| Objective Leukemia is derived from the malignant transform of haemopoietic stem cell. One of the feathers of leukemia is that the diferentiation is blocked in immature stage, and thus the haemopoietic system failures to produce functional white blood cells, which leads to anemia, infection, hematosis. Therefore, the induction of differention and apoptosis of leukemic cells is an important strategy in the treatment of leukemia. Toll-like receptors (TLRs) play a crucial role in the induction of immune response against microbial infection. By recognizing the pathogen-associated molecular patterns (PAMPs), TLRs elicit non-specific innate immune response and inflammatory response. After the activation by PAMPs, TLRs expressed on dendritic cells triggers functional maturation of dendritic cells and leads to initiation of antigen-specific adaptive immune responses. TLR2 can recognize several pathogen-derived products such as bacterial Lipoproteins,LTA,LPS. Bacterial Lipoproteins induced apoptosis of THP-1 through activation of Toll-like Receptor-2. Peptidoglycan (PGN) is a unique and essential component of cell wall of all virtually bacteria. It is recognized by TLR2 as a ligand. The objection of this research is to determine the possibility to induce apoptosis and differentiation on monocytic leukemia THP-1 cells by the activation of TLR2 by PGN in order to find a new possible strategy for the treatment of monocytic leukemia.Method (1) RT-PCR is selected to detect the gene expression in THP-1 cells. (2) FACS is used to detect the protein expression on the surface of THP-1 cells. (3) By using of ELISA, the cytokine protein in the supernatant is measured. (4) PI- Annexin V staining tests the apoptosis level of THP-1 inducing by PGN. (5) Neutralization experiment by antibody is used to verify the involvement of TNFαin the induction of apoptosis of THP-1 induced by PGN. (6) By western blotting, we assay the activation of signal transduction molecules such as P38, ERK, NF-κB in THP-1 cells. (7) To testify the differentiation of THP-1 cells induced by PGN, adhesion assay is used.Result RT-PCR results showed that THP-1 expresses all TLRs except TLR3. The expression of CD14, TLR2, TLR4 protein on the surface of THP-1 was detected by FACS. PGN, one ligand of TLR2, can up-regulated the expression of CD14 and TLR2 in THP-1 cells. PGN also up-regulated the transcript expression of IL-1α,IL-8,TNFαand induced the phospholation of P38, ERK and NF-κB which are the important molecules in the TLR2 signal pathway. Therefore, THP-1 expressed functional TLR2. By using of PI- Annexin V staining, apoptosis was detected after the incubation of THP-1 cells with TLR2 ligand PGN, with time and dose dependent manner. The autocrine of TNFαwas contributed to the apoptosis induced by PGN, because PGN significantly up-regulated the secretion of TNFα, and TNFαneutralizing antibody inhibited this apoptosis. PGN also altered the expression of inhibitors of apoptosis protein, which is similar to TNFαaltered. Moreover, PGN induced the differentiation of THP-1 cells by up-regulating the expression of CD14, CD11b, CD11 and inducing the adhesion of THP-1 cells. In addition, PGN up-regulated the expression of CD40, CD80, CD86, suggesting that PGN may decrease the tumorigenicity of TLR2 positive leukemia cells.Conclusion PGN induced apoptosis of THP-1 cells which has relationship with TNFαautocrining by activation of TLR2. Moreover, PGN induced differentiation of THP-1 and up-regulate the expression of co-stimulatory molecules.
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