151
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Wongsurawat T, Jenjaroenpun P, Kwoh CK, Kuznetsov V. Quantitative model of R-loop forming structures reveals a novel level of RNA-DNA interactome complexity. Nucleic Acids Res 2011; 40:e16. [PMID: 22121227 PMCID: PMC3258121 DOI: 10.1093/nar/gkr1075] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
R-loop is the structure co-transcriptionally formed between nascent RNA transcript and DNA template, leaving the non-transcribed DNA strand unpaired. This structure can be involved in the hyper-mutation and dsDNA breaks in mammalian immunoglobulin (Ig) genes, oncogenes and neurodegenerative disease related genes. R-loops have not been studied at the genome scale yet. To identify the R-loops, we developed a computational algorithm and mapped R-loop forming sequences (RLFS) onto 66,803 sequences defined by UCSC as 'known' genes. We found that ∼59% of these transcribed sequences contain at least one RLFS. We created R-loopDB (http://rloop.bii.a-star.edu.sg/), the database that collects all RLFS identified within over half of the human genes and links to the UCSC Genome Browser for information integration and visualisation across a variety of bioinformatics sources. We found that many oncogenes and tumour suppressors (e.g. Tp53, BRCA1, BRCA2, Kras and Ptprd) and neurodegenerative diseases related genes (e.g. ATM, Park2, Ptprd and GLDC) could be prone to significant R-loop formation. Our findings suggest that R-loops provide a novel level of RNA-DNA interactome complexity, playing key roles in gene expression controls, mutagenesis, recombination process, chromosomal rearrangement, alternative splicing, DNA-editing and epigenetic modifications. RLFSs could be used as a novel source of prospective therapeutic targets.
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Affiliation(s)
- Thidathip Wongsurawat
- Department of Genome and Gene Expression Data Analysis, Bioinformatics Institute, Singapore 138671
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152
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Clinical and neurobiological correlates of soluble amyloid precursor proteins in the cerebrospinal fluid. Alzheimers Dement 2011; 8:304-11. [PMID: 22055653 DOI: 10.1016/j.jalz.2011.04.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 03/14/2011] [Accepted: 04/27/2011] [Indexed: 01/30/2023]
Abstract
BACKGROUND According to a widely accepted hypothesis, the amyloid precursor protein (APP) is processed by two competing pathways: the amyloidogenic β-secretase-mediated pathway or the nonamyloidogenic α-secretase-mediated pathway. APP is cleaved preferentially through the nonamyloidogenic pathway in normal brain, whereas the balance shifts to the amyloidogenic pathway in Alzheimer's disease (AD). The levels of the α-secretase-cleaved soluble APP (sAPPα) and β-secretase-cleaved soluble APP (sAPPβ) in cerebrospinal fluid (CSF) are likely to reflect these competing mechanisms. METHODS We investigated the levels and the relationship between sAPPα and sAPPβ in the CSF of 64 patients with mild AD, 76 patients with mild cognitive impairment, and 12 cognitively healthy control subjects, as well as the effect of apolipoprotein E genotype and sex on soluble APP levels. RESULTS There was a significant positive correlation between sAPPα and sAPPβ levels in all three groups. sAPPα and sAPPβ concentrations were higher in patients with mild cognitive impairment compared with patients with AD. In the AD group, females exhibited higher sAPPα and sAPPβ levels than males. No influence of the apolipoprotein E genotype on soluble APP concentrations was detected. DISCUSSION The positive correlation between sAPPα and sAPPβ challenges the hypothesis that AD is caused by an imbalance of the α- and β-secretase APP proteolysis through competing mechanisms. Moreover, the differences in CSF levels of sAPPα and sAPPβ between male and female patients with AD may reflect a "sexual dimorphism" in the activity of the two APP processing pathways in AD.
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153
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Kumar-Singh S. Progranulin and TDP-43: mechanistic links and future directions. J Mol Neurosci 2011; 45:561-73. [PMID: 21863317 PMCID: PMC3207122 DOI: 10.1007/s12031-011-9625-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 08/08/2011] [Indexed: 12/12/2022]
Abstract
Loss-of-function mutations in the multifunctional growth factor progranulin (GRN) cause frontotemporal lobar degeneration (FTLD) with TDP-43 protein accumulation. Nuclear TDP-43 protein with key roles in RNA metabolism is also aggregated in amyotrophic lateral sclerosis (ALS), suggesting that ALS and FTLD constitute a broad disease continuum. However, the fact that mutations in GRN are associated with FTLD, while mutations in TDP-43 cause a preferential loss of motor neurons resulting in ALS-end of the disease spectrum, suggests involvement of both cell-autonomous and non-autonomous mechanisms. Studies on animal models and in vitro studies have been instrumental in understanding the link between GRN and TDP-43 and also their role in neurodegeneration. For instance, in mouse models, allelic deficiencies of Grn do not recapitulate human pathology of TDP-43 brain accumulations, but embryonic neurons derived from these mice do show abnormal TDP-43 accumulation after additional cellular challenges, suggesting that TDP-43 changes observed in GRN mutation carriers might also relate to stress. Recent results have shown that the dual action of GRN in growth modulation and inflammation could be due to its negative regulation of TNF-α signaling. In addition, GRN also interacts with sortilin and is endocytosed, thereby regulating its own levels and possibly also modulating the turnover of other proteins including that of TDP-43. Accumulating evidence suggests that TDP-43 abnormal cellular aggregation causes a possible gain of function, also suggested by recently constructed mouse models of TDP-43 proteinopathy; however, it would be inconvincible that sequestration of physiological TDP-43 within cellular aggregates observed in patients would be innocuous for disease pathogenesis. This review discusses some of these data on the possible link between GRN and TDP-43 as well as mechanisms involved in TDP-43-led neurodegeneration. Continued multitiered efforts on genetic, cell biological, and animal modeling approaches would prove crucial in finding a cure for GRN-related diseases.
