Takao Koichi, Rickhag Mattias, Hegardt Cecilia, Oredsson Stina, Persson Lo
Department of Experimental Medical Science, Lund University, S-22184 Lund, Sweden.
Int J Biochem Cell Biol. 2006;38(4):621-8. doi: 10.1016/j.biocel.2005.10.020. Epub 2005 Dec 1.
The polyamines are essential for cellular growth and differentiation. Ornithine decarboxylase (ODC), which catalyses the first step in the biosynthesis of the polyamines, has a very fast turnover and is subject to a strong feedback control by the polyamines. In the present study, we show that overexpression of a metabolically stable ODC in CHO cells induced a massive cell death unless the cells were grown in the presence of the ODC inhibitor alpha-difluoromethylornithine (DFMO). Cells overexpressing wild-type (unstable) ODC, on the other hand, were not dependent on the presence of DFMO for their growth. The induction of cell death was correlated with a dramatic increase in cellular putrescine levels. Analysis using flow cytometry revealed perturbed cell cycle kinetics, with a large accumulation of cells with sub-G1 amounts of DNA, which is a typical sign of apoptosis. Another strong indication of apoptosis was the finding that one of the key enzymes in the apoptotic process, caspase-3, was induced when DFMO was omitted from the growth medium. Furthermore, inhibition of the caspase activity significantly reduced the recruitment of cells to the sub-G1 fraction. In conclusion, deregulation of polyamine homeostasis may negatively affect cell proliferation and eventually lead to cell death by apoptosis if putrescine levels become too high.
多胺对于细胞生长和分化至关重要。鸟氨酸脱羧酶（ODC）催化多胺生物合成的第一步，其周转速度非常快，并受到多胺的强烈反馈调控。在本研究中，我们发现，在CHO细胞中过表达代谢稳定的ODC会导致大量细胞死亡，除非细胞在ODC抑制剂α-二氟甲基鸟氨酸（DFMO）存在的情况下生长。另一方面，过表达野生型（不稳定型）ODC的细胞生长并不依赖于DFMO的存在。细胞死亡的诱导与细胞内腐胺水平的显著增加相关。流式细胞术分析显示细胞周期动力学受到干扰，大量DNA含量低于G1期的细胞积累，这是细胞凋亡的典型标志。细胞凋亡的另一个有力迹象是，当生长培养基中不含DFMO时，凋亡过程中的关键酶之一caspase-3被诱导。此外，抑制caspase活性显著减少了细胞进入亚G1期的比例。总之，如果腐胺水平过高，多胺稳态失调可能会对细胞增殖产生负面影响，并最终导致细胞凋亡死亡。
