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Translational Control of Protein Synthesis in Muscle and Liver of Growth Hormone-Treated Pigs

United States Department of Agriculture/Agricultural Research Service Children’s Nutrition Research Center (J.A.B., P.M.J.O’C., A.S., R.A.O., H.V.N., T.A.D.), Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030; and Department of Cellular and Molecular Physiology (S.R.K., L.S.J.), Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033

Address all correspondence and requests for reprints to: Dr. Teresa A. Davis, United States Department of Agriculture/Agricultural Research Service Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030. E-mail: tdavis{at}bcm.tmc.edu.

GH treatment increases protein deposition and the efficiency of dietary protein used for growth. To identify the mechanisms that regulate tissue protein synthesis in response to exogenous GH treatment, fully fed, growing swine were treated with GH for 7 d. Fasted and fed pigs were infused with [1-¹³C]leucine to determine protein synthesis rates, and translation initiation factor activity levels were measured in skeletal muscle and liver. Feeding increased protein synthesis and translational efficiency in both muscle and liver of control and GH-treated pigs, and this was associated with increased 4E-BP1 and S6 kinase 1 phosphorylation, decreased association of eukaryotic initiation factor (eIF) 4E with 4E-BP1, and increased association of eIF4E with eIF4G. GH increased muscle protein synthesis and translational efficiency in fed pigs. GH increased liver protein synthesis of fasted and fed pigs in association with increased ribosome number. In muscle, but not liver, GH increased eIF2B activity and 4E-BP1 phosphorylation in both the fasted and fed state and increased the association of eIF4E with eIF4G in the fed state. We conclude that GH increases muscle protein synthesis in the fed state, in part, via mechanisms that enhance the binding of mRNA and methionyl-tRNA to the 40S ribosomal subunit, whereas GH increases liver protein synthesis in the fasted and fed states by increasing ribosome number. The results further indicate that the GH-induced protein synthetic response is dependent upon nutritional state and is tissue specific.

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