Department of Biology, Saint Louis University, MO 63103, USA.
Acta Physiol (Oxf). 2010 Apr;198(4):465-75. doi: 10.1111/j.1748-1716.2009.02069.x. Epub 2009 Dec 10.
Ataxia telangiectasia mutated (ATM) reportedly plays a role in insulin-stimulated activation of Akt in some cell types but not in others. The role of ATM in insulin signalling has not been firmly resolved for skeletal muscle cells, for which Akt phosphorylation is a pivotal step in stimulation of glucose transport. Accordingly, our aim was to determine the role of ATM in insulin effects for cell lines derived from skeletal muscle and for skeletal muscle.
We examined insulin effects in L6 myotubes, mouse soleus, C2C12 myotubes and differentiated rhabdomyosarcoma (RD) cells in the presence and absence of a low concentration (1 microm) of the ATM inhibitor KU55933. We also compared insulin signalling in C2C12 cells expressing shRNA against ATM and control cell lines (empty vector; cells expressing non-targeting shRNA).
In L6 myotubes and mouse soleus muscle, KU55933 inhibited insulin-stimulated phosphorylation of the 160 kDa substrate of Akt (AS160) despite no effect on Akt. In contrast, KU55933 prevented insulin-stimulated Akt phosphorylation in C2C12 myotubes. Furthermore, C2C12 myotubes expressing shRNA against ATM displayed reduced insulin-stimulated Akt phosphorylation compared to controls. KU55933 also decreased insulin-stimulated Akt phosphorylation in differentiated RD cells.
These model-dependent differences in the role of ATM in insulin action demonstrate a role of ATM in insulin-stimulated phosphorylation of Akt (in C2C12 and RD cells) but also allow the elucidation of a novel, Akt-independent role of ATM (in L6 myotubes and mouse soleus, at the level of AS160) in insulin signalling.
据报道，共济失调毛细血管扩张突变基因（ATM）在某些细胞类型中发挥作用，可使胰岛素刺激的 Akt 活化，但在其他细胞类型中则不然。ATM 在胰岛素信号中的作用尚未在骨骼肌细胞中得到明确证实，因为 Akt 磷酸化是刺激葡萄糖转运的关键步骤。因此，我们的目的是确定 ATM 在源自骨骼肌的细胞系和骨骼肌中胰岛素作用中的作用。
我们在存在和不存在低浓度（1μm）ATM 抑制剂 KU55933 的情况下，研究了 L6 肌管、小鼠比目鱼肌、C2C12 肌管和分化的横纹肌肉瘤（RD）细胞中的胰岛素作用。我们还比较了表达 ATM 短发夹 RNA（shRNA）的 C2C12 细胞和对照细胞系（空载体；表达非靶向 shRNA 的细胞）中的胰岛素信号。
在 L6 肌管和小鼠比目鱼肌中，KU55933 抑制了胰岛素刺激的 Akt 的 160kDa 底物（AS160）的磷酸化，尽管对 Akt 没有影响。相比之下，KU55933 阻止了 C2C12 肌管中胰岛素刺激的 Akt 磷酸化。此外，表达 ATM shRNA 的 C2C12 肌管与对照相比，胰岛素刺激的 Akt 磷酸化减少。KU55933 还降低了分化的 RD 细胞中胰岛素刺激的 Akt 磷酸化。
这些模型依赖性差异表明，ATM 在胰岛素作用中的作用是多方面的，既可以使 Akt（在 C2C12 和 RD 细胞中）在胰岛素刺激下磷酸化，也可以阐明 ATM 的一种新的、独立于 Akt 的作用（在 L6 肌管和小鼠比目鱼肌中，在 AS160 水平上）在胰岛素信号中。
