Koizumi S, Sone T, Otaki N, Kimura M
Biochem J. 1985 May 1;227(3):879-86. doi: 10.1042/bj2270879.
HeLa cells synthesize metallothioneins in response to Cd2+. The kinetics of thionein (apoprotein of metallothionein) synthesis was studied by pulse-labelling the cells with [35S]cysteine and measuring relative amounts of the labelled thioneins separated by electrophoresis. Thionein synthesis rapidly increases in the first 6-8 h after exposure to 0.5 micrograms of Cd2+/ml, and begins to decrease in a few hours after reaching the maximum. However, the rate of synthesis never returns to the basal value at least in 30 h after Cd2+ exposure; instead, the second increase in thionein synthesis occurs at 16-18 h. A possible regulatory mechanism of thionein synthesis is discussed from these results, together with the data on intracellular accumulation and subcellular distribution of 109Cd2+. The initial increase of thionein synthesis is accompanied by an increase of mRNA coding for thioneins (MT-mRNA). The induction of MT-mRNA is sensitive to Actinomycin D, but not to cycloheximide, suggesting transcriptional regulation without any mediating protein synthesis. Two thionein isomers are coded for by mRNA molecules of almost the same size, which is similar to that of hepatic MT-mRNA of mouse and rat.
HeLa细胞在镉离子（Cd2+）作用下合成金属硫蛋白。通过用[35S]半胱氨酸脉冲标记细胞并测量经电泳分离的标记硫蛋白的相对含量，研究了硫蛋白（金属硫蛋白的脱辅基蛋白）合成的动力学。在暴露于0.5微克/毫升Cd2+后的最初6 - 8小时内，硫蛋白合成迅速增加，并在达到最大值后的数小时内开始下降。然而，至少在Cd2+暴露后的30小时内，合成速率从未恢复到基础值；相反，硫蛋白合成的第二次增加发生在16 - 18小时。根据这些结果，结合关于109Cd2+在细胞内积累和亚细胞分布的数据，讨论了硫蛋白合成可能的调节机制。硫蛋白合成的最初增加伴随着编码硫蛋白的mRNA（MT - mRNA）的增加。MT - mRNA的诱导对放线菌素D敏感，但对环己酰亚胺不敏感，这表明是转录调控，无需任何介导的蛋白质合成。两种硫蛋白异构体由大小几乎相同的mRNA分子编码，这与小鼠和大鼠肝脏MT - mRNA的情况相似。
