VAPB regulation of ER stress and its potential involvement in ALSVIII

A mis-sense point mutation in the human VAPB gene is associated with a familial form of motor neuron disease that has been classified as Amyotrophic Lateral Sclerosis type VIII. Affected individuals suffer from a spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) or an atypical slowly progressing form of ALS. Mammals have two homologous VAP genes, vapA and vapB. VAPA and VAPB share 76% similar or identical amino acid residues; both are COOHterminally anchored membrane proteins enriched on the endoplasmic reticulum. Several functions have been ascribed to VAP proteins including membrane trafficking, cytoskeleton association and membrane docking interactions for cytoplasmic factors. It is shown here that VAPA and VAPB are expressed in tissues throughout the body but at different levels, and that they are present in overlapping but distinct regions of the endoplasmic reticulum. The disease-associated mutation in VAPB, VAPB (P56S) is within a highly conserved N-terminal region of the protein that shares extensive structural homology with the major sperm protein (MSP) from nematodes. The MSP domain of VAPA and VAPB is found to interact with the ERlocalized transcription factor ATF6. Over expression of VAPB or VAPB (P56S) attenuates the activity of ATF6-regulated transcription and the mutant protein VAPB (P56S) appears to be a more potent inhibitor of ATF6 activity. Moreover VAP proteins affect the activity of XBP1 and BiP promoter elements, two major components of the Unfolded Protein Response (UPR) of the Endoplasmic Reticulum and the different domains of VAPB have a differential effect on UPR regulation. Finally, over expression of the MSP domain of VAPB leads to cell death via apoptosis, while overexpression of other VAPB domains renders cells more susceptible to apoptotic death after ER stress. The data presented in this thesis indicate that VAP proteins interact directly with components of ER homeostatic and stress signalling systems and may therefore be parts of a previously unidentified regulatory pathway. The mis-function of such regulatory systems may contribute to the pathological mechanisms of degenerative motor neuron disease

Translational control and autism-like behaviors

Autism spectrum disorders (ASD) consist of a spectrum of neurodevelopmental diseases with three salient features: reduced social interactions, impaired communication and repetitive/stereotyped behaviors. In a recent study we found that increased eIF4E (eukaryotic initiation factor 4E)-dependent protein synthesis as a result of genetic deletion of Eif4ebp2 (eIF4E-binding protein 2) in mice, stimulates the production of neuroligins (Nlgns, synaptic cell-adhesion molecules important for synapse regulation) and engenders an imbalance of excitatory to inhibitory synaptic transmission (E/I) in CA1 pyramidal neurons. This imbalance is accompanied with deficits in social interaction, communication and repetitive/stereotyped behaviors in Eif4ebp2(−/−) mice. Using a compound that blocks cap-dependent translation or by knocking down Nlgn1, we restored the E/I balance and reversed the autism-like social deficits

GeneViTo: Visualizing gene-product functional and structural features in genomic datasets

BACKGROUND: The availability of increasing amounts of sequence data from completely sequenced genomes boosts the development of new computational methods for automated genome annotation and comparative genomics. Therefore, there is a need for tools that facilitate the visualization of raw data and results produced by bioinformatics analysis, providing new means for interactive genome exploration. Visual inspection can be used as a basis to assess the quality of various analysis algorithms and to aid in-depth genomic studies. RESULTS: GeneViTo is a JAVA-based computer application that serves as a workbench for genome-wide analysis through visual interaction. The application deals with various experimental information concerning both DNA and protein sequences (derived from public sequence databases or proprietary data sources) and meta-data obtained by various prediction algorithms, classification schemes or user-defined features. Interaction with a Graphical User Interface (GUI) allows easy extraction of genomic and proteomic data referring to the sequence itself, sequence features, or general structural and functional features. Emphasis is laid on the potential comparison between annotation and prediction data in order to offer a supplement to the provided information, especially in cases of "poor" annotation, or an evaluation of available predictions. Moreover, desired information can be output in high quality JPEG image files for further elaboration and scientific use. A compilation of properly formatted GeneViTo input data for demonstration is available to interested readers for two completely sequenced prokaryotes, Chlamydia trachomatis and Methanococcus jannaschii. CONCLUSIONS: GeneViTo offers an inspectional view of genomic functional elements, concerning data stemming both from database annotation and analysis tools for an overall analysis of existing genomes. The application is compatible with Linux or Windows ME-2000-XP operating systems, provided that the appropriate Java Runtime Environment is already installed in the system

Raptor-Mediated Proteasomal Degradation of Deamidated 4E-BP2 Regulates Postnatal Neuronal Translation and NF-κB Activity

