SNIP, a novel SNAP-25-interacting protein implicated in regulated exocytosis

SNX17 Mediates Dendritic Spine Maturation via p140Cap

Sorting nexin17 (SNX17) is a member of the sorting nexin family, which plays a crucial role in endosomal trafficking. Previous research has shown that SNX17 is involved in the recycling or degradation of various proteins associated with neurodevelopmental and neurological diseases in cell models. However, the significance of SNX17 in neurological function in the mouse brain has not been thoroughly investigated. In this study, we generated Snx17 knockout mice and observed that the homozygous deletion of Snx17 (Snx17-/-) resulted in lethality. On the other hand, heterozygous mutant mice (Snx17+/-) exhibited anxiety-like behavior with a reduced preference for social novelty. Furthermore, Snx17 haploinsufficiency led to impaired synaptic transmission and reduced maturation of dendritic spines. Through GST pulldown and interactome analysis, we identified the SRC kinase inhibitor, p140Cap, as a potential downstream target of SNX17. We also demonstrated that the interaction between p140Cap and SNX17 is crucial for dendritic spine maturation. Together, this study provides the first in vivo evidence highlighting the important role of SNX17 in maintaining neuronal function, as well as regulating social novelty and anxiety-like behaviors.

SIP30 involvement in vesicle exocytosis from PC12 cells

SNAP25 (synaptosome-associated protein of 25 kDa) is a core SNARE (soluble N-ethylmaleimide-sensitive factor attachment receptor) protein; and the interaction between SNAP25 and other SNARE proteins is essential for synaptic vesicle exocytosis. Identified as a SNAP25 interacting protein, SIP30 (SNAP25 interacting protein at 30 kDa) has been shown to modulate neuropathic pain behavior, and is potentially involved in the cellular process of vesicle exocytosis. Previous study demonstrated that using a vesicle secretion assay in PC12 cells, anti-SIP30 siRNA reduced vesicle exocytosis. We investigated vesicle exocytosis from PC12 cells with FM1-43 fluorescence dye, and demonstrated that anti-SIP30 siRNA reduced the pool of releasable vesicles and the rate of vesicle exocytosis, without affecting the endocytosis and recycling of the exocytosed vesicles. The results show that SIP30 is involved in vesicle exocytosis, suggesting a potential mechanism of SIP30 modulation of neuropathic pain.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

p140Cap Controls Female Fertility in Mice Acting via Glutamatergic Afference on Hypothalamic Gonadotropin-Releasing Hormone Neurons

p140Cap, encoded by the gene SRCIN1 (SRC kinase signaling inhibitor 1), is an adaptor/scaffold protein highly expressed in the mouse brain, participating in several pre- and post-synaptic mechanisms. p140Cap knock-out (KO) female mice show severe hypofertility, delayed puberty onset, altered estrus cycle, reduced ovulation, and defective production of luteinizing hormone and estradiol during proestrus. We investigated the role of p140Cap in the development and maturation of the hypothalamic gonadotropic system. During embryonic development, migration of Gonadotropin-Releasing Hormone (GnRH) neurons from the nasal placode to the forebrain in p140Cap KO mice appeared normal, and young p140Cap KO animals showed a normal number of GnRH-immunoreactive (-ir) neurons. In contrast, adult p140Cap KO mice showed a significant loss of GnRH-ir neurons and a decreased density of GnRH-ir projections in the median eminence, accompanied by reduced levels of GnRH and LH mRNAs in the hypothalamus and pituitary gland, respectively. We examined the number of kisspeptin (KP) neurons in the rostral periventricular region of the third ventricle, the number of KP-ir fibers in the arcuate nucleus, and the number of KP-ir punctae on GnRH neurons but we found no significant changes. Consistently, the responsiveness to exogenous KP in vivo was unchanged, excluding a cell-autonomous defect on the GnRH neurons at the level of KP receptor or its signal transduction. Since glutamatergic signaling in the hypothalamus is critical for both puberty onset and modulation of GnRH secretion, we examined the density of glutamatergic synapses in p140Cap KO mice and observed a significant reduction in the density of VGLUT-ir punctae both in the preoptic area and on GnRH neurons. Our data suggest that the glutamatergic circuitry in the hypothalamus is altered in the absence of p140Cap and is required for female fertility.

p130Cas/BCAR1 and p140Cap/SRCIN1 Adaptors: The Yin Yang in Breast Cancer?

p130Cas/BCAR1 is an adaptor protein devoid of any enzymatic or transcriptional activity, whose modular structure with various binding motifs, allows the formation of multi-protein signaling complexes. This results in the induction and/or maintenance of signaling pathways with pleiotropic effects on cell motility, cell adhesion, cytoskeleton remodeling, invasion, survival, and proliferation. Deregulation of p130Cas/BCAR1 adaptor protein has been extensively demonstrated in a variety of human cancers in which overexpression of p130Cas/BCAR1 correlates with increased malignancy. p140Cap (p130Cas associated protein), encoded by the SRCIN1 gene, has been discovered by affinity chromatography and mass spectrometry analysis of putative interactors of p130Cas. It came out that p140Cap associates with p130Cas not directly but through its interaction with the Src Kinase. p140Cap is highly expressed in neurons and to a lesser extent in epithelial tissues such as the mammary gland. Strikingly, in vivo and in vitro analysis identified its tumor suppressive role in breast cancer and in neuroblastoma, showing an inverse correlation between p140Cap expression in tumors and tumor progression. In this review, a synopsis of 15 years of research on the role of p130Cas/BCAR1 and p140Cap/SRCIN1 in breast cancer will be presented.

The p140Cap adaptor protein as a molecular hub to block cancer aggressiveness

The p140Cap adaptor protein is a scaffold molecule encoded by the SRCIN1 gene, which is physiologically expressed in several epithelial tissues and in the neurons. However, p140Cap is also strongly expressed in a significant subset of cancers including breast cancer and neuroblastoma. Notably, cancer patients with high p140Cap expression in their primary tumors have a lower probability of developing a distant event and ERBB2-positive breast cancer sufferers show better survival. In neuroblastoma patients, SRCIN1 mRNA levels represent an independent risk factor, which is inversely correlated to disease aggressiveness. Consistent with clinical data, SRCIN1 gain or loss of function mouse models demonstrated that p140Cap may affect tumor growth and metastasis formation by controlling the signaling pathways involved in tumorigenesis and metastatic features. This study reviews data showing the relevance of SRCIN1/p140Cap in cancer patients, the impact of SRCIN1 status on p140Cap expression, the specific mechanisms through which p140Cap can limit cancer progression, the molecular functions regulated by p140Cap, along with the p140Cap interactome, to unveil its key role for patient stratification in clinics.

