Nutritional Control of Cancer Cell Function by Amino Acids

 描述(由申请人提供)：限制蛋白质或氨基酸(AA)激活由几个部分表征的信号通路组成的AA反应(AAR)。其中研究得最好的涉及通过GCN2激酶感知AA，并通过表现AAR元件(AARE)功能的基因组C/EBP-ATF反应元件(CARE)增强子位点最终实现ATF4依赖的转录。以HepG2人肝细胞癌和U87人胶质母细胞瘤细胞为模型，我们最近的研究表明，在未转化的细胞中，存在GCN2/ATF4不依赖的途径，这些途径几乎没有贡献。其中一条途径是通过MAPK信号的RAS/RAF/MEK/ERK臂介导的，并以ELK1转录因子与以前未知具有AARE功能的ETS增强子序列结合而终止。我们发现ERK通路在人肝癌细胞中对数百个AA反应基因的调控有重要作用，但在正常肝细胞中不起作用。这些新颖的观察结果强调了我们对AA可用性对基本细胞功能的影响的认识上的显著差距。我们的总体假设是，在一些肿瘤细胞中，哺乳动物的AAR延伸到GCN2/ATF4之外，并且通过MAPK通路的AA信号是AAR的重要组成部分，它允许肿瘤细胞在AA限制的情况下增殖。拟议的实验将在培养细胞和荷瘤小鼠身上测试以下特定假设。(假设I)ERK通路独立于GCN2-ATF4参与新的AA信号转导。(假设II)ERK AAR途径包括以前未知的AA反应的转录因子，并终止于具有功能AARE活性的新基因组序列。(假设III)诱导ERK依赖的信号有助于肿瘤的持续生长，尽管AA限制。拟议的研究在概念上是创新的，原因如下。1)目前认为GCN2-ATF4途径诱导大多数/所有AA反应基因的教条必须扩展到包括未知的AA感受器、MAPK信号和以前未知具有AARE活性的增强子序列。2)通过ELK1依赖AA的转录揭示了AAR中一个全新的转录因子家族--ETS家族。3)ERK介导的Egr1、FOS、Jun和MYC等基因在AA缺乏的肿瘤细胞中的诱导提示蛋白质/AA营养与肿瘤增殖之间存在联系。

 DESCRIPTION (provided by applicant): Protein or amino acid (AA) limitation activates an AA response (AAR) comprised of several partially characterized signaling pathways. The best studied of these involves AA sensing by GCN2 kinase and culminates in ATF4-dependent transcription via genomic C/EBP-ATF response element (CARE) enhancer sites that exhibit AAR element (AARE) function. Using HepG2 human hepatocellular carcinoma (HCC) and U87 human glioblastoma cells as models, our recent research indicates that there are GCN2/ATF4-independent pathways that exhibit little or no contribution in non-transformed cells. One of these pathways is mediated through the RAS/RAF/MEK/ERK arm of MAPK signaling and terminates with ELK1 transcription factor binding to ETS enhancer sequences not previously known to exhibit AARE function. We have discovered that the ERK pathway makes a significant contribution to the regulation of hundreds of AA-responsive genes in human HCC cells, but not in normal hepatocytes. These novel observations underscore the significant gaps in our knowledge about the impact of AA availability on basic cell functions. Our global hypothesis is that in some tumor cells the mammalian AAR extends beyond GCN2/ATF4 and that AA signaling via MAPK pathways is a significant component of the AAR, which permits tumor cells to proliferate despite AA limitation. The proposed experiments will test the following specific hypotheses in cultured cells and tumor-bearing mice. (Hypothesis I) An ERK pathway contributes to novel AA signaling independent of GCN2-ATF4. (Hypothesis II) The ERK AAR pathway includes transcription factors not previously known to be AA-responsive and terminates in novel genomic sequences that have functional AARE activity. (Hypothesis III) Induction of ERK-dependent signaling contributes to continued tumor growth despite AA limitation. The proposed studies are conceptually innovative for the following reasons. 1) The current dogma that the GCN2-ATF4 pathway induces most/all AA- responsive genes must be expanded to include an unknown AA sensor, MAPK signaling, and enhancer sequences previously unknown to have AARE activity. 2) AA-dependent transcription via ELK1 reveals an entirely new family of transcription factors, the ETS family, within the AAR. 3) The ERK-driven induction of genes, such as EGR1, FOS, JUN, and MYC, in AA-deprived tumor cells suggests a link between protein/AA nutrition and tumor proliferation.