Molecular Psychiatry (2015) 20, 1037–1045 © 2015 Macmillan Publishers Limited All rights reserved 1359-4184/15 www.nature.com/mp REVIEW CRMPs: critical molecules for neurite morphogenesis and neuropsychiatric diseases TT Quach1,2, J Honnorat1,3,4, PE Kolattukudy5, R Khanna6 and AM Duchemin7 Neuronal polarity and spatial rearrangement of neuronal processes are central to the development of all mature nervous systems. Recent studies have highlighted the dynamic expression of Collapsin-Response-Mediator Proteins (CRMPs) in neuronal dendritic/ axonal compartments, described their interaction with cytoskeleton proteins, identified their ability to activate L- and N-type voltage-gated calcium channels (VGCCs) and delineated their crucial role as signaling molecules essential for neuron differentiation and neural network development and maintenance. In addition, evidence obtained from genome-wide/genetic linkage/proteomic/ translational approaches revealed that CRMP expression is altered in human pathologies including mental (schizophrenia and mood disorders) and neurological (Alzheimer’s, prion encephalopathy, epilepsy and others) disorders. Changes in CRMPs levels have been observed after psychotropic treatments, and disrupting CRMP2 binding to calcium channels blocked neuropathic pain. These observations, altogether with those obtained from genetically modified mice targeting individual CRMPs and RNA interference approaches, pave the way for considering CRMPs as potential early disease markers and modulation of their activity as therapeutic strategy for disorders associated with neurite abnormalities. Molecular Psychiatry (2015) 20, 1037–1045; doi:10.1038/mp.2015.77; published online 16 June 2015 The ability of the nervous system to process continuously maintenance of axodendritic arborization and discuss their changing information from the internal and external environ- potential involvement in human nervous system diseases. ments requires the development of precise networks of neurons and structural plasticity of their dendrites and axons. Considering the intricacies of specific axodendritic connectivity, it is surprising CRMPS: CHARACTERISTICS AND EXPRESSION that neurons can undergo such precise structural reorganization in CRMPs are five homologous cytosolic phosphoproteins.6–8 CRMP1, response to environmental change. However, evidence indicates 2, 3 and 4 display 75% homology with each other,9–11 whereas that far from being static structures, axons and dendrites are the phylogenetically divergent CRMP5/CRAM shares only 50% plastic and this plasticity, which is part of a lifelong process, is homology.12 CRMP1, 2 and 4 have two distinct alternatively mediated by various proteins such as neurotrophic/transcription spliced isoforms in their N termini,13 extending the number of factors, neurohormones, guidance cues, membrane receptors, active molecules in this family. All CRMPs assemble in heterophilic voltage-gated calcium channels (VGCCs) and involves rearrange- oligomers in vivo, bind to tubulin14 and are phosphorylated by ment of cytoskeletal proteins that support the structural changes.1 various kinases that regulate their activity.15 They act as signaling However, despite the rich information on mechanisms underlying phosphoproteins modulating cytoskeletal organization and neuronal differentiation, axonogenesis and dendritogenesis, the regulating neurite formation and retraction. Site-specific phos- key molecules involved in the initiation of neurites through phorylation of CRMPs determines their affinity for binding to cyto- formation of lamellopodia/filopodia, specification and maturation skeletal proteins and their neurite-promoting/collapsing activities. – of neurites, and genesis of spines still remain elusive.2 3 Because CRMP1 appears to be a target of RhoA signaling.16 The Sema3A17 such a large fraction of the genome is expressed in the brain and and reelin18 signaling pathways are regulated by the phosphor- our knowledge of mechanisms involved in neuronal connectivity ylation of CRMP1 by Cdk5 at Thr-509 and Ser-522, or by Fyn at is still in its infancy, it has been postulated that more mole- Tyr-504 that lowers its binding affinity to tubulin. Similarly, non- cular cues and pathways specialized for axonal/dendritic/spine phosphorylated CRMP2 binds strongly to tubulin leading to genesis and synaptic network formation remain to be iden- microtubule formation, whereas its phosphorylation by Rho kinase tified. Consistent with this notion, Collapsin-Response-Mediator suppresses its binding to tubulin and Numb.14 Two other kinases Proteins (CRMPs) can now be considered as building blocks for working in tandem, Cdk5 and GSK-3β, also control the interaction neuronal differentiation and neurite