Proteomic approach underlying the hippocampal neurodegeneration caused by low doses of methylmercury after long-term exposure in adult rats

Methylmercury (MeHg) is an important toxicant that causes cognitive dysfunctions in humans. This study aimed to investigate the proteomic and biochemical alterations of the hippocampus associated with behavioural consequences of low doses of MeHg in a long-term exposure model, and to realistically mimic in vivo the result of human exposure to this toxicant. Adult Wistar male rats were exposed to a dose of MeHg at 0.04 mg kg-1 day-1 by gavage for 60 days. Total mercury (Hg) content was significantly increased in the hippocampal parenchyma. The increase in the Hg levels was capable of reducing neuron and astrocyte cell density in the CA1, CA3, hilus and dentate gyrus regions, increasing both malondialdehyde and nitrite levels and decreasing antioxidant capacity against peroxyl radicals. The proteomic analysis detected 1041 proteins with altered expression due to MeHg exposure, including 364 proteins with no expression, 295 proteins with de novo expression and 382 proteins with up- or down-regulated expression. This proteomic approach revealed alterations in pathways related to chemical synapses, metabolism, amino acid transport, cell energy, neurodegenerative processes and myelin maintenance. Therefore, even at low doses of MeHg exposure, it is possible to cause hippocampal damage in adult rats at many organisational levels, triggering oxidative stress and proteome misbalance, featuring a neurodegenerative process and culminating in long- and short-term memory and learning deficits.

p140Cap Regulates GABAergic Synaptogenesis and Development of Hippocampal Inhibitory Circuits

The neuronal scaffold protein p140Cap was investigated during hippocampal network formation. p140Cap is present in presynaptic GABAergic terminals and its genetic depletion results in a marked alteration of inhibitory synaptic activity. p140Cap-/- cultured neurons display higher frequency of miniature inhibitory postsynaptic currents (mIPSCs) with no changes of their mean amplitude. Consistent with a potential presynaptic alteration of basal GABA release, p140Cap-/- neurons exhibit a larger synaptic vesicle readily releasable pool, without any variation of single GABAA receptor unitary currents and number of postsynaptic channels. Furthermore, p140Cap-/- neurons show a premature and enhanced network synchronization and appear more susceptible to 4-aminopyridine-induced seizures in vitro and to kainate-induced seizures in vivo. The hippocampus of p140Cap-/- mice showed a significant increase in the number of both inhibitory synapses and of parvalbumin- and somatostatin-expressing interneurons. Specific deletion of p140Cap in forebrain interneurons resulted in increased susceptibility to in vitro epileptic events and increased inhibitory synaptogenesis, comparable to those observed in p140Cap-/- mice. Altogether, our data demonstrate that p140Cap finely tunes inhibitory synaptogenesis and GABAergic neurotransmission, thus regulating the establishment and maintenance of the proper hippocampal excitatory/inhibitory balance.

Dissecting the Shared and Context-Dependent Pathways Mediated by the p140Cap Adaptor Protein in Cancer and in Neurons

The p140Cap adaptor protein is a scaffold molecule physiologically expressed in few epithelial tissues, such as the mammary gland, and in differentiated neurons. While the role of p140Cap in mammary gland epithelia is not still understood, we already know that a significant subset of breast cancers express p140Cap. In the subgroup of ERBB2-amplified breast cancers, a high p140Cap status predicts a significantly lower probability of developing a distant event and a clear difference in survival. p140Cap is causal in dampening ERBB2-positive tumor cell progression, impairing tumor onset and growth, and counteracting epithelial mesenchymal transition, resulting in decreased metastasis formation. Since only a few p140Cap interacting proteins have been identified in breast cancer and the molecular complexes and pathways underlying the cancer function of p140Cap are largely unknown, we generated a p140Cap interactome from ERBB2-positive breast cancer cells, identifying cancer specific components and those shared with the synaptic interactome. We identified 373 interacting proteins in cancer cells, including those with functions relevant to cell adhesion, protein homeostasis, regulation of cell cycle and apoptosis, which are frequently deregulated in cancer. Within the interactome, we identified 15 communities (clusters) with topology-functional relationships. In neurons, where p140Cap is key in regulating synaptogenesis, synaptic transmission and synaptic plasticity, it establishes an extensive interactome with proteins that cluster to sub complexes located in the postsynaptic density. p140Cap interactors converge on key synaptic processes, including synaptic transmission, actin cytoskeleton remodeling and cell-cell junction organization. Comparing the breast cancer to the synaptic interactome, we found 39 overlapping proteins, a relatively small overlap. However, cell adhesion and remodeling of actin cytoskeleton clearly emerge as common terms in the shared subset. Thus, the functional signature of the two interactomes is primarily determined by organ/tissue and functional specificity, while the overlap provides a list of shared functional terms, which might be linked to both cancer and neurological functions.

The SRCIN1/p140Cap adaptor protein negatively regulates the aggressiveness of neuroblastoma

Neuroblastoma is the most common extra-cranial pediatric solid tumor, responsible for 13–15% of pediatric cancer death. Its intrinsic heterogeneity makes it difficult to target for successful therapy. The adaptor protein p140Cap/SRCIN1 negatively regulates tumor cell features and limits breast cancer progression. This study wish to assess if p140Cap is a key biological determinant of neuroblastoma outcome. RNAseq profiles of a large cohort of neuroblastoma patients show that SRCIN1 mRNA levels are an independent risk factor inversely correlated to disease aggressiveness. In high-risk patients, CGH+SNP microarray analysis of primary neuroblastoma identifies SRCIN1 as frequently altered by hemizygous deletion, copy-neutral loss of heterozygosity, or disruption. Functional experiments show that p140Cap negatively regulates Src and STAT3 signaling, affects anchorage-independent growth and migration, in vivo tumor growth and spontaneous lung metastasis formation. p140Cap also increases sensitivity of neuroblastoma cells to doxorubicin and etoposide treatment, as well as to a combined treatment with chemotherapy drugs and Src inhibitors. Our functional findings point to a causal role of p140Cap in curbing the aggressiveness of neuroblastoma, due to its ability to impinge on specific molecular pathways, and to sensitize cells to therapeutic treatment. This study provides the first evidence that the SRCIN1/p140Cap adaptor protein is a key player in neuroblastoma as a new independent prognostic marker for patient outcome and treatment. Altogether, these data highlight the potential clinical impact of SRCIN1/p140Cap expression in neuroblastoma tumors, in terms of reducing cytotoxic effects of chemotherapy, one of the main issues for pediatric tumor treatment.

Neuronal SNARE complex: A protein folding system with intricate protein-protein interactions, and its common neuropathological hallmark, SNAP25

SNARE (Soluble NSF(N-ethylmaleimide-sensitive factor) Attachment Receptor) complex is a trimeric supramolecular organization of SNAP25, syntaxin, and VAMP which mediates fusion of synaptic vesicles with the presynaptic plasma membrane. The functioning of this entire protein assembly is dependent on its tetrahelical coiled coil structure alongside its interaction with a large spectrum of regulatory proteins like synaptotagmin, complexin, intersectin, etc. Defects arising in SNARE complex assembly due to mutations or faulty post-translational modifications are associated to severe synaptopathies like Schizophrenia and also proteopathies like Alzheimer's disease. The review primarily focuses on SNAP25, which is the prime contributor in the complex assembly. It is conceptualized that the network of protein interactions of this helical protein assists as a chaperoning system for attaining functional structure. Additionally, the innate disordered nature of SNAP25 and its amyloidogenic propensities have been highlighted employing computational methods. The intrinsic nature of SNAP25 is anticipated to form higher-order aggregates due to its cysteine rich domain, which is also a target for several post-translational modifications. Furthermore, the aberrations in the structure and expression profile of the protein display common patterns in the pathogenesis of a diverse synaptopathies and proteopathies. This work of SNARE literature aims to provide a new comprehensive outlook and research directions towards SNARE complex and presents SNAP25 as a common neuropathological hallmark which can be a diagnostic or therapeutic target.

