Post-transcriptional regulation of opioid receptors in the nervous system

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mRNA of opioid receptor (KOR) can be transported to nerve fibers, including axons of dorsal root ganglia (DRG), and can be locally translated. Yeast three-hybrid screening identifies Copb1 as a kor mRNA-associated protein that form complexes with endogenous kor mRNA, which are colocalized in the soma and axons of DRG neurons. Axonal transport of kor mRNA is demonstrated, directly, by observing mobilization of biotin-labeled kor mRNA in Campenot chambers. Efficient transport of kor mRNA into the side chamber requires Copb1 and can be blocked by a drug that disrupts microtubules. The requirement for Copb1 in mobilizing kor mRNA is confirmed by using the MS2-GFP mRNA-tagging system. Furthermore, Copb1 also facilitates the translation of kor mRNA in the soma and axons. This study provides evidence for a microtubuledependent, active axonal kor mRNA-transport process that involves Copb1 and can stimulate localized translation and suggests coupling of transport and translation of mRNAs destined to the remote areas such as axons.dorsal root ganglia neurons T hree major opioid receptor types, , ␦, and , are known (1, 2), each interacting with specific ligands to modulate pain sensation, consciousness, and autonomic functions. Pharmacological studies have demonstrated the significance of the number (3) of opioid receptors and their subcellular distribution (4-7) in the manifestation of opioid drugs. Studies of gene regulation have revealed that although transcriptional regulation is critical for cells to express opioid receptor mRNAs (8), these mRNAs are mostly silent and require extensive posttranscriptional regulation for the ultimate production of these proteins (9). Using the opioid receptor (KOR) as a model, we have begun to uncover several posttranscriptional regulatory events important for the expression of KOR protein. These include alternative mRNA splicing, changing mRNA stability (10), localized translation (11), and mRNA transport (12, 13) in neurons.

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confidence: 99%

Copb1-facilitated axonal transport and translation of κ opioid-receptor mRNA

Tsai

et al. 2007

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“…However, extensive studies of transcriptional regulation of opioid receptor genes (7,8) failed to uncover the mechanisms underlying alteration of receptor number or its protein level in neurons that bear a physiological relevance. Recently, posttranscriptional control for the expression of this gene family has begun to be unraveled, primarily, in studying -opioid receptor (KOR) expression (7,9,10).…”

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confidence: 99%

Axonal mRNA transport and localized translational regulation of κ-opioid receptor in primary neurons of dorsal root ganglia

Tsai

Lin

et al. 2006

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-opioid receptor (KOR) is detected pre-and postsynaptically, but the subcellular localization, translation, and regulation of kor mRNA in presynaptic compartments of sensory neurons remain elusive. In situ hybridization detected axonal distribution of kor mRNA in primary neurons of dorsal root ganglia (DRG). The MS2-fused GFP tracked kor mRNA transport from DRG neuronal soma to axons, requiring its 5 and 3 UTRs. In Campenot chambers, axonal translation of kor mRNA was demonstrated for DRG neurons, which depended on its 5 UTR and was stimulated by KCl depolarization. KCl depolarization of DRG neurons rendered redistribution of kor mRNA from the postpolysomal fraction to the translationally active polysomal fraction. This study provided evidence for mRNA transport and regulation of presynaptic protein synthesis of nonstructural proteins like KOR in primary sensory neurons and demonstrated a mechanism of KCl depolarizationstimulated axonal mRNA redistribution for localized translational regulation.axonal translation O pioid receptors interact with opioid drugs and endogenous opioid ligands to affect pain sensation, consciousness, and autonomic functions. Three major opioid receptor types, , ␦, and are known (1, 2), each belonging to the super family of G protein-coupled transmembrane receptors (3, 4). Gene knockout studies confirmed the functional roles for opioid receptors in mediating the pharmacological actions of various opioid compounds that are among the most commonly prescribed analgesic agents (5). Furthermore, pharmacological studies revealed that the number of opioid receptors was critical to the manifestation of opioid drugs (6). However, extensive studies of transcriptional regulation of opioid receptor genes (7,8) failed to uncover the mechanisms underlying alteration of receptor number or its protein level in neurons that bear a physiological relevance. Recently, posttranscriptional control for the expression of this gene family has begun to be unraveled, primarily, in studying -opioid receptor (KOR) expression (7, 9, 10).KOR protein is detected both pre-and postsynaptically (11)(12)(13)(14). Like many axonal proteins, presynaptic KOR proteins were thought to be synthesized in the soma and then transported to the axons via the axonal transport mechanism (15, 16). However, using in vitro differentiated neurons (17), we have demonstrated transport of kor mRNA into nerve fibers, suggesting an intriguing possibility that kor mRNA might be transported to the axons of KOR-expressing neurons for local translation and regulation. To this end, the phenomena of mRNA transport/targeting and local protein synthesis in the dendrites of invertebrate and vertebrate neurons have been established, but the source of axonal proteins remained heavily debated (18-21). Evidence for axonal mRNA transport and local protein synthesis was provided primarily for structural proteins, although local synthesis of EphA2 receptor, a protein involved in axonal pathfinding has been demonstrated (22-29). Additionally, it was shown that...

