title: Regulation of mTOR and p70 S6 kinase by the muscarinic M4 receptor in PC12 cells.
abstract: The G(i)-coupled M(4) muscarinic acetylcholine receptor (mAChR) has recently been shown to stimulate the survival of PC12 cells through the PI3K/Akt/tuberin pathway. Since mTOR and p70S6K are critical components in activating translation which lie downstream of tuberin, we examined the ability of M(4) mAChR to regulate these targets in PC12 cells. Carbachol (CCh) dose-dependently stimulated both mTOR and p70S6K phosphorylations and these responses were abolished by pertussis toxin pretreatment, indicating the involvement of the G(i)-coupled M(4) mAChR. Phosphorylations of both mTOR and p70S6K were effectively blocked upon inhibition of PI3K by wortmannin. As compared to similar responses elicited by the nerve growth factor (NGF), the M(4) mAChR-induced activation of Akt/tuberin/mTOR/p70S6K occurred in a relatively transient manner. Although inhibition of protein phosphatase 2A by okadaic acid augmented the transient effects of CCh on Akt/tuberin phosphorylations, it failed to significantly prolong these responses. The total protein level of PTEN (tumor suppressor gene phosphatase and tensin homologue deleted on chromosome ten) was attenuated upon NGF, but not CCh treatment. This indicates that downregulation of PTEN may help to sustain the phosphorylation of Akt/tuberin by NGF. Collectively, these findings suggest that PP2A and PTEN may be involved in fine tuning the regulation of Akt/tuberin/mTOR/p70S6K in PC12 cells by M(4) mAChR and TrkA, respectively.
authors.affiliation: Department of Biochemistry, The Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
authors.forename: Grace P W
authors.initials: GP
authors.lastname: Chan
authors.forename: Eddy H T
authors.initials: EH
authors.lastname: Wu
authors.forename: Yung H
authors.initials: YH
authors.lastname: Wong
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival; D020932:Nerve Growth Factor / Q000378:metabolism; D016716:PC12 Cells; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051381:Rats; D043588:Receptor, Muscarinic M4 / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002217:Carbachol; D020932:Nerve Growth Factor; D051059:PTEN Phosphohydrolase; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D054648:Protein Phosphatase 2; D043588:Receptor, Muscarinic M4; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D000077191:Wortmannin; C546845:mTOR protein, rat; C487216:Pten protein, rat