The Wilms' tumor 1 (WT1) gene is one of the regulating factors in cell proliferation and development. It is a double-functional gene: an oncogene and a tumor suppressor. This gene was found to be highly expressed in many leukemic cell lines and in patients with acute myeloid leukemia. In the present study, we demonstrated that the WT1 gene was commonly expressed in leukemic cell lines apart from U937 cells. The K562 cell line which expresses WT1 at a high level (mRNA and protein) was used in the entire experiment. By MTT and colony formation assays, we found that curcumin, an inhibitor of the WT1 protein, inhibited cell proliferation and clonogenicity in a time- and dose-dependent manner. It also caused cell cycle arrest at the G2/M phase. We then designed specific short hairpin RNAs (shRNAs) which could downregulate WT1 by 70-80% at the mRNA and protein levels. Reduction in the WT1 levels attenuated the proliferative ability and clonogenicity. Cell cycle progression analysis indicated that the proportion of cells in the G0/G1 phase increased while the proportion in the S phase decreased distinctively. ChIP-DNA selection and ligation (DSL) experiment identified a cohort of genes whose promoters are targeted by WT1. These genes were classified into different cellular signaling pathways using MAS software and included the Wnt/β-catenin pathway, MAPK signaling pathway, apoptosis pathway, and the cell cycle. We focused on the Wnt/β-catenin signaling pathway, and compared expression of several genes in the K562 cells transfected with the control shRNA and WT1-specific shRNA. β-catenin, an important gene in the Wnt canonical pathway, was downregulated after WT1 RNAi. Target genes of β-catenin which participate in cell proliferation and cell cycle regulation, such as CCND1 and MYC, were also significantly downregulated. Collectively, these data suggest that WT1 functions as an oncogene in leukemia cells, and one important mechanism is regulation of the Wnt/β-catenin pathway.

This study was to investigate the relationship between the CD34(+)CD38(-) cell population and its proportion in G(0) phase of de novo AML non-M(3) at diagnosis and the clinical and experimental characteristics. The flow cytometry was used to detect the expression of the cell surface antigen CD34 and CD38 in the bone marrow mononuclear cells (MNC) of the AML non-M(3) at diagnosis and investigate the cell cycle of the subpopulations, and then the relationships between the proportion of CD34(+)CD38(-)cell population and its G(0) state and the complete remission (CR) rate after the first induction chemotherapy was analyzed. The results showed that the proportion of the CD34(+)CD38(-) cell population and its G(0) phase had no relationship with the karyotypes and WBC count at new diagnosis and the Flt3/ITD status, but correlate with the blasts in the bone marrow after the first course induction chemotherapy. The proportion of the CD34(+)CD38(-) cells in patients who have visible blasts in the bone marrow at day 7 after completion of the first course induction chemotherapy was (12.47 ± 26.26)%, but the counterparts was (2.62 ± 7.20)% in the group of patients whose bone marrow had no visible blasts (p = 0.031). The proportion of the CD34(+) cell population in patients who had visible blasts in the bone marrow at day 1 after completion of the first course induction chemotherapy was (17.40 ± 21.20)%, yet the proportion of the CD34(+) cell populations was (5.64 ± 6.96)% in the patients who had no visible blasts in the bone marrow (p = 0.001). The proportion of the CD34(+)CD38(-) cell populations in the patients who achieved CR after the first course induction chemotherapy was (2.51 ± 9.72)%, which was lower than the proportion (24.92 ± 27.04%) of the non-CR patients (p = 0.001). Furthermore, the proportion (1.60 ± 4.82%) of the CD34(+)CD38(-) cell population in the AML non-M(2b) CR patients was more obviously lower than that in the non-CR patients (p < 0.001). In univariate analysis, whether or not achieved CR after the first course induction chemotherapy correlated with age (p = 0.022), the proportion of the CD34(+)CD38(-) cell population (p = 0.008) and the proportion of the visible blasts in the bone marrow at day 7 after induction therapy (p = 0.011). Multivariate analysis showed that only the proportion of the CD34(+)CD38(-) cells had correlation tendency with CR rate. It is concluded that the proportion of the CD34(+)CD38(-) cells in bone marrow of de novo AML non-M(3) is a prognostic factor to anticipate the CR rate of the first course for induction therapy.

Drug resistance is an important character of leukemic stem cells. To explore the mechanism of the chemotherapy resistance of N-cadherin positive leukemia cells, the quiescent state of N-cadherin positive leukemia cells was determined by flow cytometry and the relationship of G(0) phase cell ratio with the chemotherapy resistance was analyzed. After KG1a cells were induced to enter cell cycle, the G(0) phase cell ratio and the sensitivity of cells to VP16 were determined. Finally the quiescent state and drug resistance properties of KG1a cells were determined after inhibiting N-cadherin-mediated cell-cell interaction by EGTA treatment. The results showed that the G(0) phase cell ratio in N-cadherin positive KG1a cells was higher than that in N-cadherin negative KG1a cells. After KG1a cells were induced to enter cell cycle, the G(0) phase cell ratio was decreased significantly and the sensitivity of KG1a cells to VP16 increased. Following EGTA treatment for 24 hours, the G(0) phase cell ratio decreased and the drug-sensitivity was enhanced significantly. It is concluded that N-cadherin-mediated adhesion keeps N-cadherin positive leukemia cells in quiescent state of G(0) phase, thus protect these leukemia cells against VP16 chemotherapy.