP exchange in vitro. Thus, cytohesin-1 is involved in the activation of LFA-1, most probably through direct interaction with the integrin, and induces cell spreading by its ARF-GEF activity. We therefore propose that both direct regulation of the integrin and concomitant changes in the membrane topology of adherent T cells are modulated by dissectable functions of cytohesin-1. Keywords: ARF GTPase/cell adhesion/cytohesin-1/ b-2 integrin/LFA-1

Cross-Talk between CD14 and Complement Receptor 3 Promotes Phagocytosis of Mycobacteria: Regulation by Phosphatidylinositol 3-Kinase and Cytohesin-1

“…We and others have shown that cytohesin-1 is a key regulator of leukocyte adhesion with which its interaction with the cytoplasmic tail of CD18 brings about increased avidity of LFA-1 (CD18/CD11a) for ICAM-1 (12,16,56). Cytohesin-1 binds to and regulates ␤ 2 integrins and this process is positively regulated by the binding of the PI3K metabolite, PtdIns-3,4,5-P 3 , to the cytohesin-1 pleckstrin homology domain (13,36).…”

Cytohesin-1 Regulates the Arf6-Phospholipase D Signaling Axis in Human Neutrophils: Impact on Superoxide Anion Production and Secretion

“…Cytohesin-1 but not ARNO expression increases with granulocytic differentiation (10,20), suggesting a potential role of cytohesin-1 in the acquisition of a granulocytic phenotype. In lymphocytes, cytohesin-1 regulates cell adhesion via b-2 integrin activation (21,22). Furthermore, a number of reports have implicated ARNO/cytohesin-2 in cell migration (23), vesicle trafficking (24,25), and the outgrowth and branching of neurites (26,27).…”

Discriminatory aptamer reveals serum response element transcription regulated by cytohesin-2

“…T he cytohesin family members are cytoplasmic signaling proteins that are thought to be involved in integrin signaling (1), actin cytoskeleton remodeling events (2,3), and vesicle transport. They belong to a class of highly homologous guanine nucleotide exchange factors (GEFs), the small ADP-ribosylation factor (ARF)-GEFs, which catalyze the exchange of GDP for GTP on ARFs.…”

“…For example, cytohesin-1 is a positive effector of leukocyte function-associated antigen-1 (LFA-1)-mediated cell adhesion, whereas this activity has not been shown for cytohesin-2, also known as ADP-ribosylation factor nucleotide-binding site opener (ARNO) (7), or other small GEFs (1). In addition, cytohesin-1 is involved in T cell activation mediated by intercellular adhesion molecule 2 and in stimulation of T cell proliferation by IL-2 (13).…”