Suppola S, Heikkinen S, Parkkinen J J, Uusi-Oukari M, Korhonen V P, Keinänen T, Alhonen L, Jänne J
A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland.
Biochem J. 2001 Sep 1;358(Pt 2):343-8. doi: 10.1042/0264-6021:3580343.
We have generated a hybrid transgenic mouse line overexpressing both ornithine decarboxylase (ODC) and spermidine/spermine N(1)-acetyltransferase (SSAT) under the control of the mouse metallothionein (MT) I promoter. In comparison with singly transgenic animals overexpressing SSAT, the doubly transgenic mice unexpectedly displayed much more striking signs of activated polyamine catabolism, as exemplified by a massive putrescine accumulation and an extreme reduction of hepatic spermidine and spermine pools. Interestingly, the profound depletion of the higher polyamines in the hybrid animals occurred in the presence of strikingly high ODC activity and tremendous putrescine accumulation. Polyamine catabolism in the doubly transgenic mice could be enhanced further by administration of zinc or the polyamine analogue N(1),N(11)-diethylnorspermine. In tracer experiments with [(14)C]spermidine we found that, in comparison with syngenic animals, both MT-ODC and MT-SSAT mice possessed an enhanced efflux mechanism for hepatic spermidine. In the MT-ODC animals this mechanism apparently operated in the absence of measurable SSAT activity. In the hybrid animals, spermidine efflux was stimulated further in comparison with the singly transgenic animals. In spite of a dramatic accumulation of putrescine and a profound reduction of the spermidine and spermine pools, only marginal changes were seen in the level of ODC antizyme. Even though the hybrid animals showed no liver or other organ-specific overt toxicity, except an early and permanent loss of hair, their life span was greatly reduced. These results can be understood from the perspective that catabolism is the overriding regulatory mechanism in the metabolism of the polyamines and that, even under conditions of severe depletion of spermidine and spermine, extremely high tissue pools of putrescine are not driven further to replenish the pools of the higher polyamines.
我们构建了一种杂交转基因小鼠品系，该品系在小鼠金属硫蛋白（MT）I启动子的控制下同时过表达鸟氨酸脱羧酶（ODC）和亚精胺/精胺N(1)-乙酰基转移酶（SSAT）。与单独过表达SSAT的转基因动物相比，双转基因小鼠意外地表现出更为显著的多胺分解代谢激活迹象，例如大量腐胺积累以及肝脏中亚精胺和精胺池的极度减少。有趣的是，在杂交动物中，尽管ODC活性显著升高且腐胺大量积累，但高级多胺仍严重耗竭。通过给予锌或多胺类似物N(1),N(11)-二乙基亚精胺，双转基因小鼠的多胺分解代谢可进一步增强。在用[(14)C]亚精胺进行的示踪实验中，我们发现，与同基因动物相比，MT-ODC和MT-SSAT小鼠肝脏中亚精胺的外排机制均增强。在MT-ODC动物中，这种机制显然在没有可检测到的SSAT活性的情况下发挥作用。在杂交动物中，与单转基因动物相比，亚精胺外排进一步受到刺激。尽管腐胺大量积累且亚精胺和精胺池大幅减少，但ODC抗酶水平仅出现轻微变化。尽管杂交动物除了早期永久性脱发外没有表现出肝脏或其他器官特异性的明显毒性，但其寿命却大大缩短。从多胺代谢中分解代谢是主要调节机制这一角度可以理解这些结果，即即使在亚精胺和精胺严重耗竭的情况下，极高的组织腐胺池也不会进一步被驱动来补充高级多胺池。
