Akt activates the mammalian target of rapamycin by regulating cellular ATP level and AMPK activity.
The serine/threonine kinase Akt is an upstream positive regulator of the mammalian target of rapamycin (mTOR). However, the mechanism by which Akt activates mTOR is not fully understood. The known pathway by which Akt activates mTOR is via direct phosphorylation and inhibition of tuberous sclerosis complex 2 (TSC2), which is a negative regulator of mTOR. Here we establish an additional pathway by which Akt inhibits TSC2 and activates mTOR. We provide for the first time genetic evidence that Akt regulates intracellular ATP level and demonstrate that Akt is a negative regulator of the AMP-activated protein kinase (AMPK), which is an activator of TSC2. We show that in Akt1/Akt2 DKO cells AMP/ATP ratio is markedly elevated with concomitant increase in AMPK activity, whereas in cells expressing activated Akt there is a dramatic decrease in AMP/ATP ratio and a decline in AMPK activity. Currently, the Akt-mediated phosphorylation of TSC2 and the inhibition of AMPK-mediated phosphorylation of TSC2 are viewed as two separate pathways, which activate mTOR. Our results demonstrate that Akt lies upstream of these two pathways and induces full inhibition of TSC2 and activation of mTOR both through direct phosphorylation and by inhibition of AMPK-mediated phosphorylation of TSC2. We propose that the activation of mTOR by Akt-mediated cellular energy and inhibition of AMPK is the predominant pathway by which Akt activates mTOR in vivo.
Hahn-Windgassen
Annett
A
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 60607, USA.
Nogueira
Veronique
V
Chen
Chia-Chen
CC
Skeen
Jennifer E
JE
Sonenberg
Nahum
N
Hay
Nissim
N
D000225:Adenine / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000263:Adenylate Kinase / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D008954:Models, Biological; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*; D012190:Retroviridae / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors; D014162:Transfection; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C546845:mTOR protein, rat; C494918:AKT1 protein, human; C494921:AKT2 protein, human; C494920:Akt1 protein, rat; C494922:Akt2 protein, mouse; C494923:Akt2 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D000263:Adenylate Kinase; D000225:Adenine