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Department of Cellular and Molecular Physiology, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania 17033
Glucocorticoids are diabetogenic factors that not only
antagonize the action of insulin in target tissues but also render these tissues catabolic. Therefore, in rats, we endeavored to characterize the effects in skeletal muscle of glucocorticoids on
translation initiation, a regulated process that, in part, governs
overall protein synthesis through the modulated activities of
eukaryotic initiation factors (eIFs). Four hours after intraperitoneal administration of dexamethasone (100 µg/100 g body wt), protein synthesis in skeletal muscle was reduced to 59% of the value recorded in untreated control animals. Furthermore, translation initiation factor eIF4E preferred association with its endogenous inhibitor 4E-BP1
rather than eIF4G. Dexamethasone treatment resulted in dephosphorylation of both 4E-BP1 and the 40S ribosomal protein S6
kinase concomitant with enhanced phosphorylation of eIF4E. Moreover,
the guanine nucleotide exchange activity of eIF2B was unaffected as was
phosphorylation of the 
-subunit of eIF2. Hence glucocorticoids
negatively modulate the activation of a subset of the protein synthetic
machinery, thereby contributing to the catabolic properties of this
class of hormones in vivo.
dexamethasone; eukaryotic initiation factor; eIF4E; eIF2B; 4E-BP1; p70S6k
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