Amino Acid Regulation of the Fos/Jun Transcription Factors

描述（由申请人提供）：蛋白质剥夺不仅对基因表达具有即时调节作用，而且还可以通过染色质相关机制产生长期影响。然而，我们对饮食蛋白质波动对基本细胞功能（包括转录）的影响的认识存在重大差距。在个体组织/细胞水平上，膳食蛋白质缺乏反映为氨基酸（AA）限制，因此，培养细胞的AA剥夺是研究转录控制的基因组机制的有用模型。体内的饮食蛋白限制或细胞培养中的AA剥夺激活多途径AA反应（AAR），其是最终导致ATF 4合成的几种应激激活的信号传导机制之一。一项微阵列研究确定了人HepG 2肝细胞癌（HCC）细胞中FOS/JUN家族转录因子的成员为AA调控基因。随后的研究表明，cJUN调节几个已知的AAR靶点的下游基因。另外还发现了两个新的观察结果。首先，cJUN基因的诱导是不依赖于ATF 4的，因此，必须包含一个新的AA反应元件（AARE），它可能与一个新的信号通路。其次，cJUN的诱导发生在人HCC细胞中，但不在原代人肝细胞或非转化的永生化肝细胞系中。这些研究具有创新性，因为：1）它们将通过不依赖于ATF 4的机制首次研究蛋白质/AA应答基因，2）它们将在体内动物肿瘤模型以及培养的人肝癌细胞和正常肝细胞中建立cJUN基因的调节机制。我们的总体假设是，cJUN基因包含一种新的AARE，并在HCC细胞中通过一种不依赖于ATF 4的信号通路激活，并且cJUN表达升高支持饮食蛋白或AA限制期间HCC持续增殖。所提出的实验将检验以下假设：（假设I）cJUN基因是一种新的不依赖于ATF 4的AA信号通路的靶标;（假设II）cJUN基因表现出新的AA响应性转录机制;（假设III）cJUN在蛋白质/AA限制期间调节AAR基因和细胞增殖。 公共卫生相关性：充足的膳食蛋白质/氨基酸供应是维持健康的重要因素，特别是在怀孕期间，胎儿/新生儿发育以及包括糖尿病和癌症在内的各种疾病的进展中。尽管有这些重要的关系，膳食蛋白质/氨基酸波动对基本细胞过程和病理状态的影响，如肿瘤的发展和维持，是我们所知相对较少的主题。拟议的研究将调查导致FOS/JUN蛋白家族的机制，基因表达和细胞增殖的主要调节因子，由人类肿瘤细胞的氨基酸限制诱导，而不是正常的对应物。

DESCRIPTION (provided by applicant): Protein deprivation not only has immediate regulatory effects on gene expression, but can also have long-term effects through chromatin-associated mechanisms. However, there are significant gaps in our knowledge about the impact of dietary protein fluctuation on basic cell functions, including transcription. At the level of individual tissues/cells, dietary protein deficiency is reflected as amino acid (AA) limitation and therefore, AA deprivation of cultured cells is a useful model to investigate the genomic mechanisms of transcriptional control. Dietary protein limitation in vivo or AA deprivation in cell culture activates a multi-pathway AA response (AAR) that is one of several stress-activated signaling mechanisms that culminate in ATF4 synthesis. A microarray study identified members of the FOS/JUN family of transcription factors as AA-regulated genes in human HepG2 hepatocellular carcinoma (HCC) cells. Subsequent studies showed that cJUN regulates several downstream genes that are known AAR targets. Two additional novel observations were made. First, the induction of the cJUN gene is ATF4-independent, and therefore, must contain a novel AA response element (AARE), which may be linked to a novel signaling pathway. Second, the induction of cJUN occurs in human HCC cells, but not in primary human hepatocytes or in a non-transformed immortalized hepatocyte cell line. The proposed studies are innovative because: 1) they will provide the first investigation of a protein/AA responsive gene by an ATF4-independent mechanism, and 2) they will establish the mechanism for regulation of the cJUN gene in an animal tumor model in vivo, as well as in cultured human hepatoma cells and normal hepatocytes. Our global hypothesis is that the cJUN gene contains a novel AARE and is activated in HCC cells by an ATF4-independent signaling pathway, and that elevated cJUN expression supports continued HCC proliferation during dietary protein or AA limitation. The proposed experiments will test the following hypotheses: (Hypothesis I) The cJUN gene is the target of a novel ATF4-independent AA signaling pathway; (Hypothesis II) The cJUN gene exhibits novel AA-responsive transcriptional mechanisms; and (Hypothesis III) cJUN modulates AAR genes and cell proliferation during protein/AA limitation. PUBLIC HEALTH RELEVANCE: Sufficient dietary protein/amino acid availability is an important factor in maintenance of health, especially during pregnancy, fetal/neonatal development, and in the progression of a wide range of diseases, including diabetes and cancer. Despite these important relationships, the influence of dietary protein/amino acid fluctuation on fundamental cellular processes and pathological states, such as the development and maintenance of tumors, are topics about which we know relatively little. The proposed research will investigate the mechanisms that lead the FOS/JUN family of proteins, major regulators of gene expression and cell proliferation, to be induced by amino acid limitation of human tumor cells, but not their normal counterparts.