實驗室先前的研究發現，大腸直腸癌細胞在EGF刺激之下會透過轉譯調控增加Aurora-A 蛋白的表現(Journal of Cellular and Molecular Medicine 2010; 14(6B): 1520-1531)。本論文進一步去分析Aurora-A 五端非轉譯區(5’untranslated region, 5’UTR)的轉譯調控機制。實驗室先前透過RNA immunoprecipitation (RNA- IP)並結合蛋白質體分析，發現RNA結合蛋白hnRNP Q1會結合上Aurora-A mRNA五端非轉譯區，且會增加Aurora-A mRNA 的轉譯能力。透過 in vivo translational assay發現，無論是在Cap-dependent 或是 Cap- independent的核醣體結合區(internal ribosome entry sites, IRESs)， hnRNP Q1皆能顯著性的增加Aurora-A mRNA轉譯調控的效率。有趣的是，Aurora-A mRNA五端非轉譯區的IRES轉譯活性是有細胞週期依賴性的，而Cap-dependent的轉譯活性則無此現象。此外，透過建立hnRNP Q1上與Aurora-A mRNA結合位缺失的片段，發現其對於Aurora-A mRNA的轉譯調控能力相對於完整的hnRNP Q1有降低的情形，證明hnRNP Q1與Aurora-A mRNA的結合對於其轉譯調控是必要的。另一方面，hnRNP A2/B1是另一個會與Aurora-A mRNA五端非轉譯區結合的RNA 結合蛋白。實驗結果發現，hnRNP A2/B1對於Aurora-A mRNA的轉譯調控作用是抑制性的，且同樣有調控IRES轉譯活性及細胞週期依賴性的情形。進一步分析Aurora-A mRNA 3’UTR是否有參與其轉譯調控，結果顯示hnRNP Q1對於Aurora-A mRNA 3’UTR沒有影響。綜合以上結果，本研究得知hnRNP Q1和 hnRNPA2/B1是兩個重要的Aurora-A 5’UTRs轉譯調控因子，並且參與具有Aurora-A mRNA IRES的轉譯調控和細胞週期依賴性的表現。

By RNA immunoprecipitation (IP) followed by proteomic analysis, we found that the RNA-binding protein hnRNP Q1 was a potential trans-acting factor for translational regulating of Aurora-A mRNA. In vivo translation assay demonstrated that hnRNP Q1 increased the translational efficiency of Aurora-A mRNA in both Cap-dependent and Cap-independent manners. The Aurora-A 5’-UTR-binding domain of hnRNP Q1 was verified and the effect of Aurora-A mRNA translational regulation was under investigation. Interestingly, our results suggested that the IRES activity of Aurora-A mRNA 5’UTR, but not the Cap-dependent translational activity, was under cell-cycle regulated. In addition to hnRNP Q1, another potential RNA binding protein hnRNP A2/B1 was also found to be involved in regulating the translation of Aurora-A mRNA. HnRNP A2/B1 was also involved in the IRES- and cell cycle-dependent regulatory manner of Aurora-A mRNA. Our re sults suggest that hnRNP Q1 and hnRNPA2/B1 are two important regulatory factors that bind with Aurora-A 5’UTRs and regulate the translational efficiency of Aurora-A mRNA.

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