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mRNA of [kappa] 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 Copbl 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

[kappa]-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 KCI depolarization. KCI 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 KCI depolarization-stimulated axonal mRNA redistribution for localized translational regulation. axonal translation

The neural precursor cell expressed developmentally down‐regulated protein 4‐like (Nedd4‐2) is an E3 ubiquitin ligase critical for neurodevelopment and homeostasis of neural circuit excitability. While dysregulation of Nedd4‐2 has been linked to elevated seizure susceptibility through impaired ubiquitination of multiple direct substrates, it remains largely unclear whether Nedd4‐2 interconnects other cellular pathways that affect neuronal activity and seizure susceptibility. Here, we first showed that Nedd4‐2 associates with the endoplasmic reticulum (ER) and regulates the expression of multiple ER‐resident proteins. Furthermore, utilizing Nedd4‐2 conditional knockout mice, we showed that Nedd4‐2 is required for the maintenance of spontaneous neural activity and excitatory synapses following the induction of ER stress. When analyzing activation of the canonical pathways of ER stress response, we found that Nedd4‐2 is required for phosphorylation of eIF2α. While phosphorylation of eIF2α has been shown to reduce seizure susceptibility, attempts to facilitate phosphorylation of eIF2α in Nedd4‐2 conditional knockout mice failed to produce such a beneficial function, suggesting a role for Nedd4‐2 in integrating the ER stress response to modulate seizure susceptibility. Altogether, our study demonstrates neuroprotective functions of Nedd4‐2 during ER stress in neurons and could provide insight into neurological diseases in which the expression or activity of Nedd4‐2 is impaired. [ABSTRACT FROM AUTHOR]

Endoplasmic reticulum (ER) stress occurs when protein folding or maturation is disrupted. A malfunction in the ER stress response can lead to cell death and has been observed in many neurological diseases. However, how the ER stress response is regulated in neuronal cells remains largely unclear. Here, we studied an E3 ubiquitin ligase named neural precursor cell expressed developmentally down‐regulated protein 4‐like (Nedd4‐2). Nedd4‐2 is highly expressed in the brain and has a high affinity toward ubiquitinating membrane‐bound proteins. We first utilized unbiased proteomic profiling with ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) of isolated membrane fractions from mouse whole brains to identify novel targets of Nedd4‐2. Through this screen, we found that the expression and ubiquitination of ribosomal proteins are regulated by Nedd4‐2 and we confirmed an association between Nedd4‐2 and ribosomes through ribosome sedimentation and polysome profiling. Further, we utilized immunoprecipitation and western blotting to show that induction of ER stress promotes an association between Nedd4‐2 and ribosomal proteins, which is mediated through dephosphorylation of Nedd4‐2 at serine‐342. This increased interaction between Nedd4‐2 and ribosomal proteins in turn mediates ER stress‐associated translational suppression. In summary, the results of this study demonstrate a novel regulatory mechanism underlying the ER stress response and a novel function of Nedd4‐2 in translational control. Our findings may shed light on neurological diseases in which the ER stress response or the function of Nedd4‐2 is dysregulated. [ABSTRACT FROM AUTHOR]