Kyprianou N, Bains A, Rhee J G
Division of Urology, University of Maryland School of Medicine, Baltimore 21201, USA.
Prostate. 1997 Sep 1;32(4):266-71. doi: 10.1002/(sici)1097-0045(19970901)32:4<266::aid-pros6>3.0.co;2-h.
Previous studies have demonstrated that androgen-independent human prostate cancer cells undergo radiation-induced apoptosis. The present study investigated the early events that trigger the apoptotic response of prostate cancer cells after exposure to ionizing irradiation.
Human prostate cancer cells (PC-3) were exposed to single doses of ionizing irradiation, and the immediate protein phosphorylation events were temporally correlated with induction of apoptosis. Apoptosis among the irradiated cell populations was evaluated using the fluorescein-terminal transferase assay.
The kinetics of phosphorylation of a Mr 34,000 substrate followed a transient course: an initial increase was observed after 10 min postirradiation, reaching maximum levels by 60 min, and the protein subsequently underwent rapid dephosphorylation. Subsequent analysis revealed that the substrate for this tyrosine phosphorylation is the serine/ threonine p34cdc2 protein kinase, a cell cycle regulatory protein that controls cell entry into mitosis. This enhanced phosphorylation temporally preceded the radiation-induced apoptotic DNA fragmentation as detected by the terminal transferase technique. Arresting the cells in G0/G1 phase by pretreatment with suramin totally abrogated radiation-induced phosphorylation of p34cdc2 protein at the tyrosine residue, indicating that this posttranslational modification occurs in cell populations that escape G2 arrest and undergo apoptosis in response to radiation.
These results suggest that a rapid and transient phosphorylation of a protein that controls mitotic progression precedes and potentially triggers radiation-induced apoptosis in prostate cancer cells.
先前的研究表明，雄激素非依赖性人前列腺癌细胞会经历辐射诱导的凋亡。本研究调查了电离辐射暴露后触发前列腺癌细胞凋亡反应的早期事件。
将人前列腺癌细胞（PC-3）暴露于单剂量的电离辐射，并将即时蛋白质磷酸化事件与凋亡诱导在时间上进行关联。使用荧光素末端转移酶测定法评估受辐射细胞群体中的凋亡情况。
一种分子量为34,000的底物的磷酸化动力学呈短暂过程：照射后10分钟观察到初始增加，60分钟时达到最高水平，随后该蛋白质迅速去磷酸化。随后的分析表明，这种酪氨酸磷酸化的底物是丝氨酸/苏氨酸p34cdc2蛋白激酶，一种控制细胞进入有丝分裂的细胞周期调节蛋白。如通过末端转移酶技术所检测到的，这种增强的磷酸化在时间上先于辐射诱导的凋亡性DNA片段化。用苏拉明预处理使细胞停滞在G0/G1期完全消除了辐射诱导的p34cdc2蛋白酪氨酸残基的磷酸化，表明这种翻译后修饰发生在逃避G2期停滞并对辐射产生凋亡反应的细胞群体中。
这些结果表明，在前列腺癌细胞中，一种控制有丝分裂进程的蛋白质的快速且短暂的磷酸化先于并可能触发辐射诱导的凋亡。
