McCloskey D E, Coleman C S, Pegg A E
Department of Cellular and Molecular Physiology, The Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
J Biol Chem. 1999 Mar 5;274(10):6175-82. doi: 10.1074/jbc.274.10.6175.
Spermidine/spermine N1-acetyltransferase (SSAT) appears to be the rate-limiting enzyme of polyamine catabolism, yet studies of its regulation have been limited by the low amounts of SSAT in uninduced cells. A system for studying SSAT was established by stably transfecting Chinese hamster ovary cells with a construct where SSAT cDNA was under control of the cytomegalovirus promoter. Thirteen of 44 clones expressed significantly increased SSAT activity (650-1900 compared with 24 pmol/min/mg protein in control cells). SSAT activity was directly proportional to SSAT protein, which turned over very rapidly (t(1)/(2) of 29 min) and was degraded through the ubiquitin/proteasomal pathway. The increased SSAT activity caused perturbations in polyamine homeostasis and led to a reduction in the rate of growth under clonal conditions. N1,N12-bis(ethyl)spermine greatly increased SSAT activity in controls and SSAT transfected clones (to about 10 and 60 nmol/min/mg protein, respectively). N1, N12-Bis(ethyl)spermine caused an increase in the SSAT half-life and a slight increase in SSAT mRNA, but these changes were insufficient to account for the increase in SSAT protein suggesting that translational regulation of SSAT must also occur.
亚精胺/精胺N1-乙酰基转移酶（SSAT）似乎是多胺分解代谢的限速酶，然而对其调控的研究一直受到未诱导细胞中SSAT含量低的限制。通过用一种构建体稳定转染中国仓鼠卵巢细胞，建立了一个研究SSAT的系统，该构建体中SSAT cDNA受巨细胞病毒启动子控制。44个克隆中有13个表达出显著增加的SSAT活性（与对照细胞中24 pmol/分钟/毫克蛋白质相比，为650 - 1900）。SSAT活性与SSAT蛋白直接成正比，SSAT蛋白周转非常快（半衰期为29分钟），并通过泛素/蛋白酶体途径降解。增加的SSAT活性导致多胺稳态失衡，并导致克隆条件下生长速率降低。N1,N12-双（乙基）精胺极大地增加了对照细胞和转染SSAT的克隆中的SSAT活性（分别达到约10和60 nmol/分钟/毫克蛋白质）。N1,N12-双（乙基）精胺使SSAT半衰期增加，并使SSAT mRNA略有增加，但这些变化不足以解释SSAT蛋白的增加，这表明SSAT的翻译调控也必定发生。
