MECHANISM OF DIFFERENTIATION OF HUMAN ERYTHROLEUKEMIC CELL-LINE K-562 BY HEMIN

The human erythroleukaemic cell line K-562, in response to various chemical agents, undergoes differentiation and exhibits exclusive production of fetal and embryonic haemoglobins. In this study we have compared the efficiency of natural growth factors interleukin-3 and erythropoietin and three chemical inducers such as dimethyl sulfoxide (DMSO, 1.9%), phorbol-12-myristate-13-acetate (PMA, 50 ng/ml) and hemin (25 mu M) on growth and differentiation of these cells. Erythropoietin significantly stimulated the growth of K-562 cells (P<0.0001), while interleukin-3 did not (P = 0.2783). However, neither of these growth factors individually or together induced differentiation of K-562 cells. Hemin appears to be more efficient than DMSO or PMA in differentiation of K-562 cells as measured by benzidine positive cells (70% or more). The differentiation of K-562 cells by hemin occurs independently of protein kinase-C activation and the arrest of DNA synthesis. In contrast, hemin significantly stimulated RNA and protein synthesis (P<0.0001) as measured by [H-3]-uridine and [H-3]-leucine incorporation respectively. Analysis of hemin-treated K-562 nuclear extract on sodium dodecylsulphate gel electrophoresis showed that one protein band of molecular weight 70 kDa decreased after 48 h of incubation in the presence of 25 mu M hemin. The disappearance of this protein can be prevented by cycloheximide (100 mu g/ml) and actinomycin D (0.1 mu g/ml) and thus indicating that the removal of 70 kDa protein seems to be dependent on RNA and protein synthesis. The regulatory role of 70 kDa protein in hemin-induced differentiation of K-562 cells is discussed.