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Mitogen-activated protein kinase-dependent and protein kinase C-dependent pathways link the m1 muscarinic receptor to
R Haring1, A Fisher, D Marciano
1Israel Institute for Biological Research, Ness-Ziona.
Abstract:
Full and functionally selective M1 muscarinic agonists (carbachol and AF102B, respectively) activate secretion of the soluble form of amyloid precursor protein (APPs) in PC12 cells expressing the m1 muscarinic receptor (PC12M1 cells). This activation is further augmented by neurotrophins such as nerve growth factor and basic fibroblast growth factor. Muscarinic stimulation activates two transduction pathways that lead to APPs secretion: protein kinase C (PKC)-dependent and mitogen-activated protein kinase (MAPK)-dependent pathways. These pathways operate in parallel and converge with transduction pathways of neurotrophins, resulting in enhancement of APPs secretion when both muscarinic agonist and neurotrophins stimulate PC12M1 cells. These conclusions are supported by the following findings: (a) Only partial blockade of APPs secretion is observed when PKC, p21ras, or MAPK is fully inhibited by their respective specific inhibitors, GF109203X, S-trans, trans-farnesylthiosalicylic acid, and PD98059. (b) K252a, which blocks PKC and phorbol 12-myristate 13-acetate-induced APPs secretion, enhances both muscarinic-stimulated MAPK activation and APPs secretion. (c) Activation of MAPK in PC12M1 cells by muscarinic agonists is Ras-dependent but PKC-independent and is enhanced synergistically by neurotrophins. These results suggest that muscarinic stimulation of APPs secretion is mediated by at least two independent pathways that converge and enhance the signal for APPs secretion at the convergence point.
Insights
Muscarinic agonists stimulate amyloid precursor protein (APP) secretion via protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways. These pathways converge with neurotrophin signaling, enhancing APP secretion in PC12M1 cells.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Amyloid precursor protein (APP) secretion is implicated in neurological disorders.
- Muscarinic receptors, particularly the M1 subtype, play roles in neuronal function.
- Neurotrophins are crucial for neuronal survival and growth.
Purpose of the Study:
- To investigate the signaling pathways involved in M1 muscarinic receptor-mediated APP secretion.
- To determine the interplay between muscarinic signaling and neurotrophin pathways in regulating APP secretion.
Main Methods:
- Utilized PC12M1 cells expressing the M1 muscarinic receptor.
- Employed muscarinic agonists (carbachol, AF102B) and neurotrophins (NGF, bFGF).
- Investigated the roles of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways using specific inhibitors (GF109203X, S-trans, trans-farnesylthiosalicylic acid, PD98059) and K252a.
Main Results:
- Muscarinic agonists activate both PKC-dependent and MAPK-dependent pathways for APP secretion.
- These pathways operate in parallel and converge with neurotrophin signaling pathways.
- Inhibition studies indicated partial blockade of APP secretion, suggesting multiple contributing pathways.
- K252a enhanced muscarinic-stimulated MAPK activation and APP secretion.
- MAPK activation by muscarinic agonists was Ras-dependent but PKC-independent and synergistically enhanced by neurotrophins.
Conclusions:
- Muscarinic stimulation of APP secretion involves at least two independent, parallel pathways.
- These pathways converge, amplifying the signal for APP secretion.
- The convergence point integrates signals from both muscarinic and neurotrophin pathways, enhancing APP secretion.