Guan L S, Liu J J, Xu Y H, Wang Z Y
Department of Medicine, Beth Israel Deacones Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
Cancer Res. 1998 Sep 15;58(18):4180-4.
The Wilms' tumor suppressor gene, wt1, encodes a zinc-finger transcription factor, WT1, that represses transcription of a number of growth-promoting genes and inhibits cell growth. The transcripts of wt1 undergo two alternative splicing events, giving rise to four isoforms of mRNA in constant ratios. The first alternative splice introduces an extra exon 5, which encodes 17 amino acid residues inserted between the transcription regulatory domain and the DNA binding domain of WT1. Previously, we demonstrated that the 17-amino acid domain functioned as a transcription repressor when it was fused with the DNA binding domain of WT1. We have now identified a point mutation within exon 5 of wt1 in a sporadic unilateral Wilms' tumor patient. The mutation changes the last of the 17 amino acids from asparagine to serine. The protein isoform of WT1 carrying this mutation exhibited a 2-3-fold lower transcription-repressing activity than wild-type WT1 in transient cotransfection assays. The mutation also decreased growth-inhibiting activity of WT1 in two osteosarcoma cell lines, U2OS and Saos-2. By diminishing transcription-repressing and growth-inhibiting activities of WT1, this naturally occurring mutation within exon 5 of wt1 may disturb the normal function of the protein and lead to the uncontrolled cell growth characteristic of Wilms' tumor.
威尔姆斯瘤抑制基因wt1编码一种锌指转录因子WT1，它可抑制许多促进生长的基因的转录并抑制细胞生长。wt1的转录本经历两种可变剪接事件，以恒定比例产生四种mRNA异构体。第一次可变剪接引入了一个额外的外显子5，它编码插入WT1转录调节域和DNA结合域之间的17个氨基酸残基。此前，我们证明当这个17个氨基酸的结构域与WT1的DNA结合域融合时，它作为转录抑制因子发挥作用。我们现在在一名散发性单侧威尔姆斯瘤患者中鉴定出wt1外显子5内的一个点突变。该突变将17个氨基酸中的最后一个从天冬酰胺变为丝氨酸。在瞬时共转染实验中，携带此突变的WT1蛋白异构体的转录抑制活性比野生型WT1低2至3倍。该突变还降低了WT1在两种骨肉瘤细胞系U2OS和Saos-2中的生长抑制活性。通过减弱WT1的转录抑制和生长抑制活性，wt1外显子5内的这种自然发生的突变可能会扰乱该蛋白的正常功能，并导致威尔姆斯瘤特有的细胞生长失控。
