title: Rap1 GTPase-activating protein SPA-1 negatively regulates cell adhesion.
abstract: Rap1 GTPase is activated by a variety of stimulations in many types of cells, but its exact functions remain unknown. In this study we have shown that SPA-1 interferes with Rap1 activation by membrane-targeted C3G, C3G-F, in 293T cells through the GTPase activating protein (GAP) activity. SPA-1 transiently expressed in HeLa cells was mostly localized at the cortical cytoskeleton and induced rounding up of the cells, whereas C3G-F conversely induced extensive cell spreading. Conditional SPA-1 overexpression in HeLa cells by tetracycline-regulative system suppressed Rap1 activation upon plating on dishes coated with fibronectin and resulted in the reduced adhesion. When SPA-1 was conditionally induced after the established cell adhesion, the cells gradually rounded up and detached from the dish. Both effects were counteracted by exogenous fibronectin in a dose-dependent manner. Retroviral overexpression of SPA-1 in promyelocytic 32D cells also inhibited both activation of Rap1 and induction of cell adhesion by granulocyte colony stimulating factor without affecting differentiation. These results have indicated that Rap1 GTP is required for the cell adhesion induced by both extracellular matrix and soluble factors, which is negatively regulated by SPA-1.
authors.affiliation: Department of Immunology and Cell Biology, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Tsukamoto
authors.forename: M
authors.initials: M
authors.lastname: Hattori
authors.forename: H
authors.initials: H
authors.lastname: Yang
authors.forename: J L
authors.initials: JL
authors.lastname: Bos
authors.forename: N
authors.initials: N
authors.lastname: Minato
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D002454:Cell Differentiation / Q000187:drug effects; D005353:Fibronectins / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins; D016147:Genes, Tumor Suppressor; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011817:Rabbits; D012190:Retroviridae; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D020668:rap GTP-Binding Proteins
chemical_list: D005353:Fibronectins; D020690:GTPase-Activating Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C490403:SIPA1 protein, human; D014157:Transcription Factors; D016179:Granulocyte Colony-Stimulating Factor; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins