Law D J, Du M, Law G L, Merchant J L
Department of Internal Medicine, Department of Physiology, University of Michigan, Michigan, Ann Arbor 48109-0650, USA.
Biochem Biophys Res Commun. 1999 Aug 19;262(1):113-20. doi: 10.1006/bbrc.1999.1180.
Among transcription factors that regulate ornithine decarboxylase (ODC) gene expression are those that interact with GC-rich promoters, including Sp1 and ZBP-89. Sp1 functions as a transactivator and ZBP-89 as a transrepressor of both the ODC and gastrin promoters. This study reports the cloning and characterization of a second member of the ZBP family that also binds GC boxes. ZBP-99 contains four Krüppel-type zinc fingers that collectively share 91% amino acid sequence similarity and 79% sequence identity with those found in ZBP-89. In addition, there are highly conserved amino acid sequences in the carboxy-terminal segments of the two genes. In spite of their structural similarities, the two proteins are encoded at distinct loci, ZBP-89 on chromosome 3q21 and ZBP-99 on 1q32.1. The predicted open reading frame of ZBP-99 cDNA encodes a 99-kDa protein. Electrophoretic mobility shift assays showed that ZBP-99 protein specifically binds to the GC-rich promoter elements of gastrin and ODC genes. Northern blot analysis showed that a major ZBP-99 transcript of 5.6 kb is expressed ubiquitously at low levels, with elevated expression levels in placenta and in adult kidney, liver, and lymphocytes. Cotransfection of AGS gastric adenocarcinoma and HT-29 colon adenocarcinoma cells with a ZBP-99 expression construct and with an ODC reporter construct show that ZBP-99 repressed basal expression in the two cell lines by 80 and 60%, respectively. Collectively, the data suggest that ZBP-99 binds GC-rich promoters and may complement the activities mediated by ZBP-89.
在调节鸟氨酸脱羧酶（ODC）基因表达的转录因子中，有一些与富含GC的启动子相互作用，包括Sp1和ZBP - 89。Sp1作为转录激活因子发挥作用，而ZBP - 89作为ODC和胃泌素启动子的转录抑制因子。本研究报告了ZBP家族第二个成员的克隆和特性，该成员也能结合GC盒。ZBP - 99含有四个Krüppel型锌指，与ZBP - 89中的锌指相比，它们总共具有91%的氨基酸序列相似性和79%的序列同一性。此外，这两个基因的羧基末端片段存在高度保守的氨基酸序列。尽管它们在结构上相似，但这两种蛋白质由不同的基因座编码，ZBP - 89位于3q21染色体上，ZBP - 99位于1q32.1染色体上。ZBP - 99 cDNA的预测开放阅读框编码一种99 kDa的蛋白质。电泳迁移率变动分析表明，ZBP - 99蛋白特异性结合胃泌素和ODC基因富含GC的启动子元件。Northern印迹分析表明，一个5.6 kb的主要ZBP - 99转录本在各处均有低水平表达，在胎盘以及成年肾脏、肝脏和淋巴细胞中的表达水平升高。用ZBP - 99表达构建体和ODC报告基因构建体对AGS胃腺癌和HT - 29结肠腺癌细胞进行共转染，结果显示ZBP - 99分别使这两种细胞系中的基础表达降低了80%和60%。总体而言，数据表明ZBP - 99结合富含GC的启动子，可能补充由ZBP - 89介导的活性。
