Only Akt1 is required for proliferation, while Akt2 promotes cell cycle exit through p21 binding
Only Akt1 is required for proliferation, while Akt2 promotes cell cycle exit through p21 binding
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DOI：
10.1128/mcb.00201-06
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发表时间：
2006-11-01
影响因子：
5.3
通讯作者：
Lamb, Ned J. C.
中科院分区：
文献类型：
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作者：
Heron-Milhavet, Lisa;Franckhauser, Celine;Lamb, Ned J. C.
蛋白激酶 B (PKB/Akt) 是胰岛素信号传导、细胞增殖和存活的重要调节剂。在未转化的哺乳动物细胞中使用小干扰 RNA 双链体，我们发现只有 Akt1 对于细胞增殖至关重要，而 Akt2 则促进细胞周期退出。沉默 Akt1 会导致细胞周期蛋白 A 水平降低并抑制 S 期进入，这种效应在 Akt2 敲低时未见，但通过显微注射 Akt1（而非 Akt2）可显着缓解。在分化成肌细胞时，Akt2 敲除可阻止成肌细胞退出细胞周期并表现出持续的细胞周期蛋白 A 表达。相反，Akt2 的过度表达会减少细胞周期蛋白 A 并阻碍 M-G 中的细胞周期进程，同时增加核 p21。 p21 是 Akt 同工型差异效应的主要靶标，内源性 Akt2（而非 Akt1）在细胞核中结合 p21 并提高其水平。因此，Akt2 敲低细胞（而非 Akt1 敲低细胞）显示 p21 水平降低。特定的 Akt2/p21 相互作用可以在体外重现，p21 上的 Akt2 结合位点与跨 T145 至 T155 的细胞周期蛋白 A 中的结合位点相似，因为 (i) 与细胞周期蛋白 A 一起孵育可防止 Akt2 结合，(ii) Akt1 对 p21 上的 T145 磷酸化可防止 Akt2 结合，以及 (iii) 结合 Akt2 可防止 p21 磷酸化。通过 Akt1。这些数据表明 Akt2 同工型与 p21 的特异性相互作用是其对正常细胞周期进程产生负面影响的关键。
Protein kinase B (PKB/Akt) is an important modulator of insulin signaling, cell proliferation, and survival. Using small interfering RNA duplexes in nontransformed mammalian cells, we show that only Akt1 is essential for cell proliferation, while Akt2 promotes cell cycle exit. Silencing Akt1 resulted in decreased cyclin A levels and inhibition of S-phase entry, effects not seen with Akt2 knockdown and specifically rescued by microinjection of Akt1, not Akt2. In differentiating myoblasts, Akt2 knockout prevented myoblasts from exiting the cell cycle and showed sustained cyclin A expression. In contrast, overexpression of Akt2 reduced cyclin A and hindered cell cycle progression in M-G, with increased nuclear p21. p21 is a major target in the differential effects of Akt isoforms, with endogenous Akt2 and not Akt1 binding p21 in the nucleus and increasing its level. Accordingly, Akt2 knockdown cells, and not Akt1 knockdown cells, showed reduced levels of p21. A specific Akt2/p21 interaction can be reproduced in vitro, and the Akt2 binding site on p21 is similar to that in cyclin A spanning T145 to T155, since (i) prior incubation with cyclin A prevents Akt2 binding, (ii) T145 phosphorylation on p21 by Akt1 prevents Akt2 binding, and (iii) binding Akt2 prevents phosphorylation of p21. by Akt1. These data show that specific interaction of the Akt2 isoform with p21 is key to its negative effect on normal cell cycle progression.