Pyronnet S, Vagner S, Bouisson M, Prats A C, Vaysse N, Pradayrol L
INSERM U151, Laboratoire de Biologie et Pathologie Digestive, Centre Hospitalier Universitaire, Rangueil, Toulouse, France.
Cancer Res. 1996 Apr 15;56(8):1742-5.
The ornithine decarboxylase enzyme (ODC) is the key regulator of polyamine synthesis and is a member of the cellular proto-oncogene family. Its expression becomes constitutively activated by carcinogens, viruses, and oncogenes. ODC mRNA has a long 5' untranslated region that could be important in the regulation of enzyme levels by affecting translation. To test this hypothesis, we have determined the role of this region on the constitutive ODC hyperexpression measured in AR4-2J cells, an azaserine-induced, tumor-derived pancreatic acinar cell line. Construction of expression vectors in which ODC 5' leader sequence was placed flanking the chloramphenicol acetyltransferase reporter gene allowed us to identify three AR4-2J specific, different alternatively spliced ODC 5' leaders. The 5' ends of exons 2 and 3 were lengthened by 17 and 13 bases, respectively. Translation performed in a cell-free system as well as in COS7 transient transfection experiments demonstrated that AR4-2J isoforms induce a strong increase in the rate of translation. These results provide evidence that alternative splicing observed in tumoral cells, coupled with translation regulation, relieves the translation repression mediated by the long and structured 5' untranslated region of the ODC proto-oncogene.
鸟氨酸脱羧酶（ODC）是多胺合成的关键调节因子，属于细胞原癌基因家族成员。其表达会被致癌物、病毒和癌基因持续激活。ODC mRNA有一个较长的5'非翻译区，可能通过影响翻译在酶水平调节中起重要作用。为验证这一假设，我们确定了该区域在AR4-2J细胞（一种氮杂丝氨酸诱导的肿瘤来源胰腺腺泡细胞系）中组成性ODC高表达中的作用。构建ODC 5'前导序列位于氯霉素乙酰转移酶报告基因两侧的表达载体，使我们能够鉴定出三种AR4-2J特异性、不同的可变剪接ODC 5'前导序列。外显子2和3的5'端分别延长了17个和13个碱基。在无细胞系统以及COS7瞬时转染实验中进行的翻译表明，AR4-2J异构体可使翻译速率大幅提高。这些结果证明，肿瘤细胞中观察到的可变剪接与翻译调控相结合，可解除由ODC原癌基因长且结构复杂的5'非翻译区介导的翻译抑制。
