title: Tyrosine 813 is a site of JAK2 autophosphorylation critical for activation of JAK2 by SH2-B beta.
abstract: The tyrosine kinase Janus kinase 2 (JAK2) binds to the majority of the known members of the cytokine family of receptors. Ligand-receptor binding leads to activation of the associated JAK2 molecules, resulting in rapid autophosphorylation of multiple tyrosines within JAK2. Phosphotyrosines can then serve as docking sites for downstream JAK2 signaling molecules. Despite the importance of these phosphotyrosines in JAK2 function, only a few sites and binding partners have been identified. Using two-dimensional phosphopeptide mapping and a phosphospecific antibody, we identified tyrosine 813 as a site of JAK2 autophosphorylation of overexpressed JAK2 and endogenous JAK2 activated by growth hormone. Tyrosine 813 is contained within a YXXL sequence motif associated with several other identified JAK2 phosphorylation sites. We show that phosphorylation of tyrosine 813 is required for the SH2 domain-containing adapter protein SH2-B beta to bind JAK2 and to enhance the activity of JAK2 and STAT5B. The homologous tyrosine in JAK3, tyrosine 785, is autophosphorylated in response to interleukin-2 stimulation and is required for SH2-B beta to bind JAK3. Taken together these data strongly suggest that tyrosine 813 is a site of autophosphorylation in JAK2 and is the SH2-B beta-binding site within JAK2 that is required for SH2-B beta to enhance activation of JAK2.
authors.affiliation: Graduate Program in Cellular and Molecular Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0662, USA.
authors.forename: Jason H
authors.initials: JH
authors.lastname: Kurzer
authors.forename: Lawrence S
authors.initials: LS
authors.lastname: Argetsinger
authors.forename: Yong-Jie
authors.initials: YJ
authors.lastname: Zhou
authors.forename: Jean-Louis K
authors.initials: JL
authors.lastname: Kouadio
authors.forename: John J
authors.initials: JJ
authors.lastname: O'Shea
authors.forename: Christin
authors.initials: C
authors.lastname: Carter-Su
mesh_terms: D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004247:DNA / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D053614:Janus Kinase 2; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; C518910:SH2B1 protein, human; C115327:Sh2bpsm1 protein, mouse; D014443:Tyrosine; D013006:Growth Hormone; D004247:DNA; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2