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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Inhibition of insulin signaling and adipogenesis by rapamycin: effect on phosphorylation of p70 S6 kinase vs eIF4E-BP1.

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.[1]


  1. Inhibition of insulin signaling and adipogenesis by rapamycin: effect on phosphorylation of p70 S6 kinase vs eIF4E-BP1. El-Chaâr, D., Gagnon, A., Sorisky, A. Int. J. Obes. Relat. Metab. Disord. (2004) [Pubmed]
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