Abstract
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 α-globin mRNA level was related to the degree of Hb production in K562-L and -H but the γ-globin mRNA level was not. With hemin treatment, there was no increase in the α-globin mRNA level in K562-L but there was an increase in K562-H. The difference in α-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 α-globin transcription.
