Transcriptional regulation of the human ABO histo-blood group genes is dependent on the N box upstream of the proximal promoter.

BACKGROUND: Our previous studies of the transcriptional regulation of the human ABO gene indicated that negative regulatory elements are present in the sequence just upstream from the proximal promoter. The role of the -275 to -118 region in regulation of ABO gene transcription is further characterized. STUDY DESIGN AND METHODS: Transient transfection experiments into various cells were performed with luciferase reporter plasmids carrying ABO upstream sequences, and electrophoretic mobility shift assay was carried out with a nuclear extract prepared from the human gastric cancer KATOIII cells. RESULTS: It is shown that the -202 to -118 region is involved in the negative regulation of ABO gene transcription in all cell lines examined. Transient transfection experiments in KATOIII cells with a reporter plasmid carrying mutated N box at -196 to -191 demonstrate that the N box is a negative regulatory element in the -202 to -118 sequence. Electrophoretic mobility shift assays indicate that the N box binds with a nuclear factor from KATOIII cells. CONCLUSION: These results indicate that repression of transcription from the ABO proximal promoter is partially dependent upon the N box. Therefore, reduced binding of the protein with the N box might play a direct role in ABO gene expression.