“…The complexity of the KOR gene regulatory elements might have contributed to the controversy previously found in the field [i.e., stress-induced KOR mRNA reduction (14) vs. increase (15) in the striatum, no effect (16) vs. increased (15) KOR mRNA in the nucleus accumbens]. To this end, it is important to note that the different isoforms of KOR mRNA exhibit distinct stability, translation efficiency, RNA transport efficiency, and CNS expression patterns (23,37). The current research, demonstrating the effects of stress on KOR epigenetic processes is in line with the indicated ability of external stimuli, including stressors such as forced swim exposure, to affect chromatin remodeling, DNA methylation, and histone modification of stress-associated genes and/or within stress-sensitive brain area (25).…”

Section: Discussionmentioning

confidence: 99%

“…The mouse KOR gene generates three 5′ isoforms, A, B, and C through alternative splicing and promoter use [promoter 1 (Pr1) vs. promoter 2 (Pr2)] (21), and two alternative polyadenylation (PA) sites, PA1 and PA2. By combining 5′ variation and alternative PA use, at least six RNA isoforms can be generated from the KOR gene, each with distinct stability, translation, and transport efficiency, providing a rich reservoir for regulating receptor production and/or distribution (23). The development of neuropathic pain following nerve injury correlates with differential expression of KOR mRNA isoforms (24), and rodent strains with elevated stress susceptibility (1) have differential expression of KOR mRNA isoforms in the cortex, hypothalamus, and locus coeruleus (19,20).…”

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confidence: 99%

Stress-induced epigenetic regulation of κ-opioid receptor gene involves transcription factor c-Myc

Flaisher-Grinberg

Persaud

Loh

et al. 2012

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Exposure to stress is associated with adverse emotional and behavioral responses. Whereas the κ-opioid receptor (KOR) system is known to mediate some of the effects, it is unclear whether and how stress affects epigenetic regulation of this gene. Because the KOR gene can use two promoters (Pr1 and Pr2) and two polyadenylation signals (PA1 and PA2), it is also interesting whether and how these distinct regulatory mechanisms are differentially modulated by stress. The current study examined the effects of stress on these different regulatory mechanisms of the KOR gene. Results showed that stress selectively increased the expression of KOR mRNA isoforms controlled by Pr1 and terminated at PA1 in specific brain areas including the medial-prefrontal cortex, hippocampus, brainstem, and sensorimotor cortex, but not in the amygdala or hypothalamus. These effects correlated with altered epigenetic state of KOR Pr1 chromatin, as well as elevation and increased recruitment of the principal transcription factor c-Myc, which could activate Pr1. Stress-induced modulation of Pr1 was further validated using glutamate-sensitive murine hippocampal cell line, HT22. The results revealed a common molecular mechanism underlying the effect of stress on selected chromatin regions of this gene at the cellular level and in the context of whole animal and identified a critical role for c-Myc in stress-triggered epigenetic regulation of the KOR gene locus. This study sheds light on the mechanisms of stress-induced epigenetic regulation that targets specific chromatin segments and suggests certain KOR transcripts and its principal transcription factor c-Myc as potential targets for brain-area-specific intervention.