Quantitative analysis for transcriptional alteration of glycosyltransferases in colon cancer

1型碳水化合物链Gal β 1- 3glcnac是由udp -半乳糖：β- n -乙酰氨基葡萄糖β 1,3-半乳糖转移酶（β 3Gal-T）合成的。在迄今为止克隆的6个β 3gal - t中，β 3Gal-T5是消化道上皮或胰腺组织中1型链合成的必需酶。它在这些组织产生的糖蛋白上形成1型结构。在本研究中，我们发现β 3Gal-T5基因的转录调控是由同源蛋白控制的，即Cdx和肝细胞核因子（HNF）家族成员。我们发现了一个重要的区域（转录起始位点-151~-121），命名为β 3Gal-T5控制元件（GCE），用于启动子活性。GCE包含Cdx和HNF家族成员的一致序列。引入该序列的突变破坏了转录活性。Cdx1、Cdx2、HNF1 α和HNF1 β 4个因子可与GCE结合并转录激活β3Gal-T5基因，β3Gal-T5基因的转录调控与Cdx和HNF1家族成员在两个体内系统中的表达一致。1) Caco-2细胞在体外分化过程中，β 3Gal-T5的转录上调与Cdx2和HNF1 α转录上调相关。2) β 3Gal-T5转录物和蛋白在结肠癌患者癌组织中均显著下调。这种下调与肿瘤组织中Cdx1和HNF1 β表达的减少有关。这是首次发现糖基转移酶基因在同型蛋白的控制下以组织特异性的方式进行转录调节。β 3Gal-T5受肠道同型蛋白控制，可能通过改变糖蛋白的碳水化合物结构，对肠道细胞的特定功能起重要作用

The type 1 carbohydrate chain,Gal β 1-3GlcNAc,is synthesized by UDP-galactose:β-N-acetylglucoamine β 1,3-galactosyltransferase (β 3Gal-T). Among six β 3Gal-Ts cloned to date, β 3Gal-T5 is an essential enzyme for the synthesis of type 1 chain in epithelium of digestive tracts or pancreatic tissue. It forms the type 1 structure on glycoproteins produced from such tissues. In the present study,we found that the transcriptional regulation for β 3Gal-T5 gene is controlled by homeoproteins, i.e. members of Cdx and hepatocyte nuclear factor (HNF) families. We found an important region (-151~-121 from the transcription initiation site),named the β 3Gal-T5 control element(GCE), for the promoter activity. GCE contained the consensus sequences for members of Cdx and HNF families. Mutations introduced into this sequence abolished the transcriptional activity. Four factors,Cdx1,Cdx2,HNF1 α and HNF1 β,could bind to GCE and transcriptionally activated the β 3Gal-T5 geneTranscriptional regulation of the β3Gal-T5 gene was consistent with that of the members of Cdx and HNF1 families in two in vivo systems,i.e.1) During in vitro differentiation of Caco-2 cells, transcriptional up-regulation of β 3Gal-T5 was observed in correlation with the increase in transcripts for Cdx2 and HNF1 α. 2) Both transcript and protein of β 3Gal-T5 were determined to be significantly down-regulated in cancerous tissue of colon cancer patients. This down-regulation was correlated with the decrease of Cdx1 and HNF1 β expression in cancer tissueThis is the first finding that a glycosyltransferase gene is transcriptionally regulated under control of homeoproteins in a tissue-specific manner. β 3Gal-T5,controlled by the intestinal homeoproteins, may play an important role for the specific function of intestinal cells by modifying the carbohydrate structure of glycoproteins