Previous studies have shown that hST3Gal mRNA is over-expressed in colorectal 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 transcriptional regulation of the hST3Gal I gene in colon adenocarcinoma and leukemia cell lines. To determine the genomic structure of the 5′-untranslated region, we cloned and identified the 5′-untranslated region of hST3Gal I from a human genome library. The 5′-untranslated region was found to be divided into three exons, namely, exons Y, X, and C1. The transcription initiation sites map at -1035 bp from the translation initiation site. Our results indicate that the transcriptional regulation of hST3Gal I depends on the pI promoter that exists 5′-upstream of exon Y in these cell lines. The results of luciferase assay suggest that the not -304 to -145 region is important for transcriptional 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 promoter are involved in the transcription of hST3Gal I mRNA. However, the triple mutant of these sites still exhibits about 50% transcriptional activity, suggesting that there are other transcription factors involved in the transcription of hST3Gal I mRNA. These results suggest that these factors may play a critical role in the up-regulation of the hST3Gal I gene during malignant transformation.
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