The postsynaptic density and dendritic raft localization of PSD-Zip70, which contains an N-myristoylation sequence and leucine-zipper motifs

Is autism a PIN1 deficiency syndrome? A proposed etiological role for glyphosate

Autism is a neurodevelopmental disorder, the prevalence of which has increased dramatically in the United States over the past two decades. It is characterized by stereotyped behaviors and impairments in social interaction and communication. In this paper, we present evidence that autism can be viewed as a PIN1 deficiency syndrome. Peptidyl-prolyl cis/trans isomerase, NIMA-Interacting 1 (PIN1) is a peptidyl-prolyl cis/trans isomerase, and it has widespread influences in biological organisms. Broadly speaking, PIN1 deficiency is linked to many neurodegenerative diseases, whereas PIN1 over-expression is linked to cancer. Death-associated protein kinase 1 (DAPK1) strongly inhibits PIN1, and the hormone melatonin inhibits DAPK1. Melatonin deficiency is strongly linked to autism. It has recently been shown that glyphosate exposure to rats inhibits melatonin synthesis as a result of increased glutamate release from glial cells and increased expression of metabotropic glutamate receptors. Glyphosate's inhibition of melatonin leads to a reduction in PIN1 availability in neurons. In this paper, we show that PIN1 deficiency can explain many of the unique morphological features of autism, including increased dendritic spine density, missing or thin corpus callosum, and reduced bone density. We show how PIN1 deficiency disrupts the functioning of powerful high-level signaling molecules, such as nuclear factor erythroid 2-related factor 2 (NRF2) and p53. Dysregulation of both of these proteins has been linked to autism. Severe depletion of glutathione in the brain resulting from chronic exposure to oxidative stressors and extracellular glutamate leads to oxidation of the cysteine residue in PIN1, inactivating the protein and further contributing to PIN1 deficiency. Impaired autophagy leads to increased sensitivity of neurons to ferroptosis. It is imperative that further research be conducted to experimentally validate whether the mechanisms described here take place in response to chronic glyphosate exposure and whether this ultimately leads to autism.

Multisystem disorder associated with a pathogenic variant in CLCN7 in the absence of osteopetrosis

BACKGROUND

We clinically and genetically evaluated a Taiwanese boy presenting with developmental delay, organomegaly, hypogammaglobulinemia and hypopigmentation without osteopetrosis. Whole-exome sequencing revealed a de novo gain-of-function variant, p.Tyr715Cys, in the C-terminal domain of ClC-7 encoded by CLCN7.

METHODS

Nicoli et al. (2019) assessed the functional impact of p.Tyr715Cys by heterologous expression in Xenopus oocytes and evaluating resulting currents.

RESULTS

The variant led to increased outward currents, indicating it underlies the patient's phenotype of lysosomal hyperacidity, storage defects and vacuolization. This demonstrates the crucial physiological role of ClC-7 antiporter activity in maintaining appropriate lysosomal pH.

CONCLUSION

Elucidating mechanisms by which CLCN7 variants lead to lysosomal dysfunction will advance understanding of genotype-phenotype correlations. Identifying modifier genes and compensatory pathways may reveal therapeutic targets. Ongoing functional characterization of variants along with longitudinal clinical evaluations will continue advancing knowledge of ClC-7's critical roles and disease mechanisms resulting from its dysfunction. Expanded cohort studies are warranted to delineate the full spectrum of associated phenotypes.

Hippocampal proteomic changes in high-fat diet-induced obese mice associated with memory decline

Substantial evidence suggest that chronic consumption of high-fat diets (HFDs) can lead to obesity, abnormal metabolism, as well as cognitive impairment. Molecular and cellular changes regarding hippocampal dysfunctions have been identified in multiple HFD animal models. Therefore, in-depth identification of expression changes of hippocampal proteins is critical for understanding the mechanism of HFD-induced cognitive deficits. In this study, we fed 3-week-old male mice with HFD for 3 months to generate obese mice who exhibit systemic metabolic abnormality and learning and memory decline. Using an iTRAQ-labeled proteomic analysis, we identified a total of 82 differentially expressed proteins (DEPs) in the hippocampus upon HFD with 35 up-regulated proteins and 47 down-regulated proteins. Functional enrichment indicated that these DEPs were predominantly enriched in regulation of catabolic process, dendritic shaft, neuron projection morphogenesis and GTPase regulator activity. Protein-protein interaction enrichment showed that the DEPs are mostly enriched in postsynaptic functions; and of them, six proteins (i.e., DLG3, SYNGAP1, DCLK1, GRIA4, GRIP1, and ARHGAP32) were involved in several functional assemblies of the postsynaptic density including G-protein signaling, scaffolding and adaptor, kinase and AMPA signaling, respectively. Collectively, our findings suggest that these DEPs upon HFD might contribute to memory decline by disturbing neuronal and postsynaptic functions in the hippocampus.

