| Summary: | 碩士 === 國防醫學院 === 生物化學研究所 === 85 ===
The effects of macromolecular synthesis inhibitors 5,6-dichloro-1-B-D-ribofuranosy1benzimidazole (DRB), actinomycin D, and cycloheximide on human gastric cancer TMK-1 cell line were studied. These agents inhibit DNA, RNA or protein synthesis efficiently and induced cell death rapidly in a wide range of concentrations. After 8 hr of exposure to these agents, the cells exhibit morphological features of apoptosis including cell shrinkage, nuclear condensation, DNA fragmentation, and formation of apoptotic bodies. Western blot analysis revealed that these inhibitors altered the protein levels of apoptosis-related genes such as c-Myc, Bcl-xs, and the mutant p53 (mp53) in TMK-1 cells significantly. The c-myc mRNA and protein levels were decreased initially and were then induced significantly to a new level after 4 hr of exposure to the RNA polymerase Ⅱinhibitor, DRB. Northern blot analysis indicated that the c-mycd overexpression is concomitant to DRB-induced DNA fragmentation and the increased mp53 protein level was mainly a posttranscriptional event. The Bcl-xs levels were rapidly increased after treatment with all of these agents, whereas the levels of Bcl-xL and Bax remained largely unchanged. In the presence of dexamethasone the cells were protected and the whole apoptosis events were delayed though not completely blocked. It is worth noting that the up-regulation of Bcl-xs by these inhibitors was also blocked by dexamethasone. Our observations suggest that the up-regulation of Bcl-xs may serve as an important mechanism for the apoptosis triggered by these inhibitors.
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