Objective    To study the effects of overexpression of exogenous Notch1 on cell proliferation and cell cycle of human chronic myeloid leukemia cell line K562.     Methods    Plasmid pcDNA3.1-ICN1 containing exogenous intracellular fragment of Notch1 was transfected in K562 cells with Lipofectamine

TM

2000. Inverted phase contrast microscope was used to observe the morphology change of K562 cells

RT-PCR and Western blot analysis were used to detect the expression of Notch1 mRNA and protein. MTT assays and flow cytometry were used to detect the proliferation and cell cycle of K562 cells respectively.     Results    As compared with untransfected

group

the cell number of transfected K562 cells was decreased with cells aggregating. Both Notch1 mRNA and protein were up-regulated after transfection. The proliferation of transfected K562 cells were inhibited significantly (P0.01) and as we cultured more time

the cells were inhibited more significantly (P0.05). The cell cycle assay indicated that the cells at G

1

phase were increased (P0.05) and those at S phase were decreased significantly (P0.01) as compared to control group.     Conclusion    The overexpression of exogenous intracellular fragment of Notch1 can inhibit the proliferation of K562 cells by inhibiting the cell cycle in G

1

phase.