Critical band 3 multiprotein complex interactions establish early during human erythropoiesis

Band 3, the major anion transport protein of human erythrocytes, forms the core of a multiprotein complex in the erythrocyte membrane. Here we studied the spatiotemporal mechanisms of band 3 multiprotein complex assembly during erythropoiesis. Significant pools of intracellular band 3 and Rh-associated glycoprotein (RhAG) were found in the basophilic erythroblast. These intracellular pools decreased in the polychromatic erythroblast, whereas surface expression increased and were lowest in the orthochromatic erythroblast and reticulocytes. Protease treatment of intact cells to remove extracellular epitopes recognized by antibodies to band 3 and RhAG was used to study surface delivery kinetics and intracellular complex composition from the proerythroblast stage to the enucleated reticulocyte. Newly synthesized band 3 and protein 4.2 interact initially in the early stages of the secretory pathway and are found associated at the plasma membrane from the basophilic stage of erythropoiesis. Although we could successfully coimmunoprecipitate Rh with RhAG from plasma membrane pools at a similar stage, no intracellular interaction between these proteins was detectable. Knockdown of RhAG during early erythropoiesis was accompanied by a concomitant drop in membrane expression of Rh polypeptides. These data are consistent with assembly of major components of the band 3 macrocomplex at an early stage during erythropoiesis.