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Rap1GAP which regulates the GTP-GDP form switch of Rap1 is a member of the GTPase-activating protein (GAP) family and has recently received substantial attention. Rap1GAP is thought of as a putative tumor suppressor gene and plays an important role in human tumor progression including pancreatic cancer, thyroid cancer and melanoma. In the current study, we found that the expression of Rap1GAP was lower in acute myeloid leukemia (AML) patients compared to non-malignant blood disease patients. The expression of Rap1GAP was also low in HL-60, NB4, U937 and SHI-1 myeloid leukemia cell lines. Upregulated Rap1GAP in NB4 and HL-60 cells promoted cell differentiation induced by ATRA or TPA compared to the empty vector control cells. Furthermore, Rap1GAP-transfected cells also showed a higher rate of apoptosis in response to arsenic trioxide compared to the control counterpart cells. In addition, we found that increased expression of Rap1GAP promoted leukemia cell invasion may be due to matrix metalloproteinase 9 (MMP9). In conclusion, these results demonstrated that Rap1GAP promoted leukemia cell differentiation and apoptosis, but increased leukemia cell invasion in vitro.

Delta-like-1 (Dlk1, also Pref-1), a transmembrane and secreted protein, is a member of the epidermal growth factor-like family, homologous to Notch/Delta/Serrate. We found that the expression of Dlk1 was up-regulated in CD34+ cells from patients with myelodysplastic syndrome (MDS) by analyzing the gene expression profiles determined by microarray. The expression levels of Dlk1 mRNA frequently observed higher in the bone marrow mononuclear cells of MDS patients was confirmed by real-time RT-PCR. Forced expression of Dlk1 in transfected K562 cells enhanced proliferation, affected apoptosis induced by As2O3, and also influenced cell cycle induced by 12-O-tetra decanoylphorbol-acetate (TPA). By using the same experimental system we found that forced expression of Dlk1 increased the mRNA levels of HES1. It also inhibited p38 phosphorylation in transfected K562 cells treated with TPA. These results warrant further investigation of the role of Dlk1 in abnormal hematopoiesis in MDS.

The gene expression pattern of bone marrow mononuclear cells (BMNCs) from 10 patients with myelodysplastic syndrome (MDS) was studied by two-color cDNA microarray techniques. To confirm the microarray results, a semiquantitative RT-PCR was performed to analyze gene expression in fifty additional MDS patients. Ninety-five genes were shown to be abnormally expressed in at least five MDS patients compared to normal controls, involving cell growth and differentiation regulation, cell cycle control, signaling and redox; such as thrombospondin 1, phosphatase and tensin homolog, MAD, DNA-damage-inducible transcript 3 (DDIT3), ets variant gene 1 (ETV1), and G1 to S phase transition 1. CD36 was also revealed up-regulated in 4 cases. MDS patients in early and advanced stages could be clustered into two distinct groups by hierarchical clustering, wherein a case with isolated thrombocytopenia and other RA patients were clustered into two subgroups. Consistent expression patterns of 3/5 (60%) genes were confirmed by semiquantitative RT-PCR. Further analysis showed the different transcript levels of RNAHP, DDIT3 in patients with MDS in different stages, AML, and normal controls. Meanwhile, the different significance of RNAHP and ETV1 expression was revealed between RA and untypical anaplastic anemia, iron deficiency anemia, and megaloblastic anemia patients. We propose that the technology of microarray may reveal the intrinsic molecular features and the expression levels of RNAHP, DDIT3, and ETV1 may provide useful markers for the diagnosis of MDS.