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.

RTP801/REDD1 Regulates the Timing of Cortical Neurogenesis and Neuron Migration

“…For instance, in PC12 cells, NGF induces a 6-fold elevation of mTOR phosphorylation and a 14-fold increase in phosphorylation of the mTOR target p70S6 kinase within 20 min (Chan et al, 2009). The rapid RTP801 induction that follows may thus serve in vivo to prevent an over-exuberant mTOR-driven differentiation response that would otherwise impact on the proper timing of neurogenesis and on neuron migration.…”

The integrated role of ACh, ERK and mTOR in the mechanisms of hippocampal inhibitory avoidance memory

“…Specifically, M2 receptors utilize a MAPK-dependent mechanism to activate this pathway, whereas M3 receptors utilize either MAPK dependent or independent mechanisms, depending on cellular context (Slack & Blusztajn, 2008). Furthermore, in a recent paper the authors demonstrate a fine regulation of mTOR and p70S6K by the muscarinic M4 receptor in PC12 cells (Chan, Wu, & Wong, 2009).…”

Crosstalk between VEGFR2 and muscarinic receptors regulates the mTOR pathway in serum starved SK-N-SH human neuroblastoma cells

“…Akt can potentiate TORC1 signaling by inhibiting the tuberous sclerosis complex (TSC), allowing TORC1 signaling of protein translation via activation of its downstream targets p70 S6 Kinase (S6K) and its target ribosomal protein S6 (S6). In neuronal models, agonists for mAchRs were shown to stimulate activation of S6K in 1321 astrocytoma cells [23], SH-SY5Y [24] and PC12 cells [25] and S6 ribosomal protein via PKC in serum-deprived SK-N-SH neuroblastoma cells [26]. …”