REGULATION OF TRANSLATION ELONGATION FACTOR-II BY INSULIN VIA A RAPAMYCIN-SENSITIVE SIGNALING PATHWAY

It is well established that insulin and serum stimulate gene expressio n at the level of mRNA translation in animal cells, and previous studi es have mainly focused on the initiation process. Here we show that, i n Chinese hamster ovary cells expressing the human insulin receptor, i nsulin causes decreased phosphorylation of elongation factor eEF-2 and that this is associated with stimulation of the rate of peptide-chain elongation, eEF-2 is phosphorylated by a very specific Ca2+/calmoduli n-dependent protein kinase (eEF-2 kinase) causing its complete inactiv ation. The decrease in eEF-2 phosphorylation induced by insulin reflec ts a fall in eEF-2 kinase activity. Rapamycin, a macrolide immunosuppr essant which blocks the signalling pathway leading to the stimulation of the 70/85 kDa ribosomal protein S6 kinases, substantially blocks th e activation of elongation, the fall in eEF-2 phosphorylation and the decrease in eEF-2 kinase activity, suggesting that p70 S6 kinase (p70( S6k)) and eEF-2 kinase may lie on a common signalling pathway. Wortman nin, an inhibitor of phosphatidylinositide-3-OH kinase, had similar ef fects, eEF-2 kinase was phosphorylated in vitro by purified p70(S6k) b ut this had no significant effect on the in vitro activity of eEF-2 ki nase.