Developmental downregulation of Xenopus cyclin E is phosphorylation and nuclear import dependent and is mediated by ubiquitination.
Developmental downregulation of Xenopus cyclin E is phosphorylation and nuclear import dependent and is mediated by ubiquitination.
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非洲爪蟾细胞周期蛋白 E 的发育下调是磷酸化和核输入依赖性的，并且由泛素化介导。
DOI：
10.1016/j.ydbio.2011.04.014
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发表时间：
2011-07-01
影响因子：
2.7
通讯作者：
Hartley RS
中科院分区：
文献类型：
--
作者：
Brandt Y;Mitchell T;Wu Y;Hartley RS
细胞周期蛋白是结合并激活催化Cdks的调节亚基。Cyclin E与Cdk 2结合，介导细胞周期的G1/S转换。细胞周期蛋白E在乳腺癌、肺癌、皮肤癌、胃肠癌、宫颈癌和卵巢癌中过表达。其过度表达与患者预后不良相关，并参与乳腺癌的病因学。我们一直在研究细胞周期蛋白E在发育过程中通常如何下调，以确定类似机制的破坏是否会导致其在癌症中的过度表达，或者被用来减少其表达。在非洲爪蟾胚胎中，细胞周期蛋白E蛋白水平高且恒定，直到其在第12个细胞周期后通过不确定的机制突然不稳定，这对应于胚胎到成体细胞周期的中囊胚转换（MBT）和重塑。由于哺乳动物细胞周期蛋白E的降解是由泛素蛋白酶体系统调节，是磷酸化依赖性的，我们研究了磷酸化在非洲爪蟾细胞周期蛋白E营业额的作用。我们发现，类似于人类细胞周期蛋白E，丝氨酸398和苏氨酸394的磷酸化发挥了作用，在MBT细胞周期蛋白E营业额。免疫荧光分析表明，细胞周期蛋白E重新定位从细胞质到细胞核之前，其降解。当核输入被抑制时，MBT后细胞周期蛋白E的稳定性显著增加。为了研究爪蟾细胞周期蛋白E的降解是否是由蛋白酶体途径介导的，我们使用蛋白酶体抑制剂，并观察到细胞周期蛋白E在MBT后的细胞质中的逐步积累。细胞周期蛋白E的泛素化先于其在MBT的蛋白酶体降解。这些结果表明，在MBT的细胞周期蛋白E破坏需要磷酸化和核输入，以及蛋白酶体活性。
Cyclins are regulatory subunits that bind to and activate catalytic Cdks. Cyclin E associates with Cdk2 to mediate the G1/S transition of the cell cycle. Cyclin E is overexpressed in breast, lung, skin, gastrointestinal, cervical, and ovarian cancers. Its overexpression correlates with poor patient prognosis and is involved in the etiology of breast cancer. We have been studying how cyclin E is normally downregulated during development in order to determine if disruption of similar mechanisms could either contribute to its overexpression in cancer, or be exploited to decrease its expression. In Xenopus laevis embryos, cyclin E protein level is high and constant until its abrupt destabilization by an undefined mechanism after the 12th cell cycle, which corresponds to the midblastula transition (MBT) and remodeling of the embryonic to the adult cell cycle. Since degradation of mammalian cyclin E is regulated by the ubiquitin proteasome system and is phosphorylation dependent, we examined the role of phosphorylation in Xenopus cyclin E turnover. We show that similarly to human cyclin E, phosphorylation of serine 398 and threonine 394 plays a role in cyclin E turnover at the MBT. Immunofluorescence analysis shows that cyclin E relocalizes from the cytoplasm to the nucleus preceding its degradation. When nuclear import is inhibited, cyclin E stability is markedly increased after the MBT. To investigate whether degradation of Xenopus cyclin E is mediated by the proteasomal pathway, we used proteasome inhibitors and observed a progressive accumulation of cyclin E in the cytoplasm after the MBT. Ubiquitination of cyclin E precedes its proteasomal degradation at the MBT. These results show that cyclin E destruction at the MBT requires both phosphorylation and nuclear import, as well as proteasomal activity.
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