IGF I GENE EXPRESSION IN NORMAL AND DISEASE STATES

胰岛素样生长因子-I（IGF-I）基因表达受胰岛素样生长因子-I（IGF-I）的调节。 营养和代谢状态，与躯体或 组织特异性生长计划。一个重要的临床例子是肾 糖尿病肾病的早期症状有哪些？ 葡萄糖和IGF-I刺激肾基质合成和血流动力学， IGF-I在糖尿病肾脏中一过性升高。因此，根据 硒可刺激胰岛素缺乏型糖尿病肾脏IGF-1基因表达。 该研究计划的总体目标是描述这些机制 通过改变葡萄糖代谢导致转录和 IGF-I基因表达的翻译控制。 具体目标 为实现这一目标，提出了以下建议：1）检验假设， 葡萄糖或葡萄糖作用的结果直接刺激IGF-I 转录。葡萄糖和葡萄糖代谢物及类似物的作用 IGF-I mRNA水平、转录速率和启动子活性， 在C6细胞中将被表征; 2）为了测试组织- IGF-I基因表达在肝脏、肾脏和可能的 来自胰岛素缺乏性糖尿病动物的其它组织是由于不同的 低胰岛素血症和高血糖的影响。IGF-I mRNA水平和 将在链脲佐菌素（STZ）-糖尿病患者中测定转录率。 接受胰岛素替代或根皮苷以降低血液 而不恢复胰岛素水平。IGF-I mRNA水平的变化 将定位于不同的肾脏区域和细胞类型， 3）为了验证串联翻译的假设， 某些IGF-I mRNA的5'-UTR中的起始和终止密码子 需要在preproIGF-I开放阅读框重新启动， 从而降低preproIGF-I翻译的效率。 的影响 IGF-I mRNA上游起始和终止密码子突变 5'-UTR对体外和完整细胞中的翻译效率的影响将被研究。 4）为了验证假设， 含有上游起始的IGF-I mRNA中的翻译再起始 并且5'-UTR中的终止密码子可以通过以下水平调节： 起始因子eIF-2和eIF-2B的活性。外源性影响 eIF-2和eIF-2B以及内源性eIF-2磷酸化在细胞内的表达。 具有不同5 ′-UTR的IGF-I mRNA的体外翻译将是 表征了这种机制可能与葡萄糖有关 IGF-I基因表达的调节，因为葡萄糖调节 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 调节IGF-I基因表达的机制。 这些研究将提供 葡萄糖调节IGF-I的细胞机制的范例 基因表达以及其他基因的表达。 这些研究 将提供一个重要的基础，以确定如何改变葡萄糖 水平和代谢调节IGF-I的生物合成和生长在正常 生理学和疾病状态，如II型糖尿病，营养不良， 以及分解代谢和组织损耗综合征。

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.