Quantitative analysis for transcriptional alteration of glycosyltransferases in colon cancer

Galβ1-3GlcNAc是由半乳糖：β-N-乙酰氨基葡萄糖β1，3-半乳糖基转移酶(β3Gal-T)合成的。在迄今已克隆的6个β3半乳糖中，β3半乳糖T5是消化道或胰腺组织上皮细胞合成1型链所必需的酶。它在这种组织产生的糖蛋白上形成1型结构。在本研究中，我们发现β3Gal-T5基因的转录调控是由同源蛋白控制的，即CDX家族和肝细胞核因子家族的成员。我们在转录起始点发现了一个重要的启动子活性区域，命名为β3Gal-T5控制元件。GCE包含CDX和HNF家族成员的共同序列。在该序列中引入的突变取消了转录活性。CDX1、CDX2、HNF1α和HNF1β四个因子可与β结合并转录激活β3Gal-T5基因。在体内的两个系统中，β3Gal-T5基因的转录调控与CDX和HNF1家族成员的转录调控一致，即：1)在体外分化过程中，CDX2和HNF1α转录上调与3Gal-T5基因转录上调相关。2)结肠癌患者癌组织中β3Gal-T5的转录和蛋白表达均显著下调。这种下调与肿瘤组织中CDX1和HNF1β表达的减少有关。这是首次发现糖基转移酶基因以组织特异性的方式在同源蛋白的调控下转录调节。β3Gal-T5受肠道同源蛋白控制，可能通过改变糖蛋白的糖类结构对肠道细胞的特定功能发挥重要作用

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