Panagiotidis C A, Huang S C, Canellakis E S
Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510, USA.
Int J Biochem Cell Biol. 1995 Feb;27(2):157-68. doi: 10.1016/1357-2725(94)00068-m.
Polyamine biosynthesis in Escherichia coli is regulated transcriptionally and post-translationally. Antizyme and ribosomal proteins S20 and L34 participate in post-translational inhibition of the polyamine biosynthetic enzymes ornithine and arginine decarboxylase. The aim of the present study was to investigate the significance of S20 and L34 in polyamine regulation in vivo. In vivo overexpression of S20 and L34 lowered the activities of ornithine and arginine decarboxylases and decreased total polyamine production. The levels of cadaverine, a related diamine whose synthesis is not regulated by S20 and L34, did not decrease but increased. The diminished ornithine and arginine decarboxylase activities are shown to result from reversible post-translational inhibition since the enzymes could be reactivated to normal levels upon titration of the inhibitors. The effects were specific as overexpression of eight other ribosomal proteins had no influence. Overexpression of ornithine decarboxylase results in elevated polyamine production and it increases S20 and L34 levels but not those of other ribosomal proteins. Ornithine depletion decreases S20 and L34 to normal levels in the ornithine decarboxylase overproducing cells. Immunoprecipitation experiments coupled with immunoblots indicated that ornithine and arginine decarboxylases physically interact with S20 and L34. This study shows that ribosomal proteins S20 and L34 can inhibit ornithine and arginine decarboxylases and polyamine biosynthesis in vivo. It is concluded that, unlike other basic ribosomal proteins and polycationic compounds which inhibit the activities of these enzymes only in vitro, S20 and L34 are biologically relevant in the regulation of the polyamine biosynthetic pathway.
大肠杆菌中的多胺生物合成在转录和翻译后水平受到调控。抗酶以及核糖体蛋白S20和L34参与对多胺生物合成酶鸟氨酸脱羧酶和精氨酸脱羧酶的翻译后抑制。本研究的目的是探究S20和L34在体内多胺调控中的意义。在体内过表达S20和L34会降低鸟氨酸脱羧酶和精氨酸脱羧酶的活性，并减少多胺的总产量。尸胺是一种相关的二胺，其合成不受S20和L34调控，其水平并未降低反而升高。鸟氨酸脱羧酶和精氨酸脱羧酶活性的降低被证明是由可逆的翻译后抑制导致的，因为在滴定抑制剂后这些酶能够重新激活至正常水平。这些效应具有特异性，因为过表达其他八种核糖体蛋白没有影响。过表达鸟氨酸脱羧酶会导致多胺产量增加，并且会提高S20和L34的水平，但不会提高其他核糖体蛋白的水平。在鸟氨酸脱羧酶过量产生的细胞中，鸟氨酸耗尽会使S20和L34降至正常水平。免疫沉淀实验结合免疫印迹表明，鸟氨酸脱羧酶和精氨酸脱羧酶与S20和L34存在物理相互作用。本研究表明，核糖体蛋白S20和L34能够在体内抑制鸟氨酸脱羧酶和精氨酸脱羧酶以及多胺生物合成。得出的结论是，与其他仅在体外抑制这些酶活性的碱性核糖体蛋白和聚阳离子化合物不同，S20和L34在多胺生物合成途径的调控中具有生物学相关性。