MicroRNA-181a promotes angiogenesis in colorectal cancer by targeting SRCIN1 to promote the SRC/VEGF signaling pathway

Colorectal cancer (CRC) is a very common metastatic tumor with active angiogenesis that requires active angiogenesis. Recently, increased microRNA-181a-5p (miR-181a) expression was found to be significantly associated with liver metastasis and poor outcome in CRC patients. In this study, the role of miR-181a in tumor angiogenesis was further investigated. Capillary tube formation assays were used to demonstrate the ability of miR-181a to promote tumor angiogenesis. Bioinformatics analyses identified SRC kinase signaling inhibitor 1 (SRCIN1) as a potential target of miR-181a. Next, two CRC cell lines (HT29 and SW480) were used to clarify the function of miR-181a through SRCIN1 targeting. In addition, the biological effects of SRCIN1 inhibition by miR-181a were examined in vitro by quantitative RT-PCR, western blotting and enzyme-linked immunosorbent assay and in vivo by Matrigel plug angiogenesis assays and immunohistochemical staining. In clinical samples, Fluorescence in situ hybridization and immunofluorescence were performed to detect the relation between miR-181a and SRCIN1. In addition, SRCIN1 protein and miR-181a expression levels in CRC tissues were also measured by western blot and quantitative real-time polymerase chain reaction. MiR-181a markedly augmented the capability of CRC cells to advance tube formation in endothelial cells in vitro. The Matrigel plug assay showed that miR-181a promoted angiogenesis in vivo. In conclusion, miR-181a inhibited SRCIN1, which caused SRC to transform from an inactive status to an active conformation and to trigger vascular endothelial growth factor secretion, leading to increased angiogenesis. MiR-181a dysregulation contributes to angiogenesis in CRC, and downregulation of miR-181a represents a promising, novel strategy to achieve an efficient antiangiogenic response in anti-CRC therapy.

A Critical Role of Presynaptic Cadherin/Catenin/p140Cap Complexes in Stabilizing Spines and Functional Synapses in the Neocortex

The formation of functional synapses requires coordinated assembly of presynaptic transmitter release machinery and postsynaptic trafficking of functional receptors and scaffolds. Here, we demonstrate a critical role of presynaptic cadherin/catenin cell adhesion complexes in stabilizing functional synapses and spines in the developing neocortex. Importantly, presynaptic expression of stabilized β-catenin in either layer (L) 4 excitatory neurons or L2/3 pyramidal neurons significantly upregulated excitatory synaptic transmission and dendritic spine density in L2/3 pyramidal neurons, while its sparse postsynaptic expression in L2/3 neurons had no such effects. In addition, presynaptic β-catenin expression enhanced release probability of glutamatergic synapses. Newly identified β-catenin-interacting protein p140Cap is required in the presynaptic locus for mediating these effects. Together, our results demonstrate that cadherin/catenin complexes stabilize functional synapses and spines through anterograde signaling in the neocortex and provide important molecular evidence for a driving role of presynaptic components in spinogenesis in the neocortex.

Synaptic Interactome Mining Reveals p140Cap as a New Hub for PSD Proteins Involved in Psychiatric and Neurological Disorders

Altered synaptic function has been associated with neurological and psychiatric conditions including intellectual disability, schizophrenia and autism spectrum disorder (ASD). Amongst the recently discovered synaptic proteins is p140Cap, an adaptor that localizes at dendritic spines and regulates their maturation and physiology. We recently showed that p140Cap knockout mice have cognitive deficits, impaired long-term potentiation (LTP) and long-term depression (LTD), and immature, filopodia-like dendritic spines. Only a few p140Cap interacting proteins have been identified in the brain and the molecular complexes and pathways underlying p140Cap synaptic function are largely unknown. Here, we isolated and characterized the p140Cap synaptic interactome by co-immunoprecipitation from crude mouse synaptosomes, followed by mass spectrometry-based proteomics. We identified 351 p140Cap interactors and found that they cluster to sub complexes mostly located in the postsynaptic density (PSD). p140Cap interactors converge on key synaptic processes, including transmission across chemical synapses, actin cytoskeleton remodeling and cell-cell junction organization. Gene co-expression data further support convergent functions: the p140Cap interactors are tightly co-expressed with each other and with p140Cap. Importantly, the p140Cap interactome and its co-expression network show strong enrichment in genes associated with schizophrenia, autism, bipolar disorder, intellectual disability and epilepsy, supporting synaptic dysfunction as a shared biological feature in brain diseases. Overall, our data provide novel insights into the molecular organization of the synapse and indicate that p140Cap acts as a hub for postsynaptic complexes relevant to psychiatric and neurological disorders.

Gene networks in neurodegenerative disorders

Three neurodegenerative diseases [Amyotrophic Lateral Sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD)] have many characteristics like pathological mechanisms and genes. In this sense some researchers postulate that these diseases share the same alterations and that one alteration in a specific protein triggers one of these diseases. Analyses of gene expression may shed more light on how to discover pathways, pathologic mechanisms associated with the disease, biomarkers and potential therapeutic targets. In this review, we analyze four microarrays related to three neurodegenerative diseases. We will systematically examine seven genes (CHN1, MDH1, PCP4, RTN1, SLC14A1, SNAP25 and VSNL1) that are altered in the three neurodegenerative diseases. A network was built and used to identify pathways, miRNA and drugs associated with ALS, AD and PD using Cytoscape software an interaction network based on the protein interactions of these genes. The most important affected pathway is PI3K-Akt signalling. Thirteen microRNAs (miRNA-19B1, miRNA-107, miRNA-124-1, miRNA-124-2, miRNA-9-2, miRNA-29A, miRNA-9-3, miRNA-328, miRNA-19B2, miRNA-29B2, miRNA-124-3, miRNA-15A and miRNA-9-1) and four drugs (Estradiol, Acetaminophen, Resveratrol and Progesterone) for new possible treatments were identified.

Microtubule plus-end tracking proteins in neuronal development

Regulation of the microtubule cytoskeleton is of pivotal importance for neuronal development and function. One such regulatory mechanism centers on microtubule plus-end tracking proteins (+TIPs): structurally and functionally diverse regulatory factors, which can form complex macromolecular assemblies at the growing microtubule plus-ends. +TIPs modulate important properties of microtubules including their dynamics and their ability to control cell polarity, membrane transport and signaling. Several neurodevelopmental and neurodegenerative diseases are associated with mutations in +TIPs or with misregulation of these proteins. In this review, we focus on the role and regulation of +TIPs in neuronal development and associated disorders.

