Granulocyte-Macrophage Colony-stimulating Factor Stimulates JAK2 Signaling Pathway and Rapidly Activates p93 , STAT1 p91, and STAT3 p92 in Polymorphonuclear Leukocytes

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF), supports proliferation, differentiation, and functional activation of hemopoietic cells by its interaction with a heterodimeric receptor. Although GM-CSF receptor is devoid of tyrosine kinase enzymatic activity, GM-CSF-induced peripheral blood polymorphonuclear leukocytes (PMN) functional activation is mediated by the phosphorylation of a large number of intracellular signaling molecules. We have previously shown that JAK2 becomes tyrosine-phosphorylated in response to GM-CSF in PMN. In the present study we demonstrate that also the signal transducers and activators of transcription (STAT) family members STAT1 p91 and STAT3 p92 and the product of the c-fps/fes protooncogene become tyrosine-phosphorylated upon GM-CSF stimulation and physically associated with both GM-CSF receptor ␤ common subunit and JAK2. Moreover GM-CSF was able to induce JAK2 and p93 fes catalytic activity. We also demonstrate that the association of the GM-CSF receptor ␤ common subunit with JAK2 is ligand-dependent.Finally we demonstrate that GM-CSF induces a DNAbinding complex that contains both p91 and p92. These results identify a new signal transduction pathway activated by GM-CSF and provide a mechanism for rapid activation of gene expression in GM-CSF-stimulated PMN.

Regulation of the Class II MHC Pathway in Primary Human Monocytes by Granulocyte-Macrophage Colony-Stimulating Factor

“…Activated STAT5 may bind IFN-␥-activated sequence (GAS) elements found in CIITA PIII. In addition, there are reports in some cell types that GM-CSF can activate STAT1, which also could bind GAS elements (43,44). Our preliminary results suggest that in addition to STAT5, STAT1 may be phosphorylated following GM-CSF treatment (T. M. C. Hornell, unpublished data).…”

Granulocyte-Macrophage Colony-stimulating Factor-activated Signaling Pathways in Human Neutrophils

“…The GM-CSF receptor is made up of two subunits, ␣ and ␤ (19), neither of which has an intrinsic kinase domain or is linked to a G-protein (19). Instead, the receptor acts by associating with and activating a number of cytosolic tyrosine kinases including Lyn (26,27), Fes (30,65), and Jak2 (29,31), and these enzymes will, in turn, mediate the activation of the signaling pathways utilized by GM-CSF to induce its various biological responses. One of the effector systems known to be activated by GM-CSF is PI3-kinase.…”

“…The next experiments were designed to examine the possibility of an in situ association between the p85 subunit of PI3-kinase and two of the tyrosine kinases shown previously to be activated by GM-CSF, namely Lyn (26,27) and Jak2 (29,31) in situ upon activation of human neutrophils with GM-CSF. Cells were suspended at 40 ϫ 10 6 /ml and treated with 4 nM GM-CSF or diluent for 10 min at 37°C.…”

“…GM-CSF, as shown previously, induced the tyrosine phosphorylation of a number of cellular proteins. The identities of those proteins are not fully known; however, the band at 120 kDa includes Jak2 (31,44) and Cbl (69), those at 90 kDa the STATs (29,44), those at 80 kDa contain the p85 subunit of PI3-kinase (31), and the 40 kDa bands include members of the mitogen-activated protein kinases (70 -72). The proteins at 150 -140, 70, and 55 kDa remain unknown.…”

“…Signaling by the GM-CSF receptor depends on the activation of the tyrosine phosphorylation pathways mediated by the stimulation of a number of cytosolic protein tyrosine kinases (25,26). In neutrophils, we and others have shown that three tyrosine kinases, Lyn (26 -28), Fes (29,30), and Jak2 (29,31), are activated upon stimulation with GM-CSF. Each of these kinases is involved in the signaling pathways associated with various cytokines (25,(32)(33)(34).…”