EFFECTS OF TRANSCRIPTION AND TRANSLATION INHIBITORS ON A HUMAN GASTRIC-CARCINOMA CELL-LINE - POTENTIAL ROLE OF BCL-X-S IN APOPTOSIS TRIGGERED BY THESE INHIBITORS

The effects of the macromolecular synthesis inhibitors 5,6-dichloro-1- beta-D-ribofuranosyl benzimidazole (DRB), actinomycin D, and cyclohexi mide on the human gastric cancer TMK-1 cell line were studied. These a gents inhibited DNA, RNA, or protein synthesis efficiently and induced cell death rapidly in a wide range of concentrations. After 8 hr of e xposure to these agents, the cells exhibited morphological features of apoptosis, including cell shrinkage, nuclear condensation, DNA fragme ntation, and formation of apoptotic bodies. Western blot analysis reve aled that these inhibitors altered the protein levels of apoptosis-rel ated gene products such as c-Myc, Bcl-X-s, and the mutant p53 (mp53) i n TMK-1 cells markedly. The c-myc mRNA and protein levels were decreas ed initially and were then induced markedly to a new level after 4 hr of exposure to DRB, a RNA polymerase II inhibitor. The Bcl-X-S levels were increased rapidly after treatment with ail of these agents, where as the levels of Bcl-X-L and Bax remained largely unchanged. Northern blot analysis indicated that the c-myc overexpression is concomitant t o DRB-induced DNA fragmentation and that the increased mp53 protein le vel was mainly a posttranscriptional event. Our observations suggest t hat the up-regulation of Bcl-X-S may serve as an important mechanism f or the apoptosis triggered by these inhibitors. This study also provid es evidence for the notion that interference with the cellular surviva l pathway may lead to apoptosis. (C) 1997 Elsevier Science Inc.