Parkin Protects Against Misfolded SOD1 Toxicity by Promoting Its Aggresome Formation and Autophagic Clearance

Mutations in Cu/Zn superoxide dismutase (SOD1) cause autosomal dominant amyotrophic lateral sclerosis (ALS), a devastating neurodegenerative disease with no effective treatment. Despite ample evidence indicating involvement of mutation-induced SOD1 protein misfolding and aggregation in ALS pathogenesis, the molecular mechanisms that control cellular management of misfolded, aggregation-prone SOD1 mutant proteins remain unclear. Here, we report that parkin, an E3 ubiquitin-protein ligase which is linked to Parkinson's disease, is a novel regulator of cellular defense against toxicity induced by ALS-associated SOD1 mutant proteins. We find that parkin mediates K63-linked polyubiquitination of SOD1 mutants in cooperation with the UbcH13/Uev1a E2 enzyme and promotes degradation of these misfolded SOD1 proteins by the autophagy-lysosome system. In response to strong proteotoxic stress associated with proteasome impairment, parkin promotes sequestration of misfolded and aggregated SOD1 proteins to form perinuclear aggresomes, regulates positioning of lysosomes around misfolded SOD1 aggresomes, and facilitates aggresome clearance by autophagy. Our findings reveal parkin-mediated cytoprotective mechanisms against misfolded SOD1 toxicity and suggest that enhancing parkin-mediated cytoprotection may provide a novel therapeutic strategy for treating ALS.

SWATH analysis of the synaptic proteome in Alzheimer's disease

Brain tissue from Alzheimer's disease patients exhibits synaptic degeneration in selected regions. Synaptic dysfunction occurs early in the disease and is a primary pathological target for treatment. The molecular mechanisms underlying this degeneration remain unknown. Quantifying the synaptic proteome in autopsy brain and comparing tissue from Alzheimer's disease cases and subjects with normal aging are critical to understanding the molecular mechanisms associated with Alzheimer pathology. We isolated synaptosomes from hippocampus and motor cortex so as to reduce sample complexity relative to whole-tissue homogenates. Synaptosomal extracts were subjected to strong cation exchange (SCX) fractionation to further partition sample complexity; each fraction received SWATH-based information-dependent acquisition to generate a comprehensive peptide-ion library. The expression of synaptic proteins from AD hippocampus and motor cortex was then compared between groups. A total of 2077 unique proteins were identified at a critical local false discovery rate <5%. Thirty of these, including 17 novel proteins, exhibited significant expression differences between cases and controls; these proteins are involved in cellular functions including structural maintenance, signal transduction, autophagy, oxidative stress, and proteasome activity, or they have synaptic-vesicle related or energy-related functions. Differentially expressed proteins were subjected to pathway analysis to identify protein-protein interactions. This revealed that the most perturbed molecular and cellular functions were cellular assembly and organization. Core analysis revealed RhoA signaling to be the top canonical pathway. Network analysis showed that differentially expressed proteins were related to cellular assembly and organization, and cellular function and maintenance. This is the first study to combine SCX fractionation with SWATH analysis. SWATH is a promising new technique that can greatly enhance protein identification in any proteome, and has many other benefits; however, there are limitations yet to be resolved.

Endophilin A1 regulates dendritic spine morphogenesis and stability through interaction with p140Cap

Dendritic spines are actin-rich membrane protrusions that are the major sites of excitatory synaptic input in the mammalian brain, and their morphological plasticity provides structural basis for learning and memory. Here we report that endophilin A1, with a well-established role in clathrin-mediated synaptic vesicle endocytosis at the presynaptic terminal, also localizes to dendritic spines and is required for spine morphogenesis, synapse formation and synaptic function. We identify p140Cap, a regulator of cytoskeleton reorganization, as a downstream effector of endophilin A1 and demonstrate that disruption of their interaction impairs spine formation and maturation. Moreover, we demonstrate that knockdown of endophilin A1 or p140Cap impairs spine stabilization and synaptic function. We further show that endophilin A1 regulates the distribution of p140Cap and its downstream effector, the F-actin-binding protein cortactin as well as F-actin enrichment in dendritic spines. Together, these results reveal a novel function of postsynaptic endophilin A1 in spine morphogenesis, stabilization and synaptic function through the regulation of p140Cap.

Parkin-mediated K63-polyubiquitination targets ubiquitin C-terminal hydrolase L1 for degradation by the autophagy-lysosome system

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is a key neuronal deubiquitinating enzyme which is mutated in Parkinson disease (PD) and in childhood-onset neurodegenerative disorder with optic atrophy. Furthermore, reduced UCH-L1 protein levels are associated with a number of neurodegenerative diseases, whereas up-regulation of UCH-L1 protein expression is found in multiple types of cancer. However, very little is known about how UCH-L1 protein level is regulated in cells. Here, we report that UCH-L1 is a novel interactor and substrate of PD-linked E3 ubiquitin-protein ligase parkin. We find that parkin mediates K63-linked polyubiquitination of UCH-L1 in cooperation with the Ubc13/Uev1a E2 ubiquitin-conjugating enzyme complex and promotes UCH-L1 degradation by the autophagy-lysosome pathway. Targeted disruption of parkin gene expression in mice causes a significant decrease in UCH-L1 ubiquitination with a concomitant increase in UCH-L1 protein level in brain, supporting an in vivo role of parkin in regulating UCH-L1 ubiquitination and degradation. Our findings reveal a direct link between parkin-mediated ubiquitin signaling and UCH-L1 regulation, and they have important implications for understanding the roles of these two proteins in health and disease.

Drosophila SNAP-29 is an essential SNARE that binds multiple proteins involved in membrane traffic

Each membrane fusion event along the secretory and endocytic pathways requires a specific set of SNAREs to assemble into a 4-helical coiled-coil, the so-called trans-SNARE complex. Although most SNAREs contribute one helix to the trans-SNARE complex, members of the SNAP-25 family contribute two helixes. We report the characterization of the Drosophila homologue of SNAP-29 (dSNAP-29), which is expressed throughout development. Unlike the other SNAP-25 like proteins in fruit fly (i.e., dSNAP-25 and dSNAP-24), which form SDS-resistant SNARE complexes with their cognate SNAREs, dSNAP-29 does not participate in any SDS-resistant complexes, despite its interaction with dsyntaxin1 and dsyntaxin16 in vitro. Immunofluorescence studies indicated that dSNAP-29 is distributed in various tissues, locating in small intracellular puncta and on the plasma membrane, where it associates with EH domain-containing proteins implicated in the endocytic pathway. Overexpression and RNAi studies suggested that dSNAP-29 mediates an essential process in Drosophila development.

