OBJECTIVETo study the expression of annexin II (AnnII) and the fibrinolytic activity in NB4 cells and their alterations in the presence of arsenic trioxide (ATO) and daunorubicin (DNR).

METHODSLeukemia cell line NB4 was treated with ATO or DNR for 24 ∼ 72 h. Cell surface expression of AnnII and its mRNA were analysed by flow cytometry and real time PCR, respectively, the fibrinolytic activity by chromogenic assay.

RESULTSCompared with other acute leukemia cell lines, the expression of AnnII on untreated NB4 cells was relatively higher. The AnnII positive cell rates on NB4, HL-60, K562, and A3 cells were (94.5 ± 1.6)%, (40.1 ± 2.1)%, (36.3 ± 1.5)% and (11.8 ± 2.5)%, respectively. The fibrinolytic activity of NB4 cells was the greatest with a A value of 0.68 ± 0.02. The fibrinolytic activity of NB4 cells was obviously decreased by ATO, DNR or monoclonal antibody against AnnII, being decreased by 60.4%, 35.8% and 26.0% of the pretreatment level, respectively. The expressions of AnnII and its mRNA in NB4 cells were decreased dramatically after ATO and DNR treated for 48 h. Annexin II positive cells rate were (55.46 ± 4.72)% and (27.00 ± 6.18)%, respectively.

CONCLUSIONNB4 cells have strong ability to enhance the catalytic efficiency of the t-PA-dependent plasminogen activation and AnnII on the cell membrane contributes to this activity. Its high fibrinolytic activity can be corrected by ATO and DNR through down-regulating AnnII.