OBJECTIVETo investigate the role of asymmetric division in leukemia cells through detection of expression and asymmetric division of Numb in differentiated and undifferentiated K562 cells.

METHODSFirstly, Hemin was used to induce K562 cell differentiation, and the expression of Numb was detected by the real-time quantitative RT-PCR and flow cytometry. After K562 cells were synchronized by nocodazole, the Numb protein was labeled by immunohistochemical staining, followed by the determination of the terminally differentiated cells through confocal microscopy. The fluorescence intensity was calculated by Image J software, and the cell division pattern was analyzed on the basis of the fluorescence intensities of Numb in 2 divided daughter cells.

RESULTSCompared with the undifferentiated K562 cells, the level of Numb mRNA expression increased 2.3 times (P<0.001). The ratio of Numb positive cells was(67.37±5.01)% in differentiated K562 cells, while that was (43.97±5.72)% in undifferentiated K562 cells (P<0.01). Compared with undifferentiated K562 cells, the ratio of cells with asymmetric division in differentiated K562 cells increased 18.3%, the percentage of cells with symmetry self-renewal reduced 49.7%(P<0.001) and that with symmetry differentiation increased 32%(P<0.001).

CONCLUSIONIn differentiated K562 cells, expression of Numb and proportion of cells with asymmetric division were higher than that in undifferentiated cells. With the differentiation of leukemia cells, the proportion of cells with asymmetrical division increases, and the proportion of cells with symmetrical self-renewal decreases. The stemness of leukemia cells is maintained mainly through the symmetrical self-renewal.