Bruening W, Pelletier J
Department of Biochemistry, McGill University, 3655 Drummond St., Montreal, Quebec H3G 1Y6, Canada.
J Biol Chem. 1996 Apr 12;271(15):8646-54. doi: 10.1074/jbc.271.15.8646.
The Wilms' tumor (WT) suppressor gene, WT1, is mutated in a small set of WTs and is essential for proper development of the urogenital system. The gene has three sites of transcriptional initiation and produces mRNA transcripts containing 5'-untranslated regions of more than 350 nucleotides. The mRNA, through two alternative splicing events, is predicted to direct the synthesis of four protein isoforms with molecular masses of 47-49 kDa. In this report, we identify and characterize novel WT1 protein isoforms having predicted molecular masses of 54-56 kDa. Mutational analysis of the murine wt1 mRNA demonstrates that the novel isoforms are the result of translation initiation at a CUG codon 204 bases upstream of and in frame with the initiator AUG. We show that these isoforms are present in both normal murine tissue and in WTs. Like WT1, the larger isoforms localize to the cell nucleus and are capable of mediating transcriptional repression. Our results indicate that regulation of WT1 gene expression is more complex than previously suspected and have important implications for normal and abnormal urogenital system development.
威尔姆斯瘤（WT）抑制基因WT1在一小部分WT中发生突变，对泌尿生殖系统的正常发育至关重要。该基因有三个转录起始位点，产生的mRNA转录本含有超过350个核苷酸的5'非翻译区。通过两次可变剪接事件，该mRNA预计可指导合成四种分子量为47 - 49 kDa的蛋白质异构体。在本报告中，我们鉴定并表征了预测分子量为54 - 56 kDa的新型WT1蛋白质异构体。对小鼠wt1 mRNA的突变分析表明，这些新型异构体是在起始AUG上游204个碱基处的CUG密码子起始翻译的结果，且与起始密码子读码框一致。我们发现这些异构体在正常小鼠组织和WT中均有存在。与WT1一样，较大的异构体定位于细胞核，并且能够介导转录抑制。我们的结果表明，WT1基因表达的调控比之前认为的更为复杂，对泌尿生殖系统的正常和异常发育具有重要意义。