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Affiliation(s)
- Samir Kumar-Singh
- Laboratory of Molecular and Cellular Neuropathology, University of Antwerp, Universiteitsplein 1, 2610, Antwerpen, Belgium.
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154
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Petkau TL, Neal SJ, Milnerwood A, Mew A, Hill AM, Orban P, Gregg J, Lu G, Feldman HH, Mackenzie IRA, Raymond LA, Leavitt BR. Synaptic dysfunction in progranulin-deficient mice. Neurobiol Dis 2011; 45:711-22. [PMID: 22062772 DOI: 10.1016/j.nbd.2011.10.016] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 10/07/2011] [Accepted: 10/16/2011] [Indexed: 11/29/2022] Open
Abstract
Progranulin haploinsufficiency is a common cause of familial frontotemporal dementia (FTD), but the role of progranulin in the brain is poorly understood. To investigate the role of murine progranulin (Grn) in the CNS in vivo, we generated mice targeted at the progranulin locus (Grn) using a gene-trap vector. Constitutive progranulin knockout mice (GrnKO) show moderate abnormalities in anxiety-related behaviors, social interactions, motor coordination, and novel object recognition at 8months of age, many of which differ between males and females. Analysis of synaptic transmission in 10-12 month old GrnKO male mice indicates altered synaptic connectivity and impaired synaptic plasticity. Additionally, apical dendrites in pyramidal cells in the CA1 region of the hippocampus in GrnKO males display an altered morphology and have significantly decreased spine density compared to wild-type (WT) mice. The observed changes in behavior, synaptic transmission, and neuronal morphology in GrnKO mice occur prior to neuropathological abnormalities, most of which are apparent at 18 but not at 8 months of age. We conclude that progranulin deficiency leads to reduced synaptic connectivity and impaired plasticity, which may contribute to FTD pathology in human patients.
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Affiliation(s)
- Terri L Petkau
- Centre for Molecular Medicine & Therapeutics, Department of Medical Genetics, University of British Columbia, and Children's and Women's Hospital, 980 West 28th Avenue, Vancouver, BC, Canada V5Z 4H4
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155
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Geng Z, Xu FY, Huang SH, Chen ZY. Sorting protein-related receptor SorLA controls regulated secretion of glial cell line-derived neurotrophic factor. J Biol Chem 2011; 286:41871-41882. [PMID: 21994944 DOI: 10.1074/jbc.m111.246413] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Glial cell line-derived neurotrophic factor (GDNF), after secreted from cells, plays a critical role in central and peripheral neuron survival and function. The secretion of GDNF can be either constitutive or regulated by physiological stimuli; however, the detailed mechanism driving GDNF secretion is still unknown. Here, we report that sorting protein-related receptor with A-type repeats (SorLA), a member of the mammal Vps10p domain receptor, interacts with GDNF and is localized to GDNF-containing vesicles. Overexpression of SorLA significantly increases, and knockdown of SorLA by siRNA decreases, the regulated secretion of GDNF in PC12 and MN9D cells but has no effect on GDNF constitutive secretion. In addition, overexpression of a truncated form of SorLA also impairs GDNF-regulated secretion. Finally, we found that the prodomain of GDNF mediates the interaction of GDNF with SorLA under acidic conditions. Moreover, overexpression of SorLA could enhance the regulated secretion of the GDNF prodomain-GFP fusion protein, suggesting that the prodomain of GDNF is responsible for its regulated secretion. Together, these findings will advance our understanding of the molecular mechanism underlying GDNF-regulated secretion.
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Affiliation(s)
- Zhao Geng
- Department of Neurobiology, Shandong Provincial Key Laboratory of Mental Disorders, School of Medicine, Shandong University, Jinan, Shandong 250012, P.R. China
| | - Feng-Yi Xu
- Department of Neurobiology, Shandong Provincial Key Laboratory of Mental Disorders, School of Medicine, Shandong University, Jinan, Shandong 250012, P.R. China
| | - Shu-Hong Huang
- Department of Neurobiology, Shandong Provincial Key Laboratory of Mental Disorders, School of Medicine, Shandong University, Jinan, Shandong 250012, P.R. China
| | - Zhe-Yu Chen
- Department of Neurobiology, Shandong Provincial Key Laboratory of Mental Disorders, School of Medicine, Shandong University, Jinan, Shandong 250012, P.R. China.
