The M <sub>2</sub> muscarinic receptor, in association to M <sub>1</sub> , regulates the neuromuscular PKA molecular dynamics
Víctor Cilleros‐Mañé, Laia Just‐Borràs, Marta Tomàs, Neus García, Josep Tomàs, María A. Lanuza
Abstract
Abstract Muscarinic acetylcholine receptor 1 subtype (M 1 ) and muscarinic acetylcholine receptor 2 subtype (M 2 ) presynaptic muscarinic receptor subtypes increase and decrease, respectively, neurotransmitter release at neuromuscular junctions. M 2 involves protein kinase A (PKA), although the muscarinic regulation to form and inactivate the PKA holoenzyme is unknown. Here, we show that M 2 signaling inhibits PKA by downregulating Cβ subunit, upregulating RIIα/β and liberating RIβ and RIIα to the cytosol. This promotes PKA holoenzyme formation and reduces the phosphorylation of the transmitter release target synaptosome‐associated protein 25 and the gene regulator cAMP response element binding. Instead, M 1 signaling, which is downregulated by M 2 , opposes to M 2 by recruiting R subunits to the membrane. The M 1 and M 2 reciprocal actions are performed through the anchoring protein A kinase anchor protein 150 as a common node. Interestingly, M 2 modulation on protein expression needs M 1 signaling. Altogether, these results describe the dynamics of PKA subunits upon M 2 muscarinic signaling in basal and under presynaptic nerve activity, uncover a specific involvement of the M 1 receptor and reveal the M 1 /M 2 balance to activate PKA to regulate neurotransmission. This provides a molecular mechanism to the PKA holoenzyme formation and inactivation which could be general to other synapses and cellular models.