Tome M E, Fiser S M, Payne C M, Gerner E W
Department of Radiation Oncology, Arizona Health Sciences Center, University of Arizona, Tucson, AZ 85724, USA.
Biochem J. 1997 Dec 15;328 ( Pt 3)(Pt 3):847-54. doi: 10.1042/bj3280847.
DH23A cells, an alpha-difluoromethylornithine-resistant variant of the parental hepatoma tissue culture cells, express high levels of stable ornithine decarboxylase. Aberrantly high expression of ornithine decarboxylase results in a large accumulation of endogenous putrescine and increased apoptosis in DH23A cells when alpha-difluoromethylornithine is removed from the culture. Treatment of DH23A cells with exogenous putrescine in the presence of alpha-difluoromethylornithine mimics the effect of drug removal, suggesting that putrescine is a causative agent or trigger of apoptosis. Accumulation of excess intracellular putrescine inhibits the formation of hypusine in vivo, a reaction that proceeds by the transfer of the butylamine moiety of spermidine to a lysine residue in eukaryotic initiation factor 5A (eIF-5A). Treatment of DH23A cells with diaminoheptane, a competitive inhibitor of the post-translational modification of eIF-5A, causes both the suppression of eIF-5A modification in vivo and induction of apoptosis. These data support the hypothesis that rapid degradation of ornithine decarboxylase is a protective mechanism to avoid cell toxicity from putrescine accumulation. Further, these data suggest that suppression of modified eIF-5A formation is one mechanism by which cells may be induced to undergo apoptosis.
DH23A细胞是亲代肝癌组织培养细胞的一种抗α-二氟甲基鸟氨酸变体，表达高水平的稳定型鸟氨酸脱羧酶。当从培养物中去除α-二氟甲基鸟氨酸时，鸟氨酸脱羧酶的异常高表达导致内源性腐胺大量积累，并增加DH23A细胞的凋亡。在α-二氟甲基鸟氨酸存在的情况下用外源性腐胺处理DH23A细胞可模拟药物去除的效果，这表明腐胺是凋亡的致病因子或触发因素。细胞内过量腐胺的积累会抑制体内hypusine的形成，该反应是通过将亚精胺的丁胺部分转移至真核起始因子5A（eIF-5A）中的赖氨酸残基来进行的。用二氨基庚烷（一种eIF-5A翻译后修饰的竞争性抑制剂）处理DH23A细胞，会导致体内eIF-5A修饰的抑制以及凋亡的诱导。这些数据支持以下假设：鸟氨酸脱羧酶的快速降解是一种避免腐胺积累导致细胞毒性的保护机制。此外，这些数据表明抑制修饰的eIF-5A形成是细胞可能被诱导发生凋亡的一种机制。
