Ghoshal K, Jacob S T
Department of Pharmacology and Molecular Biology, The Chicago Medical School, North Chicago, IL 60064, USA.
Biochem Pharmacol. 1997 Jun 1;53(11):1569-75. doi: 10.1016/s0006-2952(97)00040-3.
It is assumed that the primary mode of action of 5-fluorouracil (5-FUra) is mediated via inhibition of thymidylate synthetase. Persistent inhibition of cellular proliferation after treatment of the 5-FUra-inhibited cells with exogenous thymidine do not support the notion that the anti-proliferitive action of 5-FUra is due exclusively to inhibition of DNA replication. Our studies have revealed an alternative mechanism of action at the level of pre-ribosomal RNA (pre-rRNA) processing. Pre-rRNA processing was inhibited completely in vitro as well as in S-100 extract from the mouse lymphosarcoma P1798 cells that were treated with 5-FUra. Under this condition, the 5-FUra-substituted pre-rRNA substrate was processed efficiently at the primary processing site. This study showed that the activity and/or the synthesis of a factor potentially involved in pre-rRNA processing is blocked in cells treated with the fluoropyrimidine. UV-cross-linking study showed that a 200 kDa polypeptide designated ribosomal RNA binding protein (RRBP) was absent in the S-100 extract from the drug-treated mouse lymphosarcoma cells. Since a polypeptide that cross-links to a processing site on RNA is usually involved in the RNA processing, RRBP may have a direct role in pre-rRNA processing. A key molecular mechanism far the antiproliferative action of 5-FUra may be due to its interference with the activity and/or synthesis of RRBP. Exposure of cells to 5-FUra did not inhibit the interaction between U3 small nucleolar RNA (snoRNA) and pre-rRNA at the primary processing site (a key step in the processing reaction) and the formation of U3 small nucleolar ribonucleoprotein (snoRNP). Treatment of cells with the fluoropyrimidine did not block the 3' end processing of pre-messenger RNA (pre-mRNA). This article also discusses the effects of 5-FUra on pre-mRNA splicing and mRNA translation, and proposes other avenues of research to explore further the mechanism of action of this important pyrimidine analog.
假定5-氟尿嘧啶（5-FUra）的主要作用方式是通过抑制胸苷酸合成酶介导的。用外源性胸苷处理5-FUra抑制的细胞后，细胞增殖的持续抑制并不支持5-FUra的抗增殖作用完全归因于抑制DNA复制这一观点。我们的研究揭示了在核糖体前体RNA（pre-rRNA）加工水平上的另一种作用机制。在体外以及在用5-FUra处理的小鼠淋巴肉瘤P1798细胞的S-100提取物中，pre-rRNA加工被完全抑制。在这种情况下，5-FUra取代的pre-rRNA底物在初级加工位点被有效加工。这项研究表明，在用氟嘧啶处理的细胞中，可能参与pre-rRNA加工的一种因子的活性和/或合成被阻断。紫外线交联研究表明，在用药物处理的小鼠淋巴肉瘤细胞的S-100提取物中，不存在一种名为核糖体RNA结合蛋白（RRBP）的200 kDa多肽。由于与RNA上加工位点交联的多肽通常参与RNA加工，RRBP可能在pre-rRNA加工中具有直接作用。5-FUra抗增殖作用的一个关键分子机制可能是由于其干扰了RRBP的活性和/或合成。细胞暴露于5-FUra并不抑制U3小核仁RNA（snoRNA）与初级加工位点（加工反应中的关键步骤）的pre-rRNA之间的相互作用以及U3小核仁核糖核蛋白（snoRNP）的形成。用氟嘧啶处理细胞并不阻断信使核糖核酸前体（pre-mRNA）的3'末端加工。本文还讨论了5-FUra对pre-mRNA剪接和mRNA翻译的影响，并提出了其他研究途径，以进一步探索这种重要嘧啶类似物的作用机制。
