Changes in the uptake of 57Co-cyanocobalamin during dimethylsulphoxide-induced differentiation of HL60 cells to neutrophils.

The uptake of serum-bound 57Co-cyanocobalamin by uninduced and dimethylsulphoxide-induced HL60 cells has been studied. The data indicate that during the maturation of promyelocytes to neutrophil granulocytes, there is a progressive and marked reduction in (a) the number of surface receptors for the transcobalamin II-cobalamin complex (TCII-Cbl) per cell up to the metamyelocyte stage and (b) the amount of TCII-Cbl entering a cell, through the entire maturation pathway. The maturation of promyelocytes to neutrophil granulocytes was also accompanied by a marked reduction in intracellular vitamin B12 content. These observations help in explaining some features of granulocytopoiesis in cobalamin deficiency.