Syk activation initiates downstream signaling events during human polymorphonuclear leukocyte phagocytosis.
We investigated the requirement for Syk activation to initiate downstream signaling events during polymorphonuclear leukocyte (PMN) phagocytosis of Ab-coated erythrocytes (EIgG). When PMN were challenged with EIgG, Syk phosphorylation increased in a time-dependent manner, paralleling the response of PMN phagocytosis. Pretreatment of PMN with piceatannol, a Syk-selective inhibitor, blocked EIgG phagocytosis and Syk phosphorylation. We found that piceatannol inhibited protein kinase Cdelta (PKCdelta) and Raf-1 translocation from cytosol to plasma membrane by >90%. Extracellular signal-regulated protein kinase-1 and -2 (ERK1 and ERK2) phosphorylation was similarly blocked. We also investigated phosphatidylinositide 3-kinase (PI 3-kinase) activity and Syk phosphorylation using piceatannol, wortmannin, and LY294002, inhibitors of PI 3-kinase. The phosphorylation of Syk preceded the activation of PI 3-kinase. Both wortmannin and piceatannol inhibited PI 3-kinase, but only piceatannol inhibited Syk. In contrast to piceatannol, wortmannin did not inhibit PKCdelta and Raf-1 translocation. To elucidate signaling downstream of Syk activation, we assessed whether the cell-permeable diacylglycerol analogue didecanoylglycerol could normalize PMN phagocytosis, PKCdelta and Raf-1 translocation, and ERK1 and ERK2 phosphorylation inhibited by piceatannol. The addition of didecanoylglycerol to the Syk-inhibited phagocytosing PMN normalized all three without a concomitant effect on PI 3-kinase activity and Syk phosphorylation. We conclude that Syk activation following Fcgamma receptor engagement initiates downstream signaling events leading to mitogen-activated protein kinase activation independent of PI 3-kinase activation.
Raeder
E M
EM
Department of Pediatrics, Division of Hematology/Oncology, University of Michigan, Ann Arbor, MI 48109, USA.
Mansfield
P J
PJ
Hinkovska-Galcheva
V
V
Shayman
J A
JA
Boxer
L A
LA
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000276:immunology; D002462:Cell Membrane / Q000201:enzymology / Q000276:immunology; D002464:Cell Migration Inhibition; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004912:Erythrocytes / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D009895:Opsonin Proteins / Q000097:blood; D010587:Phagocytosis / Q000187:drug effects / Q000276:immunology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051745:Protein Kinase C-delta; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017452:Receptors, IgG / Q000502:physiology; D012756:Sheep; D015398:Signal Transduction / Q000276:immunology*; D013267:Stilbenes / Q000494:pharmacology; D000072377:Syk Kinase; D000077191:Wortmannin
D000730:Androstadienes; D004075:Diglycerides; D004791:Enzyme Inhibitors; D004792:Enzyme Precursors; D007074:Immunoglobulin G; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009895:Opsonin Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D019000:Phosphotyrosine; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D011505:Protein-Tyrosine Kinases; D017452:Receptors, IgG; D013267:Stilbenes; D000072377:Syk Kinase; D000077191:Wortmannin; C041525:3,3',4,5'-tetrahydroxystilbene; C000606896:SYK protein, human; C497258:PRKCD protein, human