Graduate Study in Comparative Biochemistry, University of California, Berkeley, California 94720, USA.
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.
RNA. 2019 Oct;25(10):1324-1336. doi: 10.1261/rna.070193.118. Epub 2019 Jul 1.
Polypyrimidine tract-binding proteins (PTBPs) are RNA binding proteins that regulate a number of posttranscriptional events. Human PTBP1 transits between the nucleus and cytoplasm and is thought to regulate RNA processes in both. However, information about mRNA isoforms and regulation of PTPB1 expression remains incomplete. Here we mapped the major mRNA isoforms in HEK293T cells and identified alternative 5' and 3' untranslated regions (5'-UTRs, 3'-UTRs), as well as alternative splicing patterns in the protein coding region. We also assessed how the observed mRNA isoforms contribute to PTBP1 expression in different phases of the cell cycle. Previously, mRNAs were shown to crosslink to eukaryotic translation initiation factor 3 (eIF3). We find that eIF3 binds differently to each mRNA isoform in a cell cycle dependent manner. We also observe a strong correlation between eIF3 binding to mRNAs and repression of PTBP1 levels during the S phase of the cell cycle. Our results provide evidence of translational regulation of PTBP1 protein levels during the cell cycle, which may affect downstream regulation of alternative splicing and translation mediated by PTBP1 protein isoforms.
多嘧啶 tract 结合蛋白（PTBPs）是调节许多转录后事件的 RNA 结合蛋白。人 PTBP1 在核和细胞质之间穿梭，被认为在两者中都调节 RNA 过程。然而，关于 mRNA 同工型和 PTPB1 表达的调节信息仍然不完整。在这里，我们绘制了 HEK293T 细胞中的主要 mRNA 同工型，并鉴定了替代的 5'和 3'非翻译区（5'-UTR，3'-UTR），以及蛋白编码区的选择性剪接模式。我们还评估了观察到的 mRNA 同工型如何在细胞周期的不同阶段贡献于 PTBP1 的表达。先前已经表明，mRNA 与真核翻译起始因子 3（eIF3）交联。我们发现 eIF3 以细胞周期依赖性的方式与每个 mRNA 同工型不同地结合。我们还观察到 eIF3 与 mRNAs 的结合与细胞周期 S 期 PTBP1 水平的抑制之间存在很强的相关性。我们的结果提供了在细胞周期中 PTBP1 蛋白水平的翻译调节的证据，这可能会影响由 PTBP1 蛋白同工型介导的选择性剪接和翻译的下游调节。
