UPF1 Governs Synaptic Plasticity through Association with a STAU2 RNA Granule

Abstract

Neuronal mRNAs can be packaged in reversibly stalled polysome granules before their transport to distant synaptic locales. Stimulation of synaptic metabotropic glutamate receptors (mGluRs) reactivates translation of these particular mRNAs to produce plasticity-related protein; a phenomenon exhibited during mGluR-mediated LTD. This form of plasticity is deregulated in Fragile X Syndrome, a monogenic form of autism in humans, and understanding the stalling and reactivation mechanism could reveal new approaches to therapies. Here, we demonstrate that UPF1, known to stall peptide release during nonsense-mediated RNA decay, is critical for assembly of stalled polysomes in rat hippocampal neurons derived from embryos of either sex. Moreover, UPF1 and its interaction with the RNA binding protein STAU2 are necessary for proper transport and local translation from a prototypical RNA granule substrate and for mGluR-LTD in hippocampal neurons. These data highlight a new, neuronal role for UPF1, distinct from its RNA decay functions, in regulating transport and/or translation of mRNAs that are critical for synaptic plasticity. The elongation and/or termination steps of mRNA translation are emerging as important control points in mGluR-LTD, a form of synaptic plasticity that is compromised in a severe monogenic form of autism, Fragile X Syndrome. Deciphering the molecular mechanisms controlling this type of plasticity may thus open new therapeutic opportunities. Here, we describe a new role for the ATP-dependent helicase UPF1 and its interaction with the RNA localization protein STAU2 in mediating mGluR-LTD through the regulation of mRNA translation complexes stalled at the level of elongation and/or termination.

Translational Control in the Brain in Health and Disease

“…FMRP can stall polysomes through direct binding to ribosomal RNA (Chen et al 2014). The role of FMRP in stalling polysomes is consistent with the role of FMRP in regulating mGLuR-LTD (Hou et al 2006;Nosyreva and Huber 2006;Graber et al 2017). However, how phosphorylation of eEF2 regulates stalled polysomes is not immediately clear.…”

Puromycin reactivity does not accurately localize translation at the subcellular level

“…Cycloheximide and emetine, in fact, are sometimes omitted from in vivo puromycylation assays based on the claim that short (approximately 5 minutes) labeling times capture peptides near their original site of translation before significant diffusion has taken place (14)(15)(16)(17)(18). Puromycinbased imaging methods have been widely adopted, particularly in neurobiology, where translation in neuronal processes, far from the cell body, is crucial to neuronal function (14)(15)(16)(17)(18)(19)(20)(21)(22)(23).…”

Puromycin reactivity does not accurately localize translation at the subcellular level

“…Cycloheximide and emetine, in fact, are sometimes omitted from in vivo puromycylation assays based on the claim that "short" (minutes) labeling times capture peptides near their original site of translation before significant diffusion has taken place. Puromycin-based imaging methods have been widely adopted, particularly in neurobiology, where translation in neuronal processes, far from the cell body, is crucial to neuronal function (12)(13)(14)(15)(16)(17)(18)(19)(20). Other studies have combined puromycin treatment with proximity-dependent ligation (PLA) to monitor the location of translation of a specific protein (12), but this method again does not address diffusion of puromycylated peptides post-release from the ribosome.…”