title: Binding of SH2-B family members within a potential negative regulatory region maintains JAK2 in an active state.
abstract: The tyrosine kinase Janus kinase 2 (JAK2) transduces signaling for the majority of known cytokine receptor family members and is constitutively activated in some cancers. Here we examine the mechanisms by which the adapter proteins SH2-Bbeta and APS regulate the activity of JAK2. We show that like SH2-Bbeta, APS binds JAK2 at multiple sites and that binding to phosphotyrosine 813 is essential for APS to increase active JAK2 and to be phosphorylated by JAK2. Binding of APS to a phosphotyrosine 813-independent site inhibits JAK2. Both APS and SH2-Bbeta increase JAK2 activity independent of their N-terminal dimerization domains. SH2-Bbeta-induced increases in JAK2 dimerization require only the SH2 domain and only one SH2-Bbeta to be bound to a JAK2 dimer. JAK2 mutations and truncations revealed that amino acids 809 to 811 in JAK2 are a critical component of a larger regulatory region within JAK2, most likely including amino acids within the JAK homology 1 (JH1) and JH2 domains and possibly the FERM domain. Together, our data suggest that SH2-Bbeta and APS do not activate JAK2 as a consequence of their own dimerization, recruitment of an activator of JAK2, or direct competition with a JAK2 inhibitor for binding to JAK2. Rather, they most likely induce or stabilize an active conformation of JAK2.
authors.affiliation: Department of Molecular and Integrative Physiology, The University of Michigan Medical School, Ann Arbor, MI 48109-0622, USA.
authors.forename: Jason H
authors.initials: JH
authors.lastname: Kurzer
authors.forename: Pipsa
authors.initials: P
authors.lastname: Saharinen
authors.forename: Olli
authors.initials: O
authors.lastname: Silvennoinen
authors.forename: Christin
authors.initials: C
authors.lastname: Carter-Su
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D018076:DNA, Complementary / Q000235:genetics; D019281:Dimerization; D004789:Enzyme Activation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; C492010:SH2B1 protein, rat; C488162:Sh2b2 protein, rat; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; C507927:Jak2 protein, rat; D053614:Janus Kinase 2