The Src homology 2 domain-containing inositol 5-phosphatase negatively regulates Fcgamma receptor-mediated phagocytosis through immunoreceptor tyrosine-based activation motif-bearing phagocytic receptors.
Molecular mechanisms by which the Src homology 2 domain-containing inositol 5-phosphatase (SHIP) negatively regulates phagocytosis in macrophages are unclear. We addressed the issue using bone marrow-derived macrophages from FcgammaR- or SHIP-deficient mice. Phagocytic activities of macrophages from FcgammaRII(b)(-/-) and SHIP(-/-) mice were enhanced to a similar extent, relative to those from wild type. However, calcium influx was only marginally affected in FcgammaRII(b)(-/-), but greatly enhanced in SHIP(-/-) macrophages. Furthermore, SHIP was phosphorylated on tyrosine residues upon FcgammaR aggregation even in macrophages from FcgammaRII(b)(-/-) mice or upon clustering of a chimeric receptor containing CD8 and the immunoreceptor tyrosine-based activation motif (ITAM)-bearing gamma-chain or human-restricted FcgammaRIIa. These findings indicate that, unlike B cells, SHIP is efficiently phosphorylated in the absence of an immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing receptor. We further demonstrate that SHIP directly bound to phosphorylated peptides derived from FcgammaRIIa with a high affinity, comparable to that of FcgammaRII(b). Lastly, FcgammaRIIa-mediated phagocytosis was significantly enhanced in THP-1 cells overexpressing dominant-negative form of SHIP in the absence of FcgammaRII(b). These results indicate that SHIP negatively regulates FcgammaR-mediated phagocytosis through all ITAM-containing IgG receptors using a molecular mechanism distinct from that in B cells.
Nakamura
Koji
K
Program in Immunobiology and Cancer, The Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, OK 73104, USA.
Malykhin
Alexander
A
Coggeshall
K Mark
KM
D020816:Amino Acid Motifs; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000166:cytology; D016827:CD8 Antigens / Q000235:genetics / Q000502:physiology; D020013:Calcium Signaling; D058851:GPI-Linked Proteins; D006801:Humans; D008264:Macrophages / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010587:Phagocytosis / Q000502:physiology*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000502:physiology; D011499:Protein Processing, Post-Translational; D017452:Receptors, IgG / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D015703:Antigens, CD; D016827:CD8 Antigens; C428200:FCGR3B protein, human; C080568:Fc gamma receptor IIA; D058851:GPI-Linked Proteins; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D019000:Phosphotyrosine; D010744:Phosphoric Monoester Hydrolases; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases