Ghoshal K, Jacob S T
Department of Pharmacology and Molecular Biology, Chicago Medical School, North Chicago, Illinois 60064.
Cancer Res. 1994 Feb 1;54(3):632-6.
To elucidate the molecular mechanism by which the potent anticancer drug, 5-fluorouracil (5-FUra), inhibits cell proliferation, the effect of its metabolite, 5-fluorouridine triphosphate, on transcription of rat rRNA gene and processing of pre-rRNA was investigated in S-100 extract from the mouse lymphosarcoma cells. The in vitro processing of pre-rRNA substrate synthesized from the T3 promoter occurred at the correct primary processing site. Replacement of UMP with 5-fluorouridine monophosphate in the rRNA substrate did not affect the pre-rRNA processing. Similar result was obtained when coupled transcription-processing was studied. When the coupled reaction was examined using extracts from the cells treated with 5-FUra, rRNA processing was abolished whereas transcription of rRNA gene was unaffected. Treatment of cells with thymidine along with 5-FUra did not reverse the inhibitory effect of the drug on rRNA processing. In contrast to the effect on rRNA processing, treatment of cells with 5-FUra did not impede the 3' end processing of pre-mRNA. These data show that inhibition of pre-rRNA processing is a major mechanism of action of 5-FUra and suggest that the activity and/or synthesis of a trans-acting factor(s) involved in this reaction is altered by the anticancer drug.
为阐明强效抗癌药物5-氟尿嘧啶（5-FUra）抑制细胞增殖的分子机制，研究了其代谢产物5-氟尿苷三磷酸对小鼠淋巴肉瘤细胞S-100提取物中大鼠rRNA基因转录和前体rRNA加工的影响。从T3启动子合成的前体rRNA底物的体外加工发生在正确的初级加工位点。在rRNA底物中用5-氟尿苷单磷酸替代UMP不影响前体rRNA加工。研究偶联转录-加工时也得到了类似结果。当使用经5-FUra处理的细胞提取物检测偶联反应时，rRNA加工被消除，而rRNA基因转录未受影响。用胸苷与5-FUra一起处理细胞并不能逆转该药物对rRNA加工的抑制作用。与对rRNA加工的影响相反，用5-FUra处理细胞并不妨碍前体mRNA的3'端加工。这些数据表明，抑制前体rRNA加工是5-FUra的主要作用机制，并提示参与该反应的反式作用因子的活性和/或合成被抗癌药物改变。
