Xi Song, Zhao Ming, Wang Si, Ma Ling, Wang Shensen, Cong Xianling, Gjerset Ruth A, Fitzgerald Rebecca C, Huang Yinghui
College of Pharmaceutical Sciences, Jilin University, Changchun, China.
Torrey Pines Institute for Molecular Studies, San Diego CA, USA.
J Cancer. 2017 Apr 9;8(6):1082-1088. doi: 10.7150/jca.17457. eCollection 2017.
Internal ribosome entry sites (IRES elements) have attracted interest in cancer gene therapy because they can be used in the design of gene transfer vectors that provide bicistronic co-expression of two transgene products under the control of a single promoter. Unlike cellular translation of most mRNAs, a process that requires a post-translational 5' modification of the mRNA known as the cap structure, IRES-mediated translation is independent of the cap structure. The cellular conditions that may intervene to modulate IRES-mediated, cap-independent versus cap-dependent translation, however, remain poorly understood, although they could be critical to the choice of gene transfer vectors. Here we have compared the effects of the p14ARF (Alternate Reading Frame) tumor suppressor, a translational suppressor frequently overexpressed in cancer, on cap-dependent translation versus cap-independent translation from the EMCV viral IRES often used in bicistronic gene transfer vectors. We find that ectopic overexpression of p14ARF suppresses endogenous and ectopic cap-dependent protein translation, consistent with other studies. However, p14ARF has little or no effect on transgene translation initiated within an IRES element. This suggests that transgenes placed downstream of an IRES element will retain efficient translation of their gene products in the presence of high levels of ectopic or endogenous p14ARF, a finding that could be particularly relevant to therapeutic gene therapy strategies for cancer.
内部核糖体进入位点（IRES元件）在癌症基因治疗中引起了人们的兴趣，因为它们可用于设计基因转移载体，该载体能在单个启动子的控制下实现两个转基因产物的双顺反子共表达。与大多数mRNA的细胞翻译过程不同，后者需要对mRNA进行称为帽结构的翻译后5'修饰，而IRES介导的翻译独立于帽结构。然而，尽管这些细胞条件对于基因转移载体的选择可能至关重要，但目前对其如何干预以调节IRES介导的、不依赖帽结构与依赖帽结构的翻译过程仍知之甚少。在这里，我们比较了p14ARF（交替阅读框）肿瘤抑制因子（一种在癌症中经常过度表达的翻译抑制因子）对双顺反子基因转移载体中常用的EMCV病毒IRES的依赖帽结构翻译与不依赖帽结构翻译的影响。我们发现，与其他研究一致，p14ARF的异位过表达抑制内源性和异位的依赖帽结构的蛋白质翻译。然而，p14ARF对IRES元件内启动的转基因翻译几乎没有影响。这表明，在存在高水平的异位或内源性p14ARF的情况下，置于IRES元件下游的转基因将保留其基因产物的有效翻译，这一发现可能与癌症的治疗性基因治疗策略特别相关。
