Cohick W S, Clemmons D R
Department of Medicine, University of North Carolina, Chapel Hill 27599.
Endocrinology. 1991 Sep;129(3):1347-54. doi: 10.1210/endo-129-3-1347.
The Madin-Darby bovine kidney cell line was used to examine regulation of insulin-like growth factor binding protein (IGFBP) synthesis by epithelial cells. Ligand and immunoblot analysis of conditioned media indicated that IGFBP-2 was the predominant IGFBP secreted by untreated cells. Treatment with forskolin decreased secretion of IGFBP-2 by 75 +/- 3% and induced the appearance of IGFBP-3 and 24,000 Mr IGFBP. Although insulin alone did not induce the appearance of either band, in the presence of forskolin it increased the IGFBP-3 and 24,000 Mr bands 4.2 +/- 1.1 and 7.3 +/- 0.9-fold, respectively, above the values for forskolin treatment alone. Exposure to forskolin resulted in a 3-fold decrease in the abundance of IGFBP-2 messenger RNA (mRNA), and a 30-fold increase in IGFBP-3 mRNA. An additional 2- to 3-fold increase in IGFBP-3 mRNA was observed when cells were treated with insulin plus forskolin. Treatment with insulin plus forskolin increased cell number 2-fold, compared to small increases (26%) observed with forskolin treatment alone. Since treatment with IGF-I or -II did not result in similar responses to those of insulin, IGF analogs with differing affinities for IGFBP and IGF type I receptor were tested. B-chain IGF-I (decreased affinity for IGFBP) increased cell number and enhanced forskolin's effects on IGFBP-3 secretion and mRNA abundance to the same extent as insulin, whereas [Leu24,1-62]IGF-I (decreased affinity for the type I IGF receptor) did not. Therefore, activation of the type I IGF receptor was required to elicit increases in cell number and IGFBP synthesis and secretion, and the actions of IGF-I and II were likely blocked by binding to the large amounts of IGFBP-2 that were secreted. These results are in direct contrast to studies with human fibroblasts in which IGF-I and [Leu24,1-62]IGF-I stimulate IGFBP-3 secretion, whereas B-chain IGF-I has only a minimal effect. The ability to differentially regulate secretion of different forms of IGFBPs by epithelial cells and the finding that regulation is distinct from that of fibroblasts may have important implications for understanding mechanisms by which IGFs and IGFBPs interact to regulate epithelial cell growth.
采用Madin-Darby牛肾细胞系研究上皮细胞对胰岛素样生长因子结合蛋白（IGFBP）合成的调控。对条件培养基进行配体和免疫印迹分析表明，IGFBP-2是未处理细胞分泌的主要IGFBP。用福斯可林处理可使IGFBP-2的分泌减少75±3%，并诱导IGFBP-3和分子量为24000的IGFBP出现。虽然单独使用胰岛素不会诱导任何一条带的出现，但在存在福斯可林的情况下，它使IGFBP-3和分子量为24000的条带分别比单独使用福斯可林处理的值增加了4.2±1.1倍和7.3±0.9倍。暴露于福斯可林导致IGFBP-2信使核糖核酸（mRNA）丰度降低3倍，IGFBP-3 mRNA增加30倍。当细胞用胰岛素加福斯可林处理时，观察到IGFBP-3 mRNA额外增加2至3倍。与单独用福斯可林处理时观察到的小幅度增加（26%）相比，胰岛素加福斯可林处理使细胞数量增加了2倍。由于用IGF-I或-II处理未产生与胰岛素类似的反应，因此测试了对IGFBP和IGF I型受体具有不同亲和力的IGF类似物。B链IGF-I（对IGFBP的亲和力降低）增加细胞数量，并在与胰岛素相同的程度上增强福斯可林对IGFBP-3分泌和mRNA丰度的影响，而[Leu24,1-62]IGF-I（对I型IGF受体的亲和力降低）则没有。因此，I型IGF受体的激活是细胞数量增加以及IGFBP合成和分泌增加所必需的，并且IGF-I和-II的作用可能因与分泌的大量IGFBP-2结合而被阻断。这些结果与人成纤维细胞的研究结果形成直接对比，在人成纤维细胞研究中，IGF-I和[Leu24,1-62]IGF-I刺激IGFBP-3分泌，而B链IGF-I只有最小的作用。上皮细胞对不同形式IGFBPs分泌进行差异调节的能力以及调节与成纤维细胞不同的这一发现，可能对理解IGFs和IGFBPs相互作用调节上皮细胞生长的机制具有重要意义。
