Control of IGF-1 Gene Transcription by Growth Hormone

描述（由申请人提供）：GH在生理学中起着关键作用，对正常的体细胞生长、组织再生和修复以及中间代谢至关重要。GH的许多生物学效应由胰岛素样生长因子I（IGF-I）介导，IGF-I是一种保守的分泌蛋白，其表达通过激活IGF-I基因转录而被GH强力诱导。如GH和IGF-I与几种癌症的发展的联系以及它们对衰老的集体负面影响所证明的，GH对IGF-I的异常表达可能具有有害的致病后果，这意味着其产生必须受到严格调控以维持体内平衡。本申请的重点将是GH通过转录因子Stat 5 b控制IGF-I基因表达的机制。我们的研究将测试挑衅性的假设，IGF-I是从根本上不同于其他GH-Stat 5 b的靶基因，和多个分散的Stat 5 b结合转录增强子，和其他潜在的抑制元素，是一个复杂的调控程序，必须控制表达的一个有效的生长因子的积极和消极的生物学效应的关键代理。以下两个具体目标将测试这个想法：1。鉴定和表征负责GH和Stat 5 b调节Igf 1基因转录的染色体增强子和阻遏子。待检验的主要假设是具有不同功能特性的离散GH激活增强子与单个Igf 1基因启动子相互作用，并共同负责 用于介导对GH的急性转录反应。一个推论的假设是，在Igf 1染色质中的一些GH调节元件不是转录增强子，而是推定的负调节因子，并干扰Igf 1启动子功能，在没有GH或隔离GH刺激的Stat 5 b从阳性位点。2.目的探讨GH和Stat 5 b在调节Igf 1基因染色质可塑性中的作用。要测试的主要假设是，持续GH介导的信号需要建立一个开放的染色质环境中的Igf 1启动子，但Stat 5 b是不稳定的。一个必然的假设是，Stat 5 b负责 GH快速诱导Igf 1基因转录所必需的急性染色质修饰。拟议的研究具有潜在的影响，以建立一个新的范式GH的行动机制，以调节IGF-I基因的表达，并导致新的生理意义的见解GH介导的信号如何控制表观遗传途径，染色质可塑性和基因调控。 公共卫生相关性：生长激素的行动是必不可少的正常体细胞生长，组织的维护和修复，并为正常的中间代谢在人类和其他物种，主要是由IGF-I介导的，一个保守的分泌蛋白，其表达是由生长激素诱导。GH-IGF-I途径也与癌症发展和衰老的负面方面有关，这意味着其异常调节具有有害的致病后果，并且其活性必须至少在成人中受到限制以维持稳态。本申请的重点是GH通过保守的转录因子Stat 5 b调节IGF-I基因表达的机制，并且是确定GH作用如何控制表观遗传途径以及染色质修饰如何以生理学上有意义的方式有效调节Stat 5 b功能的长期目标的一部分。

DESCRIPTION (provided by applicant): GH plays a pivotal role in physiology, and is essential for normal somatic growth, tissue regeneration and repair, and intermediary metabolism. Many of the biological effects of GH are mediated by insulin- like growth factor I (IGF-I), a conserved secreted protein whose expression is potently induced by GH by activation of IGF-I gene transcription. As evidenced by linkage of GH and IGF-I with development of several cancers, and by their collective negative impact on aging, aberrant expression of IGF-I by GH may have deleterious pathogenic consequences, implying that its production must be tightly regulated to maintain homeostasis. The focus of this application will be on mechanisms by which GH controls IGF-I gene expression via the transcription factor Stat5b. Our studies will test the provocative hypothesis that IGF-I is fundamentally different from other GH-Stat5b target genes, and that multiple dispersed Stat5b-binding transcriptional enhancers, and other potentially inhibitory elements, are key agents in a complex regulatory program necessary to control expression of a potent growth factor with both positive and negative biological effects. The following two Specific Aims will test this idea: 1. To identify and characterize the chromosomal enhancers and repressors responsible for GH- and Stat5b-regulated Igf1 gene transcription. The major hypothesis to be tested is that discrete GH- activated enhancers with distinct functional properties interact with individual Igf1 gene promoters and are responsible collectively for mediating the acute transcriptional response to GH. A corollary hypothesis is that some GH-regulated elements in Igf1 chromatin are not transcriptional enhancers, but rather are putative negative regulators, and interfere with Igf1 promoter function in the absence of GH or sequester GH-stimulated Stat5b from positive sites. 2. To define the roles of GH and Stat5b in regulating chromatin plasticity of the Igf1 gene. The major hypothesis to be tested is that sustained GH-mediated signaling is required to establish an open chromatin environment at the Igf1 promoters, but that Stat5b is dispensable. A corollary hypothesis is that Stat5b is responsible for the acute chromatin modifications necessary for rapid induction of Igf1 gene transcription by GH. Proposed research has the potential impact to establish a new paradigm about mechanisms of GH action to regulate IGF-I gene expression, and to lead to new physiologically significant insights about how GH-mediated signaling controls epigenetic pathways, chromatin plasticity, and gene regulation. PUBLIC HEALTH RELEVANCE: GH actions are essential for normal somatic growth, for tissue maintenance and repair, and for normal intermediary metabolism in humans and other species, and are primarily mediated by IGF-I, a conserved secreted protein whose expression is induced by GH. The GH - IGF-I pathway also has been implicated in cancer development and in the negative aspects of aging, implying that its aberrant regulation has deleterious pathogenic consequences, and that its activity must be constrained at least in the adult to maintain homeostasis. The focus of this application is on the mechanisms by which GH regulates IGF-I gene expression through the conserved transcription factor, Stat5b, and is part of a longer-term goal to define how GH actions control epigenetic pathways and how chromatin modifications can potently regulate Stat5b functions in physiologically meaningful ways.