Cress A E, Gerner E W
Biochem J. 1980 May 15;188(2):375-80. doi: 10.1042/bj1880375.
Ornithine decarboxylase activity increases at least 4-5-fold before DNA synthesis both in synchronous cycling cells and in quiescent cells stimulated to proliferate. The purpose of our experiments was to test whether the transient peaks of ornithine decarboxylase activity in both growth situations were biochemically regulated in a similar manner. We found that the regulation of this particular enzyme activity is distinct in two ways. Firstly, the addition of 2mm-hydroxyurea will block the induction of ornithine decarboxylase in continuously dividing Chinese-hamster ovary cells, while having no effect on ornithine decarboxylase induction in stimulated quiescent cells. Hydroxyurea added after the induction occurs has no effect on the enzyme activity. The apparent half-life of the enzyme is not altered in cells treated with hydroxyurea. Hydroxyurea does not affect the enzyme directly, since incubation of cell homogenates with this drug results in no loss of measurable ornithine decarboxylase activity and hydroxyurea does not markedly alter general RNA- or protein-synthesis rates. The inactivation of ornithine decarboxylase activity by hydroxyurea does not resemble the loss of activity observed with a 90min treatment with spermidine. Thiourea, a less potent inhibitor of ribonucleoside diphosphate reductase, will also inhibit ornithine decarboxylase activity, but to a lesser extent. Secondly, the expression of ornithine decarboxylase in quiescent cells stimulated to proliferate is biphasic as these cells traverse G(1) and enter S phase, whereas only one peak of activity is apparent in synchronous cycling G(1)-phase cells. The time interval between the first peak of ornithine decarboxylase activity and the onset of DNA synthesis is approx. 5h longer in non-dividing cells stimulated to proliferate than in continuously dividing cells. The results suggest that the regulation of ornithine decarboxylase activity is different in the two growth systems in that the induction of ornithine decarboxylase in continuously dividing cells occurs closer in time to DNA synthesis and is dependent on deoxyribonucleoside triphosphates.
在同步循环的细胞以及被刺激增殖的静止细胞中，鸟氨酸脱羧酶活性在DNA合成前至少增加4至5倍。我们实验的目的是测试在这两种生长情况下鸟氨酸脱羧酶活性的瞬时峰值是否以相似的方式受到生化调节。我们发现这种特定酶活性的调节在两个方面是不同的。首先，添加2mM羟基脲会阻断连续分裂的中国仓鼠卵巢细胞中鸟氨酸脱羧酶的诱导，而对被刺激的静止细胞中鸟氨酸脱羧酶的诱导没有影响。诱导发生后添加羟基脲对酶活性没有影响。在用羟基脲处理的细胞中，该酶的表观半衰期没有改变。羟基脲不会直接影响该酶，因为用这种药物孵育细胞匀浆不会导致可测量的鸟氨酸脱羧酶活性丧失，并且羟基脲不会显著改变总体RNA或蛋白质合成速率。羟基脲使鸟氨酸脱羧酶活性失活的方式与用亚精胺处理90分钟所观察到的活性丧失不同。硫脲是一种效力较弱的核糖核苷二磷酸还原酶抑制剂，也会抑制鸟氨酸脱羧酶活性，但程度较小。其次，被刺激增殖的静止细胞中鸟氨酸脱羧酶的表达是双相的，因为这些细胞穿过G1期并进入S期，而在同步循环的G1期细胞中只有一个活性峰值明显。在被刺激增殖的非分裂细胞中，鸟氨酸脱羧酶活性的第一个峰值与DNA合成开始之间的时间间隔比在连续分裂细胞中大约长5小时。结果表明，在这两种生长系统中鸟氨酸脱羧酶活性的调节是不同的，因为在连续分裂细胞中鸟氨酸脱羧酶的诱导在时间上更接近DNA合成，并且依赖于脱氧核糖核苷三磷酸。