Myristoylation-dependent palmitoylation of cyclin Y modulates long-term potentiation and spatial learning

Many psychiatric disorders accompany deficits in cognitive functions and synaptic plasticity, and abnormal lipid modifications of neuronal proteins are associated with their pathophysiology. Lipid modifications, including palmitoylation and myristoylation, play crucial roles in the subcellular localization and trafficking of proteins. Cyclin Y (CCNY), enriched in the postsynaptic compartment, acts as an inhibitory modulator of functional and structural long-term potentiation (LTP) in the hippocampal neurons. However, cellular and molecular mechanisms underlying CCNY-mediated inhibitory functions in the synapse remain largely unknown. Here, we report that myristoylation located CCNY to the trans-Golgi network (TGN), and subsequent palmitoylation directed the myristoylated CCNY from the TGN to the synaptic cell surface. This myristoylation-dependent palmitoylation of CCNY was required for the inhibitory role of CCNY in excitatory synaptic transmission, activity-induced dynamics of AMPA receptors and PSD-95, LTP, and spatial learning. Furthermore, spatial learning significantly reduced palmitoyl- and myristoyl-CCNY levels, indicating that spatial learning lowers the synaptic abundance of CCNY. Our findings provide mechanistic insight into how CCNY is clustered adjacent to postsynaptic sites where it could play its inhibitory roles in synaptic plasticity and spatial learning.

Proximity proteomics identifies PAK4 as a component of Afadin-Nectin junctions

Human PAK4 is an ubiquitously expressed p21-activated kinase which acts downstream of Cdc42. Since PAK4 is enriched in cell-cell junctions, we probed the local protein environment around the kinase with a view to understanding its location and substrates. We report that U2OS cells expressing PAK4-BirA-GFP identify a subset of 27 PAK4-proximal proteins that are primarily cell-cell junction components. Afadin/AF6 showed the highest relative biotin labelling and links to the nectin family of homophilic junctional proteins. Reciprocally >50% of the PAK4-proximal proteins were identified by Afadin BioID. Co-precipitation experiments failed to identify junctional proteins, emphasizing the advantage of the BioID method. Mechanistically PAK4 depended on Afadin for its junctional localization, which is similar to the situation in Drosophila. A highly ranked PAK4-proximal protein LZTS2 was immuno-localized with Afadin at cell-cell junctions. Though PAK4 and Cdc42 are junctional, BioID analysis did not yield conventional cadherins, indicating their spatial segregation. To identify cellular PAK4 substrates we then assessed rapid changes (12') in phospho-proteome after treatment with two PAK inhibitors. Among the PAK4-proximal junctional proteins seventeen PAK4 sites were identified. We anticipate mammalian group II PAKs are selective for the Afadin/nectin sub-compartment, with a demonstrably distinct localization from tight and cadherin junctions.

Neuronal Delamination and Outer Radial Glia Generation in Neocortical Development

During neocortical development, many neuronally differentiating cells (neurons and intermediate progenitor cells) are generated at the apical/ventricular surface by the division of neural progenitor cells (apical radial glial cells, aRGs). Neurogenic cell delamination, in which these neuronally differentiating cells retract their apical processes and depart from the apical surface, is the first step of their migration. Since the microenvironment established by the apical endfeet is crucial for maintaining neuroepithelial (NE)/aRGs, proper timing of the detachment of the apical endfeet is critical for the quantitative control of neurogenesis in cerebral development. During delamination, the microtubule-actin-AJ (adherens junction) configuration at the apical endfeet shows dynamic changes, concurrent with the constriction of the AJ ring at the apical endfeet and downregulation of cadherin expression. This process is mediated by transcriptional suppression of AJ-related molecules and multiple cascades to regulate cell adhesion and cytoskeletal architecture in a posttranscriptional manner. Recent advances have added molecules to the latter category: the interphase centrosome protein AKNA affects microtubule dynamics to destabilize the microtubule-actin-AJ complex, and the microtubule-associated protein Lzts1 inhibits microtubule assembly and activates actomyosin systems at the apical endfeet of differentiating cells. Moreover, Lzts1 induces the oblique division of aRGs, and loss of Lzts1 reduces the generation of outer radial glia (oRGs, also called basal radial glia, bRGs), another type of neural progenitor cell in the subventricular zone. These findings suggest that neurogenic cell delamination, and in some cases oRG generation, could be caused by a spectrum of interlinked mechanisms.

Social Stress-Induced Postsynaptic Hyporesponsiveness in Glutamatergic Synapses Is Mediated by PSD-Zip70-Rap2 Pathway and Relates to Anxiety-Like Behaviors

PSD-Zip70 is a postsynaptic protein that regulates glutamatergic synapse formation and maturation by modulation of Rap2 activity. PSD-Zip70 knockout (PSD-Zip70KO) mice exhibit defective glutamatergic synaptic transmission in the prefrontal cortex (PFC) with aberrant Rap2 activation. As prefrontal dysfunction is implicated in the pathophysiology of stress-induced psychiatric diseases, we examined PSD-Zip70KO mice in a social defeat (SD) stress-induced mouse model of depression to investigate stress-induced alterations in synaptic function. Compared with wild-type (WT) mice, PSD-Zip70KO mice exhibited almost normal responses to SD stress in depression-related behaviors such as social activity, anhedonia, and depressive behavior. However, PSD-Zip70KO mice showed enhanced anxiety-like behavior irrespective of stress conditions. The density and size of dendritic spines of pyramidal neurons were reduced in the medial PFC (mPFC) in mice exposed to SD stress. Phosphorylation levels of the AMPA–type glutamate receptor (AMPA-R) GluA2 subunit at Ser880 were prominently elevated in mice exposed to SD stress, indicating internalization of surface-expressed AMPA-Rs and decreased postsynaptic responsiveness. Structural and functional impairments in postsynaptic responsiveness were associated with Rap2 GTPase activation in response to SD stress. Social stress-induced Rap2 activation was regulated by a PSD-Zip70-dependent pathway via interaction with SPAR/PDZ-GEF1. Notably, features such as Rap2 activation, dendritic spine shrinkage, and increased GluA2 phosphorylation were observed in the mPFC of PSD-Zip70KO mice even without SD stress. Together with our previous results, the present findings suggest that SD stress-induced postsynaptic hyporesponsiveness in glutamatergic synapses is mediated by PSD-Zip70-Rap2 signaling pathway and closely relates to anxiety-like behaviors.

Lzts1 controls both neuronal delamination and outer radial glial-like cell generation during mammalian cerebral development

In the developing central nervous system, cell departure from the apical surface is the initial and fundamental step to form the 3D, organized architecture. Both delamination of differentiating cells and repositioning of progenitors to generate outer radial glial cells (oRGs) contribute to mammalian neocortical expansion; however, a comprehensive understanding of their mechanisms is lacking. Here, we demonstrate that Lzts1, a molecule associated with microtubule components, promotes both cell departure events. In neuronally committed cells, Lzts1 functions in apical delamination by altering apical junctional organization. In apical RGs (aRGs), Lzts1 expression is variable, depending on Hes1 expression levels. According to its differential levels, Lzts1 induces diverse RG behaviors: planar division, oblique divisions of aRGs that generate oRGs, and their mitotic somal translocation. Loss-of-function of lzts1 impairs all these cell departure processes. Thus, Lzts1 functions as a master modulator of cellular dynamics, contributing to increasing complexity of the cerebral architecture during evolution.

Outer radial glial cells (oRGs) are undifferentiated cells that divide in the subventricular zone during neurodevelopment, but the underlying mechanisms are not fully understood. Here the authors show that Lzts1 positively controls both neuronal delamination and generation of oRG-like cell types.

Genomic regions underlying uniformity of yearling weight in Nellore cattle evaluated under different response variables

BACKGROUND

In livestock, residual variance has been studied because of the interest to improve uniformity of production. Several studies have provided evidence that residual variance is partially under genetic control; however, few investigations have elucidated genes that control it. The aim of this study was to identify genomic regions associated with within-family residual variance of yearling weight (YW; N = 423) in Nellore bulls with high density SNP data, using different response variables. For this, solutions from double hierarchical generalized linear models (DHGLM) were used to provide the response variables, as follows: a DGHLM assuming non-null genetic correlation between mean and residual variance (rmv ≠ 0) to obtain deregressed EBV for mean (dEBVm) and residual variance (dEBVv); and a DHGLM assuming rmv = 0 to obtain two alternative response variables for residual variance, dEBVv_r0 and log-transformed variance of estimated residuals (ln_[Formula: see text]).