Intracellular distribution of differentially phosphorylated dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A)

The gene encoding dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is located within the Down syndrome (DS) critical region of chromosome 21. DYRK1A interacts with a plethora of substrates in the cytosol, cytoskeleton, and nucleus. Its overexpression is a contributing factor to the developmental alterations and age-associated pathology observed in DS. We hypothesized that the intracellular distribution of DYRK1A and cell-compartment-specific functions are associated with DYRK1A posttranslational modifications. Fractionation showed that, in both human and mouse brain, almost 80% of DYRK1A was associated with the cytoskeleton, and the remaining DYRK1A was present in the cytosolic and nuclear fractions. Coimmunoprecipitation revealed that DYRK1A in the brain cytoskeleton fraction forms complexes with filamentous actin, neurofilaments, and tubulin. Two-dimensional gel analysis of the fractions revealed DYRK1A with distinct isoelectric points: 5.5-6.5 in the nucleus, 7.2-8.2 in the cytoskeleton, and 8.7 in the cytosol. Phosphate-affinity gel electrophoresis demonstrated several bands of DYRK1A with different mobility shifts for nuclear, cytoskeletal, and cytosolic DYRK1A, indicating modification by phosphorylation. Mass spectrometry analysis disclosed one phosphorylated site in the cytosolic DYRK1A and multiple phosphorylated residues in the cytoskeletal DYRK1A, including two not previously described. This study supports the hypothesis that intracellular distribution and compartment-specific functions of DYRK1A may depend on its phosphorylation pattern.

SNAP-25 regulates spine formation through postsynaptic binding to p140Cap

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a member of the Soluble N-ethylmaleimide-sensitive-factor attachment protein receptors (SNARE) protein family, required for exocytosis of synaptic vesicles and regulation of diverse ion channels. Here, we show that acute reduction of SNAP-25 expression leads to an immature phenotype of dendritic spines that are, consistently, less functional. Conversely, over-expression of SNAP-25 results in an increase in the density of mature, Postsynaptic Density protein 95 (PSD-95)-positive spines. The regulation of spine morphogenesis by SNAP-25 depends on the protein's ability to bind both the plasma membrane and the adaptor protein p140Cap, a key protein regulating actin cytoskeleton and spine formation. We propose that SNAP-25 allows the organization of the molecular apparatus needed for spine formation by recruiting and stabilizing p140Cap.

Biochemical and morphological characterization of A2BP1 in neuronal tissue

A2BP1 is considered to regulate alternative splicing of important neuronal transcripts and has been implicated in a variety of neurological and developmental disorders. A2BP1 was found in neuronal cells and was analyzed biochemically and morphologically. In this study, we prepared a specific antibody against A2BP1, anti-A2BP1, and carried out protein expression and localization analyses of A2BP1 in rat and mouse tissues. By Western blotting, A2BP1 showed tissue-dependent expression profiles and was expressed in a developmental-stage-dependent manner in the brain. A2BP1 was detected at high levels in neocortex and cerebellum in the rat brain. Immunohistochemical analyses demonstrated that A2BP1 was highly expressed in differentiated neurons but not in mitotically active progenitor cells in the cerebral cortex during developmental stages. In cortical neurons, A2BP1 had accumulated mainly in the nucleus and diffusely distributed in the cell body and dendrites. In differentiated primary cultured rat hippocampal neurons, although A2BP1 was enriched in the nucleus and diffusely distributed in the cytoplasm, it was found in a punctate distribution adjacent to synapses. The results suggest that in neuronal tissues A2BP1 plays important roles, which are regulated in a spatiotemporal manner.

A new hypothesis about hematopoietic Pbx-interaction protein (HPIP): can it be a key factor in neurodegeneration in the post-menopausal period?

Neuronal degeneration in the post-menopausal term leads to cognitive symptoms such as anxiety, difficulty in concentrating, overreacting to minor upsets, quickly becoming irritated and forgetfulness in approximately 70-80% of all women around the world. These symptoms, which result from microtubule damage in the axon extensions of hippocampal neurons in during menopause, greatly reduce individuals' life quality. Thus, an investigation of the estrogen receptor-signaling pathway-microtubule dynamic triangle and the possible links between them is important when it comes to explaining the possible mechanism of neurodegeneration. Hematopoietic Pbx-interaction protein (HPIP), a microtubule-binding protein, is a novel scaffolding protein. The detection of this protein on neurons represents the most important step in our hypothesis. The importance of the hypothesis is that it might provide important clues about the possible role of HPIP and its mechanism through in vivo and in vitro studies of estrogen receptors-microtubules and the HPIP triangle in terms of neuronal degeneration in the post-menopausal period. A preliminary study was performed to test the main part of our hypothesis using real-time PCR. According to the results, the mRNA expression of HPIP was found in hippocampal neurons. After the detection of this novel protein in neurons, it was observed that there were differences in the experimental groups when compared with the control group relating to the mRNA expression of this protein. An important scientific question remains concerning the mechanisms of neurodegeneration appearing in the post-menopausal period and the receptors, proteins, and signaling pathways that play a role in this degeneration. In consideration of the data from in vivo and in vitro studies used to test our hypothesis, we will try to address the relevant questions. As this issue is resolved, new studies and treatment procedures that can help to prevent the possible difficulties in the menopausal period will be illuminated.

Mapping of p140Cap phosphorylation sites: the EPLYA and EGLYA motifs have a key role in tyrosine phosphorylation and Csk binding, and are substrates of the Abl kinase

Protein phosphorylation tightly regulates specific binding of effector proteins that control many diverse biological functions of cells (e. g. signaling, migration and proliferation). p140Cap is an adaptor protein, specifically expressed in brain, testis and epithelial cells, that undergoes phosphorylation and tunes its interactions with other regulatory molecules via post-translation modification. In this work, using mass spectrometry, we found that p140Cap is in vivo phosphorylated on tyrosine (Y) within the peptide GEGLpYADPYGLLHEGR (from now on referred to as EGLYA) as well as on three serine residues. Consistently, EGLYA has the highest score of in silico prediction of p140Cap phosphorylation. To further investigate the p140Cap function, we performed site specific mutagenesis on tyrosines inserted in EGLYA and EPLYA, a second sequence with the same highest score of phosphorylation. The mutant protein, in which both EPLYA/EGLYA tyrosines were converted to phenylalanine, was no longer tyrosine phosphorylated, despite the presence of other tyrosine residues in p140Cap sequence. Moreover, this mutant lost its ability to bind the C-terminal Src kinase (Csk), previously shown to interact with p140Cap by Far Western analysis. In addition, we found that in vitro and in HEK-293 cells, the Abelson kinase is the major kinase involved in p140Cap tyrosine phosphorylation on the EPLYA and EGLYA sequences. Overall, these data represent an original attempt to in vivo characterise phosphorylated residues of p140Cap. Elucidating the function of p140Cap will provide novel insights into its biological activity not only in normal cells, but also in tumors.

