title: The GTPase Rap1 regulates phorbol 12-myristate 13-acetate-stimulated but not ligand-induced beta 1 integrin-dependent leukocyte adhesion.
abstract: Leukocyte migration from bloodstream to tissue requires rapid, coordinated regulation of integrin-dependent adhesion and de-adhesion. In a previous study we demonstrated that inhibition of protein geranylgeranylation inhibited phorbol ester-stimulated avidity modulation of beta(1) integrin in several leukocyte cell lines. Both RhoA and Rap1 require post-translational modification by geranylgeranylation for full function. In this report we identify Rap1, not RhoA, as a critical geranylgeranylated protein mediating phorbol ester-stimulated beta(1) and beta(2) integrin-dependent adhesion of Jurkat cells. Overexpression of the Rap1-specific GTPase-activating protein, SPA-1, or inactivated form of Rap1 (N17Rap1) blocked phorbol ester-stimulated adhesion of Jurkat cells to fibronectin (alpha(4)beta(1)) and ICAM-1 (alpha(L)beta(2)). With high concentrations of fibronectin as ligand, Jurkat cells adhered spontaneously without phorbol ester stimulation. Unlike the phorbol ester-stimulated adhesion, adhesion induced by high density ligand was not dependent upon Rap1 activation or actin cytoskeleton reorganization. Thus, the "inside-out" adhesion signal induced by phorbol ester and the "outside-in" signal induced by high density ligand involve different pathways.
authors.affiliation: Department of Medicine, Division of Hematology, University of Washington, Seattle, WA 98104, USA. liliu@u.washington.edu
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.forename: Barbara R
authors.initials: BR
authors.lastname: Schwartz
authors.forename: Joan
authors.initials: J
authors.lastname: Tupper
authors.forename: Nancy
authors.initials: N
authors.lastname: Lin
authors.forename: Robert K
authors.initials: RK
authors.lastname: Winn
authors.forename: John M
authors.initials: JM
authors.lastname: Harlan
mesh_terms: D002448:Cell Adhesion / Q000502:physiology*; D015638:Cytochalasin D / Q000494:pharmacology; D004789:Enzyme Activation; D005353:Fibronectins / Q000378:metabolism; D020690:GTPase-Activating Proteins; D006801:Humans; D019012:Integrin beta1 / Q000502:physiology*; D019169:Jurkat Cells; D007962:Leukocytes / Q000166:cytology*; D008024:Ligands; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000502:physiology*
chemical_list: D005353:Fibronectins; D020690:GTPase-Activating Proteins; D019012:Integrin beta1; D008024:Ligands; D009687:Nuclear Proteins; C490403:SIPA1 protein, human; D015638:Cytochalasin D; D014443:Tyrosine; D011493:Protein Kinase C; D020827:rap1 GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate