Dendritic mRNA Targeting of Jacob and N-Methyl-d-aspartate-induced Nuclear Translocation after Calpain-mediated Proteolysis

Abstract

Jacob is a recently identified plasticity-related protein that couples N-methyl-D-aspartate receptor activity to nuclear gene expression. An expression analysis by Northern blot and in situ hybridization shows that Jacob is almost exclusively present in brain, in particular in the cortex and the limbic system. Alternative splicing gives rise to multiple mRNA variants, all of which exhibit a prominent dendritic localization in the hippocampus. Functional analysis in primary hippocampal neurons revealed that a predominant cis-acting dendritic targeting element in the 3-untranslated region of Jacob mRNAs is responsible for dendritic mRNA localization. In the mouse brain, Jacob transcripts are associated with both the fragile X mental retardation protein, a well described trans-acting factor regulating dendritic mRNA targeting and translation, and the kinesin family member 5C motor complex, which is known to mediate dendritic mRNA transport. Jacob is susceptible to rapid protein degradation in a Ca 2؉ -and Calpain-dependent manner, and Calpainmediated clipping of the myristoylated N terminus of Jacob is required for its nuclear translocation after N-methyl-D-aspartate receptor activation. Our data suggest that local synthesis in dendrites may be necessary to replenish dendritic Jacob pools after truncation of the N-terminal membrane anchor and concomitant translocation of Jacob to the nucleus.The link between excitatory neurotransmission and transcriptional and translational regulation has attracted much interest for many years because multiple processes ranging from metabolic homeostasis to learning and memory require activity-driven gene expression in neurons (1, 2). Particularly signaling from N-methyl-D-aspartate (NMDA) 3 type glutamate receptors to the nucleus has been implicated in synaptic plasticity, and some molecules have been identified that can translocate from synaptic and extrasynaptic sites to neuronal nuclei after NMDA receptor activation (3-7). In a recent study, we have identified Jacob, a protein that triggers long lasting changes in the cytoarchitecture of dendrites and the number of spine synapses in pyramidal neurons via coupling of NMDA receptor signaling to nuclear gene expression (6). Following activation of synaptic and extrasynaptic NMDA receptors, Jacob is recruited to neuronal nuclei, and this in turn results in a rapid stripping of synaptic contacts and in a drastically altered morphology of the dendritic tree (6). Nuclear import of Jacob utilizes the classical importin pathway (6, 7), and the synaptic Ca 2ϩ

NELF knockout is associated with impaired pubertal development and subfertility

“…[17] The highly homologous (98%) rat ortholog of Nelf (Jacob protein) shows stimulus dependent nuclear translocation, and by chromatin fractionation has been localized within regions of RNA polymerase 2-containing euchromatin. Moreover, protein complexes immunopurified from euchromatin contain significant levels of DNA implying NELF association, indirectly or directly, with DNA[18,43,44]. Taken together, these findings strongly implicate a role for NELF in transcription, either as a transcription factor or in protein-protein interactions regulating transcription.…”

Macromolecular transport in synapse to nucleus communication

“…of Pages 9 transcripts traffic from nucleus to synapse in translationally silenced ribonucleoprotein granules [85,86]. This modality of nucleus-to-synapse communication sets the stage for local translation of mRNAs that are critical for synaptic plasticity, but it is not yet clear if such local translation events also generate synapse-to-nucleus messengers such as Jacob [87]. Regardless, local translation can induce longlasting changes in synapse activity [88], and ribosomal complexes are enriched at postsynaptic sites [89].…”

Distinct Molecular Regulation of Glycogen Synthase Kinase-3α Isozyme Controlled by Its N-terminal Region

“…This communication has been shown to be mediated by nuclear import of cytosolic proteins such as CREB, Jacob neuroprotein, NF-ATc, NFB, and Abelson interacting protein-1 (abi-1), which activate certain gene expression programs (65)(66)(67)(68)(69)(70). Proteases, in particular calpain, play important roles in these cellular activities (66,71). GSK-3␣ may thus link cytoplasmic calcium/calpain signaling with nuclear events.…”