Processes In Non-neuronal Cells Research Articles

Tau mediates microtubule bundle architectures mimicking fascicles of microtubules found in the axon initial segment.

Tau, an intrinsically disordered protein confined to neuronal axons, binds to and regulates microtubule dynamics. Although there have been observations of string-like microtubule fascicles in the axon initial segment (AIS) and hexagonal bundles in neurite-like processes in non-neuronal cells overexpressing Tau, cell-free reconstitutions have not replicated either geometry. Here we map out the energy landscape of Tau-mediated, GTP-dependent ‘active' microtubule bundles at 37 °C, as revealed by synchrotron SAXS and TEM. Widely spaced bundles (wall-to-wall distance Dw–w≈25–41 nm) with hexagonal and string-like symmetry are observed, the latter mimicking bundles found in the AIS. A second energy minimum (Dw–w≈16–23 nm) is revealed under osmotic pressure. The wide spacing results from a balance between repulsive forces, due to Tau's projection domain (PD), and a stabilizing sum of transient sub-kBT cationic/anionic charge–charge attractions mediated by weakly penetrating opposing PDs. This landscape would be significantly affected by charge-altering modifications of Tau associated with neurodegeneration.

Characterization and distribution of adaptor protein containing a PH domain, PTB domain and leucine zipper motif (APPL1) in Alzheimer’s disease hippocampus: an immunohistochemical study

Adaptor protein containing a PH domain, PTB domain and leucine zipper motif (APPL1) is emerging as a critical regulator of various cellular processes in non-neuronal cells as well as in neurons where it localizes to dendritic spines and synapses. It regulates the development of these structures in hippocampal neurons. Although memory impairment in Alzheimer’s disease (AD) has been attributed to disruption of synaptic plasticity, there is scant information on this protein in the human brain. In the present study, we immunohistochemically characterized the localization of APPL1 in AD and control brains. APPL1 accumulated perisomatically as granules around neurons within vulnerable sectors of the hippocampus (CA1 and subiculum) in AD brain, whilst APPL1-positive granules were rarely identified in control brains derived from elderly individuals with no known cognitive impairment. Interestingly, in the AD hippocampus, APPL1 also co-localized with perisomatic granules (non-plaque dystrophic dendrites) expressing glutamate receptor 2 and ubiquitin, suggesting the possible involvement of APPL1 in the synaptic modifications in AD. Thus, the immunohistochemical distribution of APPL1 in AD brain was distinct from that in non-AD control brains, suggesting that signaling via APPL1 might play a critical role in the memory impairment in AD.

Regulation of AMPA Receptor Function by the Human Memory-Associated Gene KIBRA

KIBRA has recently been identified as a gene associated with human memory performance. Despite the elucidation of the role of KIBRA in several diverse processes in nonneuronal cells, the molecular function of KIBRA in neurons is unknown. We found that KIBRA directly binds to the protein interacting with C-kinase 1 (PICK1) and forms a complex withα-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs), the major excitatory neurotransmitter receptors in the brain. KIBRA knockdown accelerates the rate of AMPAR recycling following N-methyl-D-aspartate receptor-induced internalization. Genetic deletion of KIBRA in mice impairs both long-term depression and long-term potentiation at hippocampal Schaffer collateral-CA1 synapses. Moreover, KIBRA knockout mice have severe deficits in contextual fear learning and memory. These results indicate that KIBRA regulates higher brain function by regulating AMPAR trafficking and synaptic plasticity.

An APPL1/Akt signaling complex regulates dendritic spine and synapse formation in hippocampal neurons

The formation and plasticity of dendritic spines and synapses, which are poorly understood on a molecular level, are critical for cognitive functions, such as learning and memory. The adaptor protein containing a PH domain, PTB domain, and leucine zipper motif (APPL1) is emerging as a critical regulator of various cellular processes in non-neuronal cells, but its function in the nervous system is not well understood. Here, we show that APPL1 localizes to dendritic spines and synapses and regulates the development of these structures in hippocampal neurons. Knockdown of endogenous APPL1 using siRNA led to a significant decrease in the number of spines as well as synapses and this defect could be rescued by expression of siRNA-resistant APPL1. Expression of exogenous APPL1 increased the spine and synaptic density and the amount of surface GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). Deletion of the C-terminal phosphotyrosine binding domain of APPL1, which binds the serine/threonine kinase Akt, resulted in a significant decrease in the spine and synaptic density, suggesting a role for Akt in regulating the development of these structures. Consistent with this, knockdown of Akt with siRNA or expression of dominant negative Akt led to a dramatic decrease in spine and synapse formation. In addition, APPL1 increased the amount of active Akt in spines and synapses and the effects of APPL1 on these structures were dependent on Akt, indicating that Akt is an effector of APPL1 in the regulation of these processes. Moreover, APPL1 signaling modulates spine and synapse formation through p21-activated kinase (PAK). Thus, our results indicate that APPL1 signaling through Akt and PAK is critical for spine and synaptic development and point to a role for APPL1 and its effectors in regulating cognitive function.

