p27Kip1 and p21Cip1 are not required for the formation of active D cyclin-cdk4 complexes
p27Kip1 and p21Cip1 are not required for the formation of active D cyclin-cdk4 complexes
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DOI：
10.1128/mcb.23.20.7285-7290.2003
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发表时间：
2003-10-01
影响因子：
5.3
通讯作者：
Pledger, WJ
中科院分区：
文献类型：
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作者：
Bagui, TK;Mohapatra, S;Pledger, WJ
我们的研究解决了与D细胞周期蛋白-cdk 4活性的调节有关的问题，并获得了以下结果。增加D细胞周期蛋白丰度的条件也增加了缺乏p27（Kip 1）和p21（Cip 1）（p27/p21（-/-））的小鼠胚胎成纤维细胞（MEFs）中酶活性D细胞周期蛋白-cdk 4复合物的丰度。这些条件包括细胞周期蛋白D1的异位表达和蛋白酶体抑制剂MG 132对D细胞周期蛋白降解的抑制。然而，通过用MG 132处理野生型MEFs确定，D细胞周期蛋白-cdk 4复合物的最大积累需要p27（Kip 1）和p21（Cip 1），并且与无活性D细胞周期蛋白-cdk 4-p27（Kip 1）或-p21（Cip 1）复合物的形成相一致。p27（Kip 1）或p21（Cip 1）在p27/p21（-/-）MEFs中异位表达时，也增加了D cyclin-cdk 4复合物的丰度，并降低了cdk 4的活性。最后，D细胞周期蛋白稳定性的增加解释了它们在野生型MEFs中比在p27/p21（-/-）MEFs中更大的丰度。我们的结论是：（i）在p27（Kip 1）和p21（Cip 1）不存在的情况下，D细胞周期蛋白-cdk 4复合物形成并变得有活性;（ii）p27（Kip 1）和p21（Cip 1）使D细胞周期蛋白-cdk 4复合物的积累最大化，但抑制其活性。我们认为，D细胞周期蛋白cdk 4复合物是更稳定的结合p27（Kip 1）或p21（Cip 1）和三元复合物的形成也稳定的D细胞周期蛋白。
Our studies address questions pertaining to the regulation of D cyclin-cdk4 activity, and the following results were obtained. Conditions that increased the abundance of the D cyclins also increased the abundance of enzymatically active D cyclin-cdk4 complexes in mouse embryo fibroblasts (MEFs) lacking both p27(Kip1) and p21(Cip1) (p27/p21(-/-)). Such conditions included ectopic expression of cyclin D1 and inhibition of D cyclin degradation by the proteasome inhibitor MG132. However, as determined by treatment of wild-type MEFs with MG132, maximal accumulation of D cyclin-cdk4 complexes required p27(Kip1) and p21(Cip1) and coincided with the formation of inactive D cyclin-cdk4-p27(Kip1) or -p21(Cip1) complexes. p27(Kip1) or p21(Cip1) also increased the abundance of D cyclin-cdk4 complexes and reduced amounts of cdk4 activity when ectopically expressed in p27/p21(-/-) MEFs. Lastly, increases in the stability of the D cyclins accounted for their greater abundance in wild-type MEFs than in p27/p21(-/-) MEFs. We conclude that (i) D cyclin-cdk4 complexes are formed and become active in the absence of p27(Kip1) and p21(Cip1) and (ii) p27(Kip1) and p21(Cip1) maximize the accumulation but inhibit the activity of D cyclin-cdk4 complexes. We suggest that D cyclin-cdk4 complexes are more stable when bound to p27(Kip1) or p21(Cip1) and that formation of ternary complexes also stabilizes the D cyclins.