Frostesjö L, Holm I, Grahn B, Page A W, Bestor T H, Heby O
Department of Cellular and Developmental Biology, Umeâ University, S-901 87 Umeâ, Sweden.
J Biol Chem. 1997 Feb 14;272(7):4359-66. doi: 10.1074/jbc.272.7.4359.
When ornithine decarboxylase, the initial and highly regulated enzyme in polyamine biosynthesis, is irreversibly inactivated by alpha-difluoromethylornithine, F9 teratocarcinoma stem cells are depleted of putrescine and spermidine and as a result differentiate into a cell type which phenotypically resembles the parietal endoderm cells of the early mouse embryo. Simultaneously the level of decarboxylated S-adenosylmethionine (dcAdoMet), the aminopropyl group donor in spermidine and spermine synthesis, increases dramatically, as the aminopropyl group acceptor molecules (putrescine and spermidine) become limiting. When this excessive accumulation of dcAdoMet is prevented by specific inhibition of the AdoMet decarboxylase activity, the differentiative effect is counteracted, despite the fact that the extent of polyamine depletion remains almost identical. Therefore, it may be concluded that dcAdoMet plays an important role in the induction of differentiation. Moreover, this key metabolite acts as a competitive inhibitor of DNA methyltransferase and is therefore capable of interfering with the maintenance methylation of newly replicated DNA. During the course of F9 cell differentiation, the highly methylated genome is gradually demethylated, and its pattern of gene expression is changed. Our present findings, that the DNA remains highly methylated and that the differentiative process is counteracted when the build-up of dcAdoMet is prevented, provide strong evidence for a causative relation between the level of dcAdoMet and the state of DNA methylation as well as cell differentiation.
当鸟氨酸脱羧酶（多胺生物合成过程中的初始且受到高度调控的酶）被α-二氟甲基鸟氨酸不可逆地失活时，F9畸胎瘤干细胞中的腐胺和亚精胺会耗尽，结果分化为一种在表型上类似于早期小鼠胚胎壁内胚层细胞的细胞类型。同时，作为亚精胺和精胺合成中的氨丙基供体，脱羧S-腺苷甲硫氨酸（dcAdoMet）的水平会急剧增加，因为氨丙基受体分子（腐胺和亚精胺）变得有限。当通过特异性抑制腺苷甲硫氨酸脱羧酶活性来阻止dcAdoMet的这种过度积累时，尽管多胺耗尽的程度几乎保持不变，但分化作用会被抵消。因此，可以得出结论，dcAdoMet在诱导分化中起重要作用。此外，这种关键代谢物作为DNA甲基转移酶的竞争性抑制剂，因此能够干扰新复制DNA的维持甲基化。在F9细胞分化过程中，高度甲基化的基因组会逐渐去甲基化，其基因表达模式也会发生变化。我们目前的研究结果表明，当阻止dcAdoMet的积累时，DNA仍然高度甲基化且分化过程会被抵消，这为dcAdoMet水平与DNA甲基化状态以及细胞分化之间的因果关系提供了有力证据。
