The carboxy-terminal region of the granulocyte colony-stimulating factor receptor transduces a phagocytic signal.
Granulocyte colony-stimulating factor (G-CSF) induces proliferation, maturation, and functional activities of myeloid progenitors and mature neutrophils through a specific receptor, the G-CSF-R. Different signals are mediated by distinct regions of the cytoplasmic domain of G-CSF-R, but the precise role of each region has not yet been fully clarified. We evaluated the involvement of Syk kinase, essential in mediating phagocytic signals by Fcgamma receptors, in G-CSF-induced phagocytosis, using murine myeloid 32D cells transfected with wild-type (WT) human G-CSF-R (hG-CSF-R) or with a G-CSF-R mutant truncated at cytoplasmic amino acid 715. The G-CSF-R mutant lacks the immunoreceptor tyrosine-based activation motif (ITAM), putative binding site for Syk. Following treatment of WT hG-CSF-R transfectants with IgG-coated particles, there was a significant increase in phagocytosis in G-CSF-stimulated cells, in which Syk tyrosine phosphorylation occurred, paralleled by enhancement of its tyrosine kinase activity. In the mutant transfectants, no significant increase in phagocytosis or Syk tyrosine phosphorylation occurred after stimulation with G-CSF. We also demonstrated that tyrosine phosphorylation of the Src kinases Hck and Lyn occurs following G-CSF stimulation of cells expressing WT G-CSF-R, but that Hck is not phosphorylated in mutant G-CSF-R transfectants. The increase in phagocytosis following G-CSF stimulation cannot be attributed to a rapid de novo increase in expression of Fcgamma receptors. G-CSF induced expression of Fcgamma receptors only after prolonged stimulation. Our data provide evidence that the carboxy-terminal region of G-CSF-R plays a role in the phagocytosis of IgG-coated particles and that Syk and Hck kinase tyrosine phosphorylation is involved.
Santini
Valeria
V
Department of Hematology, University of Florence, Florence, Italy. santini@unifi.it
Scappini
Barbara
B
Indik
Zena K
ZK
Gozzini
Antonella
A
Ferrini
Pierluigi Rossi
PR
Schreiber
Alan D
AD
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D010587:Phagocytosis; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016188:Receptors, Granulocyte Colony-Stimulating Factor / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017452:Receptors, IgG / Q000096:biosynthesis; D015398:Signal Transduction; D000072377:Syk Kinase; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D016188:Receptors, Granulocyte Colony-Stimulating Factor; D017452:Receptors, IgG; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D019061:src-Family Kinases