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156
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Schmidt V, Baum K, Lao A, Rateitschak K, Schmitz Y, Teichmann A, Wiesner B, Petersen CM, Nykjaer A, Wolf J, Wolkenhauer O, Willnow TE. Quantitative modelling of amyloidogenic processing and its influence by SORLA in Alzheimer's disease. EMBO J 2011; 31:187-200. [PMID: 21989385 DOI: 10.1038/emboj.2011.352] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2011] [Accepted: 09/05/2011] [Indexed: 11/09/2022] Open
Abstract
The extent of proteolytic processing of the amyloid precursor protein (APP) into neurotoxic amyloid-β (Aβ) peptides is central to the pathology of Alzheimer's disease (AD). Accordingly, modifiers that increase Aβ production rates are risk factors in the sporadic form of AD. In a novel systems biology approach, we combined quantitative biochemical studies with mathematical modelling to establish a kinetic model of amyloidogenic processing, and to evaluate the influence by SORLA/SORL1, an inhibitor of APP processing and important genetic risk factor. Contrary to previous hypotheses, our studies demonstrate that secretases represent allosteric enzymes that require cooperativity by APP oligomerization for efficient processing. Cooperativity enables swift adaptive changes in secretase activity with even small alterations in APP concentration. We also show that SORLA prevents APP oligomerization both in cultured cells and in the brain in vivo, eliminating the preferred form of the substrate and causing secretases to switch to a less efficient non-allosteric mode of action. These data represent the first mathematical description of the contribution of genetic risk factors to AD substantiating the relevance of subtle changes in SORLA levels for amyloidogenic processing as proposed for patients carrying SORL1 risk alleles.
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157
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Predictive validity of pharmacologic interventions in animal models of neuropathic pain. Scand J Pain 2011; 2:178-184. [DOI: 10.1016/j.sjpain.2011.06.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Accepted: 06/08/2011] [Indexed: 01/14/2023]
Abstract
Abstract
Introduction
The pathophysiologic and neurochemical characteristics of neuropathic pain must be considered in the search for new treatment targets. Breakthroughs in the understanding of the structural and biochemical changes in neuropathy have opened up possibilities to explore new treatment paradigms. However, long term sequels from the damage are still difficult to treat.
Aim of the study
To examine the validity of pharmacological treatments in humans and animals for neuropathic pain.
Method
An overview from the literature and own experiences of pharmacological treatments employed to interfere in pain behavior in different animal models was performed.
Results
The treatment principles tested in animal models of neuropathic pain may have predictive validity for treatment of human neuropathies. Opioids, neurotransmitter blockers, drugs interfering with the prostaglandin syntheses as well as voltage gated sodium channel blockers and calcium channel blockers are treatment principles having efficacy and similar potency in humans and in animals. Alternative targets have been identified and have shown promising results in the validated animal models. Modulators of the glutamate system with an increased expression of glutamate re-uptake transporters, inhibition of pain promoters as nitric oxide and prostaglandins need further exploration. Modulation of cytokines and neurotrophins in neuropathic pain implies new targets for study. Further, a combination of different analgesic treatments may as well improve management of neuropathic pain, changing the benefit/risk ratio.
Implications
Not surprisingly most pharmacologic principles that are tested in animal models of neuropathic pain are also found to be active in humans. Whereas many candidate drugs that were promising in animal models of neuropathic pain turned out not to be effective or too toxic in humans, animal models for neuropathic pain are still the best tools available to learn more about mechanisms of neuropathic pain. Better understanding of pathogenesis is the most hopeful approach to improve treatment of neuropathic pain.
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158
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Prabakaran T, Nielsen R, Larsen JV, Sørensen SS, Rasmussen UF, Saleem MA, Petersen CM, Verroust PJ, Christensen EI. Receptor-mediated endocytosis of α-galactosidase A in human podocytes in Fabry disease. PLoS One 2011; 6:e25065. [PMID: 21949853 PMCID: PMC3176300 DOI: 10.1371/journal.pone.0025065] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Accepted: 08/25/2011] [Indexed: 11/29/2022] Open
Abstract
Injury to the glomerular podocyte is a key mechanism in human glomerular disease and podocyte repair is an important therapeutic target. In Fabry disease, podocyte injury is caused by the intracellular accumulation of globotriaosylceramide. This study identifies in the human podocyte three endocytic receptors, mannose 6-phosphate/insulin-like growth II receptor, megalin, and sortilin and demonstrates their drug delivery capabilities for enzyme replacement therapy. Sortilin, a novel α-galactosidase A binding protein, reveals a predominant intracellular expression but also surface expression in the podocyte. The present study provides the rationale for the renal effect of treatment with α-galactosidase A and identifies potential pathways for future non-carbohydrate based drug delivery to the kidney podocyte and other potential affected organs.
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Affiliation(s)
- Thaneas Prabakaran
- Section of Cell Biology, Department of Anatomy, Aarhus University, Aarhus, Denmark
| | - Rikke Nielsen
- Section of Cell Biology, Department of Anatomy, Aarhus University, Aarhus, Denmark
| | - Jakob V. Larsen
- Department of Medical Biochemistry, Aarhus University, Aarhus, Denmark
| | | | | | - Moin A. Saleem
- Children's Renal Unit and Academic Renal Unit, University of Bristol, Southmead Hospital, Bristol, United Kingdom
| | - Claus M. Petersen
- Department of Medical Biochemistry, Aarhus University, Aarhus, Denmark
| | | | - Erik I. Christensen
- Section of Cell Biology, Department of Anatomy, Aarhus University, Aarhus, Denmark
- * E-mail:
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159
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Abstract
Bidirectional traffic between the Golgi apparatus and the endosomal system sustains the functions of the trans-Golgi network (TGN) in secretion and organelle biogenesis. Export of cargo from the TGN via anterograde trafficking pathways depletes the organelle of sorting receptors, processing proteases, SNARE molecules, and other factors, and these are subsequently retrieved from endosomes via the retrograde pathway. Recent studies indicate that retrograde trafficking is vital to early metazoan development, nutrient homeostasis, and for processes that protect against Alzheimer's and other neurological diseases.
