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To explore the mechanism underlying antileukaemia effect of sodium valproate, the growth and survival of the K562 cell line were investigated. Global profiles of gene expression in K562 cells exposed to sodium valproate were assessed and validated. The differentially expressed genes identified were further used to query the connectivity map database to retrieve a ranked list of compounds that act on the same intracellular targets as sodium valproate. A significant increase in cell apoptosis and a change in gene expression profile were observed in valproate-exposed K562 cells. The significant enrichment analysis of gene ontology terms for the differentially expressed genes showed that these genes were involved in many important biological processes. Eight differentially expressed genes involved in apoptosis were verified by quantitative real-time PCR. The connectivity map analysis showed gene expression profile in K562 cells exposed to sodium valproate was most similar to that of HDACi and PI3K inhibitors, suggesting that sodium valproate might exert antileukaemic action by inhibiting HDAC as well as inhibiting PI3K pathway. In conclusion, our data might provide clues to elucidate the molecular and therapeutic potential of VPA in leukaemia treatment, and the connectivity map is a useful tool for exploring the molecular mechanism of drug action. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a transcription factor important in fat metabolism and PPAR-γ agonists were recently demonstrated to affect proliferation, differentiation, and apoptosis of different cell types. In the present study, two PPAR-γ agonists, 15-deoxy-delta (12,14)-prostaglandin J2 (15d-PGJ2) and a synthetic PPAR-γ agonist troglitazone (TGZ), were used to investigate activated PPAR-γ-induced apoptosis on human monocyte leukemia U937 and Mono Mac 6 cells in vitro. The results showed that both U937 and Mono Mac 6 cells demonstrated constitutive activation of COX-2 expression; treatment by 15d-PGJ2 and TGZ could induce apoptosis remarkably in human monocyte leukemia cells by disruption of mitochondrial membrane potential, activation of caspase-3, and causing cleavage of the caspase substrate poly (ADP-ribose) polymerase (PARP). Further studies revealed that treatment by both 15d-PGJ2 and TGZ remarkably downregulated COX-2 expression in these two kind of monocyte leukemia cells as measured by reverse transcriptase PCR (RT-PCR) and Western blot. Furthermore, the expression of Bcl-2 and Bcl-Xl and Mcl-1 was downregulated while Bax expression was upregulated concurrently after the cells were treated by these two agonists, and no variations were found in other Bcl-2 family members such as Bak, Bid, and Bad. Taken together, our results demonstrate for the first time that downregulation of cyclooxygenase-2 expression, disruption of mitochondrial membrane potential, activation of caspase-3, downregulation of Bcl-2, Bcl-Xl, and Mcl-1, and upregulation of Bax are involved in PPAR-γ agonists-induced apoptosis in these two human monocyte leukemia cells. [ABSTRACT FROM AUTHOR]

Tanshinone I (Tan I), a diterpene quinone extracted from herbal medicine Salvia miltiorrhiza Bunge, has recently been reported to have antitumor effects. As the mechanism of its proapoptotic effects on human myeloid leukemia cells has not been extensively studied, we performed an in-depth evaluation of the effects of Tan I on apoptosis in human K562 and HL-60 cells. The results revealed that Tan I could inhibit the growth of leukemia cells and cause apoptosis in a time- and dose-dependent manner. Apoptosis was observed clearly by flow cytometry and Hoechst 33258 staining, as well as DNA fragmentation analysis. After treatment by Tan I for 48 h, the percentage of disruption of mitochondrial membrane potential (Δψm) was increased in a dose-dependent manner. Western blotting analysis demonstrated the cleavage of caspase-3 zymogen protein and a dose-dependent cleavage of poly-(ADP-ribose) polymerase. Tan I-induced apoptosis was accompanied by a significant decrease in survivin and an increase in Bax. Moreover, Tan I treatment remarkably downregulated the phosphorylation of both P85/PI3K and Akt in a time-dependent manner, and the PI3K/AKT-specific inhibitor (LY294002) mimicked the apoptosis-inducing effects of Tan I. We therefore conclude that the induction of apoptosis by Tan I in these leukemia cells is mainly related to the disruption of Δψm, the upregulation of Bax expression, and the activation of caspase-3. This process is highly correlated with the inactivation of PI3K/Akt/survivin signaling pathways. The results indicate that Tan I may serve as an effective adjunctive reagent in the treatment of leukemia. [ABSTRACT FROM AUTHOR]