title: Regions of the JAK2 tyrosine kinase required for coupling to the growth hormone receptor.
abstract: Growth hormone (GH) treatment of cells promotes activation of JAK2, a GH receptor (GHR)-associated tyrosine kinase. We now explore JAK2 regions required for GHR-induced signaling. Wild-type (WT) JAK2 and JAK2 molecules with deletions of the amino terminus (JAK2ATD), carboxyl terminus (JAK2CTD), or kinase-like domain (JAK2PKD) were each transiently coexpressed in COS-7 cells with the rabbit GHR. The following responses were assayed: GH-induced transactivation of a luciferase reporter governed by a c-fos enhancer element; GH-induced shift in the molecular mass of a cotransfected epitope-tagged extracellular signal-regulated kinase molecule; and GH-induced antiphosphotyrosine immunoprecipitability of the transfected JAK2 form. In each assay, WTJAK2 and JAK2PKD allowed GH-induced signaling, whereas JAK2ATD and JAK2CTD did not. Anti-GHR serum coimmunoprecipitated WTJAK2, JAK2PKD, and JAK2CTD, but not JAK2ATD. Finally, a chimera in which the JAK2 kinase domain replaced the GHR cytoplasmic domain signaled GH-induced transactivation. We conclude: 1) kinase-like domain deletion eliminates neither physical nor functional interaction between JAK2 and the GHR; 2) kinase domain deletion eliminates functional but not physical coupling of JAK2 to the GHR; 3) interaction with the GHR appears dependent on the NH2-terminal one-fifth of JAK2; and 4) a GH-responsive signaling unit can include as little as the GHR external and transmembrane domains and the JAK2 kinase domain.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Frank
authors.forename: W
authors.initials: W
authors.lastname: Yi
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: J F
authors.initials: JF
authors.lastname: Goldsmith
authors.forename: G
authors.initials: G
authors.lastname: Gilliland
authors.forename: J
authors.initials: J
authors.lastname: Jiang
authors.forename: I
authors.initials: I
authors.lastname: Sakai
authors.forename: A S
authors.initials: AS
authors.lastname: Kraft
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D000939:Epitopes / Q000378:metabolism; D016762:Genes, fos; D053614:Janus Kinase 2; D008156:Luciferases / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011986:Receptors, Somatotropin / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D000939:Epitopes; D011518:Proto-Oncogene Proteins; D011986:Receptors, Somatotropin; D011993:Recombinant Fusion Proteins; D008156:Luciferases; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2