title: RIAM (Rap1-interacting adaptor molecule) regulates complement-dependent phagocytosis.
abstract: Phagocytosis mediated by the complement receptor CR3 (also known as integrin αMß2 or Mac-1) is regulated by the recruitment of talin to the cytoplasmic tail of the ß2 integrin subunit. Talin recruitment to this integrin is dependent on Rap1 activation. However, the mechanism by which Rap1 regulates this event and CR3-dependent phagocytosis remains largely unknown. In the present work, we examined the role of the Rap1 effector RIAM, a talin-binding protein, in the regulation of complement-mediated phagocytosis. Using the human myeloid cell lines HL-60 and THP-1, we determined that knockdown of RIAM impaired αMß2 integrin affinity changes induced by stimuli fMLP and LPS. Phagocytosis of complement-opsonized RBC particles, but not of IgG-opsonized RBC particles, was impaired in RIAM knockdown cells. Rap1 activation via EPAC induced by 8-pCPT-2'-O-Me-cAMP resulted in an increase of complement-mediated phagocytosis that was abrogated by knockdown of RIAM in HL-60 and THP-1 cell lines and in macrophages derived from primary monocytes. Furthermore, recruitment of talin to ß2 integrin during complement-mediated phagocytosis was reduced in RIAM knockdown cells. These results indicate that RIAM is a critical component of the phagocytosis machinery downstream of Rap1 and mediates its function by recruiting talin to the phagocytic complement receptors.
authors: Departamento de Microbiología I, Inmunología, Facultad de Medicina, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors: Iria
authors: I
authors: Medraño-Fernandez
authors: Raquel
authors: R
authors: Reyes
authors: Isabel
authors: I
authors: Olazabal
authors: Elena
authors: E
authors: Rodriguez
authors: Francisco
authors: F
authors: Sanchez-Madrid
authors: Vassiliki A
authors: VA
authors: Boussiotis
authors: Pedro A
authors: PA
authors: Reche
authors: Carlos
authors: C
authors: Cabañas
authors: Esther M
authors: EM
authors: Lafuente
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism / Q000502:physiology*; D018821:CD18 Antigens / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D003165:Complement System Proteins / Q000502:physiology; D055785:Gene Knockdown Techniques; D018922:HL-60 Cells; D006801:Humans; D016177:Macrophage-1 Antigen / Q000502:physiology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D009504:Neutrophils / Q000166:cytology / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D016608:Talin / Q000378:metabolism / Q000502:physiology; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology
chemical_list: C493340:APBB1IP protein, human; D048868:Adaptor Proteins, Signal Transducing; D018821:CD18 Antigens; D016177:Macrophage-1 Antigen; D008565:Membrane Proteins; D016608:Talin; D003165:Complement System Proteins; D020827:rap1 GTP-Binding Proteins