Neuronal nuclear organization is controlled by cyclin-dependent kinase 5 phosphorylation of ras guanine nucleotide releasing factor-1
Neuronal nuclear organization is controlled by cyclin-dependent kinase 5 phosphorylation of ras guanine nucleotide releasing factor-1
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DOI：
10.1159/000095130
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发表时间：
2006-01-01
期刊：
影响因子：
--
通讯作者：
Pant, Harish C.
中科院分区：
文献类型：
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作者：
Kesavapany, Sashi;Pareek, Tej Kumar;Pant, Harish C.
RasGRF 1是Ras鸟嘌呤核苷酸交换因子（RasGEF）蛋白家族的成员，其直接负责Ras和Rac GTP酶的活化。RasGRF 1最初被鉴定为磷蛋白，已被证明可被蛋白激酶A磷酸化，最近被非受体酪氨酸激酶Ack 1和Src磷酸化。在这份报告中，我们表明，RasGRF 1相互作用，并被磷酸化的Cdk 5丝氨酸731调节其稳态水平在哺乳动物细胞以及神经元。Cdk 5在该位点上的磷酸化导致RasGRF 1通过钙蛋白酶依赖性机制降解。此外，来自Cdk 5敲除小鼠的皮质神经元具有较高水平的RasGRF 1，当野生型Cdk 5转染到这些神经元中时，RasGRF 1水平降低。在有丝分裂细胞中，当RasGRF 1过表达时，细胞核变得紊乱，当RasGRF 1与活性Cdk 5共表达时，这被拯救。当RasGRF 1水平在神经元中通过野生型RasGRF 1或RasGRF 1的磷酸化突变体的过表达以及通过显性负性Cdk 5构建体的转染而升高时，细胞核出现浓缩和碎片化。另一方面，通过p35/Cdk 5过表达降低RasGRF 1水平也导致神经元中的核浓缩。这些数据表明，Cdk 5对RasGRF 1的磷酸化密切调节其水平，这对适当的细胞组织至关重要。版权所有（c）2006 S. Karger AG，巴塞尔。
RasGRF1 is a member of the Ras guanine nucleotide exchange factor ( RasGEF) family of proteins which are directly responsible for the activation of Ras and Rac GTPases. Originally identified as a phosphoprotein, RasGRF1 has been shown to be phosphorylated by protein kinase A and more recently, by the non-receptor tyrosine kinases Ack1 and Src. In this report we show that RasGRF1 interacts with and is phosphorylated by Cdk5 on serine 731 to regulate its steady state levels in mammalian cells as well as in neurons. Phosphorylation on this site by Cdk5 leads to RasGRF1 degradation through a calpain-dependent mechanism. Additionally, cortical neurons from Cdk5 knockout mice have higher levels of RasGRF1 which are reduced when wild-type Cdk5 is transfected into these neurons. In mitotic cells, nuclei become disorganized when RasGRF1 is overexpressed and this is rescued when RasGRF1 is co-expressed with active Cdk5. When RasGRF1 levels are elevated in neurons through overexpression of either the wild-type RasGRF1, or the phosphorylation mutant of RasGRF1 and by the transfection of a dominant negative Cdk5 construct, nuclei appeared condensed and fragmented. On the other hand, a reduction of RasGRF1 levels through p35/Cdk5 overexpression also leads to nuclear condensation in neurons. These data show that phosphorylation of RasGRF1 by Cdk5 tightly regulates its levels, which is essential for proper cellular organization. Copyright (c) 2006 S. Karger AG, Basel.