Progress in the biological science of ABO blood group system -a pioneer work in legal medicine-

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Our studies of the transcriptional regulatory mechanism of the human ABO gene indicated that transcription of the ABO gene is regulated by the N box upstream the proximal promoter. N boxes are recognized by bHLH family of transcriptional repressers. Since α 1→2 fucosyltransferases are involved in the synthesis of A and B antigens, the ABO gene is co-expressed with the FUT genes encoding α 1→2 fucosyltransferases. Inspection of the nucleotide sequences of the upstream regions of the human FUT genes revealed E box class A and class B sites which bind bHLH family of transcriptional activators, suggesting that the bHLH family of transcriptional regulators could play crucial roles in expression of those genes. Since transcriptional bHLH repressers can form non-functional heterodimers with other transcriptional bHLH activators, thereby inhibiting the formation of functional heterodimers and repressing transcription, down-regulation of the repressers might relieve the repression of transcription from promoters of the FUT genes. Furthermore, down-regulation of a factor binding with the N box upstream the ABO promoter may relieve the repression, thereby leading to expression of the ABO gene. Therefore, reduction of bHLH family transcription represser may play a role in the co-expression of the FUT and ABO gene which leads to cooperative expression of glycosyltransferases involved in synthesis of A or B antigens.