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有即时调节作用，还可能通过染色质相关机制产生长期影响。然而，关于膳食蛋白质波动对包括转录在内的基本细胞功能的影响，我们的知识有很大的差距。在单个组织/细胞水平上，饲料蛋白质缺乏表现为氨基酸（AA）的限制，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。体内饮食蛋白质限制或细胞培养中AA剥夺可激活多途径AA反应（AAR），这是几种应激激活的信号机制之一，最终导致ATF4合成。一项微阵列研究发现，FOS/JUN转录因子家族成员是人类HepG2肝细胞癌（HCC）细胞中aa调节基因。随后的研究表明，cJUN调节了几个已知的AAR靶点下游基因。另外还有两个新的观察结果。首先，cJUN基因的诱导与atf4无关，因此必须包含一个新的AA反应元件（AARE），这可能与一个新的信号通路有关。其次，cJUN的诱导发生在人HCC细胞中，但不发生在原代人肝细胞或未转化的永生化肝细胞系中。本研究的创新之处在于：1)首次通过不依赖atf4的机制研究蛋白/AA应答基因；2)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基因的调控机制。我们的总体假设是，cJUN基因含有一种新的AARE，并在HCC细胞中通过atf4独立的信号通路被激活，并且在饮食蛋白质或AA限制期间，cJUN表达的升高支持HCC持续增殖。本实验将验证以下假设：（假设1）cJUN基因是一种新的不依赖atf4的AA信号通路的靶点；（假设二）cJUN基因表现出新的aa应答转录机制；假设三：在蛋白/AA限制期间，cJUN调节AAR基因和细胞增殖。

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.