Growth-inhibition by hemin in K562 human leukemic cells is related to hemoglobin-producing activity

To determine the mechanism of the growth inhibition associated with the induction of erythroid differentiation in K562 cells by hemin, we used two K562 subclones with different hemoglobin (Hb)-producing activity. Hemin strongly inhibited the growth of K562-L, which had a low Hb-producing activity, but not that of K562-H, which had a high Hb-producing activity. When the cell growth of K562-L was inhibited by hemin, the S phase of the cell cycle decreased and the G2/M phase increased. In contrast, hemin had no effect on the cell cycle of K562-H. Without hemin treatment, the alpha-globin mRNA level was related to the degree of Hb production in K562-L and -H but the gamma-globin mRNA level was not. With hemin treatment, there was no increase in the alpha-globin mRNA level in K562-L but there was an increase in K562-H. The difference in alpha-globin mRNA levels correlated with the Hb production in K562-L and -H induced by hemin. The levels of c-myc and c-myb mRNAs in K562-L decreased when cell growth was strongly inhibited by hemin. These findings indicate that the growth inhibition of K562 cells by hemin is due to a suppression of the progression from the G0/G1 phase to the S phase and a delay in the G2/M phase, caused by the inhibition of c-myc and c-myb transcription. It is also affected by the Hb production, reflected in alpha-globin transcription.

Effect of 12-O-tetradecanoylphorbol-13-acetate on expression of cell surface antigens in two subclones of human leukemia K562 cells

Two subclones (K562-L and -H) were previously isolated from K562 human leukemic cells according to hemoglobin production: K562-L was expressed in less than 5% and K562-H in more than 90% of dianisidine positive cells. 12-O-Tetradecanoylphorbol-13- acetate (TPA) suppressed the expression of the erythrocytic (glycophorin A) and myelocytic (CD11b) antigens in K562-L, but increased the expression of these antigens in K562-H. TPA increased the megakaryocytic (CD61) antigens in both cells. These findings suggest that there are distinct TPA responsible factors in K562-L and -H on the expression of the erythrocytic and myelocytic antigens.

Cloning and characterization of K562 cells on hemoglobin synthetic activity

Two clones of the K562 human leukemic cell line were isolated according to hemoglobin (Hb) expression. One clone was expressed less than 5% (K562-L) and the other more than 90% (K562-H). The two clones did not exhibit any difference in cell growth or cell cycle. However, the Hb expression of K562-H cells was reduced by succinylacetone (S.A.). The above results suggested that the difference in the Hb production of K562-L and K562-H cells depended on the heme synthetic activity. On the other hand, glycophorin A was expressed to a greater extent on K562-L cells than on K562-H cells. These findings suggested that heme synthesis and the expression of glycophorin A on K562 cells were not always related. The CD11b and the CD61 were also expressed to a greater extent on K562-L cells than on K562-H cells, but the CD34 was not expressed on these cells.