Westman JS, Stenfelt L, Vidovic K, Möller M, Hellberg Å, Kjellström S, Olsson ML
Blood 131 (14) 1611-1616 [2018-04-05; online 2018-02-08]
P1 and P k are glycosphingolipid antigens synthesized by the A4GALT-encoded α1,4-galactosyltransferase, using paragloboside and lactosylceramide as acceptor substrates, respectively. In addition to the compatibility aspects of these histo-blood group molecules, both constitute receptors for multiple microbes and toxins. Presence or absence of P1 antigen on erythrocytes determines the common P1 (P1+Pk+) and P2 (P1-Pk+weak) phenotypes. A4GALT transcript levels are higher in P1 individuals and single-nucleotide polymorphisms (SNPs) in noncoding regions of A4GALT, particularly rs5751348, correlate with P1/P2 status. Despite these recent findings, the molecular mechanism underlying these phenotypes remains elusive. The In(Lu) phenotype is caused by Krüppel-like factor 1 (KLF1) haploinsufficiency and shows decreased P1 levels on erythrocytes. We therefore hypothesized KLF1 regulates A4GALT expression. Intriguingly, P -specific sequences including rs5751348 revealed potential binding sites for several hematopoietic transcription factors, including KLF1. However, KLF1 binding did not explain 1 P -specific shifts in electrophoretic mobility-shift assays and small interfering RNA silencing of 1KLF1 did not affect A4GALT transcript levels. Instead, protein pull-down experiments using P but not 1 P oligonucleotide probes identified runt-related transcription factor 1 (RUNX1) by mass spectrometry. Furthermore, RUNX1 binds 2 P alleles selectively, and knockdown of 1 RUNX1 significantly decreased A4GALT transcription. These data indicate that RUNX1 regulates A4GALT and thereby the expression of clinically important glycosphingolipids implicated in blood group incompatibility and host-pathogen interactions.