Caspase 3-mediated proteolysis of the N-terminal cytoplasmic domain of the human erythroid anion exchanger 1 (band 3)

The N-terminal cytoplasmic domain of the anion exchanger 1 (AE1 or band 3) of the human erythrocyte associates with peripheral membrane proteins to regulate membrane-cytoskeleton interactions, with glycolytic enzymes such as glyceraldehyde-3-phosphate dehydrogenase and aldolase, with the protein-tyrosine kinase p72(syk), with hemoglobin and with hemichromes. We have demonstrated that the N-terminal cytoplasmic domain of band 3 (CDB3) is a substrate of the apoptosis executioner caspase 3 (1). CDB3 has two non-conventional caspase 3 cleavage sites, TATD(45) and EQGD(205) (2). In vitro treatment of recombinant CDB3 with caspase 3 generated two fragments, which could be blocked by pretreatment with the caspase 3 inhibitor Z-DEVD-fmk (3). Recombinant CDB3 in which the caspase 3 cleavage sites Asp(45) and Asp(205) were mutated, was resistant to proteolysis (4). Proteolytically derived fragments cross-reactive with polyclonal anti-band 3 antibody appeared with simultaneous cleavage of poly (ADP-ribose) polymerase and procaspase 3 in staurosporine (STS)-treated HEK293 cells transiently transfected with CDB3 (5). In vivo cleavage of CDB3 could be blocked by pretreatment of cells with Z-DEVD-fmk or in cells transfected with mutant CDB3 (D45A, D205A) (6). Co-transfection experiments showed that STS-mediated cleavage of CDB3 diminished its interaction with the N-terminal domain of protein 4.2, confirming that such cleavage interferes with the interaction of CDB3 with cytoskeletal proteins (7). Active caspase 3 was observed in aged red cells but not in young cells. This red cell caspase 3 could cleave band 3 present in inside-out vesicles prepared from young erythrocytes arguing in favor of a physiological role of caspase 3 in aged erythrocytes.