RESULTS

The dEBVm and dEBVv were highly correlated, resulting in common regions associated with mean and residual variance of YW. However, higher effects on variance than the mean showed that these regions had effects on the variance beyond scale effects. More independent association results between mean and residual variance were obtained when null rmv was assumed. While 13 and 4 single nucleotide polymorphisms (SNPs) showed a strong association (Bayes Factor > 20) with dEBVv and ln_[Formula: see text], respectively, only suggestive signals were found for dEBVv_r0. All overlapping 1-Mb windows among top 20 between dEBVm and dEBVv were previously associated with growth traits. The potential candidate genes for uniformity are involved in metabolism, stress, inflammatory and immune responses, mineralization, neuronal activity and bone formation.

CONCLUSIONS

It is necessary to use a strategy like assuming null rmv to obtain genomic regions associated with uniformity that are not associated with the mean. Genes involved not only in metabolism, but also stress, inflammatory and immune responses, mineralization, neuronal activity and bone formation were the most promising biological candidates for uniformity of YW. Although no clear evidence of using a specific response variable was found, we recommend consider different response variables to study uniformity to increase evidence on candidate regions and biological mechanisms behind it.

Protein Lipidation: Occurrence, Mechanisms, Biological Functions, and Enabling Technologies

Protein lipidation, including cysteine prenylation, N-terminal glycine myristoylation, cysteine palmitoylation, and serine and lysine fatty acylation, occurs in many proteins in eukaryotic cells and regulates numerous biological pathways, such as membrane trafficking, protein secretion, signal transduction, and apoptosis. We provide a comprehensive review of protein lipidation, including descriptions of proteins known to be modified and the functions of the modifications, the enzymes that control them, and the tools and technologies developed to study them. We also highlight key questions about protein lipidation that remain to be answered, the challenges associated with answering such questions, and possible solutions to overcome these challenges.

PSD-Zip70 Deficiency Causes Prefrontal Hypofunction Associated with Glutamatergic Synapse Maturation Defects by Dysregulation of Rap2 Activity

Dysregulation of synapse formation and plasticity is closely related to the pathophysiology of psychiatric and neurodevelopmental disorders. The prefrontal cortex (PFC) is particularly important for executive functions such as working memory, cognition, and emotional control, which are impaired in the disorders. PSD-Zip70 (Lzts1/FEZ1) is a postsynaptic density (PSD) protein predominantly expressed in the frontal cortex, olfactory bulb, striatum, and hippocampus. Here we found that PSD-Zip70 knock-out (PSD-Zip70KO) mice exhibit working memory and cognitive defects, and enhanced anxiety-like behaviors. These abnormal behaviors are caused by impaired glutamatergic synapse transmission accompanied by tiny-headed immature dendritic spines in the PFC, due to aberrant Rap2 activation, which has roles in synapse formation and plasticity. PSD-Zip70 modulates the Rap2 activity by interacting with SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) in the postsynapse. Furthermore, suppression of the aberrant Rap2 activation in the PFC rescued the behavioral defects in PSD-Zip70KO mice. Our data demonstrate a critical role for PSD-Zip70 in Rap2-dependent spine synapse development in the PFC and underscore the importance of this regulation in PFC-dependent behaviors.

SIGNIFICANCE STATEMENT

PSD-Zip70 deficiency causes behavioral defects in working memory and cognition, and enhanced anxiety due to prefrontal hypofunction. This study revealed that PSD-Zip70 plays essential roles in glutamatergic synapse maturation via modulation of the Rap2 activity in the PFC. PSD-Zip70 interacts with both SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) and modulates the Rap2 activity in postsynaptic sites. Our results provide a novel Rap2-specific regulatory mechanism in synaptic maturation involving PSD-Zip70.

