Homoharringtonine and low-dose cytarabine in the management of late chronic-phase chronic myelogenous leukemia

Homoharringtonine and low-dose cytarabine in the management of late chronic-phase chronic myelogenous leukemia. changes, viral shRNA transfection was used to suppress the expression level of the target protein candidate, and viral mRNA transfection was used for over-expression. Virtual screening revealed that smad3 from TGF- pathway might be the candidate for HHT binding. In AML cell line U937 and KG-1, HHT can induce the Ser423/425 phosphorylation of smad3, and this phosphorylation can subsequently activate the TGF- pathway, causing cell cycle arrest at G1 phase in U937 cells and apoptosis in KG-1 cells, knockdown of smad3 can impair the sensitivity of U937 cell to HHT, and over-expression of smad3 can re-establish the sensitivity in both cell lines. We conclude that smad3 is the probable target protein of HHT and plays an important role in the functioning mechanism of HHT. 0.1, Figure ?Figure3A),3A), indicating that the activation of smad3 by HHT is not closely associated with the upstream TGF- receptor activation. Open in a separate window Figure 3 Influence of activation of TGF- pathway on AML cell line survival(A) Survival of U937 cells after been treated by HHT and TbRI /TbRII inhibitor LY2109761 for 24 h (H8 means HHT 8 ng/ml, LY55 means LY2109761 55 nM, LY110 means LY2109761 110 nM, LY220 means LY2109761 220 nM, LY440 means LY2109761 440 nM). (B) G1 phase cell percentage of U937 cells measured by flowcytometry after treated by different concentrations of HHT, cells stained by Annexin V/PI. (C) Apoptosis (upper) and G1 phase cell percentage (lower) of KG-1 cells following HHT treatment at different concentrations for 24 h, detected by flowcytometry. (D) Protein level change of the downstream molecules following HHT treatment for 24 h at different concentrations. To determine which cell death pathway was induced by HHT, U937 cells were treated with different concentrations (0, 4, 8, 16 ng/ml) of HHT for 24 h, ERK5-IN-2 cell apoptosis and cell cycle status were accessed by flowcytometry, the results showed that cell apoptosis rate were 0.14%, 0.13%, 0.14%, 0.19% respectively, and there was no ERK5-IN-2 significant difference amongst the experiment groups ( 0.05) (Supplementary Figure 2A). Instead, HHT can arrest U937 cells at G1 phase, as the concentration increased, G1-phase cell proportion gradually increased from 40.8% without HHT, 46.2% with 4 ng/ml HHT, 55.0% with 8ng/ml HHT to 63.4% with ERK5-IN-2 16 ng/ml HHT, statistical analysis showed significant difference( 0.001) (Figure ?(Figure3B).3B). Since TGF- activation can lead to G1 phase arrest by suppressing c-myc, p15, p21 and up-regulating p27, p57. To further investigate the change of these Rabbit polyclonal to PROM1 proteins after HHT functioning, U937 cells were incubated with different concentrations of HHT for 24h, and the cells were then ERK5-IN-2 tested for the level of the above proteins by western blot. The result revealed that HHT could induce decrease in the protein levels of c-myc, CDK4, CDK6; increase in p15; no significant change in p21,p27 and p57 (Figure ?(Figure3D),3D), these results were all consistent with the mechanism by which TGF- activation arrests the cell cycle, indicating that HHT could arrest the cell cycle of U937 at G1 phase by activating TGF- pathway, inhibiting the downstream c-myc, CDK4, CDK6 and increasing p15 expression. For KG-1 cells, the results were quite different, after incubating with HHT for 24h at different concentrations (0, 30, 60, 120 ng/ml), flowcytometry showed that there was no significant change in cell G1 phase arrest (Figure ?(Figure3C,3C, Supplementary Figure 2B), but significant increase in cell apoptosis was observed, as the concentration of HHT increased from 0, 30, 60 ng/ml to 120 ng/ml, the apoptotic cell proportion increased from 1.5%, 12.7%, 35.8% to 59.5% respectively, and statistical analysis revealed 0.001(Figure ?0.001(Figure3C),3C), indicating that HHT can inhibit KG-1 proliferation by apoptosis induction, not cell cycle arrest. The above results showed that HHT can inhibit the proliferation of both U937 and KG-1 cells, yet with completely different mechanisms, the former by cell cycle arrest, not apoptosis; and the latter by apoptosis induction, not cell cycle arrest. We believe this is consistent with the heterogeneity of the biological effects upon TGF- pathway activation. The effects of homoharringtonine is impaired by smad3 repression In order to further investigate the importance of smad3 in HHT functioning, we artificially down-regulated the protein level of smad3 in U937 cells by lentivirus transfection, U937 cell was transfected with smad3-shRNA-loaded virus and empty vectors (smad3-shRNA-transfected U937 cells, referred to as 103 cells; empty vector transfected U937 cells, referred to as 103NC cells. smad3 shRNA sequences are shown in Supplementary Table.