title: Rap1 controls activation of the α(M)β(2) integrin in a talin-dependent manner.
abstract: The small GTPase Rap1 and the cytoskeletal protein talin regulate binding of C3bi-opsonised red blood cells (RBC) to integrin α(M)β(2) in phagocytic cells, although the mechanism has not been investigated. Using COS-7 cells transfected with α(M)β(2), we show that Rap1 acts on the β(2) and not the α(M) chain, and that residues 732-761 of the β(2) subunit are essential for Rap1-induced RBC binding. Activation of α(M)β(2) by Rap1 was dependent on W747 and F754 in the β(2) tails, which are required for talin head binding, suggesting a link between Rap1 and talin in this process. Using talin1 knock-out cells or siRNA-mediated talin1 knockdown in the THP-1 monocytic cell line, we show that Rap1 acts upstream of talin but surprisingly, RIAM knockdown had little effect on integrin-mediated RBC binding or cell spreading. Interestingly, Rap1 and talin influence each other's localisation at phagocytic cups, and co-immunoprecipitation experiments suggest that they interact together. These results show that Rap1-mediated activation of α(M)β(2) in macrophages shares both common and distinct features from Rap1 activation of α(IIb)β(3) expressed in CHO cells.
authors.affiliation: Centre for Molecular Microbiology and Infection, Division of Cell and Molecular Biology, Imperial College London, London, UK. jensons_blog@yahoo.co.uk
authors.forename: Jenson
authors.initials: J
authors.lastname: Lim
authors.forename: Aurélien G
authors.initials: AG
authors.lastname: Dupuy
authors.forename: David R
authors.initials: DR
authors.lastname: Critchley
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Caron
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003179:Complement C3b / Q000378:metabolism; D004789:Enzyme Activation; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D016177:Macrophage-1 Antigen / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D050505:Mutant Proteins / Q000378:metabolism; D009895:Opsonin Proteins / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012756:Sheep; D015398:Signal Transduction; D016608:Talin / Q000378:metabolism*; D014162:Transfection; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C493340:APBB1IP protein, human; D048868:Adaptor Proteins, Signal Transducing; D016177:Macrophage-1 Antigen; D008565:Membrane Proteins; D050505:Mutant Proteins; D009895:Opsonin Proteins; D021122:Protein Subunits; D016608:Talin; D003179:Complement C3b; D020827:rap1 GTP-Binding Proteins