Localization of multidomain adaptor proteins, p140Cap and vinexin, in the pancreatic islet of a spontaneous diabetes mellitus model, Otsuka Long-Evans Tokushima Fatty rats

We have shown that two multidomain adaptor proteins, p140Cap and vinexin, interact with each other and are likely to be involved in neurotransmitter release. Because the basic molecular mechanism governing neurotransmitter and insulin secretion is conserved, these two proteins may also to play pivotal roles in insulin secretion. We therefore performed some characterization of p140Cap and vinexin in pancreas of a wild-type rat or a spontaneous type 2 diabetes mellitus (DM) model, the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. These two proteins were detected in Wistar rat pancreas by Western blotting. Immunohistochemistry revealed that p140Cap and vinexin are enriched in β and α cells, respectively, in the rat pancreas. We then found that pancreatic islet structure was disorganized in the OLETF rat with hyperinsulinemia or with hyperglycemia, based on immunohistochemical analyses of vinexin. In β cells of these model rats, p140Cap was distributed in a cytoplasmic granular pattern as in the control rats, although its expression was reduced to various extents from cell to cell. These results may suggest possible involvement of p140Cap in insulin secretion, and reduction of p140Cap might be related to abnormal insulin secretion in DM.

Cortical F-actin affects the localization and dynamics of SNAP-25 membrane clusters in chromaffin cells

It has been proposed recently that the F-actin cytoskeleton organizes the relative disposition of the SNARE proteins and calcium channels that form part of the secretory machinery in chromaffin cells, a neurosecretory model. To test this idea, we used confocal microscopy do determine if DsRed-SNAP-25 microdomains, which define the final sites of exocytosis along with syntaxin-1, preferentially remain in contact with F-actin cortical structures labelled by lifeact-EGFP. A quantitative analysis showed that in cells over-expressing these constructs there is a preferential colocalization, rather than a random distribution of SNAP-25 patches. To analyze the possible interactions between these proteins, we designed FRET experiments and tested whether treatment with agents that affect F-actin mobility would modify SNAP-25 movement. The significant FRET efficiencies detected suggest that direct molecular interactions occur, whereas dynamic experiments using TIRFM revealed that attenuation of cortical F-actin movement clearly diminishes the mobility of SNAP-25 clusters. Taken together, these data can be explained by a model that associates components of the secretory machinery to the F-actin cortex through flexible links.

Mutations associated with Charcot-Marie-Tooth disease cause SIMPLE protein mislocalization and degradation by the proteasome and aggresome-autophagy pathways

Mutations in SIMPLE cause an autosomal dominant, demyelinating form of peripheral neuropathy termed Charcot-Marie-Tooth disease type 1C (CMT1C), but the pathogenic mechanisms of these mutations remain unknown. Here, we report that SIMPLE is an early endosomal membrane protein that is highly expressed in the peripheral nerves and Schwann cells. Our analysis has identified a transmembrane domain (TMD) embedded within the cysteine-rich (C-rich) region that anchors SIMPLE to the membrane, and suggests that SIMPLE is a post-translationally inserted, C-tail-anchored membrane protein. We found that CMT1C-linked pathogenic mutations are clustered within or around the TMD of SIMPLE and that these mutations cause mislocalization of SIMPLE from the early endosome membrane to the cytosol. The CMT1C-associated SIMPLE mutant proteins are unstable and prone to aggregation, and they are selectively degraded by both the proteasome and aggresome-autophagy pathways. Our findings suggest that SIMPLE mutations cause CMT1C peripheral neuropathy by a combination of loss-of-function and toxic gain-of-function mechanisms, and highlight the importance of both the proteasome and autophagy pathways in the clearance of CMT1C-associated mutant SIMPLE proteins.

D-amino acid oxidase activity is inhibited by an interaction with bassoon protein at the presynaptic active zone

Schizophrenia is a highly heritable neuropsychiatric disorder affecting ∼1% of the world's population. Linkage and association studies have identified multiple candidate schizophrenia susceptibility genes whose functions converge on the glutamatergic neurotransmitter system. One such susceptibility gene encoding D-amino acid oxidase (DAO), an enzyme that metabolizes the NMDA receptor (NMDAR) co-agonist D-serine, has the potential to modulate NMDAR function in the context of schizophrenia. To further investigate its cellular regulation, we sought to identify DAO-interacting proteins that participate in its functional regulation in rat cerebellum, where DAO expression is especially high. Immunoprecipitation with DAO-specific antibodies and subsequent mass spectrometric analysis of co-precipitated proteins yielded 24 putative DAO-interacting proteins. The most robust interactions occurred with known components of the presynaptic active zone, such as bassoon (BSN) and piccolo (PCLO). The interaction of DAO with BSN was confirmed through co-immunoprecipitation assays using DAO- and BSN-specific antibodies. Moreover, DAO and BSN colocalized with one another in cultured cerebellar granule cells and in synaptic junction membrane protein fractions derived from rat cerebellum. The functional consequences of this interaction were studied through enzyme assay experiments, where DAO enzymatic activity was significantly inhibited as a result of its interaction with BSN. Taking these results together, we hypothesize that synaptic D-serine concentrations may be under tight regulation by a BSN-DAO complex. We therefore predict that this mechanism plays a role in the modulation of glutamatergic signaling through NMDARs. It also furthers our understanding of the biology underlying this potential therapeutic entry point for schizophrenia and other psychiatric disorders.

Dendritic Spine Plasticity: New Regulatory Roles of Dynamic Microtubules

Dendritic spines are small actin-rich protrusions that form the postsynaptic part of most excitatory synapses. They play critical roles in synaptic function and exhibit a striking degree of structural plasticity, which is closely linked to changes in strength of synaptic connections. Here the authors summarize recent work that has revealed an important relationship between the microtubule and actin cytoskeleton in controlling spine morphology and plasticity. Dynamic microtubules and the proteins that specifically associate with the growing microtubule plus-ends recently emerged as temporal and spatial regulators of actin organization, which controls dynamic changes in structure and function of dendritic spines.

Integrin signalling adaptors: not only figurants in the cancer story

Current evidence highlights the ability of adaptor (or scaffold) proteins to create signalling platforms that drive cellular transformation upon integrin-dependent adhesion and growth factor receptor activation. The understanding of the biological effects that are regulated by these adaptors in tumours might be crucial for the identification of new targets and the development of innovative therapeutic strategies for human cancer. In this Review we discuss the relevance of adaptor proteins in signalling that originates from integrin-mediated cell-extracellular matrix (ECM) adhesion and growth factor stimulation in the context of cell transformation and tumour progression. We specifically underline the contribution of p130 Crk-associated substrate (p130CAS; also known as BCAR1), neural precursor cell expressed, developmentally down-regulated 9 (NEDD9; also known as HEF1), CRK and the integrin-linked kinase (ILK)-pinch-parvin (IPP) complex to cancer, along with the more recently identified p140 Cas-associated protein (p140CAP; also known as SRCIN1).