Intracellular localization and functional effects of mutant Protein kinase D expression in hippocampal neurons

Event Abstract Back to Event Intracellular localization and functional effects of mutant Protein kinase D expression in hippocampal neurons Flóra Vajda1*, Angelika Hausser2 and Katalin Schlett1 1 Eötvös Loránd University, Department of Physiology and Neurobiology, Hungary 2 University of Stuttgart, Inst. Cell Biology and Immunology, Germany Protein Kinase D (PKD) is a serine/threonine kinase known to regulate various cellular processes in non neuronal cells. Despite the fact that PKD isoforms are expressed in the central nervous system already from early embryonic stages, so far little is known about PKD-directed cellular processes in neurons. In the present study, several fluorescently tagged PKD mutants were introduced into mouse embryonal hippocampal neurons. Upon transfection by an EGFP tagged dominant-negative kinase-inactive form of PKD1 (kdPKD1-EGFP) or a construct lacking the kinase domain, overexpressed proteins were found to be excluded from the axons and to be restricted to the somatodendritic compartment of pyramidal neurons. Similar uneven intracellular localization was observed when PKD1 mutants lacking the PH (Pleckstrin homology) domain or amino acids 80-146 were used. These findings suggested that beside kinase activity, the N terminal region also regulates PKD’s axonal entry. Functional effects of PKD mutant overexpression on axonal growth cone motility were also analyzed by fluorescent fast live cell imaging. Growth cones of neurons overexpressing wild type PKD1 seemed to be more rigid with less filopodial movement, which is concordant with the role of PKD in cytoskeletal remodeling. In vivo experiments were also carried out by using a transgenic mouse line expressing kdPKD1-EGFP in a forebrain-specific manner upon doxycyclin treatment to describe kdPKD1-EGFP expression pattern after 2, 4, 6 and 8 weeks of tetracycline induction. In accordance with our in vitro results, kdPKD1-EGFP expression was restricted to the somatodendritic compartment of pyramidal neurons in the hippocampus and in the entorhinal cortex. Surprisingly, kdPKD1-EGFP expression was detected in the axons of the primary sensory neurons in the olfactory bulb. Further experiments are planned to elucidate PKD1 features causing distinct distribution of the mutant enzyme in different cell types in the brain.. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Cellular neuroscience Citation: Vajda F, Hausser A and Schlett K (2010). Intracellular localization and functional effects of mutant Protein kinase D expression in hippocampal neurons. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00173 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Apr 2010; Published Online: 30 Apr 2010. * Correspondence: Flóra Vajda, Eötvös Loránd University, Department of Physiology and Neurobiology, Budapest, Hungary, floravajda@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Flóra Vajda Angelika Hausser Katalin Schlett Google Flóra Vajda Angelika Hausser Katalin Schlett Google Scholar Flóra Vajda Angelika Hausser Katalin Schlett PubMed Flóra Vajda Angelika Hausser Katalin Schlett Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

OnTrk—The TrkB Signal Transduction Pathway Is an Increasingly Important Target in Cancer Biology

In the beginning, Trk was an oncogene. Yet Neurotrophin-Trk signaling came to preeminence in the field of neurobiology. Now it is appreciated that Trks regulate important processes in nonneuronal cells and, in addition to their impact on tumors of neural origin, may contribute to the pathogenesis of carcinomas, myelomas, and prostate and lymphoid tumors. Although mutations and rearrangements of Trk are seen only sporadically in human cancers, such as medullary thyroid carcinoma, a number of recent studies indicate that expression of TrkB contributes to tumor pathology. In neuroblastoma, TrkA expression marks good prognosis which TrkB and Brain-derived neurotrophic factor (BDNF) expression marks poor prognosis. Activation of the BDNF/TrkB signal transduction pathway also stimulates tumor cell survival and angiogenesis and contributes to resistance to cytotoxic drugs and anoikis, enabling cells to acquire many of the characteristic features required for tumorigenesis. Small molecule inhibitors, such as Cephalon's CEP-701, are in phase 1 and 2 clinical trials, and a series of AstraZeneca Trk inhibitors are poised to enter the clinic. As monotherapy, inhibitors may be effective only in tumors with activating Trk mutations. Important clinical follow-up will be the assessment of Trk inhibitors in combination with standard chemo- or radiotherapy or other signal transduction pathway inhibitors.

Microtubule stabilization by assembly-promoting microtubule-associated proteins: a repeat performance.

Microtubules (MTs) are important in a variety of dynamic cellular events such as chromosome segregation during meiosis and mitosis, vesicle and organelle transport, and organization of cellular components during morphogenetic events (e.g., polarization, directed migration, and process outgrowth). In addition, MTs are major components of many stable cellular structures such as ciliary and flagellar axonemes, axons and dendrites, and asymmetric processes in nonneuronal cells. The versatility that allows MTs to participate in such diverse functions may be conferred by several biochemical changes in the constituents of MTs; these include the expression of multiple a and p tubulins encoded by distinct genes [reviewed in Joshi and Cleveland, 19901, the posttranslational modification of a and p tubulin [reviewed in Joshi and Cleveland, 1990; Bulinski and Gundersen, 19911, and the expression or modification of various microtubule-associated proteins (MAPs). A critical feature of MT function is the balance between two antithetical properties of MTs: stability and instability. Stability allows MTs to act as a skeletal framework, while instability allows plasticity in the organization of this framework. MT stabilization is of undisputed importance in the generation and maintenance of asymmetries in differentiating cells such as neurons, myoblasts, and epithelia [reviewed in Bulinski and Gundersen, 19911. However, inappropriate or excessive stabilization of MTs can be deleterious to cellular structure and function. Evidence has accumulated that implicates MAPs as major effectors of MT stability in vivo. Clearly, an understanding of the complexity of MT functions will require elucidation of the role of MAPS in the modulation of MT dynamics.