Journal of Experimental & Clinical Cancer Research 2008, 27:87 http://www.jeccr.com/content/27/1/87 dTFehigteeucrteeelld4cbyycleflodwistcryibtoumtioentroyf K562 cells transfected with Ad-PTEN-GFP or Ad-GFP and treated with or without 10 nM RAPA The cell cycle distribution of K562 cells transfected with Ad-PTEN-GFP or Ad-GFP and treated with or with- out 10 nM RAPA detected by flow cytometry. A: transfected with Ad-GFP; B: transfected with Ad-GFP and treated with 10 nmol/L RAPA; C: transfected with Ad-PTEN-GFP; D: transfected with Ad- PTEN-GFP and treated with 10 nmol/L RAPA. After treated with 10 nmol/L RAPA for three days, the apoptosis rate of K562 cells was 31.5% in Ad-PTEN-GFP group, which significantly higher than that of 6.8% in Ad-GFP group_P < 0.01). without RAPA treatment (0.447 ± 0.032, P < 0.01), or that in Ad-GFP transfected K562 cells (0.060 ± 0.007, P < 0.01). Discussion PTEN gene is a novel tumor suppressor gene. PTEN pro- tein has protein phosphatase and lipid phosphatase dual activity, and has the activity against phosphatidylinositol 3, 4, 5- trisphosphate (PIP3), the major bioactive product of PI3-kinase. The reduction of PIP3 level suppresses the activation of Akt and allows apoptosis to occur. Homozygous PTEN deletion is embryonic lethal in mice and PTEN+/- heterozygote mice may develop multiple Table 2: The comparison of Apoptosis rate and cell cycle change in K562 cells transfected with or without PTEN gene for different time.(%) Group 2d 5d 7d Untransfected Apoptosis G2/M Ad-GFP Apoptosis G2/M Ad-PTEN-GFP Apoptosis G2/M 0.2 0.5 1.1 30.2 30.8 29.7 0.8 2.8 4.1 29.3 26.9 32.9 1.5 22.4 30 28.1 23.3 13.6 tumors or immune system abnormalities. The inactiva- tion of PTEN in leukemia can be induced by gene silenc- ing, DNA methylation, transcriptional regulation or post- transcriptional modifications [14-16]. Our results showed that PTEN mNRA and protein expressed at very low level in K562 cells, a cell line established from a chronic myel- ogenous leukemia patient in blast crisis. The over-expres- sion of wild-type PTEN protein after PTEN gene transfection showed an anti-proliferation and apoptosis induction effect in the K562 cells in a time-dependent manner, indicating that the wild type PTEN might have anti-leukemia effect. Although previous studies showed that a close correlation was found between the low expres- sion of PTEN and the poor prognosis in some tumor patients including hematological malignancies [6,14,17,18] and the loss of PTEN gene disturbed the maintenance of quiescent HSCs and promoted leukemo- genesis in mice [19], the exact mechanism of hypo-expres- sion of PTEN in human leukemogenesis was not clear. The mammalian target of rapamycin (mTOR) is a serine/ threonine protein kinase, a downstream partner in PI3K/ Akt pathway, which regulates protein translation, cell Page 6 of 9 (page number not for citation purposes)