title: Regulation of Jak2 through the ubiquitin-proteasome pathway involves phosphorylation of Jak2 on Y1007 and interaction with SOCS-1.
abstract: The family of cytoplasmic Janus (Jak) tyrosine kinases plays an essential role in cytokine signal transduction, regulating cell survival and gene expression. Ligand-induced receptor dimerization results in phosphorylation of Jak2 on activation loop tyrosine Y1007 and stimulation of its catalytic activity, which, in turn, results in activation of several downstream signaling cascades. Recently, the catalytic activity of Jak2 has been found to be subject to negative regulation through various mechanisms including association with SOCS proteins. Here we show that the ubiquitin-dependent proteolysis pathway is involved in the regulation of the turnover of activated Jak2. In unstimulated cells Jak2 was monoubiquitinated, and interleukin-3 or gamma interferon stimulation induced polyubiquitination of Jak2. The polyubiquitinated Jak2 was rapidly degraded through proteasomes. By using different Jak2 mutants we show that tyrosine-phosphorylated Jak2 is preferentially polyubiquitinated and degraded. Furthermore, phosphorylation of Y1007 on Jak2 was required for proteasomal degradation and for SOCS-1-mediated downregulation of Jak2. The proteasome inhibitor treatment stabilized the Jak2-SOCS-1 protein complex and inhibited the proteolysis of Jak2. In summary, these results indicate that the ubiquitin-proteasome pathway negatively regulates tyrosine-phosphorylated Jak2 in cytokine receptor signaling, which provides an additional mechanism to control activation of Jak2 and maintain cellular homeostasis.
authors.affiliation: Institute of Medical Technology, University of Tampere, FIN-33014 Tampere, Finland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Ungureanu
authors.forename: Pipsa
authors.initials: P
authors.lastname: Saharinen
authors.forename: Ilkka
authors.initials: I
authors.lastname: Junttila
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Hilton
authors.forename: Olli
authors.initials: O
authors.lastname: Silvennoinen
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002458:Cell Fractionation; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D007377:Interleukin-3 / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014443:Tyrosine / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D007377:Interleukin-3; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D025801:Ubiquitin; D014443:Tyrosine; D007371:Interferon-gamma; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde