Webb T E, Hughes A, Smalley D S, Spriggs K A
School of Pharmacy, University of Nottingham, Nottingham, UK.
Oncogenesis. 2015 Jan 26;4(1):e134. doi: 10.1038/oncsis.2014.43.
The expression of epidermal growth factor receptor (EGFR/ERBB1/HER1) is implicated in the progress of numerous cancers, a feature that has been exploited in the development of EGFR antibodies and EGFR tyrosine kinase inhibitors as anti-cancer drugs. However, EGFR also has important normal cellular functions, leading to serious side effects when EGFR is inhibited. One damaging characteristic of many oncogenes is the ability to be expressed in the hypoxic conditions associated with the tumour interior. It has previously been demonstrated that expression of EGFR is maintained in hypoxic conditions via an unknown mechanism of translational control, despite global translation rates generally being attenuated under hypoxic conditions. In this report, we demonstrate that the human EGFR 5' untranslated region (UTR) sequence can initiate the expression of a downstream open reading frame via an internal ribosome entry site (IRES). We show that this effect is not due to either cryptic promoter activity or splicing events. We have investigated the requirement of the EGFR IRES for eukaryotic initiation factor 4A (eIF4A), which is an RNA helicase responsible for processing RNA secondary structure as part of translation initiation. Treatment with hippuristanol (a potent inhibitor of eIF4A) caused a decrease in EGFR 5' UTR-driven reporter activity and also a reduction in EGFR protein level. Importantly, we show that expression of a reporter gene under the control of the EGFR IRES is maintained under hypoxic conditions despite a fall in global translation rates.
表皮生长因子受体（EGFR/ERBB1/HER1）的表达与多种癌症的进展有关，这一特性已被用于开发EGFR抗体和EGFR酪氨酸激酶抑制剂作为抗癌药物。然而，EGFR也具有重要的正常细胞功能，当EGFR被抑制时会导致严重的副作用。许多癌基因的一个有害特征是能够在与肿瘤内部相关的缺氧条件下表达。此前已经证明，尽管在缺氧条件下整体翻译速率通常会减弱，但EGFR的表达通过一种未知的翻译控制机制在缺氧条件下得以维持。在本报告中，我们证明人类EGFR 5'非翻译区（UTR）序列可以通过内部核糖体进入位点（IRES）启动下游开放阅读框的表达。我们表明这种效应不是由于隐秘的启动子活性或剪接事件。我们研究了EGFR IRES对真核起始因子4A（eIF4A）的需求，eIF4A是一种RNA解旋酶，负责处理RNA二级结构作为翻译起始的一部分。用马尿酸甾醇（一种有效的eIF4A抑制剂）处理导致EGFR 5'UTR驱动的报告基因活性降低，同时EGFR蛋白水平也降低。重要的是，我们表明尽管整体翻译速率下降，但在缺氧条件下，EGFR IRES控制下的报告基因的表达仍得以维持。
