Abstract
The translation initiation complex eIF3 imparts specialized functions to regulate protein expression. However, understanding of eIF3 activities in neurons remains limited despite widespread dysregulation of eIF3 subunits in neurological disorders. Here, we report a selective role of the C. elegans RNA-binding subunit EIF-3.G in shaping the neuronal protein landscape. We identify a missense mutation in the conserved Zinc-Finger (ZF) of EIF-3.G that acts in a gain-of-function manner to dampen neuronal hyperexcitation. Using neuron-type-specific seCLIP, we systematically mapped EIF-3.G-mRNA interactions and identified EIF-3.G occupancy on GC-rich 5'UTRs of a select set of mRNAs enriched in activity-dependent functions. We demonstrate that the ZF mutation in EIF-3.G alters translation in a 5'UTR-dependent manner. Our study reveals an in vivo mechanism for eIF3 in governing neuronal protein levels to control neuronal activity states and offers insights into how eIF3 dysregulation contributes to neurological disorders.
Highlights
Protein synthesis is principally regulated by variations in the translation initiation mechanism, whereby multiple eukaryotic initiation factors engage elongation-competent ribosomes with the mRNA open reading frame (Sonenberg and Hinnebusch, 2009). eIF3 is the largest translation initiation complex, composed of 13 subunits in metazoans, with versatile functions throughout the general translation initiation pathway (Valasek et al, 2017)
C. elegans EIF-3.G is composed of 262 amino acids, sharing overall 35% or 32% sequence identity with human eIF3g and S. cerevisiae TIF35 orthologs, respectively (Figure 1—figure supplement 1A)
Both biochemical and structural data show that eIF3g/ TIF35 proteins bind eIF3i/TIF34 through a domain in the N-terminus (Figure 1B; Valasek et al, 2017). eIF3g/EIF-3.G has a predicted CCHC zinc finger followed by an RNA recognition motif (RRM) at the C-terminus (Figure 1B and Figure 1—figure supplement 1A)
Summary
Protein synthesis is principally regulated by variations in the translation initiation mechanism, whereby multiple eukaryotic initiation factors (eIF1 through 6) engage elongation-competent ribosomes with the mRNA open reading frame (Sonenberg and Hinnebusch, 2009). eIF3 is the largest translation initiation complex, composed of 13 subunits in metazoans, with versatile functions throughout the general translation initiation pathway (Valasek et al, 2017). Interaction of eIF3 RNA-binding subunits with specific 50UTR stem-loop structures of mRNAs can trigger a translational switch for cell proliferation in human 293 T cells (Lee et al, 2015), and can act as a translational repressor, such as the case for human Ferritin mRNA (Pulos-Holmes et al, 2019) Under cellular stress, such as heat shock, the eIF3 complex circumvents cap-dependent protein translation initiation and recruits ribosomes directly to m6A marks within the 50UTR of mRNAs encoding stress response proteins (Meyer et al, 2015). A singlenucleotide polymorphism located in the intron of human eIF3g elevates its mRNA levels and is associated with narcolepsy (Holm et al, 2015) While these data suggest that eIF3 function in neurons is crucial, mechanistic understanding will require experimental models enabling in vivo investigation of how eIF3 affects protein translation with neuron-type specificity. Our findings illustrate the selectivity of EIF-3.G in augmenting mRNA translation to mediate neuronal activity changes
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