A nonproteolytic function of the proteasome is required for the dissociation of Cdc2 and cyclin B at the end of M phase
A nonproteolytic function of the proteasome is required for the dissociation of Cdc2 and cyclin B at the end of M phase
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DOI：
10.1101/gad.823200
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发表时间：
2000-09-15
影响因子：
10.5
通讯作者：
Kishimoto, T
中科院分区：
文献类型：
--
作者：
Nishiyama, A;Tachibana, K;Kishimoto, T
细胞周期蛋白B-CDC2亚基在M期的失活依赖于细胞周期蛋白B亚基的特异性蛋白分解，而CDC2亚基在整个细胞周期中几乎保持恒定的水平。目前尚不清楚当细胞周期蛋白B被破坏时，Cdc2是如何逃脱降解的。在体外复制M期退出的非洲爪哇卵提取液中，我们发现在细胞周期蛋白B与26S蛋白酶体结合但尚未降解的条件下，细胞周期蛋白B-CDC2复合体发生解离。Thr161在Cdc2上的去磷酸化不太可能是这两个亚基解离所必需的。然而，这种解离依赖于Cyclin B中功能破坏盒的存在，Cyclin B泛素化本身也不足以分离CDc2和Cyclin B。26S蛋白酶体，而不是20S蛋白酶体，能够分离这两个亚基。这些结果表明，蛋白酶体通过一种先于Cyclin B的蛋白分解的机制来分离Cyclin B和CDC2亚基，并且不依赖于蛋白分解。结果，细胞周期蛋白B水平在退出M期时下降，而Cdc2水平保持不变。
Inactivation of cyclin B-Cdc2 kinase at the exit from M phase depends on the specific proteolysis of the cyclin B subunit, whereas the Cdc2 subunit remains present at nearly constant levels throughout the cell cycle. It is unknown how Cdc2 escapes degradation when cyclin B is destroyed. In Xenopus egg extracts that reproduce the exit from M phase in vitro, we have found that dissociation of the cyclin B-Cdc2 complex occurred under conditions where cyclin B was tethered to the 26S proteasome but not yet degraded. The dephosphorylation of Thr 161 on Cdc2 was unlikely to be necessary for the dissociation of the two subunits. However, the dissociation was dependent on the presence of a functional destruction box in cyclin B. Cyclin B ubiquitination was also, by itself, not sufficient for separation of Cdc2 and cyclin B. The 26S proteasome, but not the 20S proteasome, was capable of dissociating the two subunits. These results indicate that the cyclin B and Cdc2 subunits are separated by the proteasome through a mechanism that precedes proteolysis of cyclin B and is independent of proteolysis. As a result, cyclin B levels decrease on exit from M phase but Cdc2 levels remain constant.