S/T phosphorylation of DLL1 is required for full ligand activity in vitro but dispensable for DLL1 function in vivo during embryonic patterning and marginal zone B cell development

Interaction of Notch receptors with Delta- and Serrate-type ligands is an evolutionarily conserved mechanism that mediates direct communication between adjacent cells and thereby regulates multiple developmental processes. Posttranslational modifications of both receptors and ligands are pivotal for normal Notch pathway function. We have identified by mass spectrometric analysis two serine and one threonine phosphorylation sites in the intracellular domain of the mouse Notch ligand DLL1. Phosphorylation requires cell membrane association of DLL1 and occurs sequentially at the two serine residues. Phosphorylation of one serine residue most likely by protein kinase B primes phosphorylation of the other serine. A DLL1 variant, in which all three identified phosphorylated serine/threonine residues are mutated to alanine and valine, was more stable than wild-type DLL1 but had reduced relative levels on the cell surface and was more effectively cleaved in the extracellular domain. In addition, the mutant variant activated Notch1 significantly less efficient than wild-type DLL1 in a coculture assay in vitro. Mice, however, whose endogenous DLL1 was replaced with the phosphorylation-deficient triple mutant developed normally, suggesting compensatory mechanisms under physiological conditions in vivo.

Primary cilia and dendritic spines: different but similar signaling compartments

Primary non-motile cilia and dendritic spines are cellular compartments that are specialized to sense and transduce environmental cues and presynaptic signals, respectively. Despite their unique cellular roles, both compartments exhibit remarkable parallels in the general principles, as well as molecular mechanisms, by which their protein composition, membrane domain architecture, cellular interactions, and structural and functional plasticity are regulated. We compare and contrast the pathways required for the generation and function of cilia and dendritic spines, and suggest that insights from the study of one may inform investigations into the other of these critically important signaling structures.

Postsynaptic density protein (PSD)-95 expression is markedly decreased in the hippocampal CA1 region after experimental ischemia-reperfusion injury

Synaptic plasticity is important for functional recovery after cerebral ischemic injury. In the present study, we investigated chronological change in the immunoreactivity of PSD-95, a kind of postsynaptic density protein, in the hippocampus proper (CA1-3 regions) after 5 min of transient cerebral ischemia in gerbils. PSD-95 immunoreactivity was observed in MAP-2-immunoreactive dendrites in the CA1-3 regions of the sham group. The PSD-95 immunoreactivity was shown as beaded structure in the MAP-2-immunoreactive dendrites. However, PSD-95 immunoreactivity began to be dramatically decreased in MAP-2-immunoreactive dendrites in the CA1 region, not CA2-3 region, at early time after ischemia-reperfusion. At 5 days after ischemia-reperfusion, MAP-2 immunoreactivity almost disappeared in the ischemic CA1 region, and PSD-95 immunoreactivity was much lower than that in the sham group. In brief, PSD-95 immunoreactivity in the CA1 dendrites was markedly decreased at early time after ischemia-reperfusion. We suggest that decreased PSD-95 immunoreactivity in the ischemic CA1 region may lead to a deficit of postsynaptic plasticity in the brain.

Synaptic cross-talk between N-methyl-D-aspartate receptors and LAPSER1-beta-catenin at excitatory synapses

Memory formation in the brain is thought to be depending upon long lasting plastic changes of synaptic contacts that require alterations on the transcriptional level. Here, we characterize LAPSER1, a putative cytokinetic tumor suppressor that binds directly to ProSAP2/Shank3 and the synaptic Rap-Gap protein SPAR1 as a novel postsynaptic density component. Postsynaptic LAPSER1 is in complex with all important members of the canonical Wnt pathway including beta-catenin. Upon N-methyl-D-aspartate receptor-dependent activation, LAPSER1 and beta-catenin comigrate from the postsynaptic density to the nucleus and induce the transcription and translation of known beta-catenin target genes, including Tcfe2a and c-Myc. The nuclear export and cytoplasmic redistribution of beta-catenin is tightly regulated by LAPSER1. We postulate a postsynaptic cross-talk between N-methyl-D-aspartate receptors and a LAPSER1-beta-catenin complex that results in a self-regulated, synaptic activity-dependent expression of beta-catenin target genes. This calls for a novel role of Tcfe2a and c-Myc in plastic changes of neural tissue.

