Isolation of a cDNA clone encoding rat insulin-like growth factor-II precursor
Isolation of a cDNA clone encoding rat insulin-like growth factor-II precursor
复制标题
编码大鼠胰岛素样生长因子-II 前体的 cDNA 克隆的分离
作者：
Harvey J. Whitfield;Carmelo B. Bruni;R. Frunzio;Jeffrey E. Terrell;S. Nissley;M. Rechler
胰岛素样生长因子-I（IGF-I）和IGF-II是从人血浆中分离的相对分子质量（Mr）为107，500的促有丝分裂多肽1，2每个多肽在单链中含有4个肽结构域，并且在其60%以上的氨基酸位点处相同。IGFs的B和A结构域与人胰岛素的B链和A链的相同性约为40% 1，2。IGF-I和IGF-II具有相似的体外生物学活性2和受体反应性3，但在免疫学上不同4，5。IGF-I似乎介导生长激素对软骨的影响，以促进骨骼生长5，6，而IGF-II可能在胎儿发育7，8和中枢神经系统9中发挥特殊作用。为了研究IGF-II的体内作用，我们研究了BRL-3A大鼠肝细胞系中IGF-II的生物合成10。BRL-3A细胞合成并分泌一种7，484 Mr蛋白质，与人IGF-II有93%相同，代表大鼠IGF-II（rIGF-II）11。大鼠IGF-II由12 S poly（A）+mRNA 13合成为约22，000 Mr prepro-rIGF-II（参考文献12）。此外，已在生物合成标记的完整BRL-3A细胞的裂解物中鉴定出1020，000 Mr pro-rIGF-II 14。我们在这里报告的分离rIGF-II的一个几乎完整的cDNA克隆。我们的研究结果表明，pro-rIGF-II合成为156个氨基酸的肽前体（17，619 Mr），在其氨基末端含有成熟的rIGF-II 1-67和89个残基的羧基末端肽延伸。
Insulin-like growth factor-I (IGF-I) and IGF-II are mitogenic polypeptides of relative molecular mass (Mr) ∼7,500 isolated from human plasma1,2 each containing four peptide domains in a single chain and identical at more than 60% of their amino acid loci. The B- and A-domains of the IGFs are ∼40% identical to the B-and A-chains of human insulin1,2. IGF-I and IGF-II have similar in vitro biological activities2 and receptor reactivity3, but are immunologically distinct4,5. IGF-I appears to mediate the effects of growth hormone on cartilage to promote skeletal growth5,6, whereas IGF-II may have a special role in fetal development7,8 and in the central nervous system9. To investigate the in vivo role of IGF-II, we have studied IGF-II biosynthesis in the BRL-3A rat liver cell line10. BRL-3A cells synthesize and secrete a 7,484 Mr protein 93% identical to human IGF-II and representing rat IGF-II (rIGF-II)11. Rat IGF-II is synthesized as a ∼22,000 Mr prepro-rIGF-II (ref. 12) from 12 S poly(A)+mRNA13. In addition, ∼20,000 Mr pro-rIGF-II has been identified in lysates of biosynthetically labelled intact BRL-3A cells14. We report here the isolation of an almost complete cDNA clone for rIGF-II. Our results indicate that pro-rIGF-II is synthesized as a 156 amino acid peptide precursor (17,619 Mr) containing mature rIGF-II 1–67 at its amino-terminus and an 89-residue carboxy-terminal peptide extension.