Department of Pathology and Brain Korea 21 PLUS Projects for Medical Science, Yonsei University College of Medicine, Seoul, 03722, Republic of Korea.
Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA.
Sci Rep. 2017 Nov 20;7(1):15833. doi: 10.1038/s41598-017-16177-9.
mRNAs containing premature termination codons (PTCs) are rapidly degraded through nonsense-mediated mRNA decay (NMD). However, some PTC-containing mRNAs evade NMD, and might generate mutant proteins responsible for various diseases, including cancers. Using PTC-containing human genomic β-globin constructs, we show that a fraction (~30%) of PTC-containing mRNAs expressed from NMD-competent PTC-containing constructs were as stable as their PTC-free counterparts in a steady state. These PTC-containing mRNAs were monosome-enriched and rarely contributed to expression of mutant proteins. Expression of trace amounts of mutant proteins from NMD-competent PTC-containing constructs was not affected by inhibition of eIF4E-dependent translation and such expression was dependent on a continuous influx of newly synthesized PTC-containing mRNAs, indicating that truncated mutant proteins originated primarily in the pioneer round of translation. The generation of mutant proteins was promoted by UPF1 depletion, which induced polysome association of PTC-containing mRNAs, increased eIF4E-bound PTC-containing mRNA levels, and subsequent eIF4E-dependent translation. Our findings suggest that PTC-containing mRNAs are potent and regulatable sources of mutant protein generation.
含有过早终止密码子（PTCs）的 mRNAs 通过无意义介导的 mRNA 降解（NMD）迅速降解。然而，一些含有 PTC 的 mRNAs 逃避了 NMD，并可能产生导致各种疾病（包括癌症）的突变蛋白。使用含有 PTC 的人类基因组 β-珠蛋白构建体，我们表明，在稳态下，从具有 NMD 能力的含有 PTC 的构建体表达的含有 PTC 的 mRNAs 的一部分（约 30%）与无 PTC 的对应物一样稳定。这些含有 PTC 的 mRNAs 富含单核糖体，很少有助于突变蛋白的表达。痕量突变蛋白的表达不受抑制 eIF4E 依赖性翻译的影响，并且这种表达依赖于新合成的含有 PTC 的 mRNAs 的持续流入，表明截短的突变蛋白主要源自翻译的先锋轮。UPF1 耗竭促进了突变蛋白的产生，这诱导了含有 PTC 的 mRNAs 与多核糖体的关联，增加了 eIF4E 结合的含有 PTC 的 mRNA 水平，以及随后的 eIF4E 依赖性翻译。我们的研究结果表明，含有 PTC 的 mRNAs 是产生突变蛋白的有效且可调节的来源。