network organization and of CRMP2 with tubulin. In addition, CRMP2 regulates the stability remodeling.4–5 In this review, we outline the current evidence of actin filaments.19 CRMP3 is phosphorylated by Fyn in vitro15 but showing that CRMPs are important in the establishment and is unique among CRMPs in that the three GSK-3β phosphorylation 1Lyon Neuroscience Research Center, INSERM U1028/CNRS UMR 5292, F-69372 Lyon, France; 2Department of Neuroscience, The Ohio State University, Columbus, OH, USA; 3French Reference Center on Paraneoplastic Neurological Syndrome, Hospices Civils de Lyon, Hôpital Neurologique, Neurologie B, Bron, France; 4Université de Lyon, Université Claude Bernard Lyon 1, F-69372 Lyon, France; 5Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, USA; 6Department of Pharmacology and Neuroscience, Graduate Interdisciplinary Program, College of Medicine, The University of Arizona, Tucson, AZ, USA and 7Department of Psychiatry, College of Medicine, The Ohio State University, Columbus, OH, USA. Correspondence: Dr AM Duchemin, Department of Psychiatry, College of Medicine, The Ohio State University, Columbus, OH 43210, USA. E-mail: [email protected] Received 7 November 2014; revised 29 April 2015; accepted 8 May 2015; published online 16 June 2015 CRMPs in neuron development and diseases TT Quach et al 1038 Table 1. Summary of relative CRMP expression pattern in mouse nervous system Cortex Hippocampus Dentate gyrus Striatum Cerebellum Pons DRG CRMP1 ePN + + + ? +++ ? ? Adult ++ +++ ++ ? +++ ? ? CRMP2 ePN ++ ++ ++ ++ ++ ? ++ Adult ++ +++ ++ + ++ ? + CRMP3 ePN − +++ +++ − +++1 ++ Adult − +++ +++ −−++1 − CRMP4 ePN ++ +++ +++ + + +2 ? Adult − ++−−−+ CRMP5 ePN + + + ? + ? ? Adult + ++ ++ + ++ ? ? Abbreviations: DRG, dorsal root ganglia; ePN, early postnatal. (1), inferior olive complex and reticular formation; (2), pontine nuclei. Data from refs 9,12,13,23,29,31,32,44,46,48,127–129; +++, high level; ++, moderate level; +, low level; − , undetectable signal; ?, not determined. sites identified in other CRMPs are not conserved in this molecule. activation of L- and N-type VGCCs by CRMP3 provide strong CRMP4, which binds to F-actin and regulates F-actin bundling,20 is support for an inductive role of CRMP3 in neurite initiation and also a physiological partner of GSK-3β.21 Of note, GSK-3β is a dendritic development and plasticity, at least partly via Ca2+ ubiquitous protein kinase having a pivotal role in neurodevelop- influx29 (Figure 1d). In contrast, CRMP5 depletion by RNA ment and is suspected to be involved in neuropsychiatric interference enhances the length and number of neurites, disorders such as schizophrenia,22 bipolar disorders23 and whereas its overexpression induces mitophagy and reduces Alzheimer’s disease (AD).24 CRMP5 is a substrate for Cdk525 and dendritic length. Further, overexpression of mutated-Threo-516 26 is tyrosine-phosphorylated by Fes/Fps and TrkB. In view of these CRMP5 (ref. 34) and/or its truncated dominant-negative isoform observations, we can conclude that, depending on the character- lacking the tubulin-binding domain35 has no effect on dendrite istics of their phosphorylation status, CRMPs may associate with formation or length, demonstrating the critical role of the tubulin- 27 various partners and signaling pathways, some of which may binding domain in the neurite outgrowth inhibition induced by exclude direct interaction between them in different brain areas. CRMP5. The interaction of CRMP5 with tubulin has important 28 29 30 In addition, CRMP2, CRMP3 and CRMP4 have been shown to ramifications for the function of CRMP2. Consistent with the modulate calcium flux, another mechanism of neurite regulation. 10 31 notion that the activities of CRMPs are inter-related, dendritic According to in situ hybridization, immunostaining and arborization induced by CRMP2 is considerably enhanced by 32 fi gene replacement analyses, all ve CRMPs are highly expressed CRMP5 deficiency.36 There is also evidence that CRMP4 regulates in the brain during early postnatal development and continue to dendritic outgrowth: CRMP4–short hairpin RNA-transfected be present in specific regions into adulthood, especially in areas and CRMP4 − / − cultured hippocampal neurons show increased with extensive neuronal plasticity (Table 1). They are found in dendritic branching without significant changes in primary axons and dendrites of the neurons where they contribute to dendrite number.37 This effect is partly dependent on Sema3A specific signaling mechanisms involved in the regulation of axonal signaling through F-actin bundling.20 Phosphorylated CRMP1 and and dendritic development and maintenance. CRMP2 are localized in the dendrites of cortical neurons where they regulate dendritic branch