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Affiliation(s)
- Christopher G Burd
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058, USA.
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160
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Fu R, Wang X, Li C, Santiago-Miranda AN, Pielak GJ, Tian F. In situ structural characterization of a recombinant protein in native Escherichia coli membranes with solid-state magic-angle-spinning NMR. J Am Chem Soc 2011; 133:12370-3. [PMID: 21774553 DOI: 10.1021/ja204062v] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The feasibility of using solid-state magic-angle-spinning NMR spectroscopy for in situ structural characterization of the LR11 (sorLA) transmembrane domain (TM) in native Escherichia coli membranes is presented. LR11 interacts with the human amyloid precursor protein (APP), a central player in the pathology of Alzheimer's disease. The background signals from E. coli lipids and membrane proteins had only minor effects on the LR11 TM resonances. Approximately 50% of the LR11 TM residues were assigned by using (13)C PARIS data. These assignments allowed comparisons of the secondary structure of the LR11 TM in native membrane environments and commonly used membrane mimics (e.g., micelles). In situ spectroscopy bypasses several obstacles in the preparation of membrane proteins for structural analysis and offers the opportunity to investigate how membrane heterogeneity, bilayer asymmetry, chemical gradients, and macromolecular crowding affect the protein structure.
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Affiliation(s)
- Riqiang Fu
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
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161
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A mutation in VPS35, encoding a subunit of the retromer complex, causes late-onset Parkinson disease. Am J Hum Genet 2011; 89:168-75. [PMID: 21763483 DOI: 10.1016/j.ajhg.2011.06.008] [Citation(s) in RCA: 650] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2011] [Revised: 06/15/2011] [Accepted: 06/21/2011] [Indexed: 11/24/2022] Open
Abstract
To identify rare causal variants in late-onset Parkinson disease (PD), we investigated an Austrian family with 16 affected individuals by exome sequencing. We found a missense mutation, c.1858G>A (p.Asp620Asn), in the VPS35 gene in all seven affected family members who are alive. By screening additional PD cases, we saw the same variant cosegregating with the disease in an autosomal-dominant mode with high but incomplete penetrance in two further families with five and ten affected members, respectively. The mean age of onset in the affected individuals was 53 years. Genotyping showed that the shared haplotype extends across 65 kilobases around VPS35. Screening the entire VPS35 coding sequence in an additional 860 cases and 1014 controls revealed six further nonsynonymous missense variants. Three were only present in cases, two were only present in controls, and one was present in cases and controls. The familial mutation p.Asp620Asn and a further variant, c.1570C>T (p.Arg524Trp), detected in a sporadic PD case were predicted to be damaging by sequence-based and molecular-dynamics analyses. VPS35 is a component of the retromer complex and mediates retrograde transport between endosomes and the trans-Golgi network, and it has recently been found to be involved in Alzheimer disease.
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162
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Skeldal S, Matusica D, Nykjaer A, Coulson EJ. Proteolytic processing of the p75 neurotrophin receptor: A prerequisite for signalling?: Neuronal life, growth and death signalling are crucially regulated by intra-membrane proteolysis and trafficking of p75(NTR). Bioessays 2011; 33:614-25. [PMID: 21717487 DOI: 10.1002/bies.201100036] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The common neurotrophin receptor (p75(NTR) ) regulates various functions in the developing and adult nervous system. Cell survival, cell death, axonal and growth cone retraction, and regulation of the cell cycle can be regulated by p75(NTR) -mediated signals following activation by either mature or pro-neurotrophins and in combination with various co-receptors, including Trk receptors and sortilin. Here, we review the known functions of p75(NTR) by cell type, receptor-ligand combination, and whether regulated intra-membrane proteolysis of p75(NTR) is required for signalling. We highlight that the generation of the intracellular domain fragment of p75(NTR) is associated with many of the receptor functions, regardless of its ligand and co-receptor interactions.
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Affiliation(s)
- Sune Skeldal
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Aarhus University, Aarhus, Denmark.
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163
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Kwon S, Christian JL. Sortilin associates with transforming growth factor-beta family proteins to enhance lysosome-mediated degradation. J Biol Chem 2011; 286:21876-85. [PMID: 21521695 PMCID: PMC3122242 DOI: 10.1074/jbc.m111.228262] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Revised: 04/15/2011] [Indexed: 01/17/2023] Open
Abstract
Transforming growth factor (TGF)-β family proteins are synthesized as precursors that are cleaved to generate an active ligand. Previous studies suggest that TGF-β activity can be controlled by lysosomal degradation of both precursor proteins and ligands, but how these soluble proteins are trafficked to the lysosome is incompletely understood. The current studies show that sortilin selectively co-immunoprecipitates with the cleaved prodomain and/or precursor form of TGF-β family members. Furthermore, sortilin co-localizes with, and enhances accumulation of a nodal family member in the Golgi. Co-expression of sortilin with TGF-β family members leads to decreased accumulation of precursor proteins and cleavage products and this is attenuated by lysosomal, but not proteosomal inhibitors. In Xenopus embryos, overexpression of sortilin leads to a decrease in phospho-Smad2 levels and phenocopies loss of nodal signaling. Conversely, down-regulation of sortilin expression in HeLa cells leads to an up-regulation of endogenous bone morphogenic protein pathway activation, as indicated by an increase in phospho-Smad1/5/8 levels. Our results suggest that sortilin negatively regulates TGF-β signaling by diverting trafficking of precursor proteins to the lysosome during transit through the biosynthetic pathway.
