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BCR-ABL tyrosine kinase inhibitor imatinib fails to eradicate leukemia stem cells (LSCs), the underlying mechanisms maintaining CML LSCs remain poorly understood. Here, we showed that transient inhibition of miR-21 by antagomiR-21 markedly increased imatinib-induced apoptosis in CML, but not normal CD34+ stem/progenitor cells. Furthermore, PI3K inhibitors also significantly sensitized CML CD34+ cells to imatinib-induced apoptosis. MiR-21 or PI3K inhibitor in combination with imatinib treatment significantly decreased AKT phosphorylation and c-Myc expression than either agent did alone, but did not affect Bim and Bcl-6 expresssion. These findings indicate that miR-21 is required for maintaining the imatinib-resistant phenotype of CML CD34+ cells through PI3K/AKT signaling pathway, thus providing the basis for a promising therapeutic approach to eliminate CML LSCs.

Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL) cells are insensitive to BCR-ABL tyrosine kinase inhibitor imatinib, the underlying mechanisms remain largely unknown. Here, we showed that imatinib treatment induced significant upregulation of miR-21 and downregulation of PTEN in Ph+ ALL cell line Sup-b15. Transient inhibition of miR-21 resulted in increased apoptosis, PTEN upregulation and AKT dephosphorylation, whereas ectopic overexpression of miR-21 further conferred imatinib resistance. Furthermore, knockdown of PTEN protected the cells from imatinib-induced apoptosis achieved by inhibition of miR-21. Additionally, PI3K inhibitors also notably enhanced the effects of imatinib on Sup-b15 cells and primary Ph+ ALL cells similar to miR-21 inhibitor. Therefore, miR-21 contributes to imatinib resistance in Ph+ ALL cells and antagonizing miR-21 demonstrates therapeutic potential by sensitizing the malignancy to imatinib therapy.

Plasminogen activator inhibitor-1 (PAI-1) expression are increased in adipose tissues/adipocytes of obese mice, which is associated with a hypofibrinolytic state that contributes to thrombosis. We recently demonstrated that PAI-1 expression increases in adipose tissues/adipocytes of cholesterol-fed rabbits. In this study, we evaluated the ability of atorvastatin to modulate PAI-1 expression in cholesterol-fed rabbits and the regulatory mechanism.Male rabbits were randomly fed with normal diet and high-cholesterol diet for 8 weeks, following 4 weeks, those fed high-cholesterol diet were randomly assigned to 2.5 mg/kg/day atorvastatin or starch. At the end of 12 weeks, subcutaneous adipose was collected, and culture adipocyte. PAI-1 mRNA was detected by RT-PCR. PAI-1 concentrations were determined with ELISA. The effect of atorvastatin and mevalonate (MVA) on PAI-1 production in adipocytes in vitro was observed.Atorvastatin significantly reduced serum TC and LDL-C concentrations (p0.05), and decreased plasma PAI-1 concentration and PAI-1 expression in adipose tissues/adipocytes from cholesterol-fed rabbits. In vitro, atorvastatin dose-dependently suppressed PAI-1 expression and protein secretion in adipocytes. MVA reversed the inhibitory effect of atorvastatin on PAI-1 expression in concentration-dependent manner.Atorvastatin reduces plasma PAI-1 concentration and PAI-1 expression in adipose tissue and adipocyte of atherosclerotic rabbit, and inhibits PAI-1 expression and protein secretion in adipocytes in vitro, suggesting that it may have an antithrombtic effect. We also suggest that the mevalonate pathway may play an important role in PAI-1 expression in adipocyte.