Abstract
SIRPbeta (signal-regulatory protein beta) is a transmembrane protein that is expressed in hematopoietic cells but whose functions are unknown. We have now cloned mouse SIRPbeta cDNA and have shown that the gene is expressed in various tissues in addition to cells of the macrophage lineage. Engagement of SIRPbeta by specific monoclonal antibodies promoted Fcgamma receptor-dependent or -independent phagocytosis in mouse peritoneal macrophages. It also induced marked activation of MAPK and the upstream kinase MEK but weak activation of Akt. MEK inhibitors markedly blocked the promotion of phagocytosis by SIRPbeta, whereas an inhibitor of phosphoinositide 3-kinase partly blocked such response. In addition, inhibitors of myosin light chain kinase or of myosin ATPase blocked the promotion of phagocytosis by SIRPbeta. Furthermore, SIRPbeta induced the formation of filopodia and lamellipodia in macrophages as well as the translocation of activated MAPK to these structures. It also elicited tyrosine phosphorylation of DAP12, Syk, and SLP-76, and a Syk inhibitor blocked the promotion of phagocytosis and activation of MAPK by SIRPbeta. Our results suggest that engagement of SIRPbeta promotes phagocytosis in macrophages by inducing the tyrosine phosphorylation of DAP12, Syk, and SLP-76 and the subsequent activation of a MEK-MAPK-myosin light chain kinase cascade.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing*
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Adaptor Proteins, Vesicular Transport / metabolism
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Amino Acid Sequence
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Animals
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Antibodies, Monoclonal / metabolism
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Antigens, Differentiation / genetics
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Antigens, Differentiation / metabolism*
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Carrier Proteins / metabolism
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Cell Surface Extensions / metabolism
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Cells, Cultured
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Cytoskeleton / metabolism
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Enzyme Activation
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Enzyme Precursors / metabolism
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Humans
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Intracellular Signaling Peptides and Proteins
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Macrophages, Peritoneal / cytology
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Macrophages, Peritoneal / metabolism*
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Membrane Glycoproteins / genetics
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Membrane Glycoproteins / metabolism*
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Mice
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Mice, Inbred BALB C
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Mice, Inbred C57BL
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Mitogen-Activated Protein Kinases / metabolism
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Molecular Sequence Data
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Myosin-Light-Chain Kinase / metabolism
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Neural Cell Adhesion Molecule L1 / genetics
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Neural Cell Adhesion Molecule L1 / metabolism*
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Phagocytosis / physiology*
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Phosphoproteins / metabolism
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Phosphorylation
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Protein-Tyrosine Kinases / metabolism
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RNA, Messenger / metabolism
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Receptors, Immunologic / genetics
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Receptors, Immunologic / metabolism*
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Sequence Alignment
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Signal Transduction / physiology*
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Syk Kinase
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Tissue Distribution
Substances
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Adaptor Proteins, Signal Transducing
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Adaptor Proteins, Vesicular Transport
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Antibodies, Monoclonal
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Antigens, Differentiation
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B cell linker protein
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Carrier Proteins
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Enzyme Precursors
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Intracellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Neural Cell Adhesion Molecule L1
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Phosphoproteins
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RNA, Messenger
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Receptors, Immunologic
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SLP-76 signal Transducing adaptor proteins
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Tyrobp protein, mouse
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Protein-Tyrosine Kinases
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SYK protein, human
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Syk Kinase
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Syk protein, mouse
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Myosin-Light-Chain Kinase
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Mitogen-Activated Protein Kinases
Associated data
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GENBANK/AB112022
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GENBANK/AB112023
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GENBANK/AB112024
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GENBANK/AB112025