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Fos-Zippered GH Receptor Cytosolic Tails Act as Jak2 Substrates and Signal Transducers.

Authors
  • Nespital, Tobias1
  • van der Velden, Lieke M1
  • Mensinga, Anneloes1
  • van der Vaart, Elisabeth D1
  • Strous, Ger J1
  • 1 Department of Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, 3584CX Utrecht, The Netherlands. , (Netherlands)
Type
Published Article
Journal
Molecular Endocrinology
Publisher
The Endocrine Society
Publication Date
Mar 01, 2016
Volume
30
Issue
3
Pages
290–301
Identifiers
DOI: 10.1210/me.2015-1315
PMID: 26859362
Source
Medline
License
Unknown

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.

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