Caspase processing and nuclear export of CTP:phosphocholine cytidylyltransferase α during farnesol-induced apoptosis
Caspase processing and nuclear export of CTP:phosphocholine cytidylyltransferase α during farnesol-induced apoptosis
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DOI：
10.1128/mcb.22.13.4851-4862.2002
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发表时间：
2002-07-01
影响因子：
5.3
通讯作者：
Ridgway, ND
中科院分区：
文献类型：
--
作者：
Lagace, TA;Miller, JR;Ridgway, ND
CTP：磷酸胆碱胞苷转移酶α(CCTpha)是一种核酶，催化CDP-胆碱途径中的限速步骤，这是真核细胞合成磷脂酰胆碱(PtdCho)的主要途径。研究表明，法尼醇(FOH)和其他细胞毒性药物诱导的细胞凋亡通过CDP-胆碱途径改变PtdCho的合成。在这里，我们报道了FOH诱导的CHO细胞的凋亡导致CCTpha的剂量依赖性激活，抑制了该途径的最后一步，导致了对PtdCho合成的两相效应。在FOH加入细胞后30分钟内，CCTAlpha的激活伴随着酶移位到核膜。在转位到膜上后，CCTpha从细胞核中排出，并经历了caspase介导的蛋白分解，这与聚(ADP-核糖)聚合酶的切割是一致的。定点突变和体内和体外表达研究将caspase 6和/或8裂解位点定位到CCTpha核定位信号的最终残基Ted 28G。在FOH处理的CHO细胞中，CCTpha的核输出似乎是一个活跃的过程，这一过程不依赖于caspase对核定位信号的去除。在紫外线或白屈菜红碱诱导的细胞凋亡过程中，CCTbeta的caspase发生了裂解，但在此条件下核膜移位和核输出不明显。因此，CCTα的caspase裂解是发生在细胞核或核膜上的几个凋亡程序的晚期特征。CCTAlpha的激活和核输出是FOH诱导的细胞凋亡的早期事件，导致PtdCho合成改变，并与caspase切割一起将CCTAlpha排除在细胞核之外。
CTP:phosphocholine cytidylyltransferase alpha (CCTalpha) is a nuclear enzyme that catalyzes the rate-limiting step in the CDP-choline pathway, the primary route for synthesis of phosphatidylcholine (PtdCho) in eukaryotic cells. Induction of apoptosis by farnesol (FOH) and other cytotoxic drugs has been shown to alter PtdCho synthesis via the CDP-choline pathway. Here we report that FOH-induced apoptosis in CHO cells caused a dose-dependent activation of CCTalpha an inhibition of the final step in the pathway, resulting in a biphasic effect on PtdCho synthesis. Activation of CCTalpha was accompanied by enzyme translocation to the nuclear envelope within 30 min of FOH addition to cells. Following translocation to membranes, CCTalpha was exported from the nucleus and underwent caspase-mediated proteolysis that coincided with poly (ADP-ribose) polymerase cleavage. Site-directed mutagenesis and in vivo and in vitro expression studies mapped a caspase 6 and/or 8 cleavage site to TEED 28 G, the final residue in the CCTalpha nuclear localization signal. Nuclear export of CCTalpha appeared to be an active process in FOH-treated CHO cells that was independent of caspase removal of the nuclear localization signal. Caspase cleavage of CCTbeta occurred during UV or chelerythrine-induced apoptosis; however, nuclear membrane translocation and nuclear export were not evident under these conditions. Thus, caspase cleavage of CCTalpha was a late feature of several apoptotic programs that occurred in the nucleus or at the nuclear envelope. Activation and nuclear export of CCTalpha were early events in FOH-induced apoptosis that contributed to altered PtdCho synthesis and, in conjunction with caspase cleavage, excluded CCTalpha from the nucleus.