The translation initiation repressor 4E-BP2 is deamidated in the brain on asparagines N99/N102 during early postnatal brain development. This post-translational modification enhances 4E-BP2 association with Raptor, a central component of mTORC1 and alters the kinetics of excitatory synaptic transmission. We show that 4E-BP2 deamidation is neuron specific, occurs in the human brain, and changes 4E-BP2 subcellular localization, but not its disordered structure state. We demonstrate that deamidated 4E-BP2 is ubiquitinated more and degrades faster than the unmodified protein. We find that enhanced deamidated 4E-BP2 degradation is dependent on Raptor binding, concomitant with increased association with a Raptor-CUL4B E3 ubiquitin ligase complex. Deamidated 4E-BP2 stability is promoted by inhibiting mTORC1 or glutamate receptors. We further demonstrate that deamidated 4E-BP2 regulates the translation of a distinct pool of mRNAs linked to cerebral development, mitochondria, and NF-κB activity, and thus may be crucial for postnatal brain development in neurodevelopmental disorders, such as ASD

G3BP1 promotes stress-induced RNA granule interactions to preserve polyadenylated mRNA

G3BP1, a target of TDP-43, is required for normal stress granule (SG) assembly, but the functional consequences of failed SG assembly remain unknown. Here, using both transformed cell lines and primary neurons, we investigated the functional impact of this disruption in SG dynamics. While stress-induced translational repression and recruitment of key SG proteins was undisturbed, depletion of G3BP1 or its upstream regulator TDP-43 disturbed normal interactions between SGs and processing bodies (PBs). This was concomitant with decreased SG size, reduced SG–PB docking, and impaired preservation of polyadenylated mRNA. Reintroduction of G3BP1 alone was sufficient to rescue all of these phenotypes, indicating that G3BP1 is essential for normal SG–PB interactions and SG function

Reversal of memory and autism-related phenotypes in Tsc2+/− mice via inhibition of Nlgn1

Tuberous sclerosis complex (TSC) is a rare monogenic disorder co-diagnosed with high rates of autism and is caused by loss of function mutations in the TSC1 or TSC2 genes. A key pathway hyperactivated in TSC is the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which regulates cap-dependent mRNA translation. We previously demonstrated that exaggerated cap-dependent translation leads to autism-related phenotypes and increased mRNA translation and protein expression of Neuroligin 1 (Nlgn1) in mice. Inhibition of Nlgn1 expression reversed social behavior deficits in mice with increased cap-dependent translation. Herein, we report elevated translation of Nlgn1 mRNA and an increase in its protein expression. Genetic or pharmacological inhibition of Nlgn1 expression in Tsc2+/− mice rescued impaired hippocampal mGluR-LTD, contextual discrimination and social behavior deficits in Tsc2+/− mice, without correcting mTORC1 hyperactivation. Thus, we demonstrate that reduction of Nlgn1 expression in Tsc2+/− mice is a new therapeutic strategy for TSC and potentially other neurodevelopmental disorders

Uncovering memory-related gene expression in contextual fear conditioning using ribosome profiling

Contextual fear conditioning (CFC) in rodents is the most widely used behavioural paradigm in neuroscience research to elucidate the neurobiological mechanisms underlying learning and memory. It is based on the pairing of an aversive unconditioned stimulus (US; e.g. mild footshock) with a neutral conditioned stimulus (CS; e.g. context of the test chamber) in order to acquire associative long-term memory (LTM), which persists for days and even months. Using genome-wide analysis, several studies have generated lists of genes modulated in response to CFC in an attempt to identify the "memory genes", which orchestrate memory formation. Yet, most studies use naïve animals as a baseline for assessing gene-expression changes, while only few studies have examined the effect of the US alone, without pairing to context, using genome-wide analysis of gene-expression. Herein, using the ribosome profiling methodology, we show that in male mice an immediate shock, which does not lead to LTM formation, elicits pervasive translational and transcriptional changes in the expression of Immediate Early Genes (IEGs) in dorsal hippocampus (such as Fos and Arc), a fact which has been disregarded by the majority of CFC studies. By removing the effect of the immediate shock, we identify and validate a new set of genes, which are translationally and transcriptionally responsive to the association of context-to-footshock in CFC, and thus constitute salient "memory genes"

Cap-binding protein 4EHP effects translation silencing by microRNAs

Significance miRNAs are important components of gene regulatory networks and affect all aspects of cell biology by controlling the stability and translation efficiency of their target mRNAs. Here, we identified the mRNA cap-binding eIF4E-related protein 4EHP as an effector of miRNA-mediated translation repression. Through screening for protein interactions in cells via the BioID method, we identified 4EHP as a component of the CCR4–NOT/DDX6/4E-T axis. Direct interaction between 4E-T and 4EHP increases the latter’s cap-binding affinity, suggesting that this interaction potentiates its competition with the eIF4F complex for binding to the mRNA 5′ cap. Our findings suggest that 4EHP facilitates the formation of a closed-loop structure between the 3′ UTR of the mRNA and its 5′ cap, which causes repression of mRNA translation.</jats:p