Kurzer Jason H, Saharinen Pipsa, Silvennoinen Olli, Carter-Su Christin
Department of Molecular and Integrative Physiology, The University of Michigan Medical School, Ann Arbor, MI 48109-0622, USA.
Mol Cell Biol. 2006 Sep;26(17):6381-94. doi: 10.1128/MCB.00570-06.
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.
酪氨酸激酶Janus激酶2（JAK2）可转导大多数已知细胞因子受体家族成员的信号，并且在某些癌症中持续激活。在此，我们研究衔接蛋白SH2 - Bβ和APS调节JAK2活性的机制。我们发现，与SH2 - Bβ一样，APS在多个位点与JAK2结合，并且与磷酸化酪氨酸813结合对于APS增加活性JAK2以及被JAK2磷酸化至关重要。APS与磷酸化酪氨酸813非依赖性位点的结合会抑制JAK2。APS和SH2 - Bβ均独立于其N端二聚化结构域增加JAK2活性。SH2 - Bβ诱导的JAK2二聚化增加仅需要SH2结构域，并且仅一个SH2 - Bβ与JAK2二聚体结合。JAK2突变和截短显示，JAK2中的氨基酸809至811是JAK2内更大调节区域的关键组成部分，很可能包括JAK同源性1（JH1）和JH2结构域内的氨基酸以及可能的FERM结构域。总之，我们的数据表明，SH2 - Bβ和APS激活JAK2并非因其自身二聚化、募集JAK2激活剂或与JAK2抑制剂直接竞争结合JAK2。相反，它们很可能诱导或稳定JAK2的活性构象。
