Byers T L, Wiest L, Wechter R S, Pegg A E
Department of Cellular and Molecular Physiology, M. S. Hershey Medical Center, Hershey, PA 17033.
Biochem J. 1993 Feb 15;290 ( Pt 1)(Pt 1):115-21. doi: 10.1042/bj2900115.
We have previously reported that prolonged chronic exposure to the S-adenosyl-L-methionine decarboxylase (AdoMetDC) inhibitor, 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxy-adenosine (MDL 73811, AbeAdo), leads to cytostasis of L1210 cells [Byers, Ganem and Pegg (1992) Biochem. J. 287, 717-724]. Further studies to investigate the mechanism by which these effects are brought about were carried out by comparing an L1210-derived cell line (R20) that is resistant to AbeAdo with the parent cells. The R20 cells were derived by two rounds of AbeAdo-induced cytostasis followed by rescue with exogenous polyamines. Cytostasis was induced in L1210 cells treated for 12 days with 10 microM AbeAdo; however, exposure to up to 40 microM AbeAdo did not induce cytostasis in R20 cells. Putrescine levels were elevated and spermine levels were depleted in both treated L1210 and treated R20 cells. Spermidine was depleted in treated L1210 cells but was only partly reduced in treated R20 cells. AdoMetDC activity was below the limit of detection in treated L1210 cells but, although greatly reduced, could be measured in the treated R20 cells. The resistance of the R20 cells to the effects of AbeAdo on cell growth and spermidine depletion correlated with reduced AbeAdo accumulation by R20 cells. In the absence of spermidine synthesis, unhypusinated eukaryotic translation initiation factor 5A (eIF-5A) accumulated in AbeAdo-treated L1210 cells. There was no detectable accumulation of unhypusinated eIF-5A in R20 cells. Unhypusinated eIF-5A accumulated during AbeAdo treatment was depleted in L1210 cells rescued by exogenous spermidine. These findings are consistent with the hypothesis that AbeAdo-induced cytostasis is due to the loss of hypusinated eIF-5A. However, spermine was able to rescue AbeAdo-treated L1210 cells without significantly reducing the unhypusinated eIF-5A accumulated during AbeAdo treatment, suggesting that only a small amount of the unmodified protein must be hypusinated to restore cell growth.
我们之前曾报道，长期慢性暴露于S-腺苷-L-甲硫氨酸脱羧酶（AdoMetDC）抑制剂5'-([(Z)-4-氨基-2-丁烯基]甲基氨基)-5'-脱氧腺苷（MDL 73811，AbeAdo）会导致L1210细胞生长停滞[拜尔斯、加内姆和佩格（1992年）《生物化学杂志》287卷，717 - 724页]。通过将对AbeAdo有抗性的L1210衍生细胞系（R20）与亲本细胞进行比较，开展了进一步研究以探究产生这些效应的机制。R20细胞是通过两轮AbeAdo诱导的生长停滞，随后用外源性多胺挽救而获得的。用10微摩尔AbeAdo处理12天可诱导L1210细胞生长停滞；然而，暴露于高达40微摩尔AbeAdo并不会诱导R20细胞生长停滞。在经处理的L1210细胞和经处理的R20细胞中，腐胺水平均升高，精胺水平均降低。在经处理的L1210细胞中，亚精胺水平降低，但在经处理的R20细胞中仅部分降低。在经处理的L1210细胞中，AdoMetDC活性低于检测限，但在经处理的R20细胞中，尽管活性大幅降低，但仍可检测到。R20细胞对AbeAdo对细胞生长和亚精胺消耗效应的抗性与R20细胞中AbeAdo积累减少相关。在缺乏亚精胺合成的情况下，未进行hypusination修饰的真核翻译起始因子5A（eIF - 5A）在AbeAdo处理的L1210细胞中积累。在R20细胞中未检测到未进行hypusination修饰的eIF - 5A积累。在AbeAdo处理期间积累的未进行hypusination修饰的eIF - 5A在经外源性亚精胺挽救的L1210细胞中减少。这些发现与AbeAdo诱导的生长停滞是由于hypusinated eIF - 5A缺失这一假说一致。然而，精胺能够挽救AbeAdo处理的L1210细胞，而不会显著降低在AbeAdo处理期间积累的未进行hypusination修饰的eIF - 5A，这表明仅需少量未修饰的蛋白进行hypusination修饰就能恢复细胞生长。
