IGF I GENE EXPRESSION IN NORMAL AND DISEASE STATES

胰岛素样生长因子-I(IGF-I)基因表达受 营养和代谢状态，与体细胞或 特定组织生长计划。一个重要的临床例子是肾脏 糖尿病肾病初期的肥大。 葡萄糖和IGF-I刺激肾脏基质合成和血流动力学 胰岛素样生长因子-I在糖尿病肾脏一过性升高。因此，每个人都会出现高血糖 硒可能促进胰岛素依赖型糖尿病大鼠肾脏胰岛素样生长因子-L基因表达。 研究计划的总体目标是确定这些机制的特征。 通过改变葡萄糖代谢导致转录和 IGF-I基因表达的翻译调控。具体目标 为实现这一目标而提出的建议是：1)检验假设 葡萄糖或葡萄糖作用的结果直接刺激IGF-I 抄写。葡萄糖及其代谢物及其类似物的作用 GH_3和GH_3中IGF-I基因表达水平、转录速率和启动子活性的研究 C6细胞的特性；2)检验组织- 肝、肾组织中IGF-I基因表达的特异性变化 胰岛素缺乏性糖尿病动物的其他组织是由于不同的 低胰岛素血症和高血糖的影响。胰岛素样生长因子-I的mRNA水平和 将测定链脲佐菌素(STZ)-糖尿病患者的转录速率 接受胰岛素替代或根茎叶皂苷降血糖的大鼠 在不恢复胰岛素水平的情况下减少血糖。胰岛素样生长因子-I基因表达水平的变化 将使用原位技术定位到不同的肾脏区域和细胞类型 杂交；3)检验串联翻译的假设 某些IGF-I基因5‘端非编码区的起始和终止密码子 有必要在前IGF-I开放阅读框重新启动 从而降低了preproIGF-I翻译的效率。的影响 胰岛素样生长因子-I基因上游起始和终止密码子的突变 5‘-UTRs在体外和完整细胞中的翻译效率将是 特征；4)检验以下假设： 含有上游起始基因的IGF-I mRNAs的翻译再起始 并且5‘-UTR中的终止密码子可以由水平或 启动因子eIF-2和ELF-2B的活性。外源效应 EIF-2和eIF-2B与内源性eIF-2在IN上的磷酸化 具有不同5‘-UTRs的IGF-I mRNAs的体外翻译 特色化的。这一机制可能与葡萄糖有关。 葡萄糖调节胰岛素样生长因子-L基因表达 EIF-2和EIF-2B的活性。这些具体目标的积极成果 将为转录和翻译控制提供新的见解 调控IGF-I基因表达的机制。这些研究将提供 葡萄糖调节胰岛素样生长因子-I的细胞机制范例 基因表达以及其他基因的表达。这些研究 将为确定血糖如何改变提供必要的基础 胰岛素样生长因子-I的水平和代谢调节正常人体的生长 生理和疾病状态，如II型糖尿病、营养不良、 以及分解代谢和组织损耗综合症。

Insulin-like growth factor-I (IGF-I) gene expression is regulated by the nutritional and metabolic state, consistent with changes in the somatic or tissue-specific growth program. An important clinical example is the renal hypertrophy which occurs in the initial stages of diabetic nephropathy. Glucose and IGF-I stimulate renal matrix synthesis and hemodynamics, and IGF-I is transiently increased in diabetic kidney. Thus, hyperglycemia per se may stimulate kidney IGF-l gene expression in insulinopenic diabetes. The overall goal of the research program is to characterize the mechanisms by which altered glucose metabolism leads to transcriptional and translational control of IGF-I gene expression. The specific aims proposed toward achieving this goal are: 1) To test the hypothesis that glucose or a consequence of glucose action directly stimulates IGF-I transcription. The effects of glucose and glucose metabolites and analogs on IGF-I mRNA levels, transcription rates and promoter activity in GH3 and in C6 cells will be characterized; 2) To test the hypothesis that tissue- specific changes in IGF-I gene expression in liver, kidney and possibly other tissues from insulinopenic diabetic animals are due to distinct effects of hypoinsulinemia and hyperglycemia. IGF-I mRNA levels and transcription rates will be determined in streptozotocin (STZ)-diabetic rats receiving either insulin replacement, or phlorizin to lower blood glucose without restoring insulin levels. Changes in IGF-I mRNA levels will be localized to distinct kidney regions and cell types using in situ hybridization; 3) To test the hypothesis that the tandem translation initiation and termination codons in the 5'-UTR of some IGF-I mRNAs necessitate re-initiation at the preproIGF-I open reading frame and thereby reduce the efficiency of preproIGF-I translation. The effect of mutation of the upstream initiation and termination codons in IGF-I mRNA 5'-UTRs on translational efficiency in vitro and in intact cells will be characterized; 4) To test the hypothesis that the efficiency of translation re-initiation in IGF-I mRNAs containing upstream initiation and termination codons in the 5'-UTR can be regulated by the level or activity of initiation factors eIF-2 and elF-2B. The effect of exogenous eIF-2 and eIF-2B and of phosphorylation of endogenous eIF-2 on the in vitro translation of IGF-I mRNAs with different 5'-UTRs will be characterized. This mechanism is potentially pertinent to glucose regulation of IGF-l gene expression because glucose regulates the activities of eIF-2 and eIF-2B. Positive outcomes of these specific aims will provide novel insights into transcriptional and translational control mechanisms which regulate IGF-I gene expression. The studies will provide a paradigm for the cellular mechanisms by which glucose regulates IGF-I gene expression as well as the expression of other genes. These studies will provide an essential foundation for determining how altered glucose levels and metabolism regulate IGF-I biosynthesis and growth in normal physiology and in disease states such as type II diabetes, malnutrition, and catabolic and tissue-wasting syndromes.