Mechanisms of Leptin Receptors Signal Attenuation

描述(申请人提供)：这项题为“体内瘦素受体信号衰减的机制”的提案是DK57768的续订申请。瘦素受体的长亚型(或LRB)介导瘦素调节能量平衡(减少摄食和增加能量消耗)和神经内分泌功能的信号和生理作用。目前尚不清楚为什么瘦素不能充分预防肥胖和人类2型糖尿病的易感性；因此，了解LRB信号的分子细节，特别是LRB信号减弱的机制，对于了解瘦素抵抗的潜在机制和/或确定肥胖治疗的潜在靶点至关重要。我们之前和未来研究的长期展望是了解LRB对信号的调节和机制以及它们在生理性瘦素作用中的作用。LRB是一种1型细胞因子受体，虽然没有酶活性，但通过细胞内的JAK2酪氨酸激酶和两个磷酸化位点来介导磷酸酪氨酸依赖的信号转导。Tyr1138激活STAT3，它负责重要的阳性瘦素信号以及瘦素诱导的SOCS3。除了在培养细胞中的SHP-2/ERK信号转导中发挥作用外，Tyr985还与SOCS3结合，以介导体内和培养细胞中LRB信号衰减的某些元件；SOCS3还与LRB相关的JAK2结合，直接抑制JAK2信号。我们建议研究SOCS3与JAK2和Tyr985结合在培养细胞和体内信号衰减中的作用。除了阐明LRB的生物学特性外，我们的分析还将阐明细胞因子受体/酪氨酸激酶信号转导的基本机制。我们建议： 具体目标1：确定LRB信号在培养细胞中衰减的分子机制。具体目的2：研究LRB磷酸化位点在体内瘦素敏感性中的作用。 具体目标3：探讨SOCS3介导的体内抑制LRB作用的机制(S)。这些目标中的每一个都是解决这一建议的核心假设的关键，即瘦素诱导的SOCS3表达通过多种机制介导对LRB作用的反馈抑制，并且这些机制中的每一种都不同地影响哺乳动物的瘦素敏感性。

DESCRIPTION (provided by applicant): This proposal, entitled,"Mechanisms of Leptin Receptor Signal Attenuation in vivo, "is an application for renewal of DK57768. The long (or LRb) isoform of the leptin receptor mediates signaling and the physiologic action of leptin to regulate energy balance (decreasing feeding and increasing energy expenditure) and neuroendocrine function. It is not clear why leptin fails to adequately protect from obesity and the predisposition to Type 2 diabetes in humans; it is thus critical to understand the molecular details of LRb signaling and especially mechanisms by which LRb signaling is attenuated in order to understand potential mechanisms of leptin resistance and/or to identify potential targets for the therapy of obesity. The long-term outlook of our previous and future studies is to understand the regulation and mechanisms of signaling by LRb and their role in physiologic leptin action. LRb is a type 1 cytokine receptor that, although devoid of enzymatic activity, mediates phosphotyrosine-dependent signaling by means of an associated Jak2 tyrosine kinase and two phosphorylation sites on the intracellular LRb. Tyr1138 activates STAT3, which is responsible for important positive leptin signals as well as for the induction of SOCS3 by leptin. In addition to its role in SHP- 2/ERK signaling in cultured cells, Tyr985 binds SOCS3 to mediate some elements of LRb signal attenuation in vivo as well as in cultured cells; SOCS3 also binds to the LRb-associated Jak2 to directly inhibit Jak2 signaling. We propose to study the function of SOCS3 binding to Jak2 and Tyr985 in signal attenuation in cultured cells and in vivo. In addition to shedding light upon the biology of LRb specifically, our analysis will illuminate basic mechanisms of cytokine receptor/tyrosine kinase signaling. We propose: Specific Aim 1: Determine the molecular mechanisms of LRb signal attenuation in cultured cells. Specific Aim 2: Examine the role of LRb phosphorylation sites in leptin sensitivity in vivo. Specific Aim 3: Address the mechanism(s) of SOCS3-mediated inhibition of LRb action in vivo. Each of these aims is crucial to addressing the central hypothesis of this proposal- that leptin-induced SOCS3 expression mediates feedback inhibition on LRb action in vi\o by multiple mechanisms, and that each of these mechanisms differentially affects leptin sensitivity in mammals.