Ishida-Takahashi Ryoko, Rosario Felicia, Gong Yusong, Kopp Keely, Stancheva Zlatina, Chen Xiaohong, Feener Edward P, Myers Martin G
Research Division, Joslin Diabetes Center, 1 Joslin Place, Boston, MA 02215, USA.
Mol Cell Biol. 2006 Jun;26(11):4063-73. doi: 10.1128/MCB.01589-05.
The leptin receptor, LRb, and other cytokine receptors are devoid of intrinsic enzymatic activity and rely upon the activity of constitutively associated Jak family tyrosine kinases to mediate intracellular signaling. In order to clarify mechanisms by which Jak2, the cognate LRb-associated Jak kinase, is regulated and mediates downstream signaling, we employed tandem mass spectroscopic analysis to identify phosphorylation sites on Jak2. We identified Ser523 as the first-described site of Jak2 serine phosphorylation and demonstrated that this site is phosphorylated on Jak2 from intact cells and mouse spleen. Ser523 was highly phosphorylated in HEK293 cells independently of LRb-Jak2 activation, suggesting a potential role for the phosphorylation of Ser523 in the regulation of LRb by other pathways. Indeed, mutation of Ser523 sensitized and prolonged signaling by Jak2 following activation by the intracellular domain of LRb. The effect of Ser523 on Jak2 function was independent of Tyr570-mediated inhibition. Thus, the phosphorylation of Jak2 on Ser523 inhibits Jak2 activity and represents a novel mechanism for the regulation of Jak2-dependent cytokine signaling.
瘦素受体LRb以及其他细胞因子受体缺乏内在酶活性，它们依赖组成型相关的Jak家族酪氨酸激酶的活性来介导细胞内信号传导。为了阐明与LRb相关的同源Jak激酶Jak2的调节机制及其介导下游信号传导的机制，我们采用串联质谱分析来鉴定Jak2上的磷酸化位点。我们鉴定出Ser523是首次描述的Jak2丝氨酸磷酸化位点，并证明该位点在完整细胞和小鼠脾脏中的Jak2上发生了磷酸化。Ser523在HEK293细胞中高度磷酸化，且不依赖于LRb-Jak2的激活，这表明Ser523的磷酸化在其他途径对LRb的调节中可能具有潜在作用。实际上，Ser523突变会使LRb细胞内结构域激活后Jak2的信号传导敏感化并延长。Ser523对Jak2功能的影响独立于Tyr570介导的抑制作用。因此，Jak2在Ser523上的磷酸化会抑制Jak2活性，这代表了一种调节Jak2依赖性细胞因子信号传导的新机制。
