Bai G, Nichols R A, Weiss B
Department of Pharmacology, Medical College of Pennsylvania, Philadelphia 19129.
Biochim Biophys Acta. 1992 Mar 24;1130(2):189-96. doi: 10.1016/0167-4781(92)90527-7.
Calmodulin is encoded by three genes in rat tissues, which collectively transcribe five different mRNAs. We showed previously that the pheochromocytoma cell line, PC12, expresses all five of these mRNAs and that treating PC12 cells with nerve growth factor differentially induces the calmodulin mRNAs; the greatest increase was seen by 24 h in the 1.4 kb transcript from calmodulin gene II. In the present study we found that treating PC12 cells with dibutyryl cyclic AMP also differentially increased the levels of the calmodulin mRNAs. However, dibutyryl cyclic AMP produced increases as early as 3 to 6 h, with the greatest increase (about 3-fold) being seen in the level of the 1.7 kb mRNA transcribed from calmodulin gene I. The transcripts of 4.1 kb (calmodulin gene I) and 1.4 kb (calmodulin gene II) were also increased, but the 2.3 kb transcript from calmodulin gene III remained stable. Another cyclic AMP analogue, chlorophenylthio cyclic AMP, produced effects similar to those of dibutyryl cyclic AMP, but dibutyryl cyclic GMP did not. Pretreatment with cycloheximide blocked the increase in the 4.1 kb calmodulin mRNA induced by dibutyryl cyclic AMP, but only partially blocked the increase in the 1.4 kb and 1.7 kb transcripts. Phorbol 12-myristate 13-acetate, which can induce some cyclic AMP responsive genes, failed to significantly change the levels of any of the calmodulin mRNAs. These studies show that, like nerve growth factor, cyclic AMP can selectively up-regulate the transcripts from calmodulin genes in PC12 cells, but the time-course and type of transcripts induced by cyclic AMP are distinct. These results suggest that the mechanisms by which these two agents alter the calmodulin transcripts are different.
钙调蛋白在大鼠组织中由三个基因编码，这些基因共同转录出五种不同的mRNA。我们先前表明，嗜铬细胞瘤细胞系PC12表达所有这五种mRNA，并且用神经生长因子处理PC12细胞会差异性地诱导钙调蛋白mRNA；在24小时时，钙调蛋白基因II的1.4 kb转录本增加最为显著。在本研究中，我们发现用二丁酰环磷酸腺苷处理PC12细胞也会差异性地增加钙调蛋白mRNA的水平。然而，二丁酰环磷酸腺苷早在3至6小时就会产生增加，钙调蛋白基因I转录的1.7 kb mRNA水平增加最为显著（约3倍）。4.1 kb（钙调蛋白基因I）和1.4 kb（钙调蛋白基因II）的转录本也增加了，但钙调蛋白基因III的2.3 kb转录本保持稳定。另一种环磷酸腺苷类似物，氯苯硫基环磷酸腺苷，产生的效果与二丁酰环磷酸腺苷相似，但二丁酰环磷酸鸟苷则没有。用环己酰亚胺预处理可阻断二丁酰环磷酸腺苷诱导的4.1 kb钙调蛋白mRNA的增加，但仅部分阻断1.4 kb和1.7 kb转录本的增加。佛波酯12 -肉豆蔻酸酯13 -乙酸酯可诱导一些环磷酸腺苷反应性基因，但未能显著改变任何一种钙调蛋白mRNA的水平。这些研究表明，与神经生长因子一样，环磷酸腺苷可以选择性地上调PC12细胞中钙调蛋白基因的转录本，但环磷酸腺苷诱导的转录本的时间进程和类型是不同的。这些结果表明，这两种物质改变钙调蛋白转录本的机制是不同的。
