Institute of Pharmacology and Toxicology, Medical Faculty of the RWTH Aachen University, Wendlingweg 2, 52074 Aachen, Germany.
BMC Biochem. 2010 Jan 8;11:2. doi: 10.1186/1471-2091-11-2.
Leptin is an adipocyte-derived hormone that acts via its hypothalamic receptor (LEPRb) to regulate energy balance. A downstream effect essential for the weight-regulatory action of leptin is the phosphorylation and activation of the latent transcription factor STAT3 by LEPRb-associated Janus kinases (JAKs). Obesity is typically associated with chronically elevated leptin levels and a decreased ability of LEPRb to activate intracellular signal transduction pathways (leptin resistance). Here we have studied the roles of the intracellular tyrosine residues in the negative feedback regulation of LEPRb-signaling under chronic leptin stimulation.
Mutational analysis showed that the presence of either Tyr985 and Tyr1077 in the intracellular domain of LEPRb was sufficient for the attenuation of STAT3 phosphorylation, whereas mutation of both tyrosines rendered LEPRb resistant to feedback regulation. Overexpression and RNA interference-mediated downregulation of suppressor of cytokine signaling 3 (SOCS3) revealed that both Tyr985 and Tyr1077 were capable of supporting the negative modulatory effect of SOCS3 in reporter gene assays. In contrast, the inhibitory effect of SOCS1 was enhanced by the presence of Tyr985 but not Tyr1077. Finally, the reduction of the STAT-phosphorylating activity of the LEPRb complex after 2 h of leptin stimulation was not accompanied by the dephosphorylation or degradation of LEPRb or the receptor-associated JAK molecule, but depended on Tyr985 and/or Tyr1077.
Both Tyr985 and Tyr1077 contribute to the negative regulation of LEPRb signaling. The inhibitory effects of SOCS1 and SOCS3 differ in the dependence on the tyrosine residues in the intracellular domain of LEPRb.
瘦素是一种脂肪细胞衍生的激素，通过其在下丘脑的受体（LEPRb）发挥作用，以调节能量平衡。瘦素调节体重的一个关键下游效应是 LEPRb 相关的 Janus 激酶（JAKs）使潜在转录因子 STAT3 磷酸化和激活。肥胖通常与慢性升高的瘦素水平和 LEPRb 激活细胞内信号转导途径（瘦素抵抗）的能力下降有关。在这里，我们研究了在慢性瘦素刺激下，LEPRb 信号转导的负反馈调节中细胞内酪氨酸残基的作用。
突变分析表明，LEPRb 细胞内结构域中的 Tyr985 和 Tyr1077 的存在足以减弱 STAT3 的磷酸化，而两个酪氨酸的突变使 LEPRb 对反馈调节具有抗性。细胞因子信号转导抑制剂 3（SOCS3）的过表达和 RNA 干扰介导的下调显示，Tyr985 和 Tyr1077 均能支持 SOCS3 在报告基因检测中的负调节作用。相比之下，SOCS1 的抑制作用因 Tyr985 的存在而增强，但不因 Tyr1077 的存在而增强。最后，在瘦素刺激 2 小时后，LEPRb 复合物的 STAT 磷酸化活性的降低并不伴随着 LEPRb 或受体相关 JAK 分子的去磷酸化或降解，而是依赖于 Tyr985 和/或 Tyr1077。
Tyr985 和 Tyr1077 均有助于 LEPRb 信号的负调节。SOCS1 和 SOCS3 的抑制作用在依赖 LEPRb 细胞内结构域中的酪氨酸残基方面存在差异。
