title: Vav1 phosphorylation is induced by beta2 integrin engagement on natural killer cells upstream of actin cytoskeleton and lipid raft reorganization.
abstract: The guanine nucleotide exchange factor Vav1 regulates actin polymerization and contributes to cytotoxicity by natural killer (NK) cells. An open question is how Vav1 becomes activated and what receptor can signal upstream of actin cytoskeleton rearrangement upon NK cell contact with target cells. Using transfected insect cells that express ligands of human NK cell receptors, we show that engagement of the beta2 integrin LFA-1 on NK cells by intercellular adhesion molecule (ICAM)-1 led to a tyrosine phosphorylation of Vav1 that was not sensitive to cholesterol depletion and to inhibition of actin polymerization. Vav1 phosphorylation was blocked by an inhibitor of Src-family kinases, and correlated with activation of its downstream effector PAK. Binding of activation receptor 2B4 to its ligand CD48 was not sufficient for Vav1 phosphorylation. However, coengagement of 2B4 with LFA-1 resulted in an enhancement of Vav1 phosphorylation that was sensitive to cholesterol depletion and to inhibition of actin polymerization. Vav1 was recruited to a detergent-resistant membrane (DRM) fraction only when 2B4 and LFA-1 were coengaged, but not after LFA-1 engagement. Therefore, binding of LFA-1 to ICAM-1 on target cells may initiate an early signaling cascade in NK cells through activation of Vav1, leading to cytoskeleton reorganization and amplification of signals from other activation receptors.
authors.affiliation: Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Riteau
authors.forename: Domingo F
authors.initials: DF
authors.lastname: Barber
authors.forename: Eric O
authors.initials: EO
authors.lastname: Long
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D018821:CD18 Antigens / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D007694:Killer Cells, Natural / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000199:Actins; D018821:CD18 Antigens; D018797:Cell Cycle Proteins; D016169:Lymphocyte Function-Associated Antigen-1; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011971:Receptors, Immunologic; C496618:VAV1 protein, human; D018799:Intercellular Adhesion Molecule-1; D014443:Tyrosine