Journal of Experimental & Clinical Cancer Research 2008, 27:87 http://www.jeccr.com/content/27/1/87 A C B D TFhigeucreell5growth inhibition effect of rapamycin combined with PTEN transfection The cell growth inhibition effect of rapamycin combined with PTEN transfection. growth and apoptosis [20]. Abnormalities in the PI3K/ AKT/mTOR signal pathway occurs in many solid or hema- tological malignancies. The present study also showed that mTOR mRNA and p-Akt protein expressed at high levels in K562 cells. After the cells were transfected with PTEN gene and treated with rapamycin, the expression levels of mTOR mRNA and p-Akt protein decreased accordingly. This result demonstrated that deregulated PI3K/AKT/mTOR signal pathway might contribute to the development of leukemia, and could be considered as a candidate target for the treatment of leukemia. Rapamycin can stabilize the inhibitors of PI3K/AKT/ mTOR signaling pathway and down-regulate the activity of mTOR. Studies showed that inhibiting mTOR with rapamycin decreased the phosphorylation of proteins in mTOR signaling pathway, induced cell cycle arrest at G / 0 G1 phase and distinctly rescued the differentiation of nor- mal hematolpoietic stem cells (HSCs) and depleted leuke- mic stem cells. The regulation of HSCs and leukemic cells might be governed by cell-context-dependent, PTEN- mediated inhibition of mTOR [21]. The cell cycle arrest associated with the down-regulation of cyclinD1 and up- Page 7 of 9 (page number not for citation purposes)