Tyrosine 813 is a site of JAK2 autophosphorylation critical for activation of JAK2 by SH2-B beta.

Graduate Program in Cellular and Molecular Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0662, USA.
Molecular and Cellular Biology (Impact Factor: 5.04). 06/2004; 24(10):4557-70.
Source: PubMed

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.

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Available from: Christin Carter-Su, Jan 03, 2015
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    • "Jude Children's Research Hospital, Memphis, TN) (Silvennoinen et al., 1993). FLAG-JAK2, and the various rat SH2B1b constructs, FLAG-SH2B1b, GFP-SH2B1b WT, GFP-SH2B1b D198– 268 (DNES), GFP-SH2B1b point mutations (9YF, Y439/494F, S161A, S165A, 2SA(S161/165A), 13SA, S161E, S165E, S161/165E, mNLS), myc-SH2B1b WT, and myc-SH2B1b point mutations (Y439/494F, Y439F, Y494F) have been described previously (Chen and Carter-Su, 2004; Kurzer et al., 2004; Maures et al., 2009; Maures et al., 2011; O'Brien et al., 2003). When expressed in 293T and RAW cells, all mutant SH2B1b proteins migrated in SDS-PAGE gels at the predicted size (data not shown). "
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    • "Jak2 tyrosine phosphorylation during LRb stimulation mediates some signals independently of tyrosine phosphorylation sites on LRb, at least in cultured cells (Banks et al. 2000). The individual phosphorylation sites on Jak2 are beginning to be enumerated (Feng et al. 1997, Carpino et al. 2002, Argetsinger et al. 2004, Feener et al. 2004, Kurzer et al. 2004, Matsuda et al. 2004, Funakoshi-Tago et al. 2006, Ishida- Takahashi et al. 2006), but many more remain to be identified. Unfortunately, the binding partners and signals mediated by many Jak2 phosphorylation sites remain unknown, limiting our understanding of the mechanisms by which Jak2-dependent signals are mediated . "
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    ABSTRACT: The adipose tissue-derived hormone, leptin, acts via its receptor (LRb) in the brain to regulate energy balance and neuroendocrine function. In order to understand leptin action we have explored the physiological function of LRb signalling pathways, defining important roles for signal transducer and activator of transcription-3 (STAT3) in positive signalling and for LRbTyr(985)-mediated feedback inhibition in leptin signal attenuation. As the cells on which leptin acts are not homogeneous, but rather represent a broadly distributed network of neurones with divergent projections and functions, it is also crucial to consider how each of these populations responds to LRb signals to contribute to leptin action. While well-known LRb-expressing neurones within the arcuate nucleus of the hypothalamus mediate crucial effects on satiety and energy expenditure, other populations of LRb-expressing neurones in the ventral tegmental area and elsewhere likely control the mesolimbic dopamine system. Additional populations of LRb-expressing neurones likely contribute to other aspects of neuroendocrine regulation. It will be important to define the molecular mechanisms by which leptin acts to regulate neurophysiology in each of these LRb-expressing neural populations in order to understand the totality of leptin action.
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    • "Based on mutagenesis studies, phosphorylation of Y 221 slightly increased its kinase activity; on the other hand, phosphorylation of Y 570 decreased kinase activity. Although phosphorylation of Y 813 does not affect the intrinsic activity of Jak2 in contrast to these tyrosines, this site is required for Jak2 to bind the b splicing variant of SH2-B and for the ability of SH2-Bb to enhance Jak2 activation (Kurzer et al, 2004). The significance to Jak2 signaling in vivo, however, is unclear since deletion of the gene for SH2-B in mice does not affect Jak2 signaling (Duan et al, 2004). "
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