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Affiliation(s)
- Sunjong Kwon
- From the Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon 97239
| | - Jan L. Christian
- From the Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon 97239
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164
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Yang M, Lim Y, Li X, Zhong JH, Zhou XF. Precursor of brain-derived neurotrophic factor (proBDNF) forms a complex with Huntingtin-associated protein-1 (HAP1) and sortilin that modulates proBDNF trafficking, degradation, and processing. J Biol Chem 2011; 286:16272-84. [PMID: 21357693 PMCID: PMC3091234 DOI: 10.1074/jbc.m110.195347] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Revised: 02/24/2011] [Indexed: 01/17/2023] Open
Abstract
proBDNF, a precursor of brain-derived neurotrophic factor (BDNF), is anterogradely transported and released from nerve terminals, but the mechanism underlying this process remains unclear. In this study, we report that proBDNF forms a complex with Huntingtin associated protein-1 (HAP1) and sortilin, which plays an important role in proBDNF intracellular trafficking and stabilization. The interaction of proBDNF with both HAP1A and sortilin in co-transfected HEK293 cells is confirmed by both fluorescence resonance energy transfer and co-immunoprecipitation. The frequent co-localization (>90%) of endogenous HAP1, sortilin, and proBDNF is also found in cultured cortical neurons. Mapping studies using GST pulldown and competition assays has defined the interacting region of HAP1 with proBDNF within amino acids 371-445 and the binding sequences of proBDNF to HAP1 between amino acids 65 and 90. Fluorescence recovery after photobleaching confirms the defective movement of proBDNF-containing vesicles in neurites of HAP1(-/-) neurons, which can be partially restored by reintroducing HAP1 cDNA into the neurons. However, the effect is significantly increased by simultaneously reintroducing both HAP1 and sortilin. proBDNF and HAP1 are highly co-localized with organelle markers for the Golgi network, microtubules, molecular motor, or endosomes in normal neurons, but this co-localization is reduced in HAP1(-/-) neurons. Co-immunoprecipitation and Western blot showed that sortilin stabilizes the proBDNF·HAP1 complex in co-transfected HEK293 cells, helping to prevent proBDNF degradation. Furthermore, the complex facilitates furin cleavage to release mature BDNF.
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Affiliation(s)
- Miao Yang
- From the Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia 5001, Australia and
| | - Yoon Lim
- From the Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia 5001, Australia and
| | - Xiaojiang Li
- the Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Jin-Hua Zhong
- From the Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia 5001, Australia and
| | - Xin-Fu Zhou
- From the Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia 5001, Australia and
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165
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Wu X, Ye Y, Rosell R, Amos CI, Stewart DJ, Hildebrandt MAT, Roth JA, Minna JD, Gu J, Lin J, Buch SC, Nukui T, Ramirez Serrano JL, Taron M, Cassidy A, Lu C, Chang JY, Lippman SM, Hong WK, Spitz MR, Romkes M, Yang P. Genome-wide association study of survival in non-small cell lung cancer patients receiving platinum-based chemotherapy. J Natl Cancer Inst 2011; 103:817-25. [PMID: 21483023 DOI: 10.1093/jnci/djr075] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Interindividual variation in genetic background may influence the response to chemotherapy and overall survival for patients with advanced-stage non-small cell lung cancer (NSCLC). METHODS To identify genetic variants associated with poor overall survival in these patients, we conducted a genome-wide scan of 307,260 single-nucleotide polymorphisms (SNPs) in 327 advanced-stage NSCLC patients who received platinum-based chemotherapy with or without radiation at the University of Texas MD Anderson Cancer Center (the discovery population). A fast-track replication was performed for 315 patients from the Mayo Clinic followed by a second validation at the University of Pittsburgh in 420 patients enrolled in the Spanish Lung Cancer Group PLATAX clinical trial. A pooled analysis combining the Mayo Clinic and PLATAX populations or all three populations was also used to validate the results. We assessed the association of each SNP with overall survival by multivariable Cox proportional hazard regression analysis. All statistical tests were two-sided. RESULTS SNP rs1878022 in the chemokine-like receptor 1 (CMKLR1) was statistically significantly associated with poor overall survival in the MD Anderson discovery population (hazard ratio [HR] of death = 1.59, 95% confidence interval [CI] = 1.32 to 1.92, P = 1.42 × 10(-6)), in the PLATAX clinical trial (HR of death = 1.23, 95% CI = 1.00 to 1.51, P = .05), in the pooled Mayo Clinic and PLATAX validation (HR of death = 1.22, 95% CI = 1.06 to 1.40, P = .005), and in pooled analysis of all three populations (HR of death = 1.33, 95% CI = 1.19 to 1.48, P = 5.13 × 10(-7)). Carrying a variant genotype of rs10937823 was associated with decreased overall survival (HR of death = 1.82, 95% CI = 1.42 to 2.33, P = 1.73 × 10(-6)) in the pooled MD Anderson and Mayo Clinic populations but not in the PLATAX trial patient population (HR of death = 0.96, 95% CI = 0.69 to 1.35). CONCLUSION These results have the potential to contribute to the future development of personalized chemotherapy treatments for individual NSCLC patients.
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Affiliation(s)
- Xifeng Wu
- Department of Epidemiology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1340, Houston, TX 77030, USA.
