Sumrejkanchanakij Piyamas, Tamamori-Adachi Mimi, Matsunaga Yuko, Eto Kazuhiro, Ikeda Masa-Aki
Section of Molecular Embryology, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
Oncogene. 2003 Nov 27;22(54):8723-30. doi: 10.1038/sj.onc.1206870.
Cyclin D-dependent kinases phosphorylate the retinoblastoma (Rb) protein and play a critical role in neuronal cell cycle control and apoptosis. Here we show that cyclin D1 became predominantly cytoplasmic as primary cortical progenitor cells underwent cell cycle withdrawal and terminal differentiation. Furthermore, ectopically expressed cyclin D1 sequestered in the cytoplasm of postmitotic neurons, whereas it efficiently entered the nucleus of proliferating progenitor cells. Cytoplasmic cyclin D1 were complexed with cyclin-dependent kinase 4 (CDK4), and also with CDK inhibitors, p27(Kip)(I) or p21(Cip)(I), which positively regulate assembly and nuclear accumulation of the cyclin D1-CDK4 complex. Although overexpression of p21(Cip)(I) promoted cyclin D1 nuclear localization, inhibition of either glycogen synthase kinase 3beta- or CRM1-mediated cyclin D1 nuclear export did not, suggesting that the inhibition of its nuclear import, rather than the acceleration of nuclear export, contributes to cytoplasmic sequestration of cyclin D1 in postmitotic neurons. In differentiated progenitor cells, nuclear localization of ectopic cyclin D1 induced apoptosis, and the DNA-damaging compound camptothecin caused nuclear accumulation of endogenous cyclin D1, accompanied by Rb phosphorylation. These results indicate that nuclear accumulation of cyclin D1 is inhibited in postmitotic neurons and suggest a role of its subcellular localization in neuronal death and survival.
细胞周期蛋白D依赖性激酶使视网膜母细胞瘤（Rb）蛋白磷酸化，并在神经元细胞周期调控和细胞凋亡中发挥关键作用。在此我们发现，随着原代皮质祖细胞退出细胞周期并进行终末分化，细胞周期蛋白D1主要定位于细胞质中。此外，异位表达的细胞周期蛋白D1在有丝分裂后神经元的细胞质中被隔离，而它能有效进入增殖祖细胞的细胞核。细胞质中的细胞周期蛋白D1与细胞周期蛋白依赖性激酶4（CDK4）结合，也与CDK抑制剂p27（Kip）（I）或p21（Cip）（I）结合，这些抑制剂正向调节细胞周期蛋白D1-CDK4复合物的组装和核积累。虽然p21（Cip）（I）的过表达促进了细胞周期蛋白D1的核定位，但抑制糖原合酶激酶3β或CRM1介导的细胞周期蛋白D1核输出却没有这种作用，这表明抑制其核输入而非加速核输出，有助于有丝分裂后神经元中细胞周期蛋白D1的细胞质隔离。在分化的祖细胞中，异位细胞周期蛋白D1的核定位诱导细胞凋亡，DNA损伤化合物喜树碱导致内源性细胞周期蛋白D1的核积累，并伴有Rb磷酸化。这些结果表明，有丝分裂后神经元中细胞周期蛋白D1的核积累受到抑制，并提示其亚细胞定位在神经元死亡和存活中的作用。
