title: Cytohesin-1 regulates fMLF-mediated activation and functions of the β2 integrin Mac-1 in human neutrophils.
abstract: The nucleotide exchange factor cytohesin-1 was previously reported to interact with the cytoplasmic domains of the integrin β-chain common to all β(2) integrins such as LFA-1 and Mac-1. We show here that cytohesin-1, which contributes to fMLF-induced functional responses in PMNs through activation of Arf6, restrains the activation of the β(2) integrin Mac-1 (αMβ(2)) in PMNs or dcAMP-differentiated PLB-985 cells. We found that the cytohesin-1 inhibitor SecinH3 or siRNA increased cell adhesion to immobilized fibrinogen and fMLF-mediated conformational changes of Mac-1, monitored using mAb CBRM1/5, specific for the activation epitope of the αM subunit. In contrast, PLB-985 cells overexpressing cytohesin-1 showed little adhesion to fibrinogen. The use of SecinH3 and siRNA also revealed that interference with cytohesin-1 signaling also enhanced phagocytosis of zymosan particles and chemotaxis toward fMLF in transwell migration assays. These increments of phagocytosis and chemotaxis in cells treated with SecinH3 and cytohesin-1 siRNA were reversed by a blocking mAb to the integrin-αM subunit. We provide evidence for increased polymerized cortical actin in cells treated with SecinH3 and that altered signaling through cytohesin-1 increased cell surface expression of FPRL-1 and impairs the late calcium mobilization response elicited by fMLF. The data provide evidence that stimulation with fMLF initiates a signaling cascade that restrains Mac-1 activation in PMNs. Such crosstalk between FPRL-1 and Mac-1 involves cytohesin-1. We suggest that cytohesin-1 may coordinate activation of the β(2) integrins to regulate PMN adhesion, phagocytosis, and chemotaxis.
authors.affiliation: Centre de Recherche en Rhumatologie et Immunologie, Centre de Recherche du CHUQ-CHUL, Faculté de Médecine, Université Laval, Québec, Canada.
authors.forename: Mohammed-Amine
authors.initials: MA
authors.lastname: El Azreq
authors.forename: Valérie
authors.initials: V
authors.lastname: Garceau
authors.forename: Sylvain G
authors.initials: SG
authors.lastname: Bourgoin
mesh_terms: D000199:Actins / Q000378:metabolism; D000328:Adult; D015153:Blotting, Western; D018821:CD18 Antigens / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D002454:Cell Differentiation; D002465:Cell Movement; D002633:Chemotaxis; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000737:chemistry* / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D018375:Neutrophil Activation / Q000187:drug effects; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism*; D010587:Phagocytosis; D011487:Protein Conformation / Q000187:drug effects
chemical_list: D000199:Actins; D018821:CD18 Antigens; D020662:Guanine Nucleotide Exchange Factors; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; C100723:cytohesin-1; D009240:N-Formylmethionine Leucyl-Phenylalanine; D005340:Fibrinogen; D002118:Calcium