Transcriptional regulation of the fucosyltransferase VI gene in hepatocellular carcinoma cells.

The alpha1,3-fucosyltransferase VI (FUT VI) protein is a key enzyme for synthesis of sialyl Lewis X and Lewis X in epithelial cells. Despite its importance, how FUT VI expression is regulated has not previously been elucidated. In this work, we examined transcriptional regulation of the FUT VI gene in hepatocellular carcinoma HepG2 cells. 5'-Rapid amplification of cDNA ends analysis revealed transcription start sites of FUT VI in HepG2 cells at +65 and +278 nucleotides (nt) downstream of the position registered in the Data Base of Human Transcription Start Sites. We determined promoter regions for FUT VI in HepG2 cells using a luciferase reporter gene assay. The promoter activities of constructs located 5'-upstream of the transcription start site decreased when the -186 to -156 and -56 to -19 nt regions were deleted. Site-directed mutagenesis of these regions revealed that two hepatocyte nuclear factor-4 alpha (HNF-4 alpha) and one octamer binding transcription factor-1 (Oct-1) binding sites are essential for FUT VI transcription. Furthermore, transient over-expression of HNF-4 alpha but not Oct-1 enhanced both FUT VI promoter activities and FUT VI mRNA levels in HuH-7 cells. These results suggest that two defined regions in the 5'-flanking region of the FUT VI transcription start site are critical for FUT VI transcription in HepG2 cells.