Alternative Splicing of Opioid Receptor Genes Shows a Conserved Pattern for 6TM Receptor Variants

Marjo Piltonen,Svetlana A Shabalina,Pierre Bérubé,Luda Diatchenko,Marc Parisien,Rob Sladek,Haig Djambazian,Svetlana A Shabalina,Rob Sladek,Nikolay V Dokholyan,Haig Djambazian,Nikolay V Dokholyan,Andrey Krokhotin

doi:10.1007/s10571-020-00971-7

Abstract

The opioid receptor (OPR) family comprises the mu-, delta-, and kappa-opioid, and nociceptin receptors that belong to the superfamily of 7-transmembrane spanning G protein-coupled receptors (GPCRs). The mu-opioid receptor is the main target for clinically used opioid analgesics, and its biology has been extensively studied. The N-terminally truncated 6TM receptors isoform produced through alternative splicing of the OPRM1 gene displays unique signaling and analgesic properties, but it is unclear if other OPRs have the same ability. In this study, we have built a comprehensive map of alternative splicing events that produce 6TM receptor variants in all the OPRs and demonstrated their evolutionary conservation. We then obtained evidence for their translation through ribosomal footprint analysis. We discovered that N-terminally truncated 6TM GPCRs are rare in the human genome and OPRs are overrepresented in this group. Finally, we also observed a significant enrichment of 6TM GPCR genes among genes associated with pain, psychiatric disorders, and addiction. Understanding the biology of 6TM receptors and leveraging this knowledge for drug development should pave the way for novel therapies.

Highlights

G protein-coupled receptors (GPCRs) are a superfamily of complex signaling proteins with over 800 members
Since we focused on N-terminus variants of OPRM1, we initiated our Rapid amplification of cDNA ends (RACE) amplicons from exon 2
The vast majority of PCR products corresponded to a combination of exons 1 and 2, as expected, because they are found in all 7TM receptor isoforms (Table 1) and they represent the majority of OPRM1 isoforms (Xu et al 2014)

Summary

Introduction

G protein-coupled receptors (GPCRs) are a superfamily of complex signaling proteins with over 800 members. GPCRs respond to a plethora of stimuli from photons to neurotransmitters and hormones, conveying their message on intracellular effector proteins. While differential RNA processing affects many GPCR transcripts, not much is known about the roles of truncated GPCR variants. Truncated GPCRs are created by alternative splicing, usage of an alternative transcription start site, or alternative polyadenylation site in the GPCR gene, typically in a very context-dependent manner (e.g., tissue-specific expression) (Wise 2012). We are only beginning to understand the diversity they create in the signaling landscape of a particular receptor

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