Allosteric Modulation of M1 Muscarinic Acetylcholine Receptor Internalisation and Subcellular Trafficking [Signal Transduction]

April 21st, 2014 by Yeatman, H. R., Lane, J. R., Choy, K. H. C., Lambert, N. A., Sexton, P. M., Christopoulos, A., Canals, M.

Allosteric modulators are an attractive approach to achieve receptor-subtype selective targeting of G protein-coupled receptors (GPCRs). Benzyl quinolone carboxylic acid (BQCA) is an unprecedented example of a highly selective positive allosteric modulator of the M1 muscarinic acetylcholine receptor (mAChR). However, despite favourable pharmacological characteristics of BQCA in vitro and in vivo, there is limited evidence of the impact of allosteric modulation on receptor regulatory mechanisms such as β-arrestin recruitment or receptor internalisation and endocytic trafficking. In the present study, we investigated the impact of BQCA on M1 mAChR regulation. We show that BQCA potentiates agonist-induced β-arrestin recruitment to M1 mAChRs. Using a BRET approach to monitor intracellular trafficking of M1 mAChRs, we show that once internalised, M1 mAChRs traffic to early endosomes, recycling endosomes and late endosomes. We also show that BQCA potentiates agonist-induced subcellular trafficking. M1 mAChR internalisation is both β-arrestin and G protein-dependent, with the third intracellular loop playing an important role in the dynamics of β-arrestin recruitment. As the global effect of receptor activation ultimately depends on the levels of receptor expression at the cell surface, these results illustrate the need to extend the characterisation of novel allosteric modulators of GPCRs to encapsulate the consequences of chronic exposure to this family of ligands.