Ray R, Chakraborty B K, Ray K, Mukherji S, Chowdhury J R, Panda C K
Department of Biochemistry, Chittaranjan National Cancer Institute, Calcutta, India.
Mol Cell Biochem. 1996 Sep 6;162(1):75-82. doi: 10.1007/BF00250998.
In the present study, anthracycline antitumor antibiotics (e.g. adriamycin and nogalamycin), the potent RNA synthesis inhibitors and cycloheximide, the protein synthesis inhibitor, have been used to understand the events of biosynthesis and processing of major UsnRNAs (U1-U6). The anthracyclines inhibit the UsnRNAs biosynthesis (in terms of labelling) differentially in a dose dependent manner. The inhibitory effect of adriamycin and nogalamycin reached plateau at a concentration of 2.5 micrograms/ 10(6) cells/ml and 0.1 microgram/10(6) cells/ml respectively and indicates that nogalamycin is more inhibitory than adriamycin. The inhibition of the UsnRNAs synthesis (in terms of labelling) became maximum within 30 min of incubation and remained unaltered even after 2 h. Thus, it shows that the anthracyclines preferentially inhibit the initiation of the UsnRNA genes' transcription as it has been seen in cases of other large RNAs' synthesis by some other laboratories. The higher inhibitory effect of the anthracyclines on the biosynthesis of U5 and U6 compared to other UsnRNAs indicates the presence of more binding sites on the U5 and U6 snRNA genes. In presence of the anthracyclines, there was high retention of cytoplasmic major pre-UsnRNAs/ UsnRNAs which indicates that the elongation of the UsnRNA synthesis is probably impaired along with initiation; because for the proper processing of the pre-UsnRNAs, formation of the correct secondary structure of that pre-UsnRNA is necessary. Cycloheximide showed some differential effect on the pol II transcribed UsnRNAs (U1-U5) biosynthesis (in terms of labelling) however it has no effect on the pol III transcribed U6 snRNA. It implies that in the pol II transcribed UsnRNAs, some transacting labile factors, either activator or inhibitor, are involved. Whereas, the processing of the UsnRNAs (either pol II or pol III transcribed) was affected more or less in a similar fashion in presence of cycloheximide, indicating the involvement of some transacting labile factors in this event.
在本研究中，使用了蒽环类抗肿瘤抗生素（如阿霉素和诺加霉素），它们是强效的RNA合成抑制剂，以及环己酰亚胺，一种蛋白质合成抑制剂，以了解主要U小核RNA（U1 - U6）的生物合成和加工过程。蒽环类药物以剂量依赖的方式对U小核RNA的生物合成（就标记而言）有不同程度的抑制作用。阿霉素和诺加霉素的抑制作用分别在浓度为2.5微克/10⁶细胞/毫升和0.1微克/10⁶细胞/毫升时达到平台期，这表明诺加霉素的抑制作用比阿霉素更强。U小核RNA合成（就标记而言）的抑制在孵育30分钟内达到最大，即使在2小时后也保持不变。因此，这表明蒽环类药物优先抑制U小核RNA基因转录的起始，正如其他一些实验室在其他大RNA合成的情况中所观察到的那样。与其他U小核RNA相比，蒽环类药物对U5和U6生物合成的抑制作用更强，这表明U5和U6小核仁RNA基因上存在更多的结合位点。在存在蒽环类药物的情况下，细胞质中的主要前体U小核RNA/U小核RNA有高度滞留现象，这表明U小核RNA合成的延伸可能与起始一起受到损害；因为对于前体U小核RNA的正确加工，该前体U小核RNA形成正确的二级结构是必要的。环己酰亚胺对RNA聚合酶II转录的U小核RNA（U1 - U5）的生物合成（就标记而言）显示出一些不同的影响，然而它对RNA聚合酶III转录的U6小核RNA没有影响。这意味着在RNA聚合酶II转录的U小核RNA中，涉及一些反式作用的不稳定因子，无论是激活剂还是抑制剂。而在存在环己酰亚胺的情况下，U小核RNA（无论是RNA聚合酶II还是RNA聚合酶III转录的）的加工或多或少以类似的方式受到影响，这表明在这一过程中涉及一些反式作用的不稳定因子。
