Functional consequences of a MAPK docking site on human FcgammaRIIb.
Type IIb Fcgamma receptors (FcgammaRIIb) have a major role in regulating B cell activation. Upon its co-aggregation with the B cell receptors (BCR) via immune complexes FcgammaRIIb become phosphorylated on tyrosine within its immunoreceptor tyrosine based inhibitory motif (ITIM) and in turn recruit protein- and inositol phosphatases, inhibiting thereby signal transduction. The intracellular domain of the human FcgammaRIIb has a membrane proximal motif that is very similar to those of MAPK docking site in MAPK-interacting molecules. Additionally, in contrast to the mouse, a serine residue is located next to this motif that is a potential phosphorylation site for Ser/Thr kinases. Our aim was to study the role of the putative MAPK docking motif on FcgammaRIIb mediated function. We report here that MAPKs bind to FcgammaRIIb affinity purified from the detergent extracts of anti-IgM activated and BCR-FcgammaRIIb co-clustered B cells. We detected extracellular signal regulated kinase (ERK) activity in FcgammaRIIb immunoprecipitates and identified the bound proteins as 85, 44 and 42kDa ERKs by Western blots. Active ERKs bound to the synthetic peptide representing the putative docking site of FcgammaRIIb on a Ser/Thr phosphatase dependent manner. The FcgammaRIIb-associated ERKs may phosphorylate the membrane proximal serine of the receptor. We examined the consequences of serine phosphorylation by comparing the proteins that interact with synthetic peptides comprising the combined sequences of the MAPK docking site and the ITIM either in phosphorylated or in non-phosphorylated forms. The results indicate that phosphorylation on serine modifies the binding of Lyn to FcgammaRIIb, thus might negatively regulate phosphorylation of ITIM.
Medgyesi
Dávid
D
Research Group of the Hungarian Academy of Science at the Department of Immunology, Eötvös Loránd University, Budapest, Hungary.
Sárközi
Rita
R
Koncz
Gábor
G
Arató
Krisztina
K
Váradi
Györgyi
G
Tóth
Gábor K
GK
Sármay
Gabriella
G
D020816:Amino Acid Motifs; D015703:Antigens, CD / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000276:immunology* / Q000378:metabolism; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D010766:Phosphorylation; D017452:Receptors, IgG / Q000276:immunology* / Q000378:metabolism; D012694:Serine / Q000378:metabolism
D015703:Antigens, CD; C080571:Fc gamma receptor IIB; D010446:Peptide Fragments; D017452:Receptors, IgG; D012694:Serine; D020928:Mitogen-Activated Protein Kinases