Mechanical Regulation of Glycogen Synthase Kinase 3β (GSK3β) in Mesenchymal Stem Cells Is Dependent on Akt Protein Serine 473 Phosphorylation via mTORC2 Protein
Mechanical Regulation of Glycogen Synthase Kinase 3β (GSK3β) in Mesenchymal Stem Cells Is Dependent on Akt Protein Serine 473 Phosphorylation via mTORC2 Protein
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DOI：
10.1074/jbc.m111.265330
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发表时间：
2011-11-11
影响因子：
4.8
通讯作者：
Rubin, Janet
中科院分区：
文献类型：
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作者：
Case, Natasha;Thomas, Jacob;Rubin, Janet
机械信号可以抑制糖原合成酶激酶3 β（GSK 3 β），导致β-连环蛋白的稳定。这种信号级联对于抑制由每日应变方案产生的间充质干细胞（MSC）中的脂肪形成是必需的。我们研究了Akt是否是MSC中负责GSK 3 β磷酸化和失活的机械活化激酶。机械应变（2%量级，0.17 Hz）诱导Akt在Ser-473和Thr-308处的磷酸化，同时诱导GSK 3 β在Ser-9处的磷酸化。抑制Akt（Akt 1/2激酶抑制剂处理或Akt敲低）可防止菌株诱导的GSK 3 β Ser-9磷酸化。PI 3 K的抑制阻止了Thr-308磷酸化，但菌株诱导的Ser-473磷酸化是可测量的，并诱导了GSK 3 β的磷酸化，表明Ser-473磷酸化足以用于下游机械应答。由于已知Rictor/mTORC 2（雷帕霉素复合物2的哺乳动物靶蛋白）抑制胰岛素对Akt在Ser-473处的磷酸化，因此我们研究了它是否有助于菌株诱导的Ser-473磷酸化。mTOR抑制剂KU 0063794阻止MSC中通过机械和胰岛素处理的Ser-473磷酸化。当mTORC 2被阻断时，GSK 3 β的机械失活被阻止，而胰岛素对GSK 3 β的抑制作用在Ser-473磷酸化不存在的情况下仍然可以测量，推测是通过Akt在Thr-308的磷酸化。总之，机械输入启动信号级联反应，该信号级联反应唯一依赖于mTORC 2激活和Akt在Ser-473处的磷酸化，该作用足以引起GSK 3 β的失活。因此，Akt下游GSK 3 β的机械调节依赖于Akt在Ser-473的磷酸化，其方式与生长因子不同。因此，Akt显示其本身是多效性信号传导分子，其下游靶标根据激活输入的性质而被差异调节。
Mechanical signals can inactivate glycogen synthase kinase 3 beta (GSK3 beta), resulting in stabilization of beta-catenin. This signaling cascade is necessary for the inhibition of adipogenesis in mesenchymal stem cells (MSC) that is produced by a daily strain regimen. We investigated whether Akt is the mechanically activated kinase responsible for phosphorylation and inactivation of GSK3 beta in MSC. Mechanical strain (2% magnitude, 0.17 Hz) induced phosphorylation of Akt at Ser-473 and Thr-308 in parallel with phosphorylation of GSK3 beta at Ser-9. Inhibiting Akt (Akt1/2 kinase inhibitor treatment or Akt knockdown) prevented strain-induced phosphorylation of GSK3 beta at Ser-9. Inhibition of PI3K prevented Thr-308 phosphorylation, but strain-induced Ser-473 phosphorylation was measurable and induced phosphorylation of GSK3 beta, suggesting that Ser-473 phosphorylation is sufficient for the downstream mechanoresponse. As Rictor/mTORC2 (mammalian target of rapamycin complex 2) is known to transduce phosphorylation of Akt at Ser-473 by insulin, we investigated whether it contributes to strain-induced Ser-473 phosphorylation. Phosphorylation of Ser-473 by both mechanical and insulin treatment in MSC was prevented by the mTOR inhibitor KU0063794. When mTORC2 was blocked, mechanical GSK3 beta inactivation was prevented, whereas insulin inhibition of GSK3 beta was still measured in the absence of Ser-473 phosphorylation, presumably through phosphorylation of Akt at Thr-308. In sum, mechanical input initiates a signaling cascade that is uniquely dependent on mTORC2 activation and phosphorylation of Akt at Ser-473, an effect sufficient to cause inactivation of GSK3 beta. Thus, mechanical regulation of GSK3 beta downstream of Akt is dependent on phosphorylation of Akt at Ser-473 in a manner distinct from that of growth factors. As such, Akt reveals itself to be a pleiotropic signaling molecule whose downstream targets are differentially regulated depending upon the nature of the activating input.