Chacko M S, Adamo M L
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78229-3900, USA.
Endocrinology. 2000 Oct;141(10):3546-55. doi: 10.1210/endo.141.10.7729.
Poly(IC), a synthetic double-stranded RNA copolymer of inosinic and cytidilic acids, decreases the growth of normal and tumorigenic cells. We tested the hypothesis that Poly(IC) decreases C6 glioma cell growth by disrupting an autocrine insulin-like growth factor I (IGF-I) growth loop. Addition of Poly(IC) decreased C6 cell number in confluent and sparse cultures in a dose-dependent manner. Addition of exogenous IGF-I partially compensated for the decrease in cell number caused by Poly(IC) in confluent and subconfluent cultures of C6 cells, suggesting that one mechanism of Poly(IC) action is through down-regulation of IGF-I gene expression and/or action. Treatment of confluent C6 cells with 10 and 200 microg/ml Poly(IC) for 24 h decreased IGF-I messenger RNA (mRNA) levels to 50% and 25% of the control value, respectively. Treatment of C6 cells with 200 microg/ml Poly(IC) for 24 h reduced IGF-I receptor mRNA levels to 50% of the control level. IGF-binding protein-1 (IGFBP-1), -2, and -6 mRNAs were not expressed in the C6 cells used in this study. Treatment of C6 cells with 200 microg/ml Poly(IC) for 24 h reduced IGFBP-4 mRNA and IGFBP-5 mRNA levels to 26% and 29% of the control level, respectively. There was no significant change in IGFBP-3, insulin receptor, or actin mRNA levels with Poly(IC) treatment. Treatment of confluent C6 cells with 200 microg/ml Poly(IC) for 24 h decreased levels of immunoreactive IGF-I in conditioned medium (CM) to 55% of the control value, decreased IGF-I receptor beta-subunit levels to 28% of the control value, and decreased levels of IGFBP-3, IGFBP-4, and IGFBP-5 protein in CM to 45%, 50%, and 30% of the control values, respectively. There was no significant change in actin and tubulin protein levels with Poly(IC) treatment. These results suggest that IGF-I gene expression is down-regulated by Poly(IC) treatment and that IGF-I bioavailability and action in C6 cells are also altered due to decreases in IGF-I receptor and binding protein levels.
聚肌胞苷酸（Poly(IC)）是一种肌苷酸和胞苷酸的合成双链RNA共聚物，可抑制正常细胞和致瘤细胞的生长。我们检验了以下假设：Poly(IC)通过破坏自分泌胰岛素样生长因子I（IGF-I）生长环来抑制C6胶质瘤细胞的生长。添加Poly(IC)以剂量依赖的方式降低了汇合和稀疏培养物中C6细胞的数量。在C6细胞的汇合和亚汇合培养物中添加外源性IGF-I部分补偿了由Poly(IC)引起的细胞数量减少，这表明Poly(IC)作用的一种机制是通过下调IGF-I基因表达和/或作用。用10和200μg/ml的Poly(IC)处理汇合的C6细胞24小时，分别将IGF-I信使核糖核酸（mRNA）水平降至对照值的50%和25%。用200μg/ml的Poly(IC)处理C6细胞24小时，将IGF-I受体mRNA水平降至对照水平的50%。在本研究中使用的C6细胞中未检测到IGF结合蛋白-1（IGFBP-1）、-2和-6的mRNA表达。用200μg/ml的Poly(IC)处理C6细胞24小时，分别将IGFBP-4 mRNA和IGFBP-5 mRNA水平降至对照水平的26%和29%。Poly(IC)处理后，IGFBP-3、胰岛素受体或肌动蛋白mRNA水平无显著变化。用200μg/ml的Poly(IC)处理汇合的C6细胞24小时，使条件培养基（CM）中免疫反应性IGF-I水平降至对照值的55%，IGF-I受体β亚基水平降至对照值的28%，CM中IGFBP-3、IGFBP-4和IGFBP-5蛋白水平分别降至对照值的45%、50%和30%。Poly(IC)处理后，肌动蛋白和微管蛋白蛋白水平无显著变化。这些结果表明，Poly(IC)处理可下调IGF-I基因表达，并且由于IGF-I受体和结合蛋白水平的降低，C6细胞中IGF-I的生物利用度和作用也发生了改变。