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166
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Dubé JB, Johansen CT, Hegele RA. Sortilin: An unusual suspect in cholesterol metabolism. Bioessays 2011; 33:430-7. [DOI: 10.1002/bies.201100003] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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167
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Abstract
Translocation of Glut4 to the plasma membrane of fat and skeletal muscle cells is mediated by specialized insulin-responsive vesicles (IRVs), whose protein composition consists primarily of glucose transporter isoform 4 (Glut4), insulin-responsive amino peptidase (IRAP), sortilin, lipoprotein receptor-related protein 1 (LRP1) and v-SNAREs. How can these proteins find each other in the cell and form functional vesicles after endocytosis from the plasma membrane? We are proposing a model according to which the IRV component proteins are internalized into sorting endosomes and are delivered to the IRV donor compartment(s), recycling endosomes and/or the trans-Golgi network (TGN), by cellugyrin-positive transport vesicles. The cytoplasmic tails of Glut4, IRAP, LRP1 and sortilin play an important targeting role in this process. Once these proteins arrive in the donor compartment, they interact with each other via their lumenal domains. This facilitates clustering of the IRV proteins into an oligomeric complex, which can then be distributed from the donor membranes to the IRV as a single entity with the help of adaptors, such as Golgi-localized, gamma-adaptin ear-containing, ARF-binding (GGA).
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Affiliation(s)
- Konstantin V Kandror
- Department of Biochemistry, Boston University School of Medicine, 72 E. Concord Street, Boston, MA 02118, USA
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168
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Convergence of linkage, association and GWAS findings for a candidate region for bipolar disorder and schizophrenia on chromosome 4p. Mol Psychiatry 2011; 16:240-2. [PMID: 20351716 DOI: 10.1038/mp.2010.25] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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169
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Wang X, Gill RL, Zhu Q, Tian F. Bacterial expression, purification, and model membrane reconstitution of the transmembrane and cytoplasmic domains of the human APP binding protein LR11/SorLA for NMR studies. Protein Expr Purif 2011; 77:224-30. [PMID: 21320603 DOI: 10.1016/j.pep.2011.02.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 02/07/2011] [Accepted: 02/08/2011] [Indexed: 11/24/2022]
Abstract
LR11 (SorLA) is a recently identified neuronal protein that interacts with amyloid precursor protein (APP), a central player in the pathology of the Alzheimer's disease (AD). AD is a neurodegenerative disease and the most common cause of dementia in the elderly. Current estimates suggest that as many as 5.3 million Americans are living with AD. Recent investigations have uncovered the pathophysiological relevance of APP intracellular trafficking in AD. LR11 is of particular importance due to its role in regulating APP transport and processing. LR11 is a type I transmembrane protein and belongs to a novel family of Vps10p receptors. Using a new expression vector, pMTTH (MBP-MCS1 (multiple cloning site)-Thrombin protease cleavage site-MCS2-TEV protease cleavage site-MCS3-His(6)), we successfully expressed, purified and reconstituted the LR11 transmembrane (TM) and cytoplasmic (CT) domains into bicelles and detergent micelles for NMR structural studies. This new construct allowed us to overcome several obstacles during sample preparation. MBP fused LR11TM and LR11TMCT proteins are preferably expressed at high levels in Escherichia coli membrane, making a refolding of the protein unnecessary. The C-terminal His-tag allows for easy separation of the target protein from the truncated products from the C-terminus, and provides a convenient route for screening detergents to produce high quality 2D (1)H-(15)N TROSY spectra. Thrombin protease cleavage is compatible with most of the commonly used detergents, including a direct cleavage at the E. coli membrane surface. This new MBP construct may provide an effective route for the preparation of small proteins with TM domains.
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Affiliation(s)
- Xingsheng Wang
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, Hershey, PA 17033, USA
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170
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171
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172
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Finan GM, Okada H, Kim TW. BACE1 retrograde trafficking is uniquely regulated by the cytoplasmic domain of sortilin. J Biol Chem 2011; 286:12602-16. [PMID: 21245145 DOI: 10.1074/jbc.m110.170217] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
BACE1 (β-site β-amyloid precursor protein (APP)-cleaving enzyme 1) mediates the first proteolytic cleavage of APP, leading to amyloid β-peptide (Aβ) production. It has been reported that BACE1 intracellular trafficking, in particular endosome-to-TGN sorting, is mediated by adaptor complexes, such as retromer and Golgi-localized γ-ear-containing ARF-binding proteins (GGAs). Here we investigated whether sortilin, a Vps10p domain-sorting receptor believed to participate in retromer-mediated transport of select membrane cargoes, contributes to the subcellular trafficking and activity of BACE1. Our initial studies revealed increased levels of sortilin in post-mortem brain tissue of AD patients and that overexpression of sortilin leads to increased BACE1-mediated cleavage of APP in cultured cells. In contrast, RNAi suppression of sortilin results in decreased BACE1-mediated cleavage of APP. We also found that sortilin interacts with BACE1 and that a sortilin construct lacking its cytoplasmic domain, which contains putative retromer sorting motifs, remains bound to BACE1. However, expression of this truncated sortilin redistributes BACE1 from the trans-Golgi network to the endosomes and substantially reduces the retrograde trafficking of BACE1. Site-directed mutagenesis and chimera experiments reveal that the cytoplasmic tail of sortilin, but not those from other VPS10p domain receptors (e.g. SorCs1b and SorLA), plays a unique role in BACE1 trafficking. Our studies suggest a new function for sortilin as a modulator of BACE1 retrograde trafficking and subsequent generation of Aβ.
