Defatta Robert J, De Benedetti Arrigo
Department of Biochemistry and Molecular Biology and the Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, LA 71130-3932, USA.
Int J Oncol. 2003 Dec;23(6):1709-13.
Overexpression of the translation initiation factor eIF4E results in transformation of normal fibroblasts as a single-hit oncogene. This implies that eIF4E must affect several pathways leading to transformation. The oncogenic potential of eIF4E is probably realized by elevating the translational efficiency of some oncogene and growth-promotion transcripts that are normally repressed by their 5'UTR (untranslated region). To address this possibility, we have cloned mRNAs whose polysomal representation increases upon overexpression of eIF4E. Among these mRNAs, we now report the isolation of a clone corresponding to the src-like kinase yes. The yes mRNA contains a long 5'UTR with characteristic features of a typical translationally repressed transcript. This was confirmed by analysis of the distribution of yes mRNA after sedimentation in sucrose gradients. Increased utilization of yes mRNA resulted in elevated expression of the protein product in cells transformed with eIF4E, and suggested that overexpression of Yes could contribute to eIF4E-mediated transformation. To test this, we monitored the malignant properties of MM3MG-4E cells after treatment with PP2, a specific inhibitor of src kinases. Growth in soft agar and saturation densities were significantly reduced after treatment with PP2, but treatment of mice harboring MM3MG-4E tumors with PP2 did not affect tumor growth. However, transformation of yes-null fibroblasts by eIF4E was significantly impaired.
翻译起始因子eIF4E的过表达作为一种单基因致癌基因可导致正常成纤维细胞发生转化。这意味着eIF4E必定影响多条导致转化的途径。eIF4E的致癌潜能可能是通过提高一些癌基因和生长促进转录本的翻译效率来实现的，这些转录本通常受其5'非翻译区（UTR）的抑制。为了探究这种可能性，我们克隆了一些mRNA，其在eIF4E过表达时多核糖体分布增加。在这些mRNA中，我们现在报告分离出一个与src样激酶yes对应的克隆。yes mRNA含有一个长的5'UTR，具有典型翻译抑制转录本的特征。通过蔗糖梯度沉降后对yes mRNA分布的分析证实了这一点。yes mRNA利用率的增加导致在eIF4E转化的细胞中蛋白质产物表达升高，这表明Yes的过表达可能有助于eIF4E介导的转化。为了验证这一点，我们在用src激酶的特异性抑制剂PP2处理后监测了MM3MG - 4E细胞的恶性特性。用PP2处理后，软琼脂中的生长和饱和密度显著降低，但用PP2处理携带MM3MG - 4E肿瘤的小鼠并未影响肿瘤生长。然而，eIF4E对yes基因缺失的成纤维细胞的转化显著受损。
