title: cAMP inhibits mammalian target of rapamycin complex-1 and -2 (mTORC1 and 2) by promoting complex dissociation and inhibiting mTOR kinase activity.
abstract: cAMP and mTOR signalling pathways control a number of critical cellular processes including metabolism, protein synthesis, proliferation and cell survival and therefore understanding the signalling events which integrate these two signalling pathways is of particular interest. In this study, we show that the pharmacological elevation of [cAMP](i) in mouse embryonic fibroblasts (MEFs) and human embryonic kidney 293 (HEK293) cells inhibits mTORC1 activation via a PKA-dependent mechanism. Although the inhibitory effect of cAMP on mTOR could be mediated by impinging on signalling cascades (i.e. PKB, MAPK and AMPK) that inhibit TSC1/2, an upstream negative regulator of mTORC1, we show that cAMP inhibits mTORC1 in TSC2 knockout (TSC2(-/-)) MEFs. We also show that cAMP inhibits insulin and amino acid-stimulated mTORC1 activation independently of Rheb, Rag GTPases, TSC2, PKB, MAPK and AMPK, indicating that cAMP may act independently of known regulatory inputs into mTOR. Moreover, we show that the prolonged elevation in [cAMP](i) can also inhibit mTORC2. We provide evidence that this cAMP-dependent inhibition of mTORC1/2 is caused by the dissociation of mTORC1 and 2 and a reduction in mTOR catalytic activity, as determined by its auto-phosphorylation on Ser2481. Taken together, these results provide an important insight into how cAMP signals to mTOR and down-regulates its activity, which may lead to the identification of novel drug targets to inhibit mTOR that could be used for the treatment and prevention of human diseases such as cancer.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, The Henry Wellcome Building, University Road, Leicester LE1 9HN, UK.
authors.forename: Jianling
authors.initials: J
authors.lastname: Xie
authors.forename: Godwin A
authors.initials: GA
authors.lastname: Ponuwei
authors.forename: Claire E
authors.initials: CE
authors.lastname: Moore
authors.forename: Gary B
authors.initials: GB
authors.lastname: Willars
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Tee
authors.forename: Terence P
authors.initials: TP
authors.lastname: Herbert
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D048868:Adaptor Proteins, Signal Transducing; D000263:Adenylate Kinase / Q000378:metabolism; D000596:Amino Acids / Q000494:pharmacology / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D039642:Eukaryotic Initiation Factors; D017353:Gene Deletion; D055786:Gene Knockout Techniques; D006801:Humans; D007328:Insulin / Q000494:pharmacology / Q000502:physiology; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000076205:Ras Homolog Enriched in Brain Protein; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; C493245:CRTC2 protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D007328:Insulin; D046912:Multiprotein Complexes; D009479:Neuropeptides; D010726:Phosphodiesterase Inhibitors; D010750:Phosphoproteins; D011506:Proteins; D000076205:Ras Homolog Enriched in Brain Protein; D011994:Recombinant Proteins; C490213:Rheb protein, mouse; C000624653:TSC2 protein, human; D014157:Transcription Factors; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D005576:Colforsin; D000242:Cyclic AMP; D011494:Protein Kinases; D000076222:Mechanistic Target of Rapamycin Complex 1; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D058570:TOR Serine-Threonine Kinases; D000263:Adenylate Kinase; D020559:Monomeric GTP-Binding Proteins; D015056:1-Methyl-3-isobutylxanthine