During erythropoiesis, some organelles such as mitochondria and nucleus are lost 
by autophagy and enucleation processes in the presence of macrophages in vivo. 
In vitro production of erythrocytes has raised many questions about the 
mechanism of enucleation. The aim of this work was to study the DNA breakdown, 
enucleation, hemoglobin synthesis and telomerase activity of K562 cells during 
erythroid differentiation. For these purposes, K562 cells were induced to 
differentiate by erythropoietin + rhGM-CSF, DMSO, and sodium butyrate separately 
up to 14 d. In different time intervals, hemoglobin synthesis was evaluated by 
benzidine staining and RT-PCR for γ-globin gene expression. DNA breakdown was 
analyzed by 4',6-diamidino-2-phenylindole (DAPI) staining, DNA ladder 
electrophoresis and comet assay. The telomerase activity was evaluated by TRAP 
assay. Our result indicated that, sodium butyrate and DMSO inhibited K562 cell 
growth about 50-60% in comparison to untreated control cells. The percentage of 
benzidine-positive cells was about 45% in the presence of sodium butyrate after 
10 d. Densitometric analysis of RT-PCR and calculated data indicated a 1.5-fold 
increase in relative γ-globin gene expression at 96 h, in the presence of 1 mM 
sodium butyrate in comparison with untreated cells. DAPI staining did not reveal 
any evidence of internal lysis of the nucleus during erythroid differentiation 
at first wk, but this was obvious in the second wk. DNA laddering pattern was 
not observed in differentiated cells during 14 d. In comet assay, the percentage 
of DNA in tail, tail length, and tail moment were significantly different 
between untreated and treated cells (p < 0.05). Telomerase activity was 
inhibited up to 90.3% during erythroid differentiation of these cells.