Inhibition of insulin signaling and adipogenesis by rapamycin:: effect on phosphorylation of p70 S6 kinase vs eIF4E-BP1
Inhibition of insulin signaling and adipogenesis by rapamycin:: effect on phosphorylation of p70 S6 kinase vs eIF4E-BP1
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DOI：
10.1038/sj.ijo.0802554
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发表时间：
2004-02-01
影响因子：
4.9
通讯作者：
Sorisky, A
中科院分区：
文献类型：
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作者：
El-Chaâr, D;Gagnon, A;Sorisky, A
目的：胰岛素反应性脂肪生成信号分子包括胰岛素受体底物 (IRS)-1 和 -2、磷酸肌醇 3-激酶 (PI3K) 和蛋白激酶 B (PKB；也称为 Akt)。哺乳动物雷帕霉素靶标 (mTOR) 是 PKB 底物，可调节 p70 S6 激酶 (p70 S6K)。由于 p70 S6K 是 PI3K 和 PKB 下游的胰岛素反应性激酶，因此研究了其在脂肪生成胰岛素信号传导中的潜在作用。设计：我们测量了雷帕霉素（mTOR 的特异性抑制剂）对胰岛素诱导的 3T3-L1 脂肪生成和胰岛素刺激的 p70 S6K 激活的影响。结果：雷帕霉素 通过油红 O 染色、三酰甘油积累（高达 46%）和过氧化物酶体增殖物激活受体 γ 蛋白表达（高达 50%）测量，分化部分减少。相反，通过 p70 S6K 及其底物 S6 的磷酸化评估，雷帕霉素完全抑制胰岛素刺激的 p70 S6K 激活。 p70 S6K 的组成型激活形式的表达不会促进 3T3-L1 脂肪生成。尽管完全阻断了 p70 S6K 的激活，但雷帕霉素存在下仍存在相当大的残余分化，这促使我们测量另一种雷帕霉素敏感蛋白、真核起始因子 4E (eIF4E) 结合蛋白 1 (4E-BP1) 的磷酸化。 3T3-L1 前脂肪细胞中胰岛素刺激的 4E-BP1 磷酸化仅部分受到雷帕霉素的影响，与分化数据一致。 eIF4E 本身的磷酸化（4E-BP1 磷酸化的预期结果）也仅部分受到抑制。结论：我们的数据表明，脂肪形成 mTOR 信号传导通过 4E-BP1/eIF4E 途径发生，而不是通过 p70 S6K。
OBJECTIVE: Insulin-responsive adipogenic signaling molecules include insulin receptor substrates (IRS)-1 and -2, phosphoinositide 3-kinase (PI3K), and protein kinase B (PKB; also known as Akt). Mammalian target of rapamycin (mTOR) is a PKB substrate, and regulates p70 S6 kinase (p70 S6K). Since p70 S6K is an insulin-responsive kinase downstream of PI3K and PKB, its potential role in adipogenic insulin signaling was investigated.DESIGN: We measured the effect of rapamycin, a specific inhibitor of mTOR, on insulin-induced 3T3-L1 adipogenesis and on insulin-stimulated p70 S6K activation.RESULTS: Rapamycin partially reduced differentiation, measured by Oil Red O staining, triacylglycerol accumulation (by up to 46%), and peroxisome proliferator-activated receptor gamma protein expression (by 50%). In contrast, rapamycin completely inhibited insulin-stimulated p70 S6K activation, assessed by phosphorylation of p70 S6K and its substrate, S6. Expression of a constitutively activated form of p70 S6K did not promote 3T3-L1 adipogenesis. The considerable residual differentiation in the presence of rapamycin, despite the complete blockade of p70 S6K activation, prompted us to measure the phosphorylation of another rapamycin- sensitive protein, eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1). Insulin-stimulated 4E-BP1 phosphorylation in 3T3-L1 preadipocytes was only partially affected by rapamycin, consistent with the differentiation data. Phosphorylation of eIF4E itself, an expected consequence of 4E-BP1 phosphorylation, was also only partially inhibited.CONCLUSION: Our data suggest that adipogenic mTOR signaling occurs via the 4E-BP1/eIF4E pathway, rather than through p70 S6K.