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Identification and Characterization of Novel Phosphorylation Sites on Jak2
Author(s) -
Robertson Scott Andrew,
Koleva Rositsa Ivanova,
Marto Jarrod A.,
Argetsinger Lawrence Stanton,
CarterSu Christin,
Feener Edward P.,
Myers Martin G.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.2_supplement.86
Subject(s) - phosphorylation , janus kinase 2 , tyrosine phosphorylation , microbiology and biotechnology , signal transduction , receptor , cytokine receptor , biology , phosphotyrosine binding domain , glycoprotein 130 , sh2 domain , janus kinase 1 , kinase , janus kinase , chemistry , biochemistry , stat3
Members of the Janus (Jak) family of tyrosine kinases, including Jak2, mediate signaling via many cytokine receptors. Cytokine binding to cognate receptors (such as the leptin receptor, LepRb) activates Jak2 to promote the multisite phosphorylation of Jak2. In order to understand the function of Jak2 phosphorylation, we used mass spectrometry to identify phosphorylation sites on exogenously expressed Jak2 purified from 293 cells during LepRb signaling. Of the seventeen Jak2 phosphorylation sites we identified, we closely examined two sites: Tyr317 in the COOH‐terminus of the FERM domain and Tyr637 in the SH2‐like domain. Multiple cytokines stimulated the phosphorylation of each of these sites on endogenous as well as overexpressed Jak2. While the phosphorylation of Tyr637 peaked between 15–30 minutes of stimulation, the maximal phosphorylation of Tyr317 occurred hours later. Furthermore, while mutation of Tyr317 to Phe or Glu increased Jak2 activity, similar substitution of Tyr637 blunted Jak2 activity. The altered activity of the mutants compared to normal Jak2 was independent of cytokine receptor expression, suggesting that these sites regulate Jak2 activity per se ‐ as opposed to indirectly via receptor association. Thus, the phosphorylation of Tyr317 mediates feedback inhibition of Jak2 during prolonged signaling, whereas Tyr 637 rapidly stimulates kinase activity. (AHA 0715806Z)