Ca2+/calmodulin-dependent protein kinase IIalpha clusters are associated with stable lipid rafts and their formation traps PSD-95

Relatively large number of post-synaptic density (PSD) proteins, including Ca2+/calmodulin-dependent protein kinase II (CaMKII), have the potential to associate with lipid rafts. We in this study demonstrate that the CaMKIIalpha clusters induced by ionomycin in human embryonic kidney 293 cells, as well as unclustered CaMKIIalpha (Du F., Saitoh F., Tian Q. B., Miyazawa S., Endo S. and Suzuki T, 2006, Biochem. Biophys. Res. Commun 347, 814-820), were associated with lipid rafts. The CaMKIIalpha clusters associated with lipid raft fraction became resistant to treatment with methyl-beta-cyclodextrin and subsequent cold Triton X-100, which suggests the stabilization of CaMKIIalpha cluster-associated lipid rafts. Next, we found that PSD-95, which is also a component of lipid raft fraction and does not interact directly with CaMKII, was trapped by stable CaMKIIalpha cluster-containing structure. Association of PSD-95 with CaMKIIalpha clusters was also observed in cultured neuronal cells. These results suggest the CaMKIIalpha clusters associated with the lipid rafts in the cytoplasmic region play a role in the assembly and stabilization of certain PSD proteins that have the potential to associate with lipid rafts.

SPAR2, a novel SPAR-related protein with GAP activity for Rap1 and Rap2

Spine-associated RapGAP 2 (SPAR2) is a novel GTPase activating protein (GAP) for the small GTPase Rap that shows significant sequence homology to SPAR, a synaptic RapGAP that was reported to regulate spine morphology in hippocampal neurons. SPAR2, like SPAR, interacts with the recently described synaptic scaffolding protein ProSAP-interacting protein (ProSAPiP), which in turn binds to the PDZ domain of ProSAP/Shank post-synaptic density proteins. In subcellular fractionation experiments, SPAR2 is enriched in synaptosomes and post-synaptic density fractions indicating that it is a synaptic protein. Furthermore, we could show using in vitro GAP assays that SPAR2 has GAP activity for Rap1 and Rap2. Expression in COS-7 cells, however, revealed different actin-binding properties of SPAR2 and SPAR. Additionally, over-expression of SPAR2 in cultured hippocampal neurons did not affect spine morphology as it was reported for SPAR. In situ hybridization studies also revealed a differential tissue distribution of SPAR and SPAR2 with SPAR2 transcripts being mainly expressed in cerebellar and hippocampal granule cells. Moreover, in the cerebellum SPAR2 is developmentally regulated with a peak of expression around the period of synapse formation. Our results imply that SPAR2 is a new RapGAP with specific functions in cerebellar and hippocampal granule cells.

LAPSER1 is a putative cytokinetic tumor suppressor that shows the same centrosome and midbody subcellular localization pattern as p80 katanin

Prostate cancer is one of the most common cancers in men, with more than 500,000 new worldwide cases reported annually, resulting in 200,000 deaths of mainly older men in developed countries. Existing treatments have not proved very effective in managing prostate cancer, and continuing efforts therefore are ongoing to explore novel targets and strategies for future therapies. LAPSER1 has been identified as a candidate tumor suppressor gene in prostate cancer, but its true functions remain unknown. We report here that LAPSER1 colocalizes to the centrosomes and midbodies in mitotic cells with gamma-tubulin, MKLP1, and p80 katanin, and is involved in cytokinesis. Moreover, RNAi-mediated disruption of LAPSER1, which is accompanied by the mislocalization of p80 katanin, results in malformation of the central spindle. Significantly, the enhanced expression of LAPSER1 induces binucleation and renders the cells resistant to oncogenic transformation. In cells transformed by the v-Fps oncogene, overexpressed LAPSER1 induces abortive cytokinesis, followed by mitotic catastrophe in a p80 katanin-dependent manner. Cells that are rescued from this apoptotic pathway with Z-VAD-fmk display karyokinesis. These results suggest that LAPSER1 participates in cytokinesis by interacting with p80 katanin, the disruption of which may potentially cause genetic instability and cancer.

