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Objective: To investigate the expression level of Shp-2 tyrosine phosphatase in chronic myeloid leukemia (CML) and its relationship with the unlimited growth and apoptosis resistance of p210 bcr/abl-induced malignant cells., Methods: In this study, p210 bcr/abl positive leukemia cell specimens were obtained from 25 CML cases, meanwhile, bone marrow and peripheral blood cell samples from 8 non-tumor individuals and 10 normal individuals were used as p210 bcr/abl negative controls. K562 and KU812 leukemia cells were used as p210 bcr/abl positive controls, and KG-1 leukemia cell line was used as Shp-2 positive control. Specimens of peripheral blood and bone marrow of 25 adult patients of chronic myelocytic leukemia, 15 males and 10 females, aged 28-64, were collected. Specimens of bone marrow of 8 basically healthy adult volunteers and specimens of peripheral blood of 10 healthy adult volunteers were used as controls. The total cell protein was collected and the expression of Shp-2 was examined by Western blotting. Human leukemia cells of the line K562 were cultured. Shp-2 specific sense and antisense oligonucleotides were added into the culture fluid respectively. The cell apoptosis was detected by flow cytometry (FCM). STI571, specific inhibitor of p210 bcr/abl was added into the cultured fluid of K562 cells, then Western blotting and FCM were used to detect the protein expression of Shp-2 and p210 bcr/abl, and cell apoptosis., Results: Phosphorylated Shp-2 (pShp)-2 protein was overexpressed in 92% (23/25) of the CML cells, but lowly expressed or not expressed in the normal hematopoietic cells. The mean pShp-2 protein/beta-actin ratio of the primary CML leukemia cells was 0.91 +/- 0.62, significantly higher than those of the normal bone marrow cells and peripheral blood hematopoietic cells (0.16 +/- 0.09 and 0.03 +/- 0.05 respectively, both P < 0.01). The apoptotic rates of the CML cells treated by Shp-2 specific antisense oligonucleotide of the concentrations of 1 micromol/L and 4 micromol/L respectively for 72 h was 7.98% and 20.29% respectively, both significantly higher than that of the control group (4.06%, P < 0.01). The number of clone of CML cells treated by 0.25 micromol/L and 1.0 micromol/L Shp-2 specific antisense oligonucleotide for 7 days were 67% (37/60) and 11.9% (5/42) that of the control group. Twenty-four and 48 hours after the stimulation of STI571 the expression level of Shp-2 protein in the CML cells decreased time-dependently and the CML cell apoptotic rates were 31.15% and 38.69% respectively, both lower than that of the control group (33.6%). The number of clone of CML cells effected by 0.25 micromol/L and 1.0 micromol/L Shp-2 specific antisense oligonucleotide for 7 days was 67% (37/60) and 11.9% (5/42) that of the control group. Twenty-four and 48 hours after the stimulation of STI571 the expression level of Shp-2 protein in the CML cells decreased time-dependently and the CML cell apoptotic rates were 31.15% and 38.69% respectively, both lower than that of the control group (33.6%)., Conclusion: (1) The pShp-2 protein is overexpressed in CML cells, which is associated with the unlimited growth and apoptosis resistance of malignant cells. (2) Shp-2 is upregulated by p210 bcr/abl oncoprotein in CML.