Kanamoto R, Kameji T, Iwashita S, Igarashi K, Hayashi S
Department of Nutrition, Jikei University School of Medicine, Tokyo, Japan.
J Biol Chem. 1993 May 5;268(13):9393-9.
The mechanism of spermidine-induced destabilization of ornithine decarboxylase (ODC) was examined in newly isolated ODC-overproducing variant cells by use of an in vitro ODC degrading system. The cells accumulated ODC protein in the presence of alpha-difluoromethylornithine. Addition of spermidine to the medium accelerated degradation of ODC protein concomitantly with induction of antizyme, a regulatory protein that binds to ODC, inhibiting its activity. Both the acceleration of ODC degradation and the induction of antizyme were inhibited by cycloheximide, but not by actinomycin D. ODC was degraded rapidly in extracts from spermidine-treated cells. The rate of ODC degradation correlated with the amount of antizyme in the extracts, and the degradation activity was abolished by treatment of the extracts with anti-antizyme antibody. Thus, antizyme induced by spermidine was essential for the accelerated degradation of ODC in the cells. ODC was phosphorylated in the cells, probably at serine residue 303 in the first internal PEST region. ODC phosphorylation occurred even when its new synthesis was inhibited by cycloheximide. Antizyme accelerated the degradations of both dephosphorylated ODC and native ODC.
通过使用体外鸟氨酸脱羧酶（ODC）降解系统，在新分离的ODC过表达变异细胞中研究了亚精胺诱导的ODC不稳定机制。在α-二氟甲基鸟氨酸存在下，细胞积累了ODC蛋白。向培养基中添加亚精胺加速了ODC蛋白的降解，同时诱导了抗酶，抗酶是一种与ODC结合并抑制其活性的调节蛋白。ODC降解的加速和抗酶的诱导均受到环己酰亚胺的抑制，但不受放线菌素D的抑制。在亚精胺处理的细胞提取物中，ODC迅速降解。ODC降解速率与提取物中抗酶的量相关，并且通过用抗抗酶抗体处理提取物消除了降解活性。因此，亚精胺诱导的抗酶对于细胞中ODC的加速降解至关重要。ODC在细胞中被磷酸化，可能在第一个内部PEST区域的丝氨酸残基303处。即使其新合成被环己酰亚胺抑制，ODC磷酸化仍会发生。抗酶加速了去磷酸化ODC和天然ODC的降解。