Potential role of N-myristoyltransferase in cancer

Colorectal cancer is the second leading cause of malignant death, and better preventive strategies are needed. The treatment of colonic cancer remains difficult because of the lack of effective chemotherapeutic agents; therefore it is important to continue to search for cellular functions that can be disrupted by chemotherapeutic drugs resulting in the inhibition of the development and progression of cancer. The current knowledge of the modification of proteins by myristoylation involving myristoyl-CoA: protein N-myristoyltransferase (NMT) is in its infancy. This process is involved in the pathogenesis of cancer. We have reported for the first time that NMT activity and protein expression were higher in human colorectal cancer, gallbladder carcinoma and brain tumors. In addition, an increase in NMT activity appeared at an early stage in colonic carcinogenesis. It is conceivable therefore that NMT can be used as a potential marker for the early detection of cancer. These observations lead to the possibility of developing NMT specific inhibitors, which may be therapeutically useful. We proposed that HSC70 and/or enolase could be used as an anticancer therapeutic target. This review summarized the status of NMT in cancer which has been carried in our laboratory.

Agrin elicits membrane lipid condensation at sites of acetylcholine receptor clusters in C2C12 myotubes

The formation of the neuromuscular junction is characterized by the progressive accumulation of nicotinic acetylcholine receptors (AChRs) in the postsynaptic membrane facing the nerve terminal, induced predominantly through the agrin/muscle-specific kinase (MuSK) signaling cascade. However, the cellular mechanisms linking MuSK activation to AChR clustering are still poorly understood. Here, we investigate whether lipid rafts are involved in agrin-elicited AChR clustering in a mouse C2C12 cell line. We observed that in C2C12 myotubes, both AChR clustering and cluster stability were dependent on cholesterol, because depletion by methyl-beta-cyclodextrin inhibited cluster formation or dispersed established clusters. Importantly, AChR clusters resided in ordered membrane domains, a biophysical property of rafts, as probed by Laurdan two-photon fluorescence microscopy. We isolated detergent-resistant membranes (DRMs) by three different biochemical procedures, all of which generate membranes with similar cholesterol/GM1 ganglioside contents, and these were enriched in several postsynaptic components, notably AChR, syntrophin, and raft markers flotillin-2 and caveolin-3. Agrin did not recruit AChRs into DRMs, suggesting that they are present in rafts independently of agrin activation. Consequently, in C2C12 myotubes, agrin likely triggers AChR clustering or maintains clusters through the coalescence of lipid rafts. These data led us to propose a model in which lipid rafts play a pivotal role in the assembly of the postsynaptic membrane at the neuromuscular junction upon agrin signaling.

ProSAP-interacting protein 1 (ProSAPiP1), a novel protein of the postsynaptic density that links the spine-associated Rap-Gap (SPAR) to the scaffolding protein ProSAP2/Shank3

ProSAPs/Shanks are a family of proteins that have a major scaffolding function for components of the postsynaptic density (PSD) of excitatory brain synapses. Members of the family harbor a variety of domains for protein-protein interactions, one of which is a unique PDZ domain that differs significantly from those of other proteins. We have identified a novel binding partner for this PDZ domain, termed ProSAPiP1, that is highly enriched in the PSD and shares significant sequence homology with the PSD protein PSD-Zip70. Both molecules code for a Fez1 domain that can be found in a total of four related proteins. ProSAPiP1 is widely expressed in rat brain and co-localizes with ProSAP2/Shank3 in excitatory spines and synapses. ProSAP2/Shank3 co-immunoprecipitates with ProSAPiP1 but not with PSD-Zip70. Both proteins, however, bind and recruit SPAR to synapses with a central coiled-coil region that harbors a leucine zipper motif. This region is also responsible for homo- and heteromultimerization of ProSAPiP1 and PSD-Zip70. Thus, ProSAPiP1 and PSD-Zip70 are founders of a novel family of scaffolding proteins, the "Fezzins," which adds further complexity to the organization of the PSD protein network.

NMDA receptor-dependent synaptic translocation of insulin receptor substrate p53 via protein kinase C signaling

The activity-dependent remodeling of postsynaptic structure is a fundamental process underlying learning and memory. Insulin receptor substrate p53 (IRSp53), a key player in cytoskeletal dynamics, is enriched in the postsynaptic density (PSD) fraction, but its significance in synaptic functions remains unclear. We report here that IRSp53 is accumulated rapidly at the postsynaptic sites of cultured hippocampal neurons after glutamate or NMDA stimulation in an actin cytoskeleton-dependent manner. Pharmacological profiles showed that a PKC inhibitor, but not other kinase inhibitors, specifically suppressed the synaptic translocation of IRSp53 in response to NMDA, and the selective activation of PKC with phorbol ester markedly induced the synaptic translocation. Reverse transcriptase-PCR and Western blotting showed that IRSp53-S is the major isoform expressed in cultured hippocampal neurons. The synaptic targeting of IRSp53-S was found to be mediated through N-terminal coiled-coil domain and the PDZ (PSD-95/Discs large/zona occludens-1)-binding sequence at its C-terminal end and regulated by the PKC phosphorylation of its N terminus. In electrophysiological experiments, overexpression of IRSp53-S wild type and IRSp53-S mutant that is spontaneously accumulated at the postsynaptic sites enhanced the postsynaptic function as detected by an increased miniature EPSC amplitude. These data suggest that IRSp53 is involved in NMDA receptor-linked synaptic plasticity via PKC signaling.

