We have previously shown that the expression of β-galactoside α2,6-sialyltransferase (hST6Gal I) mRNA decreases during HL-60 differentiation induced with dimethyl sulfoxide (DMSO) and that transcriptional regulation depends on the P3 promoter that exists S-upstream of exon Y. The regulation of hST6Gal I may be important for the expression of sialyl-Le(X) in HL-60 cells. In the present report, we studied the transcriptional regulation of hST6Gal I gene during DMSO-induced differentiation of HL-60 cells. To elucidate the molecular basis of hST6Gal I gene expression, the genomic region containing the P3 promoter of hST6Gal I was isolated and functionally characterized. Using a luciferase assay, we identified a functional DNA portion that confers an enhancer, located at nucleotide number (nt) -317 to -174 within the P3 promoter of hST6Gal I genomic DNA. This element contains two sequences similar to Sp1 (GC-box) and one sequence similar to Oct-1 recognition motifs (octamer sequence). Site-directed mutagenesis of Sp1 and Oct-1 sites showed that two Sp1 motifs and one Oct-1 motif are essential for transcriptional activity in HL-60 cells. Enhancer activity is suppressed during HL-60 cell differentiation induced with DMSO. These results suggest that GC-hox and octamer sequence may play a critical role in the transcriptional regulation of the hST6Gal I gene during HL-60 cell differentiation.
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