Regulation of protein-synthesis elongation-factor-2 kinase by cAMP in adipocytes

Treatment of primary rat epididymal adipocytes or 3T3-L1 adipocytes with va rious agents which increase cAMP led to the phosphorylation of eukaryotic t ranslation elongation factor-2 (eEF-2). The increase in eEF-2 phosphorylati on was a consequence of the activation of eEF-2 kinase (eEF-2K), which is a Ca2+/calmodulin-dependent kinase. eEF-2K was shown to be essentially inact ive at less than 0.1 mu M free Ca2+ when measured in cell-free extracts. Tr eatment of adipocytes with isoproterenol induced Ca2+-independent eEF-2K ac tivity, and an 8-10-fold activation of eEF-2K was observed at Ca2+ concentr ations of less than 0.1 mu M. Increased cAMP in 3T3-L1 adipocytes led to th e inhibition of total protein synthesis and decreased the rate of polypepti de-chain elongation. We also show that the phosphorylation of eEF-2 and the activity of eEF-2K are insulin-regulated in adipocytes, These results demo nstrate a novel mechanism for the control of protein synthesis by hormones which act by increasing cytoplasmic cAMP.