National Institute of Cancer Research, National Health Research Institutes, Tainan, Taiwan.
FEBS J. 2010 Oct;277(20):4308-21. doi: 10.1111/j.1742-4658.2010.07819.x. Epub 2010 Sep 16.
The c-myc promoter-binding protein-1 (MBP-1) is a transcriptional suppressor of tumorigenesis and thought to be the product of alternative translation initiation of the α-enolase (ENO1) transcript. In the present study, we cloned a 2552-bp novel cDNA with a putative coding sequence of MBP-1 and functionally examined its ability to encode the MBP-1 protein. Similarly to ENO1, the obtained MBP-1 was widely and differentially expressed in a variety of normal tissues and cancer cells. Experiments using MBP-1 promoter-driven luciferase reporter assays, biochemical cell fractionation followed by RT-PCR detection of the cytoplasmic mRNA, and transcription/translation-coupled reactions, consistently demonstrated that this novel transcript was alternatively transcribed from intron III of the ENO1 gene and was feasible for MBP-1 production. Hypoxia treatments significantly increased the transcriptional activation of the MBP-1 gene. Blocking the proteasomal degradation by MG132 stabilized the MBP-1 protein in cells. Compared with the translation efficiency for production of the MBP-1 protein, the MBP-1 transcript was 17.8 times more efficient than the ENO1 transcript. Thus, we suggest that this newly discovered transcript is a genuine template for the protein synthesis of MBP-1 in cells, and optimal expression of this gene in tumors may lead to effective clinical therapies for cancers.
c-myc 启动子结合蛋白-1(MBP-1)是一种肿瘤发生的转录抑制剂,被认为是 α-烯醇酶(ENO1)转录本选择性翻译起始的产物。在本研究中,我们克隆了一种 2552bp 的新型 cDNA,具有 MBP-1 的推定编码序列,并对其编码 MBP-1 蛋白的能力进行了功能检验。与 ENO1 相似,获得的 MBP-1 在各种正常组织和癌细胞中广泛且差异表达。使用 MBP-1 启动子驱动的荧光素酶报告基因检测、生物化学细胞分级分离后通过 RT-PCR 检测细胞质 mRNA 以及转录/翻译偶联反应的实验,一致表明这种新型转录本是从 ENO1 基因的内含子 III 选择性转录的,并且可行用于 MBP-1 的产生。缺氧处理显著增加了 MBP-1 基因的转录激活。用 MG132 阻断蛋白酶体降解可稳定细胞中的 MBP-1 蛋白。与产生 MBP-1 蛋白的翻译效率相比,MBP-1 转录本的效率比 ENO1 转录本高 17.8 倍。因此,我们认为这种新发现的转录本是细胞中 MBP-1 蛋白合成的真实模板,并且该基因在肿瘤中的最佳表达可能导致癌症的有效临床治疗。