Abstract
The biased signaling has been extensively studied in the original mu opioid receptor (MOR-1), particularly through G protein and β-arrestin2 signaling pathways. The concept that the G protein pathway is often linked to the therapeutic effect of the drug, while the β-arrestin pathway is associated to the side effects has been proposed to develop biased analgesic compounds with limited side-effects associated with traditional opiates. The mu opioid receptor gene, OPRM1, undergoes extensive alternative pre-mRNA splicing, generating multiple splice variants or isoforms that are conserved from rodent to human. One type of the Oprm1 splice variants are the full-length 7 transmembrane (7TM) C-terminal splice variants, which have identical receptor structures including entire binding pocket, but contain a different intracellular C-terminal tail resulted from 3′ alternative splicing. Increasing evidence suggest that these full-length 7TM C-terminal variants play important roles in mu opioid pharmacology, raising questions regarding biased signaling at these multiple C-terminal variants. In the present study, we investigated the effect of different C-terminal variants on mu agonist-induced G protein coupling, β-arrestin2 recruitment, and ultimately, signaling bias. We found that mu agonists produced marked differences in G protein activation and β-arrestin2 recruitment among various C-terminal variants, leading to biased signaling at various level. Particularly, MOR-1O, an exon 7-associated variant, showed greater β-arrestin2 bias for most mu agonists than MOR-1, an exon 4-associated variant. Biased signaling of G protein-coupled receptors has been defined by evidences that different agonists can produce divergent signaling transduction pathways through a single receptor. Our findings that a single mu agonist can induce differential signaling through multiple 7TM splice variants provide a new perspective on biased signaling at least for Oprm1, which perhaps is important for our understanding of the complex mu opioid actions in vivo where all the 7TM splice variants co-exist.
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31 October 2020
A Correction to this paper has been published: https://doi.org/10.1007/s10571-020-00990-4
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Acknowledgements
This work was supported, in part, by Grants from the National Institute on Drug Abuse of the National Institutes of Health, DA042888, DA046714 and DA007242, the Mayday Foundation and the Peter F. McManus Charitable Trust to YXP, and a core Grant from the National Cancer Institute (CA008748) to Memorial Sloan Kettering Cancer Center.
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AN, GWP and YXP conceived and designed the study. AN, AH, JX, DIB and YXP performed experiments. AN, AH and YXP analyzed data. AN, GWP and YXP wrote the manuscript. All authors read and approved the final manuscript.
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YXP is a co-scientific founder of Sparian Biosciences. All other authors declare that there is no conflict of interest.
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This article is dedicated to the memory of our dear mentor, colleague, and friend, Dr. Gavril W. Pasternak (deceased February 22, 2019), whose pioneering work over four decades contributed enormously to our understanding of opioid pharmacology.
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Narayan, A., Hunkele, A., Xu, J. et al. Mu Opioids Induce Biased Signaling at the Full-Length Seven Transmembrane C-Terminal Splice Variants of the mu Opioid Receptor Gene, Oprm1. Cell Mol Neurobiol 41, 1059–1074 (2021). https://doi.org/10.1007/s10571-020-00973-5
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DOI: https://doi.org/10.1007/s10571-020-00973-5