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Objective: To investigate the effect of arsenic sulfide （tetra-arsenic tetra-suffide As

4

S

4

; diarsenic trisulfideAs

2

S

3

）on tissue factor （TF） expression and procoagulant activity （PCA） of acute promyelocytic leukemia（APL） celllines （NB

4

and MR

2

） and the basic mechanism of their role. Methods: NB

4

and MR

2

cells were respectively treatedwith As

4

S

4

As

2

S

3

As

4

S

4

and Cyclohexamide（CHX）. PCA of the cells was detected using one-stage clotting assay.TF antigen was detected by ELISA. TF and PML/RARα fusion gene mRNA by semi-quantitive RT-PCR. The PCA andTF antigen of HL-60 and K562 cells were also examined. Results: The PCA and TF antigen level in NB

4

and MR

2

cells were significantly higher than that in HL-60 and K562 cells. Both As

4

S

4

and As

2

S

3

can down-regulate the TF anti-gen

TF mRNA transcription and membrane PCA of NB

4

and MR

2

cells in vitro in a time-dependent manner. The roleof As

4

S

4

was stronger than that of As

2

S

3

. Both As

4

S

4

and As

2

S

3

had no effect on PML/RAR

α

fusion gene