A novel mTOR-regulated phosphorylation site in elongation factor 2 kinase modulates the activity of the kinase and its binding to calmodulin.
Eukaryotic elongation factor 2 (eEF2) kinase is an unusual calcium- and calmodulin-dependent protein kinase that is regulated by insulin through the rapamycin-sensitive mTOR pathway. Here we show that insulin decreases the ability of eEF2 kinase to bind calmodulin in a rapamycin-sensitive manner. We identify a novel phosphorylation site in eEF2 kinase (Ser78) that is located immediately next to its calmodulin-binding motif. Phosphorylation of this site is increased by insulin in a rapamycin-sensitive fashion. Regulation of the phosphorylation of Ser78 also requires amino acids and the protein kinase phosphoinositide-dependent kinase 1. Mutation of this site to alanine strongly attenuates the effects of insulin and rapamycin both on the binding of calmodulin to eEF2 kinase and on eEF2 kinase activity. Phosphorylation of Ser78 is thus likely to link insulin and mTOR signaling to the control of eEF2 phosphorylation and chain elongation. This site is not a target for known kinases in the mTOR pathway, e.g., the S6 kinases, implying that it is phosphorylated by a novel mTOR-linked protein kinase that serves to couple hormones and amino acids to the control of translation elongation. eEF2 kinase is thus a target for mTOR signaling independently of previously known downstream components of the pathway.
Browne
Gareth J
GJ
Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
Proud
Christopher G
CG
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D054736:Elongation Factor 2 Kinase; D006801:Humans; D007328:Insulin / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
D000596:Amino Acids; D002147:Calmodulin; D007328:Insulin; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D012694:Serine; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C517689:EEF2K protein, human; D064413:3-Phosphoinositide-Dependent Protein Kinases; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517690:Eef2k protein, mouse; D054736:Elongation Factor 2 Kinase