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Affiliation(s)
- Gina M Finan
- Graduate Program in Pathobiology and Molecular Medicine, Department of Pathology and cell Biology, Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, NY 10032, USA
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173
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Abstract
Mutations within the granulin (GRN) gene that encodes progranulin (PGRN) cause the neurodegenerative disease frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U). The receptor for PGRN in the CNS has not been previously identified. In this issue of Neuron, Hu and colleagues identify Sortilin (SORT1) as a key neuronal receptor for PGRN that facilitates its endocytosis and regulates PGRN levels in vitro and in vivo.
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174
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Hu F, Padukkavidana T, Vægter CB, Brady OA, Zheng Y, Mackenzie IR, Feldman HH, Nykjaer A, Strittmatter SM. Sortilin-mediated endocytosis determines levels of the frontotemporal dementia protein, progranulin. Neuron 2011; 68:654-67. [PMID: 21092856 DOI: 10.1016/j.neuron.2010.09.034] [Citation(s) in RCA: 413] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2010] [Indexed: 12/12/2022]
Abstract
VIDEO ABSTRACT The most common inherited form of Frontotemporal Lobar Degeneration (FTLD) known stems from Progranulin (GRN) mutation and exhibits TDP-43 plus ubiquitin aggregates. Despite the causative role of GRN haploinsufficiency in FTLD-TDP, the neurobiology of this secreted glycoprotein is unclear. Here, we examined PGRN binding to the cell surface. PGRN binds to cortical neurons via its C terminus, and unbiased expression cloning identifies Sortilin (Sort1) as a binding site. Sort1⁻/⁻ neurons exhibit reduced PGRN binding. In the CNS, Sortilin is expressed by neurons and PGRN is most strongly expressed by activated microglial cells after injury. Sortilin rapidly endocytoses and delivers PGRN to lysosomes. Mice lacking Sortilin have elevations in brain and serum PGRN levels of 2.5- to 5-fold. The 50% PGRN decrease causative in FTLD-TDP cases is mimicked in GRN+/⁻ mice, and is fully normalized by Sort1 ablation. Sortilin-mediated PGRN endocytosis is likely to play a central role in FTLD-TDP pathophysiology.
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Affiliation(s)
- Fenghua Hu
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06536, USA
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175
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Vaegter CB, Jansen P, Fjorback AW, Glerup S, Skeldal S, Richner M, Erdmann B, Nyengaard JR, Tessarollo L, Lewin GR, Willnow TE, Chao MV, Nykjaer A. Sortilin associates with Trk receptors to enhance anterograde transport and neurotrophin signaling. Nat Neurosci 2011; 14:54-61. [PMID: 21102451 PMCID: PMC3808973 DOI: 10.1038/nn.2689] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Accepted: 10/12/2010] [Indexed: 02/05/2023]
Abstract
Binding of target-derived neurotrophins to Trk receptors at nerve terminals is required to stimulate neuronal survival, differentiation, innervation and synaptic plasticity. The distance between the soma and nerve terminal is great, making efficient anterograde Trk transport critical for Trk synaptic translocation and signaling. The mechanism responsible for this trafficking remains poorly understood. Here we show that the sorting receptor sortilin interacts with TrkA, TrkB and TrkC and enables their anterograde axonal transport, thereby enhancing neurotrophin signaling. Cultured DRG neurons lacking sortilin showed blunted MAP kinase signaling and reduced neurite outgrowth upon stimulation with NGF. Moreover, deficiency for sortilin markedly aggravated TrkA, TrkB and TrkC phenotypes present in p75(NTR) knockouts, and resulted in increased embryonic lethality and sympathetic neuropathy in mice heterozygous for TrkA. Our findings demonstrate a role for sortilin as an anterograde trafficking receptor for Trk and a positive modulator of neurotrophin-induced neuronal survival.
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MESH Headings
- Adaptor Proteins, Vesicular Transport/deficiency
- Adaptor Proteins, Vesicular Transport/genetics
- Adaptor Proteins, Vesicular Transport/metabolism
- Adaptor Proteins, Vesicular Transport/physiology
- Animals
- Axonal Transport/genetics
- Axonal Transport/physiology
- Cell Culture Techniques
- Cerebral Cortex/metabolism
- Embryo, Mammalian/pathology
- Ganglia, Spinal/cytology
- Ganglia, Spinal/metabolism
- HEK293 Cells
- Hippocampus/metabolism
- Humans
- Mice
- Mice, Knockout
- Nerve Growth Factor/pharmacology
- Nerve Growth Factors/physiology
- Neurites/drug effects
- Neurites/physiology
- Receptor Cross-Talk/physiology
- Receptor, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/metabolism
- Receptors, Nerve Growth Factor/physiology
- Signal Transduction/physiology
- Superior Cervical Ganglion/metabolism
- Superior Cervical Ganglion/pathology
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Affiliation(s)
- Christian B. Vaegter
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Pernille Jansen
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Anja W. Fjorback
- MIND Center, Stereology and Electron Microscopy Laboratory, Aarhus University, 8000 Aarhus C, Denmark
| | - Simon Glerup
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Sune Skeldal
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Mette Richner
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Bettina Erdmann
- Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany
| | - Jens R. Nyengaard
- MIND Center, Stereology and Electron Microscopy Laboratory, Aarhus University, 8000 Aarhus C, Denmark
| | - Lino Tessarollo
- Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, USA
| | - Gary R. Lewin
- Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany
| | | | - Moses V. Chao
- Kimmel Center at Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York 10016, USA
| | - Anders Nykjaer
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Ole Worms Allé 1170, Aarhus University, DK-8000 Aarhus C, Denmark
- NeuronIcon, Gustav Wieds vej 10, DK-8000 Aarhus C, Denmark
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176
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Nakata Z, Nagae M, Yasui N, Bujo H, Nogi T, Takagi J. Crystallization and preliminary crystallographic analysis of human LR11 Vps10p domain. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:129-32. [PMID: 21206043 PMCID: PMC3079991 DOI: 10.1107/s1744309110048153] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Accepted: 11/18/2010] [Indexed: 03/16/2023]
Abstract
Low-density lipoprotein receptor (LDLR) relative with 11 binding repeats (LR11; also known as sorLA) is genetically associated with late-onset Alzheimer's disease and is thought to be involved in neurodegenerative processes. LR11 contains a vacuolar protein-sorting 10 protein (Vps10p) domain. As this domain has been implicated in protein-protein interaction in other receptors, its structure and function are of great biological interest. Human LR11 Vps10p domain was expressed in mammalian cells and the purified protein was crystallized using the hanging-drop vapour-diffusion method. Enzymatic deglycosylation of the sample was critical to obtaining diffraction-quality crystals. Deglycosylated LR11 Vps10p-domain crystals belonged to the hexagonal space group P6(1)22. A diffraction data set was collected to 2.4 Å resolution and a clear molecular-replacement solution was obtained.
