OBJECTIVETo explore the effects of mTOR inhibitor rapamycin on proliferation, cell cycle and apoptosis of Burkitt's lymphoma cell line Raji and CA46 cells and its mechanism, so as to provide the experimental evidence for a therapeutic target of Burkitt's lymphoma.

METHODS3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide(MTT) assay was performed to assess the inhibitory effect of rapamycin on proliferation of Burkitt's lymphoma cell line Raji and CA46 cells. The cell cycle distribution of Raji and CA46 cells was analyzed by flow cytometry with propidium iodide(PI) single staining. The cell apoptosis of Raji and CA46 cells was analyzed by flow cytometry with FITC Annexin V+PI double staining. The expressions of RPS6, p-RPS6, survivin and caspase-3 proteins were detected by Western blot after treating with rapamycin.

RESULTSRapamycin markedly inhibited the proliferation of both Raji and CA46 cells in a time- and concentration-dependent manners, showing good biological activity, the cell proliferation inhibition rate reached about 20% after treatment with 1 nmol/L rapamycin. After treatment with different concentrations of rapamycin for 24 and 48 hours, the proportion of both cells in G/Gphase in the treated groups was significantly increased in a time- and concentration-dependent manners in comparison with the solvent control group. With regard to the cells in S and G/M phase, the decreased population was accompanied by the increase of G/Gphase cells. After treatment with 100 nmol/L rapamycin for 48 hours, both Raji and CA46 cells demonstrated an apparent apoptosis,especially late apoptosis by flow cytometry with Annexin V+PI staining. After treatment with rapamycin, the expression of p-RPS6 and survivin of Raji and CA46 cells was obviously down-regulated, the expression of caspase-3 was obviously up-regulated in a time- and dose-dependent manners. However, rapamycin did not obviously affect the expression of RPS6.

CONCLUSIONThe rapamycin can effectively inhibit cell proliferation, arrest Raji and CA46 cells in G/Gphase, and this effect associates with inhibiting the activation of mTOR/RPS6 signal pathway through down-regulating the expression of phosphorylated RPS6, i.e. mTOR downstream signal pathway. It also can induce apoptosis by down-regulating the expression of anti-apoptotic protein survivin and activating the intrinsic pro-apoptotic protein caspase-3.