In clinical transfusion and transplantation medicine, AB0 is the most important blood group system. A and B antigens are synthesized by glycosyltransferases A and B encoded by co-dominantly inherited A and B genes. The 0 phenotype derives from a single nucleotide deletion; the resulting stop codon in the exon 7 of glycosyltransferase A leads to a lack of glycosylation activity to A and/or B. The DNA structure of the three major alleles of the human blood group AB0 system was first described in 1990. Besides the 4 major AB0 blood groups (A, B, AB, 0), weak expression variants commonly occur. Beside introns and exons, two regions were found to be critical for transcriptional activity of AB0 genes: a promotor sequence upstream of the translation start site and a CBF/NF-Y-binding enhancer element. However, the molecular basis for the weak expression levels of AB0 blood group receptors is not fully understood. Here we asked whether microRNA´s may play a role in the regulation of blood group A and B antigens. MiRNA's are small, non-protein encoding RNA sequences that bind to the 3' untranslated region (UTR) of target mRNAs resulting in translation repression or mRNA degradation. By distinct complementary approaches, including gene array analysis and overexpression of glycosyltransferase specific micro-RNAs (miRNAs) in primary hematopoietic stem cells, we identify here that miR-331-3p and miR-1908-5p directly target glycosyltransferase A and B. Consistently, overexpression of miR-331-3p and -1908-5p in hematopoietic stem cells (HSCs) leads to a 30-50% reduction of blood group A antigens per cell in differentiated RBCs. Downregulation of endogenous miR-1908-5p but not miR-331-3p leads to increased amount of blood group A antigen per red blood cell compared to control cells. This discrepancy between the effects of downregulation of miR-1908-5p and of miR-331-3p is likely explained by the constitutive expression levels of both miRNAs during erythropoiesis. In particular, miR-1908-5p is expressed throughout erythroid differentiation, while miR-331 displays low expression, thus, further downregulation of miR-331-3p could not further affect blood group A antigen levels. Furthermore miR-331-3p and -1908-5p were enhanced in red blood cells of Aweak variants. Sequencing of the 3'UTR of 6 Aweak variants revealed the presence of more miRNA binding sites for miR-1908-5p compared to normal controls.
These data identify microRNAs as regulators of blood group glycosyltransferase expression, thereby extending our understanding of blood group regulation in carriers of weak blood group variants. Regulating blood groups by microRNAs could pave the way for the development of universal blood.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.