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Am J Physiol Endocrinol Metab (March 27, 2007). doi:10.1152/ajpendo.00037.2007
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Submitted on January 15, 2007
Accepted on March 21, 2007

Rapamycin Blunts Nutrient Stimulation of eIF4G, but not PKC{epsilon} Phosphorylation in Skeletal Muscle

Thomas C. Vary1*, Joshua C. Anthony2, Leonard S. Jefferson1, Scot R. Kimball1, and Christopher J. Lynch1

1 Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey,, Pennsylvania, United States
2 Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey,, Pennsylvania, United States; Principal Scientist, Global Discovery, Mead Johnson Nutritionals, Evansville, Indiana, United States

* To whom correspondence should be addressed. E-mail: tvary{at}psu.edu.

Phosphorylation of eukaryotic initiation factor 4G (eIF4G) is hypothesized to be an important contributor to the stimulation of protein synthesis in skeletal muscle following meal feeding. The experiments reported herein examined the potential role for a rapamycin-sensitive signaling pathway in mediating the meal-feeding-induced elevations in phosphorylation of eIF4G. Gastrocnemius from male Sprague-Dawley rats trained to consume a meal consisting of rat chow was sampled prior to and following 3h of providing the meal in the presence or absence of treatment with rapamycin, an inhibitor of the mammalian Target of Rapamycin (mTOR) complex 1 (TORC 1). Pretreatment with rapamycin prevented the feeding-induced phosphorylation of mTOR, eIF4G and S6K1 but only partially attenuated the shift in 4E-BP1 into the {gamma}-form. In contrast, the feeding-induced increase in phosphorylation of PKC{epsilon} was not reduced by rapamycin. Rapamycin also prevented the augmented association of eIF4G with eIF4E, and the decreased association of eIF4E with 4E-BP1. Similar findings were observed in gastrocnemius from animals after oral administration of leucine. Lastly, perfusion of gastrocnemius with medium containing rapamycin partially prevented the leucine induced increase in phosphorylation of eIF4G. Thus, rapamycin attenuated a feeding or leucine-induced phosphorylation of eIF4G in skeletal muscle both in vivo and in situ. The latter observation implies that the effects observed with rapamycin were the result of modulation of skeletal muscle signaling mechanisms responsible for eIF4G phosphorylation.




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