Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan.
Agricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan.
Cell Signal. 2014 Jul;26(7):1400-8. doi: 10.1016/j.cellsig.2014.03.004. Epub 2014 Mar 17.
Ceramide is a negative regulator of insulin activity. At the molecular level, it causes a decrease in insulin-stimulated Akt Ser473 phosphorylation in C2C12 myotubes. Interestingly, we found that the phosphorylation of S6K at Thr389 was increased under the same conditions. Utilizing both rapamycin to inhibit mTORC1 activity and shRNA to knock down Rheb, we demonstrated that the decrease in Akt Ser473 phosphorylation stimulated by insulin after C2-ceramide incubation can be prevented. The mechanism by which C2-ceramide impairs signaling would seem to involve a negative feedback of activated S6K via phosphorylation of insulin receptor substrate-1 at Ser636/639, since S6K inhibitor can block this phenomenon. Finally, rapamycin treatment was found not to affect C2-ceramide-induced PKCζ activation, suggesting that the pathway revealed in this study is parallel to the one involving PKCζ activation. We proposed a novel pathway/mechanism involving Rheb/mTORC1/S6K signaling to explain how C2-ceramide impairs insulin signaling via Akt phosphorylation. The existence of multiple pathways involved in insulin signaling impairment by C2-ceramide treatment implies that different strategies might be needed to ameliorate insulin resistance caused by C2-ceramide.
神经酰胺是胰岛素活性的负调节剂。在分子水平上，它会导致 C2C12 肌管中胰岛素刺激的 Akt Ser473 磷酸化减少。有趣的是，我们发现相同条件下 S6K 的 Thr389 磷酸化增加。利用雷帕霉素抑制 mTORC1 活性和 shRNA 敲低 Rheb，我们证明了 C2-神经酰胺孵育后胰岛素刺激的 Akt Ser473 磷酸化减少可以被阻止。C2-神经酰胺损害信号转导的机制似乎涉及通过 Ser636/639 磷酸化胰岛素受体底物-1 对激活的 S6K 的负反馈，因为 S6K 抑制剂可以阻断这种现象。最后，发现雷帕霉素处理不会影响 C2-神经酰胺诱导的 PKCζ 激活，表明该研究中揭示的途径与涉及 PKCζ 激活的途径平行。我们提出了一种涉及 Rheb/mTORC1/S6K 信号的新途径/机制，以解释 C2-神经酰胺如何通过 Akt 磷酸化损害胰岛素信号。C2-神经酰胺处理通过多种途径损害胰岛素信号的存在意味着需要采取不同的策略来改善 C2-神经酰胺引起的胰岛素抵抗。
