Mechanisms of Leptin Receptors Signal Attenuation

描述（由申请人提供）：该提案题为“体内瘦素受体信号衰减机制”，是DK57768的续期申请。瘦素受体的长（或LRb）亚型介导瘦素的信号传导和生理作用，以调节能量平衡（减少摄食和增加能量消耗）和神经内分泌功能。目前尚不清楚为什么瘦素不能充分防止人类肥胖和易患2型糖尿病；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。了解LRb的信号调控机制及其在瘦素生理性作用中的作用是我们以往和未来研究的长期展望。LRb是一种1型细胞因子受体，虽然缺乏酶活性，但通过相关的Jak2酪氨酸激酶和细胞内LRb上的两个磷酸化位点介导磷酸酪氨酸依赖的信号传导。Tyr1138激活STAT3， STAT3负责重要的瘦素阳性信号以及瘦素诱导SOCS3。Tyr985除了在培养细胞中参与SHP- 2/ERK信号传导外，还结合SOCS3介导了体内和培养细胞中LRb信号衰减的一些因素；SOCS3还与lrb相关的Jak2结合，直接抑制Jak2信号传导。我们拟在培养细胞和体内研究SOCS3结合Jak2和Tyr985在信号衰减中的作用。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/酪氨酸激酶信号传导的基本机制。我们建议:

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.