FUNCTIONAL-ANALYSIS OF THE RAT INSULIN-LIKE GROWTH FACTOR-I GENE AND IDENTIFICATION OF AN IGF-I GENE PROMOTER
FUNCTIONAL-ANALYSIS OF THE RAT INSULIN-LIKE GROWTH FACTOR-I GENE AND IDENTIFICATION OF AN IGF-I GENE PROMOTER
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DOI：
10.1089/dna.1992.11.301
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发表时间：
1992-05-01
影响因子：
3.1
通讯作者：
ROTWEIN, P
中科院分区：
文献类型：
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作者：
HALL, LJ;KAJIMOTO, Y;ROTWEIN, P
胰岛素样生长因子I（IGF-I）介导生长激素的许多全身性生长促进作用，并且还作为局部作用的生长刺激剂起作用。在哺乳动物中，IGF-I基因表达是复杂的，因为基因被转录并加工成编码至少两种蛋白质前体的多个mRNA（长度范围从小于1 kb到近7.5 kb）。作为了解IGF-I调控的一步，我们报告了大鼠IGF-I基因的完整组织，包括所有IGF-I mRNA种类的结构决定因素的鉴定，及其启动子的初步功能分析。该基因由6个外显子组成，分布在近80 kb的染色体DNA上，结构异质。在IGF-I外显子1和2内确定了几个转录起始位点，分别与推定的启动子1和2相邻，并且至少有三个多聚腺苷酸化位点被映射到外显子6。为了测试启动子功能，构建了将IGF-I DNA片段连接至报告质粒的融合基因。含有至少395 bp的外显子1 5 ′侧翼区DNA的嵌合基因在转染到产生IGF-1的SK-N-MC细胞系中后增强了荧光素酶活性，而含有多达1，300 bp的外显子2 5 ′侧翼区DNA的融合质粒则无活性。含有外显子1或2的IGF-I mRNA的相对水平在不同的大鼠组织中不同，虽然在急性或慢性生长激素治疗的两个类的成绩单诱导协调大鼠肝脏。这些观察结果代表了第一次彻底的哺乳动物IGF-I基因的特性，并提供了一个起点，定义生长激素和其他营养因子调节IGF-I基因表达的机制。
Insulin-like growth factor I (IGF-I) mediates many of the systemic growth-promoting effects of growth hormone and also functions as a locally acting growth stimulator. In mammals, IGF-I gene expression is complicated, as the gene is transcribed and processed into multiple mRNAs (ranging in length from less than 1 to nearly 7.5 kb) that encode at least two protein precursors. As a step toward understanding the regulation of IGF-I, we report the complete organization of the rat IGF-I gene, including identification of the structural determinants for all IGF-I mRNA species, and an initial functional analysis of its promoters. The gene is composed of 6 exons distributed over nearly 80 kb of chromosomal DNA and is structurally heterogeneous. Several transcription start sites were identified within IGF-I exons 1 and 2, adjacent to presumptive promoters 1 and 2, respectively, and at least three polyadenylation sites were mapped to exon 6. To test promoter function, fusion genes were constructed linking fragments of IGF-I DNA to a reporter plasmid. Chimeric genes containing at least 395 bp of DNA from the 5'-flanking region of exon 1 enhanced luciferase activity after transfection into the IGF-I-producing SK-N-MC cell line, while fusion plasmids containing up to 1,300 bp of DNA from the 5'-flanking region of exon 2 were inactive. Relative levels of IGF-I mRNAs containing exons 1 or 2 varied among different rat tissues, although in response to acute or chronic growth hormone treatment both classes of transcripts were induced coordinately in rat liver. These observations represent the first thorough characterization of a mammalian IGF-I gene, and provide a starting point for defining the mechanisms by which growth hormone and other trophic factors regulate IGF-I gene expression.