Bcl-2 over-expression and activation of protein kinase C suppress the Trail-induced apoptosis in Jurkat T cells

Trail, a tumor necrosis factor-related apoptosis-inducing ligand, is a novel potent endogenous activator of the cell death pathway through the activation of cell surface death receptors Trail-R1 and Trail-R2. Its role, like FasL in activation-induced cell death (AICD), has been demonstrated in immune system. However the mechanism of Trail induced apoptosis remains unclear. In this report, the recombinant Trail protein was expressed and purified. The apoptosis-inducing activity and the regulation mechanism of recombinant Trail on Jurkat T cells were explored in vitro. Trypan blue exclusion assay demonstrated that the recombinant Trail protein actively killed Jurkat T cells in a dose-dependent manner. Trail-induced apoptosis in Jurkat T cells were remarkably reduced by Bcl-2 over expression in Bcl-2 gene transfected cells. Treatment with PMA (phorbol 12-myristate 13-acetate), a PKC activator, suppressed Trail-induced apoptosis in Jurkat T cells. The inhibition of apoptosis by PMA was abolished by pretreatment with Bis, a PKC inhibitor. Taken together, it was suggested that Bcl-2 over-expression and PMA activated PKC actively down-regulated the Trail-mediated apoptosis in Jurkat T cell.

Induction of apoptosis by TPA and VP-16 is through translocation of TR3

AIM: To investigate the role of TR3 in induction of apoptosis in gastric cancer cells. METHODS: Human gastric cancer cell line, MGC80-3, was used. Expression of TR3 mRNA and its protein was detected by Northern blot and Western blot. Localization of TR3 protein was showed by immunofluorescence analysis under laser-scanning confocal microscope. Apoptotic morphology was observed by DAPI fluorescence staining, and apoptotic index was counted among 1000 cells randomly. Stable transfection assay was carried out by Lipofectamine. RESULTS: Treatment of MGC80-3 cells with TPA and VP-16 resulted in apoptosis, accompanied by the repression of Bcl-2 protein in a time-dependent manner. At the same time, TPA and VP-16 also up-regulated expression level of TR3 mRNA in MGC80-3 cells that expressed TR3 mRNA. When antisense-TR3 expression vector was transfected into the cells, expression of TR3 protein was repressed. In this case, TPA and VP-16 did not induce apoptosis. In addition, TPA and VP-16-induced apoptosis involved in translocation of TR3. In MGC80-3 cells, TR3 localized concentrative in nucleus, after treatment of cells with TPA and VP-16, TR3 translocated from nucleus to cytosol obviously. However, when this nuclear translocation was blocked by LMB, apoptosis was not occurred in MGC80-3 cells even in the presence of TPA and VP-16. CONCLUSION: Induction of apoptosis by TPA and VP-16 is through induction of TR3 expression and translocation of TR3 from nucleus to cytosol, which may be a novel signal pathway for TR3, and represent the new biological function of TR3 to exert its effect on apoptosis in gastric cancer cells.

Effects of Nicotinamide on Mouse Skin Tumor Development and Its Mode of Action

Nicotinamide (NA), a naturally occuring vitamin and a protease inhibitor, has been shown to be effective in treating some skin ailments. It inhibits cell proiferaion and induces cell differentiation. This report shows the effects of NA on mouse skin tumor development and on the critical events involved in this process. NA reduced tumor growth, inhibited the 12-O-tetradecanoylphorbol-13-acetate (TPA) induced ornithine decarboxylase activity, but induced the transglutaminare activity which was inhibited by TPA under different experimental conditions.The effects of NA on ornithine decarboxylare (ODC) and transglutaminase (TG) indicated that nicotinamide (NA) probably programmmed the cells for their death in the natural course of time, i.e. programed cell death. This observation indicates that NA might be a better agent for the detailed study and for the better use in prevention of cancer alone or in combination with other drugs.

Epstein-Barr virus induces human nasopharyngeal epithelial cells to escape from the replicative senescence

OBJECTIVE: To observe the biological changes of primary human nasopharyngeal epithelial cells in the early stage of immortalization. METHODS: The morphological changes of nasopharyngeal epithelial cells were observed by phase contrast microscopy, and the activity profile of senescence-associated beta-galactosidase (SA-beta-Gal) was detected by SA-beta-Gal staining. The expression of p16(INK4a) protein was tested by immunochemical assay, and the life span in vitro of nasopharyngeal epithelial cells was calculated as population doublings. In addition, the expression of Epstein-Barr (EB) virus latent membrane protein 1 (LMP1) was also detected by immunofluorescence staining. RESULTS: Morphologically, cells treated with EB virus and 12-o-tetradecanoyl-phorbol-13-acetate (TPA) formed multi-layer foci, and their cellular life span in vitro was extended (about 155 days of culture). A low percentage of cells (about 4.8%) expressed SA-beta-Gal activity at late primary culture, and did not always express p16(INK4a) protein in the progression of culture. CONCLUSIONS: Nasopharyngeal epithelial cells treated with EB virus in cooperation with TPA can pass through the stage of senescence and enter the early stage of immortalization. Some changes of phenotype occur in these cells.Our results provide data for further studying the mechanism of immortalization and the establishment of a human nasopharyngeal epithelial cell line.