Genomic structure and transcriptional regulation of human Gal beta 1,3GalNAc alpha 2,3-sialyltransferase (hST3Gal I) gene

Previous studies have shown that hST3Gal I mRNA is overexpressed in colorec tal cancer tissues and primary breast carcinoma compared with nonmalignant or benign tissue, suggesting that the transcriptional regulation of hST3Gal I gene is altered during malignant transformation. We report transcription al regulation of the hST3Gal I gene in colon adenocarcinoma and leukemia ce ll lines. To determine the genomic structure of the 5'-untranslated region, we cloned and identified the 5'-untranslated region of hST3Gal I from a hu man genome library. The 5'-untranslated region was found to be divided into three exons, namely, exons Y, X, and C1. The transcription initiation site s map at -1035 bp from the translation initiation site. Our results indicat e that the transcriptional regulation of hST3Gal I depends on the pi promot er that exists 5'-upstream of exon Y in these cell lines. The results of lu ciferase assay suggest that the nt -304 to -145 region is important for tra nscriptional activity of hST3Gal I gene in both cell lines. The nt -304 to -145 region contains two sequences similar to the Sp1 recognition elements (GC-box) and one USF binding site. The results of site-directed mutagenesis indicated that the Sp1 binding sites and USF binding site of the pI promot er are involved in the transcription of hST3Gal I mRNA. However, the triple mutant of these sites still exhibits about 50% transcriptional activity, s uggesting that there are other transcription factors involved in the transc ription of hST3Gal I mRNA. These results suggest that these factors may pla y a critical role in the up-regulation of the hST3Gal I gene during maligna nt transformation.