[Overexpression of bcl-2 suppresses apoptosis in the human leukemia cell line TF-1]

It is generally recognized that bcl-2 gene strongly protects cells from apoptosis in various situations. But its function is still to be examined. We analyzed the effect of bcl-2 gene using growth factor dependent cell line, TF-1, derived from an erythroleukemia patient. On GM-CSF removal TF-1 (bcl-2) cells which were transfected with bcl-2 cDNA by retrovirus vector system survived and arrested in G0-1 phase of the cell cycle, while TF-1 (mock) cells which were transfected with vector only also arrested in G0-1 but decreased in number in several days and showed typical apoptosis. N-acetylcysteine, one of antioxidants, did not show such anti-apoptotic effect as bcl-2 in the preincubation experiment. By centrifugal elutriation system the G0-1 arrested subfraction of TF-1 (bcl-2) showed time delay at the re-entry into cell after GM-CSF re-addition when compared with the G0-1 arrested subfraction of TF-1 (mock). Similar delay in cell cycle progression was observed after 24hs-exposure of staurosporine, a protein kinase C (PKC) inhibitor. The expression of cell cycle genes including cyclin A, C, D1, E, cdk2, 4, c-myc, bax and bcl-x showed no difference between these two cell lines upon growth factor removal. These results imply that the functional commitment of bcl-2 into cell cycle progression under the situation of apoptosis especially at the restriction point of G1-S transition.