Human ribosomal protein L13a is dispensable for canonical ribosome function but indispensable for efficient rRNA methylation
Human ribosomal protein L13a is dispensable for canonical ribosome function but indispensable for efficient rRNA methylation
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DOI：
10.1261/rna.694007
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发表时间：
2007-12-01
期刊：
影响因子：
4.5
通讯作者：
Mazumder, Barsanjit
中科院分区：
文献类型：
--
作者：
Chaudhuri, Sujan;Vyas, Keyur;Mazumder, Barsanjit
先前，我们证明了用干扰素 -γ处理单核细胞会导致核糖体蛋白L13a从60S核糖体释放，进而使铜蓝蛋白（Cp）mRNA发生翻译沉默。在此，利用培养细胞获得的证据表明，Cp mRNA沉默依赖于L13a，并且缺乏L13a的核糖体具有整体翻译活性。人类单核细胞U937细胞用针对L13a的两种不同的短发夹RNA（shRNA）序列进行稳定转染，并通过克隆筛选使总L13a表达降低超过98%。对这些细胞进行代谢标记显示，Cp翻译从干扰素 -γ介导的翻译沉默活性中得到恢复。L13a的缺失导致核糖体RNA甲基化以及由p27、p53和SNAT2 mRNA衍生的内部核糖体进入位点（IRES）元件介导的不依赖帽子结构的翻译显著减少。然而，在缺乏L13a的细胞和野生型对照细胞之间，在核糖体RNA加工、多聚核糖体形成、整体翻译活性、翻译保真度和细胞增殖方面未观察到显著差异。这些结果支持这样一种观点，即核糖体可作为一个储存库，储存与其基础多肽合成功能无关的可释放的翻译调节因子。与哺乳动物细胞不同，酵母中的L13a同源物对生长是必不可少的。因此，L13a可能从低等真核生物中的一种必需的核糖体蛋白进化为在高等真核生物中具有一种可有可无的核外功能。
Previously, we demonstrated that treatment of monocytic cells with IFN-gamma causes release of ribosomal protein L13a from the 60S ribosome and subsequent translational silencing of Ceruloplasmin (Cp) mRNA. Here, evidence using cultured cells demonstrates that Cp mRNA silencing is dependent on L13a and that L13a-deficient ribosomes are competent for global translational activity. Human monocytic U937 cells were stably transfected with two different shRNA sequences for L13a and clonally selected for more than 98% abrogation of total L13a expression. Metabolic labeling of these cells showed rescue of Cp translation from the IFN-gamma mediated translational silencing activity. Depletion of L13a caused significant reduction of methylation of ribosomal RNA and of cap-independent translation mediated by Internal Ribosome Entry Site (IRES) elements derived from p27, p53, and SNAT2 mRNAs. However, no significant differences in the ribosomal RNA processing, polysome formation, global translational activity, translational fidelity, and cell proliferation were observed between L13a-deficient and wild-type control cells. These results support the notion that ribosome can serve as a depot for releasable translation-regulatory factors unrelated to its basal polypeptide synthetic function. Unlike mammalian cells, the L13a homolog in yeast is indispensable for growth. Thus, L13a may have evolved from an essential ribosomal protein in lower eukaryotes to having a role as a dispensable extra-ribosomal function in higher eukaryotes.