Role of SIP30 in the development and maintenance of peripheral nerve injury-induced neuropathic pain

Using the chronic constriction injury (CCI) model of neuropathic pain, we profiled gene expression in the rat spinal cord, and identified SIP30 as a gene whose expression was elevated after CCI. SIP30 was previously shown to interact with SNAP25, but whose function was otherwise unknown. We now show that in the spinal cord, SIP30 was present in the dorsal horn laminae where the peripheral nociceptive inputs first synapse, co-localizing with nociception-related neuropeptides CGRP and substance P. With the onset of neuropathic pain after CCI surgery, SIP30 mRNA and protein levels increased in the ipsilateral side of the spinal cord, suggesting a potential association between SIP30 and neuropathic pain. When CCI-upregulated SIP30 was inhibited by intrathecal antisense oligonucleotide administration, neuropathic pain was attenuated. This neuropathic pain-reducing effect was observed both during neuropathic pain onset following CCI, and after neuropathic pain was fully established, implicating SIP30 involvement in the development and maintenance phases of neuropathic pain. Using a secretion assay in PC12 cells, anti-SIP30 siRNA decreased the total pool of synaptic vesicles available for exocytosis, pointing to a potential function for SIP30. These results suggest a role of SIP30 in the development and maintenance of peripheral nerve injury-induced neuropathic pain.

Association of the tag SNPs in the human SKT gene (KIAA1217) with lumbar disc herniation

Lumbar disc herniation (LDH) is one of the most common musculo-skeletal diseases. Recent studies have indicated that LDH has strong genetic determinants, and several susceptibility genes have been reported to associate with LDH; however, its etiology and pathogenesis still remain unclear. KIAA1217 (alias SKT, the human homolog of murine Skt [Sickle tail]) is a good candidate for an LDH susceptibility gene because SKT is specifically expressed in nucleus pulposa of intervertebral discs (IVDs) in humans and mice, and Skt(Gt) mice, which are established through a large-scale gene-trap mutagenesis, exhibit progressive, postnatal onset abnormality of the IVDs. Here, we report the association of SKT with LDH. Using tag SNPs, we examined the association in two independent Japanese case-control populations and found a significant association with SKT rs16924573 in the allele frequency model (p = 0.0015). The association was replicated in a Finnish case-control population (p = 0.026). The combined p value of the two population by meta-analysis is 0.00040 (OR, 1.34; 95% CI, 1.14-1.58). Our data indicate that SKT is involved in the etiology of LDH.

Printor, a novel torsinA-interacting protein implicated in dystonia pathogenesis

Early onset generalized dystonia (DYT1) is an autosomal dominant neurological disorder caused by deletion of a single glutamate residue (torsinA DeltaE) in the C-terminal region of the AAA(+) (ATPases associated with a variety of cellular activities) protein torsinA. The pathogenic mechanism by which torsinA DeltaE mutation leads to dystonia remains unknown. Here we report the identification and characterization of a 628-amino acid novel protein, printor, that interacts with torsinA. Printor co-distributes with torsinA in multiple brain regions and co-localizes with torsinA in the endoplasmic reticulum. Interestingly, printor selectively binds to the ATP-free form but not to the ATP-bound form of torsinA, supporting a role for printor as a cofactor rather than a substrate of torsinA. The interaction of printor with torsinA is completely abolished by the dystonia-associated torsinA DeltaE mutation. Our findings suggest that printor is a new component of the DYT1 pathogenic pathway and provide a potential molecular target for therapeutic intervention in dystonia.

Sept8 controls the binding of vesicle-associated membrane protein 2 to synaptophysin

Septins, a conserved family of GTP/GDP-binding proteins, are present in organisms as diverse as yeast and mammals. We analyzed the distribution of five septins, Sept6, Sept7, Sept8, Sept9 and Sept11, in various rat tissues by western blot analyses and found all septins to be expressed in brain. We also examined the developmental changes of expression of these septins in the rat brain and found that the level of Sept8 increased during post-natal development. Morphological analyses revealed that Sept8 is enriched at pre-synapses. Using yeast two-hybrid screening, we identified vesicle-associated membrane protein 2 (VAMP2), a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), as an interacting protein for Sept8. Synaptophysin is reported to associate with and recruit VAMP2 to synaptic vesicles and dissociate prior to forming the SNARE complex consisting of VAMP2, syntaxin and synaptosome-associated protein of 25 kDa. We showed that Sept8 suppresses the interaction between VAMP2 and synaptophysin through binding to VAMP2. In addition, we found that Sept8 forms a complex with syntaxin1A, and the Sept8-VAMP2 interaction is disrupted by synaptosome-associated protein of 25 kDa. These results suggest that Sept8 may participate in the process of the SNARE complex formation and subsequent neurotransmitter release.

Dynamic microtubules regulate dendritic spine morphology and synaptic plasticity

Dendritic spines are the major sites of excitatory synaptic input, and their morphological changes have been linked to learning and memory processes. Here, we report that growing microtubule plus ends decorated by the microtubule tip-tracking protein EB3 enter spines and can modulate spine morphology. We describe p140Cap/SNIP, a regulator of Src tyrosine kinase, as an EB3 interacting partner that is predominantly localized to spines and enriched in the postsynaptic density. Inhibition of microtubule dynamics, or knockdown of either EB3 or p140Cap, modulates spine shape via regulation of the actin cytoskeleton. Fluorescence recovery after photobleaching revealed that EB3-binding is required for p140Cap accumulation within spines. In addition, we found that p140Cap interacts with Src substrate and F-actin-binding protein cortactin. We propose that EB3-labeled growing microtubule ends regulate the localization of p140Cap, control cortactin function, and modulate actin dynamics within dendritic spines, thus linking dynamic microtubules to spine changes and synaptic plasticity.

Proteomic analysis reveals Hrs ubiquitin-interacting motif-mediated ubiquitin signaling in multiple cellular processes

Despite the critical importance of protein ubiquitination in the regulation of diverse cellular processes, the molecular mechanisms by which cells recognize and transmit ubiquitin signals remain poorly understood. The endosomal sorting machinery component hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) contains a ubiquitin-interacting motif (UIM), which is believed to bind ubiquitinated membrane cargo proteins and mediate their sorting to the lysosomal degradation pathway. To gain insight into the role of Hrs UIM-mediated ubiquitin signaling in cells, we performed a proteomic screen for Hrs UIM-interacting ubiquitinated proteins in human brain by using an in vitro expression cloning screening approach. We have identified 48 ubiquitinated proteins that are specifically recognized by the UIM domain of Hrs. Among them, 12 are membrane proteins that are likely to be Hrs cargo proteins, and four are membrane protein-associated adaptor proteins whose ubiquitination may act as a signal to target their associated membrane cargo for Hrs-mediated endosomal sorting. Other classes of the identified proteins include components of the vesicular trafficking machinery, cell signaling molecules, proteins associated with the cytoskeleton and cytoskeleton-dependent transport, and enzymes involved in ubiquitination and metabolism, suggesting the involvement of Hrs UIM-mediated ubiquitin signaling in the regulation of multiple cellular processes. We have characterized the ubiquitination of two identified proteins, Munc18-1 and Hsc70, and their interaction with Hrs UIM, and provided functional evidence supporting a role for Hsc70 in the regulation of Hrs-mediated endosome-to-lysosome trafficking.

