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

The human erythroleukaemic cell line K-562, in response to various che mical agents, undergoes differentiation and exhibits exclusive product ion of fetal and embryonic haemoglobins. In this study we have compare d the efficiency of natural growth factors interleukin-3 and erythropo ietin 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 signif icantly stimulated the growth of K-562 cells (P<0.0001), while interle ukin-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 protei n kinase-C activation and the arrest of DNA synthesis. In contrast, he min significantly stimulated RNA and protein synthesis (P<0.0001) as m easured by [H-3]-uridine and [H-3]-leucine incorporation respectively. Analysis of hemin-treated K-562 nuclear extract on sodium dodecylsulp hate gel electrophoresis showed that one protein band of molecular wei ght 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 cycloh eximide (100 mu g/ml) and actinomycin D (0.1 mu g/ml) and thus indicat ing that the removal of 70 kDa protein seems to be dependent on RNA an d protein synthesis. The regulatory role of 70 kDa protein in hemin-in duced differentiation of K-562 cells is discussed.