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Apoptosis is also called programmed cell death,which is an autonomic orderliness cell death controlled by gene in order to keep the homeostasis. Apoptosis is an active process,it involves in a series of gene activing,expressing and regulating. Apoptosis is not a phenomenon of self-impairing in pathology condition,it is a initiative death process which can fit survivable environment better.The activations of intra-cellular caspase protease result in Apoptosis.Now,it was considered several caspase activating pathways, two of these were elucidated detailedly and became the focus of rencent years. Those are intrinsic pathway and extrinsic pathway. Intrinsic pathway concentrates at mitochondria,is the promoter of cell death. Extrinsic pathway promot apoptosis depending on TNF deatfh receptor. Imbalance of Proapoptosis and antiapoptotic protein exists in diseases, including cancer, the anti-apoptotic protein is dominant, choose to give cell survival advantages, and promote the formation of a malignant tumor. Currently, there are a variety of apoptosis drugs. TRAIL and arsenic trioxide is one of these.TRAIL is one of the member of TNF death ligand family, and associated with four different membrane receptors (DR4/TRAIL-R1, DR5/TRAIL-R2, DcRl/TRAIL-R3 and DcR2/TRAIL-R4). DR4 and DR5 include a conservative region known as the cytoplasm death regional (DD) which is necessary for the TRAIL - induced apoptosis, DcR1 has no cytoplasmic region while DcR2 only contain a brief DD sequence,DcRl and DcR2 exist as a decoy receptors. Only DR4 and DR5 ligand can promot apoptosis, TRAIL binding with the DR4 and DR5 result in receptor trimerization and the formation of the death-inducing signaling complex (DISC). DISC can be activated by Caspase-8. Follow-up activities can be divided into two types of apoptosis signaling pathways in the first pathway (type I cells), Caspase-8 activates caspases enzyme (caspase-3, -6, -7) inducing apoptosis by extrinsic pathway. However, in type 2 cells, Caspase-8 link mitochondrial by activating Bid, activating intrinsic to induce apoptosis. TRAIL is an attractive anticancer drug, because it priority to the promotion of tumor cell apoptosis with little effect on the normal cells. In addition, TRAIL can overcome the resistance caused by P53 imbalance and over-expression of Bcl-2 family members. In type 2 cells, a a series of anticancer treatment including cytotoxic chemotherapy、radiotherapy and new anticancer treatment have synergistic or superimposed effect with TRAIL.Arsenic trioxide inhibit tumor cell growth by inducing apoptosis and cell cycle escape. In certain circumstances, arsenic trioxide can induce leukemia cell differentiation. Arsenic trioxide induce apoptosis by different pathways, and partly the function of mitochondria. Arsenic trioxide-induced apoptosis relate with mitochondrial membrane potential and the loss of cytochrome c releasing into the cytoplasm. Arsenic trioxide can promote permeability transition pore opening, membrane proteins releasing, and lead to the activation of caspase. Arsenic trioxide can stimulate neuroblastoma, multiple myeloma and other hematopoietic tumor cells apoptosis. That suggest in the treatment of some hematopoietic malignancies Arsenic trioxide may be useful. In leukemia cell lines, Arsenic trioxide inhibit cell growth, down regulate Bcl-2 protein, induce apoptosis. It is assumed that some of molecular targets, including, other nuclear body proteins of PML, NF-κB, nuclear glucocorticoid receptor, MAPK caspases, p53-mdm2 way is also the target of arsenic trioxide.TRAIL and arsenic trioxide both are tumor cell apoptosis inducers with little cytotoxic to normal cells. Currently, arsenic trioxide has been successfully used in the treatment of acute promyelocytic leukemia, other leukemia cells are less sensitive to arsenic trioxide,so is not applied to other leukemia treatment. We combinate TRAIL with arsenic trioxide in some leukemia cell lines, to observe whether they can induce apoptosis synergyly in leukemia cell lines. We used Jurkat, K562, NB4, U937 for the objects of the experiment,cells were treated with different concentrations (1-10Um) ATO、TRAIL、and ATO+TRAIL for 24 hours,and assayed cell activity and inhibition rate by MTT. The results showed that the ATO inhibited Jurkat, K562, NB4 growth in a dose、time-dependent manner, and the dose larger、the time longer, the rate of inhibition was higher. While U937 is not sensitive to arsenic trioxide, the cell activity has no obvious change. Different leukemia cell line has different sensitivity to TRAIL, Jurkat is the most sensitive, followed by the U937; TRAIL is synergistic with arsenic trioxide to inhibit the activity of cells. We used 2uM ATO and different concentrations of TRAIL to treat leukemia cell lines, 24 hours later, Applicating annexin V labeled apoptosis cell and detected apoptosis rate by flow cytometry. The results showed that the combined treatment can improve leukemia cell line apoptosis rate, P<0.05.In this experiment, different leukemia cell lines showed different sensitivities to arsenic trioxide and TRAIL - induced apoptosis. NB4 cells was the most sensitive cell line to arsenic trioxide, U937 was least. Jurkat was the most sensitive cell line to TRAIL, followed by the U937. Arsenic Trioxide and TRAIL can inhibit the cell activities of four leukemia cell lines and induce leukemia synergies apoptosis synergyly. Arsenic trioxide may upregulate the expression of p53, increase the DR5 receptor expression, thus synergy with TRAIL to induce apoptosis. Using 2uM arsenic trioxide and different concentrations of TRAIL in cell lines, in certain concentrations of TRAIL, inhibition rate reached the highest, increasing the concentration of TRAIL, the inhibitory rate has not changed significantly, probably because arsenic trioxide-induced upward adjustment for DR5 is limited; They may also common role in the mitochondrial pathway, in common down regulate Bcl-2 gene, then induce apoptosis. The Specific mechanisms remain to be studied further.
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