title: JAK2 associates with the beta c chain of the receptor for granulocyte-macrophage colony-stimulating factor, and its activation requires the membrane-proximal region.
abstract: The high-affinity receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) consists of a unique alpha chain and a beta c subunit that is shared with the receptors for interleukin-3 (IL-3) and IL-5. Two regions of the beta c chain have been defined; these include a membrane-proximal region of the cytoplasmic domain that is required for mitogenesis and a membrane-distal region that is required for activation of Ras, Raf-1, mitogen-activated protein kinase, and S6 kinase. Recent studies have implicated the cytoplasmic protein tyrosine kinase JAK2 in signalling through a number of the cytokine receptors, including the IL-3 and erythropoietin receptors. In the studies described here, we demonstrate that GM-CSF stimulation of cells induces the tyrosine phosphorylation of JAK2 and activates its in vitro kinase activity. Mutational analysis of the beta c chain demonstrates that only the membrane-proximal 62 amino acids of the cytosolic domain are required for JAK2 activation. Thus, JAK2 activation is correlated with induction of mitogenesis but does not, alone, activate the Ras pathway. Carboxyl truncations of the alpha chain, which inactivate the receptor for mitogenesis, are unable to mediate GM-CSF-induced JAK2 activation. Using baculovirus-expressed proteins, we further demonstrate that JAK2 physically associates with the beta c chain but not with the alpha chain. Together, the results further support the hypothesis that the JAK family of kinase are critical to coupling cytokine binding to tyrosine phosphorylation and ultimately mitogenesis.
authors.affiliation: Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
authors.forename: F W
authors.initials: FW
authors.lastname: Quelle
authors.forename: N
authors.initials: N
authors.lastname: Sato
authors.forename: B A
authors.initials: BA
authors.lastname: Witthuhn
authors.forename: R C
authors.initials: RC
authors.lastname: Inhorn
authors.forename: M
authors.initials: M
authors.lastname: Eder
authors.forename: A
authors.initials: A
authors.lastname: Miyajima
authors.forename: J D
authors.initials: JD
authors.lastname: Griffin
authors.forename: J N
authors.initials: JN
authors.lastname: Ihle
mesh_terms: D000818:Animals; D002460:Cell Line; D004252:DNA Mutational Analysis; D004789:Enzyme Activation; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D053614:Janus Kinase 2; D046911:Macromolecular Substances; D009036:Moths; D016296:Mutagenesis; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D046911:Macromolecular Substances; D011518:Proto-Oncogene Proteins; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2