Identification and characterization of neuronal mitogen-activated protein kinase substrates using a specific phosphomotif antibody

Mitogen-activated protein kinases (MAPKs) control neuronal synaptic function; however, little is known about the synaptic substrates regulated by MAPKs. A phosphopeptide library incorporating the MAPK consensus motif (PX(pS/pT)P where pS is phosphoserine and pT is phosphothreonine) was used to raise a phosphospecific antibody that detected MAPK-mediated phosphorylation. The antibody (termed “5557”) recognized a variety of phosphoproteins in the brain, many of which were enriched in postsynaptic density fractions. The immunoblot pattern changed rapidly in response to altered synaptic activity and with the inhibition of specific MAPKs and protein phosphatases. By immunoaffinity purification with 5557 antibody followed by mass spectrometry, we identified 449 putative MAPK substrates of which many appeared dynamically regulated in neuron cultures. Several of the novel candidate MAPK substrates were validated by in vitro phosphorylation assays. Additionally 82 specific phosphorylation sites were identified in 34 proteins, including Ser-447 in δ-catenin, a component of the cadherin adhesion complex. We further raised another phosphospecific antibody to confirm that δ-catenin Ser-447 is modified in neurons by the MAPK JNK in a synaptic activity-dependent manner. Ser-447 phosphorylation by JNK appears to be correlated with δ-catenin degradation, and a δ-catenin mutant defective in Ser-447 phosphorylation showed enhanced ability to promote dendrite branching in cultured neurons. Thus, phosphomotif-based affinity purification is a powerful approach to identify novel substrates of MAPKs in vivo and to reveal functionally significant phosphorylation events.

The effects of acute 17beta-estradiol treatment on gene expression in the young female mouse hippocampus

Previous studies have demonstrated that treatment with 17beta-estradiol (E(2)) improves both spatial and nonspatial memory in young female mice. Still unclear, however, are the molecular mechanisms underlying the beneficial effects of E(2) on memory. We have previously demonstrated that a single post-training intraperitoneal (i.p.) injection of 0.2 mg/kg E(2) can enhance hippocampal-dependent spatial and object memory consolidation (e.g., Gresack & Frick, 2006b). Therefore, in the present study, we performed a microarray analysis on the dorsal hippocampi of 4-month-old female mice injected i.p. with vehicle or 0.2 mg/kg E(2). Genes were considered differentially expressed following E(2) treatment if they showed a greater than 2-fold change in RNA expression levels compared to controls. Overall, out of a total of approximately 25,000 genes represented on the array, 204 genes showed altered mRNA expression levels upon E(2) treatment, with 111 up-regulated and 93 down-regulated. Of these, 17 of the up-regulated and 6 of the down-regulated genes are known to be involved in learning and memory. mRNA expression changes in 5 of the genes were confirmed by real-time quantitative PCR analysis, and protein changes in these same genes were confirmed by Western blot analysis: Hsp70, a heat shock protein known to be estrogen responsive; Igfbp2, an IGF-I binding protein; Actn4, an actin binding protein involved in protein trafficking; Tubb2a, the major component of microtubules; and Snap25, a synaptosome-specific protein required for neurotransmitter release. The types of genes altered indicate that E(2) may induce changes in the structural mechanics of cells within the dorsal hippocampus that could be conducive to promoting memory consolidation.

Agonist-induced internalization of histamine H2 receptor and activation of extracellular signal-regulated kinases are dynamin-dependent

Histamine H2 receptor (H2R) is a member of G protein-coupled receptor family. Agonist stimulation of H2R results in several cellular events including activation of adenylate cyclase and phospholipase C, desensitization of the receptor, activation of extracellular signal-regulated kinases ERK1/2, and receptor endocytosis. In this study, we identified a GTPase dynamin as a binding partner of H2R. Dynamin could associate with H2R both in vitro and in vivo. Functional analyses using dominant-negative form of dynamin (K44E-dynamin) revealed that cAMP production and the following H2R desensitization are independent of dynamin. However, the agonist-induced H2R internalization was inhibited by co-expression of K44E-dynamin. Furthermore, activation of extracellular-signal regulated kinases ERK1/2 in response to dimaprit, an H2R agonist, was attenuated by K44E-dynamin. Although H2R with truncation of 51 amino acids at its carboxy-terminus did not internalize after agonist stimulation, it still activated ERK1/2, but the degree of this activation was less than that of the wild-type receptor. Finally, K44E dynamin did not affect ERK1/2 activation induced by internalization-deficient H2R. These results suggest that the agonist-induced H2R internalization and ERK1/2 activation are partially dynamin-dependent. Furthermore, ERK1/2 activation via H2R is likely dependent of the endocytotic process rather than dynamin itself.

Hypertonia-associated protein Trak1 is a novel regulator of endosome-to-lysosome trafficking

Hypertonia, which is characterized by stiff gait, abnormal posture, jerky movements, and tremor, is associated with a number of neurological disorders, including cerebral palsy, dystonia, Parkinson's disease, stroke, and spinal cord injury. Recently, a spontaneous mutation in the gene encoding trafficking protein, kinesin-binding 1 (Trak1), was identified as the genetic defect that causes hypertonia in mice. The subcellular localization and biological function of Trak1 remain unclear. Here we report that Trak1 interacts with hepatocyte-growth-factor-regulated tyrosine kinase substrate (Hrs), an essential component of the endosomal sorting and trafficking machinery. Double-label immunofluorescence confocal studies show that the endogenous Trak1 protein partially colocalizes with Hrs on early endosomes. Like Hrs, both overexpression and small-interfering-RNA-mediated knockdown of Trak1 inhibit degradation of internalized epidermal growth factor receptors through a block in endosome-to-lysosome trafficking. Our findings support a role for Trak1 in the regulation of Hrs-mediated endosomal sorting and have important implications for understanding hypertonia associated with neurological disorders.

Characterization of a multidomain adaptor protein, p140Cap, as part of a pre-synaptic complex

p140Cap (Cas-associated protein) is an adaptor protein considered to play pivotal roles in cell adhesion, growth and Src tyrosine kinase-related signaling in non-neuronal cells. It is also reported to interact with a pre-synaptic membrane protein, synaptosome-associated protein of 25 kDa, and may participate in neuronal secretion. However, properties and precise functions of p140Cap in neuronal cells are almost unknown. Here we show, using biochemical analyses, that p140Cap is expressed in rat brain in a developmental stage-dependent manner, and is relatively abundant in the synaptic plasma membrane fraction in adults. Immunohistochemistry showed localization of p140Cap in the neuropil in rat brain and immunofluorescent analyses detected p140Cap at synapses of primary cultured rat hippocampal neurons. Electron microscopy further revealed localization at pre- and post-synapses. Screening of p140Cap-binding proteins identified a multidomain adaptor protein, vinexin, whose third Src-homology 3 domain interacts with the C-terminal Pro-rich motif of p140Cap. Immunocomplexes between the two proteins were confirmed in COS7 and rat brain. We also clarified that a pre-synaptic protein, synaptophysin, interacts with p140Cap. These results suggest that p140Cap is involved in neurotransmitter release, synapse formation/maintenance, and signaling.