ATF家族成員的上游開放閱讀框架(uORF)對於調控其轉譯作用之探討

Abstract

活化轉錄因子(ATF)家族成員為受壓力所誘導而表現的蛋白。活化轉錄因子牽涉細胞的增生、存活或細胞凋亡。它們的表現受到轉錄與轉譯層次上的調控，且可能在各種壓力的刺激下被誘導而表現。目前已知某些存在於活化轉錄因子的5端非轉譯區(5’ UTR)中的上游開放閱讀框架(uORF)為其下游本身開放閱讀框架(ORF)的轉譯調控者，但有許多此類元素仍未被知道其調控機制。在本篇研究中，吾人利用雙重螢光素酶報導基因檢驗(dual-luciferase reporter assay)以探討活化轉錄因子的上游開放閱讀框架所扮演的角色：我們發現並確認了它們在一般狀況下都會抑制下游自身的開放閱讀框架之轉譯作用；然而，上游開放閱讀框架的壓抑效力會受到特定的壓力信號刺激下而減弱。我們更進一步發現了活化轉錄因子間組成特徵相同的上游開放閱讀框架，會對同樣的壓力刺激有反應。此外，我們亦發現了在紫外線的照射下，有兩種不同的訊息傳遞路徑會影響到活化轉錄因子2的上游開放閱讀框架所調控的轉譯作用。

Members of the activating transcription factor (ATF) family are stress-induced proteins. ATFs are involved in cell proliferation, survival or apoptosis. Their expression is regulated at both transcriptional and translational levels and may be induced by diverse stress stimuli. Some upstream open reading frames (uORFs) in the 5’ untranslated region (5’ UTR) of the ATF mRNAs have been identified as translational regulators for their downstream open reading frames (ORFs), but the regulatory mechanisms for many of these elements remain unknown. In this thesis, I used dual- luciferase reporter assay to study the regulatory roles of uORFs on the translation of ATFs. All uORFs of ATFs repress downstream ORF translation under normal growth conditions. However, the repressive effect of uORFs can be relieved under specific stress signals. Some common features of uORFs between members of ATF family apparently respond to similar kinds of stress stimuli. On the other hand, our studies uncovered two different signaling pathways that mediate the uORFatf2-regulated translation under UV irradiation.