title: Fos-Zippered GH Receptor Cytosolic Tails Act as Jak2 Substrates and Signal Transducers.
abstract: Members of the Janus kinase (Jak) family initiate the majority of downstream signaling events of the cytokine receptor family. The prevailing principle is that the receptors act in dimers: 2 Jak2 molecules bind to the cytosolic tails of a cytokine receptor family member and initiate Jak-signal transducer and activator of transcription signaling upon a conformational change in the receptor complex, induced by the cognate cytokine. Due to the complexity of signaling complexes, there is a strong need for in vitro model systems. To investigate the molecular details of the Jak2 interaction with the GH receptor (GHR), we used cytosolic tails provided with leucine zippers derived from c-Fos to mimic the dimerized state of GHR. Expressed together with Jak2, fos-zippered tails, but not unzippered tails, were stabilized. In addition, the Jak-signal transducer and activator of transcription signaling pathway was activated by the fos-zippered tails. The stabilization depended also on α-helix rotation of the zippers. Fos-zippered GHR tails and Jak2, both purified from baculovirus-infected insect cells, interacted via box1 with a binding affinity of approximately 40nM. As expected, the Jak kinase inhibitor Ruxolitinib inhibited the stabilization but did not affect the c-Fos-zippered GHR tail-Jak2 interaction. Analysis by blue-native gel electrophoresis revealed high molecular-weight complexes containing both Jak2 and nonphosphorylated GHR tails, whereas Jak2-dissociated tails were highly phosphorylated and monomeric, implying that Jak2 detaches from its substrate upon phosphorylation.
authors: Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands.
authors: Tobias
authors: T
authors: Nespital
authors: Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands.
authors: Lieke M
authors: LM
authors: van der Velden
authors: Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands.
authors: Anneloes
authors: A
authors: Mensinga
authors: Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands.
authors: Elisabeth D
authors: ED
authors: van der Vaart
authors: Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands.
authors: Ger J
authors: GJ
authors: Strous
mesh_terms: D000409:Alanine / Q000235:genetics; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D003600:Cytosol / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D053614:Janus Kinase 2 / Q000737:chemistry / Q000378:metabolism*; D016350:Leucine Zippers; D051379:Mice; D016254:Mutagenesis, Insertional / Q000235:genetics; D063347:Native Polyacrylamide Gel Electrophoresis; D010766:Phosphorylation; D011485:Protein Binding; D055550:Protein Stability; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D011817:Rabbits; D011986:Receptors, Somatotropin / Q000737:chemistry* / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D011986:Receptors, Somatotropin; D050799:STAT5 Transcription Factor; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D000409:Alanine