L6 myoblast differentiation is modulated by Cdk5 via the PI3K-AKT-p70S6K signaling pathway
L6 myoblast differentiation is modulated by Cdk5 via the PI3K-AKT-p70S6K signaling pathway
复制标题
DOI：
10.1038/sj.onc.1207819
复制
发表时间：
2004-08-12
期刊：
影响因子：
8
通讯作者：
Lee, KY
中科院分区：
文献类型：
--
作者：
Sarker, KP;Lee, KY
Cdk 5调节肌生成，但Cdk 5调节这一过程的信号级联反应仍有待鉴定。在这里，我们调查是否PI 3 K，Akt，p70 S6 K，p38 MAPK，p44/42 MAPK，和Egr-1作为Cdk 5的上游调节剂在L 6成肌细胞分化。在血清减少时，我们发现除了Cdk 5及其激活剂p35的表达升高和Cdk 5/p35活性增加之外，Egr-1、Akt、p70 S6 K和p38 MAPK活性在分化中的L 6细胞中上调。而p44/42 MAPK表达下调，SAPK/JNK表达不受影响。PI 3 K抑制剂LY 294002可阻断Akt和p70 S6 K的激活，表明Akt和p70 S6 K的激活与PI 3 K的激活有关。LY 294002对p38 MAPK无影响提示p38 MAPK激活与PI 3 K激活无关。雷帕霉素是FRAP/mTOR（p70 S6 K的上游激酶）的特异性抑制剂，也阻断了p70 S6 K的活化，表明FRAP/mTOR活化参与其中。LY 294002和雷帕霉素也阻断了Egr-1水平、Cdk 5活性和肌细胞生成素表达的增强，表明这些因子的上调与PI 3 K-p70 S6 K激活偶联。显性失活Akt的过表达也降低了Cdk 5/p35活性和肌细胞生成素的表达，表明PI 3 K-p70 S6 K-Egr-1-Cdk 5信号级联与Akt活化有关。SB 2023580是一种p38 MAPK抑制剂，对p70 S6 K、Egr-1或Cdk 5活性没有影响，表明p38 MAPK激活位于与PI 3 K-Akt-p70 S6 K-Egr-1通路不同的通路中，我们将PI 3 K-Akt-p70 S6 K-Egr-1通路鉴定为L 6成肌细胞分化过程中Cdk 5活性的上游调节剂。
Cdk5 regulates myogenesis but the signaling cascade through which Cdk5 modulates this process remains to be characterized. Here, we investigated whether PI3K, Akt, p70S6K, p38 MAPK, p44/42 MAPK, and Egr-1 serve as upstream regulators of Cdk5 during L6 myoblast differentiation. Upon serum reduction, we found that besides elevated expression of Cdk5 and its activator, p35, and increased Cdk5/p35 activity, Egr-1, Akt, p70S6K, and p38 MAPK activity were upregulated in differentiating L6 cells. However, p44/42 MAPK was downregulated and SAPK/JNK was unaffected. LY294002, a PI3K inhibitor, blocked the activation of Akt and p70S6K, indicating that Akt and p70S6K activation is linked to PI3K activation. The lack of LY294002 effect on p38 MAPK suggests that p38 MAPK activation is not associated with PI3K activation. Rapamycin, a specific inhibitor of FRAP/mTOR (the upstream kinase of p70S6K), also blocked p70S6K activation, indicating the involvement of FRAP/mTOR activation. LY294002 and rapamycin also blocked the enhancement of Egr-1 level, Cdk5 activity, and myogenin expression, suggesting that upregulation of these factors is coupled to PI3K-p70S6K activation. Overexpression of dominant-negative-Akt also reduced Cdk5/p35 activity and myogenin expression, indicating that the PI3K-p70S6K-Egr-1-Cdk5 signaling cascade is linked to Akt activation. SB2023580, a p38 MAPK inhibitor, had no effect on p70S6K, Egr-1, or Cdk5 activity, suggesting that p38 MAPK activation lies in a pathway distinct from the PI3K-Akt-p70S6K-Egr-1 pathway that we identify as the upstream modulator of Cdk5 activity during L6 myoblast differentiation.