Blood group B gene is barely expressed inin vitroerythroid culture of Bm-derived CD34+cells without an erythroid cell-specific regulatory element

Background and Objectives Previously, a weak phenotype Am or Bm was assumed to be caused by a reduction of A or B gene expression in bone marrow cells, but not in mucus-secreting cells. However, ABO expression has not been examined in erythroid progenitor cells of Am or Bm individuals. Materials and Methods We carried out in vitro erythroid differentiation of CD34+ cells from peripheral blood of a Bm individual harbouring a 3·0-kb deletion including an erythroid cell-specific regulatory element, named the +5·8-kb site, in intron 1 of the human ABO blood group gene. Results During the in vitro differentiation of CD34+ cells from this Bm individual into erythroid cells, B-antigens were not detectable on the cultured cells by flow cytometric analysis, and allele-specific RT-PCR consistently detected the transcripts from the O allele, but not from the B allele. Moreover, chromatin immunoprecipitation assay demonstrated that both RUNX1 and GATA-2 or GATA-1 were bound to the +5·8-kb site in cultured erythroid cells expressing ABO. Conclusion It is likely that the +5·8-kb site enhances transcription from the ABO promoter in erythroid cells through binding of RUNX1 and GATA-2 or GATA-1.