Collaboration of PSD-Zip70 with its binding partner, SPAR, in dendritic spine maturity

Recent studies have reported on the molecular mechanisms underlying dendritic spine (spine) dynamics. Because most of these studies investigated spine dynamics by overexpressing constitutively active or dominant-negative PSD (postsynaptic density) proteins in cultured mature neurons, the results represent the enlargement of mature spines or their return to an immature state. Here, we developed the technique of in utero electroporation to investigate spine dynamics. Using this technique, we demonstrated the suppression of spine maturation by the C-terminal variants of PSD-Zip70 in vitro and in vivo. Transient overexpression of the C terminus of PSD-Zip70 and knock-down of PSD-Zip70 also displayed the destabilization of mature spines. We further found the PSD-Zip70 and SPAR (spine-associated RapGAP) interaction via the short C-terminal region of PSD-Zip70 and the GK-binding domain of SPAR. In association with immature spines induced by overexpression of the PSD-Zip70 C terminus or knock-down of PSD-Zip70, SPAR lost its spine localization. Overexpression of the GK-binding domain of SPAR also induced to form immature spines without affecting the localization of PSD-Zip70 in the small heads of filopodial spines. Our results suggest that PSD-Zip70 in collaboration with SPAR is critically involved in spine maturity, especially in the mature spine formation and the maintenance of spine maturity.

BAALC 1-6-8 protein is targeted to postsynaptic lipid rafts by its N-terminal myristoylation and palmitoylation, and interacts with alpha, but not beta, subunit of Ca/calmodulin-dependent protein kinase II

We cloned a rat BAALC 1-6-8 isoform cDNA (GenBank Accession No. AB073318) that encoded a 22-kDa protein, and identified endogenous BAALC 1-6-8 protein in the brain. The gene was expressed widely in the frontal part of the brain, and the protein was localized to the synaptic sites and was increased in parallel with synaptogenesis. The protein interacted with the alpha, but not beta, subunit of Ca(2+)/calmodulin-dependent protein kinase II (CaMKIIalpha). The interaction occurred between the N-terminal 35-amino-acid region of BAALC 1-6-8 protein and the C-terminal end of the regulatory domain of CaMKIIalpha, which contains alpha isoform-specific sequence. Thus, the interaction may be CaMKIIalpha-specific. We also found that BAALC 1-6-8 protein, as well as CaMKIIalpha, was localized to lipid rafts and that both myristoylation and palmitoylation of BAALC 1-6-8 N-terminal portion were required for targeting of the protein into lipid rafts. These findings suggest that BAALC 1-6-8 protein play a synaptic role at the postsynaptic lipid raft possibly through interaction with CaMKIIalpha.

MYRbase: analysis of genome-wide glycine myristoylation enlarges the functional spectrum of eukaryotic myristoylated proteins

We evaluated the evolutionary conservation of glycine myristoylation within eukaryotic sequences. Our large-scale cross-genome analyses, available as MYRbase, show that the functional spectrum of myristoylated proteins is currently largely underestimated. We give experimental evidence for in vitro myristoylation of selected predictions. Furthermore, we classify five membrane-attachment factors that occur most frequently in combination with, or even replacing, myristoyl anchors, as some protein family examples show.

Transport protein trafficking in polarized cells

In order to carry out their physiological functions, ion transport proteins must be targeted to the appropriate domains of cell membranes. Regulation of ion transport activity frequently involves the tightly controlled delivery of intracellular populations of transport proteins to the plasma membrane or the endocytic retrieval of transport proteins from the cell surface. Transport proteins carry signals embedded within their structures that specify their subcellular distributions and endow them with the capacity to participate in regulated membrane trafficking processes. Recently, a great deal has been learned about the biochemical nature of these signals, as well as about the cellular machinery that interprets them and acts upon their messages.