The red blood cell band 3 variant (band 3Biceêtrel:R490C) associated with dominant hereditary spherocytosis causes defective membrane targeting of the molecule and a dominant negative effect.

Hereditary spherocytosis (HS), a common human inherited haemolytic anaemia, is associated with partial deficiency of different erythrocyte membrane proteins. In a subset of dominant HS, a partial membrane expression deficiency of band 3, the erythrocyte anion exchanger (AE1), have previously been characterized, and several mutations in the band 3 gene have been found: amino acid substitutions at conserved positions in the membrane domain, nonsense and frameshift mutations. In HS patients bearing missense mutations, the mutated transcript was present, whereas only the normal transcript was found in HS patients with frameshift mutations. In the former group, the membrane expression deficiency of band 3 was significantly more important than that observed in the latter group of HS patients with frameshift mutations, suggesting that missense mutations may have a dominant negative effect. In the present study, transient and stable transfections of K562 and COS-7 cells were used to demonstrate, by immunoblots of cell lysates and immunofluorescence studies, that the band 3 membrane domain bearing the R490C mutation (band 3Bicetrel) is not targeted to the plasma membrane and is retained in the endoplasmic reticulum. Transient cotransfections of K562 cells with plasmid coding for the normal membrane domain of band 3, together with increasing amounts of plasmid coding for the mutated R490C membrane domain, demonstrated that the band 3 mutant polypeptide exerts a dominant negative effect on the plasma membrane targeting of the normal band 3.