title: Identification of signaling motifs within human Fc gamma RIIa and Fc gamma RIIb isoforms.
abstract: To assess the functional capacity of the heterogeneous Fc gamma RII (CD32) family and to identify critical regions for functioning, we generated a panel of B-cell transfectants. The Fc gamma R-negative B-cell line IIA1.6 was transfected with wild-type or mutant human Fc gamma RIIa and IIb molecules. Solely Fc gamma RIIa-expressing IIA1.6 cells were capable of phagocytosing opsonized Staphylococcus aureus bacteria, and cross-linking of Fc gamma RIIa triggered a rapid induction of tyrosine phosphorylation after 20 seconds. Analysis of Fc gamma RIIa mutants identified the immunoreceptor tyrosine-based activation motif (ITAM; previously described as ARH-1 motif) within the IIa cytoplasmic tail to be critical for B-cell activation. In contrast, Fc gamma RIIb isoforms triggered tyrosine phosphorylation on cross-linking with much slower kinetics (> 3 minutes) than Fc gamma RIIa. Furthermore, solely Fc gamma RIIb molecules proved capable of downregulating [Ca2+]i and interleukin-2 production on co-cross-linking with sIgG in IIA1.6. The Fc gamma RIIb-mediated functions were absent in Fc gamma RIIb mutants in which the tyrosine or leucine within the YSLL motif in a conserved 13-aa region (now known as immunoreceptor tyrosine-based inhibitor motif [ITIM]) were changed into phenylalanines. In conclusion, these data show the presence of functionally critical motifs within Fc gamma RII cytoplasmic tails. Fc gamma RIIa contains an ITAM involved in B-cell activatory functions, whereas the downregulatory activity of Fc gamma RIIb isoforms is linked to an ITIM.
authors.affiliation: Department of Immunology, University Hospital Utrecht, The Netherlands.
authors.forename: I E
authors.initials: IE
authors.lastname: Van den Herik-Oudijk
authors.forename: P J
authors.initials: PJ
authors.lastname: Capel
authors.forename: T
authors.initials: T
authors.lastname: van der Bruggen
authors.forename: J G
authors.initials: JG
authors.lastname: Van de Winkel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D001402:B-Lymphocytes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D007152:Immunologic Capping; D008213:Lymphocyte Activation / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D017452:Receptors, IgG / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D013211:Staphylococcus aureus; D014162:Transfection
chemical_list: D015703:Antigens, CD; C080568:Fc gamma receptor IIA; C080571:Fc gamma receptor IIB; D007074:Immunoglobulin G; D009895:Opsonin Proteins; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D011505:Protein-Tyrosine Kinases; D002118:Calcium