Heimer R, Sartorelli A C
Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510.
Cancer Commun. 1990;2(1):45-53. doi: 10.3727/095535490820874759.
RNA synthesis in K-562 human erythroleukemia cells was markedly curtailed by exposure to the uridine analogue 5-fluorouridine (FUrd). The inhibition of ribosomal RNA synthesis was accompanied by rapid declines in the steady-state levels of several, but not all, mRNAs, including gamma-globin mRNA. In this report, we demonstrate that gamma-globin mRNA species were decreased by as much as 40% within 2 hr of exposure to micromolar concentrations of FUrd. The decline in gamma-globin mRNA occurred at a rate that outstripped the normal rate of degradation of this mRNA by a factor of 25. The decline in cytoplasmic mRNA was not mirrored in the nucleus; northern blotting revealed that pre-mRNA levels were not reduced. Nuclease protection analyses of precursors from FUrd treated and untreated control cells did not reveal any qualitative differences. Thus, the decrease was not accounted for by drug-induced inhibition of new gamma-globin mRNA synthesis or misincorporation but must have been due to an FUrd-induced increase in gamma-globin mRNA degradation. Drug-induced instability of RNA was not a generalized feature of FUrd exposure, since neither beta-actin mRNA nor cytoplasmic rRNA, whose stabilities in untreated cells are similar to that of gamma-globin mRNA, were affected. Furthermore, the instability of gamma-globin mRNA did not decrease globin protein levels, presumably because the stability of the protein was not altered. The mechanism by which specific increased degradation of gamma-globin mRNA occurred is unknown, but it may have been due to the activation of cytoplasmic endonuclease.
K-562人红白血病细胞中的RNA合成在暴露于尿苷类似物5-氟尿苷（FUrd）后显著减少。核糖体RNA合成的抑制伴随着几种（但不是所有）mRNA稳态水平的迅速下降，包括γ-珠蛋白mRNA。在本报告中，我们证明，在暴露于微摩尔浓度的FUrd后2小时内，γ-珠蛋白mRNA种类减少了多达40%。γ-珠蛋白mRNA的下降速度超过了该mRNA正常降解速度的25倍。细胞质mRNA的下降在细胞核中并未体现；Northern印迹显示前体mRNA水平未降低。对FUrd处理和未处理的对照细胞前体的核酸酶保护分析未发现任何定性差异。因此，这种下降不是由药物诱导的新γ-珠蛋白mRNA合成抑制或错误掺入引起的，而一定是由于FUrd诱导的γ-珠蛋白mRNA降解增加。药物诱导的RNA不稳定性不是FUrd暴露的普遍特征，因为在未处理细胞中稳定性与γ-珠蛋白mRNA相似的β-肌动蛋白mRNA和细胞质rRNA均未受到影响。此外，γ-珠蛋白mRNA的不稳定性并未降低珠蛋白水平，推测是因为蛋白质的稳定性未改变。γ-珠蛋白mRNA特异性降解增加发生的机制尚不清楚，但可能是由于细胞质核酸内切酶的激活。