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Affiliation(s)
- Zenzaburo Nakata
- Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Masamichi Nagae
- Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Norihisa Yasui
- Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hideaki Bujo
- Department of Genome Research and Clinical Application (M6), Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
| | - Terukazu Nogi
- Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Junichi Takagi
- Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
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177
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Kim E, Lee Y, Lee HJ, Kim JS, Song BS, Huh JW, Lee SR, Kim SU, Kim SH, Hong Y, Shim I, Chang KT. Implication of mouse Vps26b-Vps29-Vps35 retromer complex in sortilin trafficking. Biochem Biophys Res Commun 2010; 403:167-71. [PMID: 21040701 DOI: 10.1016/j.bbrc.2010.10.121] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Accepted: 10/26/2010] [Indexed: 11/30/2022]
Abstract
The retromer complex, which mediates retrograde transport from endosomes to the trans-Golgi network, is a heteropentameric complex that contains a multifunctional cargo recognition heterotrimer consisted of the vacuolar protein sorting (Vps) subunits Vps26, Vps29, and Vps35. In mammals, there are two different isoforms of Vps26, Vps26a and Vps26b, that localize to the endosome, and to the plasma membrane, respectively. To elucidate the biological significance of the Vps26b isoform, we generated Vps26b knockout mice and studied their molecular, histological, and behavioral phenotypes. We found that the loss of Vps26b results in no significant defects in the behavior, body size, and health of the mice. Vps26b-deficient mice showed a severe reduction of Vps35 protein at cellular level and lacked the Vps26b-Vps29-Vps35 retromer complex, despite the normal presence of the Vps26a-Vps29-Vps35 retromer complex. Relatively, the amount of sortilin was increased approximately 20% in the Vps26b-deficient mice, whereas the sorLA was normal. These results suggest that mouse Vps26b-Vps29-Vps35 retromer complex is implicated in the transport of sortilin from endosomes to the trans-Golgi network (TGN).
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Affiliation(s)
- Ekyune Kim
- National Primate Research Center, Korea Research Institute of Bioscience and Biotechnology, 685-1 Yangcheong-ri, Ochang-eup, Chung-buk 363-883, Republic of Korea
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178
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Kjolby M, Andersen OM, Breiderhoff T, Fjorback AW, Pedersen KM, Madsen P, Jansen P, Heeren J, Willnow TE, Nykjaer A. Sort1, encoded by the cardiovascular risk locus 1p13.3, is a regulator of hepatic lipoprotein export. Cell Metab 2010; 12:213-23. [PMID: 20816088 DOI: 10.1016/j.cmet.2010.08.006] [Citation(s) in RCA: 213] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Revised: 07/08/2010] [Accepted: 08/03/2010] [Indexed: 01/17/2023]
Abstract
Recent genome-wide association studies (GWAS) have revealed strong association of hypercholesterolemia and myocardial infarction with SNPs on human chromosome 1p13.3. This locus covers three genes: SORT1, CELSR2, and PSRC1. We demonstrate that sortilin, encoded by SORT1, is an intracellular sorting receptor for apolipoprotein (apo) B100. It interacts with apoB100 in the Golgi and facilitates the formation and hepatic export of apoB100-containing lipoproteins, thereby regulating plasma low-density lipoprotein (LDL) cholesterol. Absence of sortilin in gene-targeted mice reduces secretion of lipoproteins from the liver and ameliorates hypercholesterolemia and atherosclerotic lesion formation in LDL receptor-deficient animals. In contrast, sortilin overexpression stimulates hepatic release of lipoproteins and increases plasma LDL levels. Our data have uncovered a regulatory pathway in hepatic lipoprotein export and suggest a molecular explanation for the cardiovascular risk being associated with 1p13.3.
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Affiliation(s)
- Mads Kjolby
- The Lundbeck Foundation Research Center MIND, Department of Medical Biochemistry, Aarhus University, Denmark
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179
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Teng KK, Felice S, Kim T, Hempstead BL. Understanding proneurotrophin actions: Recent advances and challenges. Dev Neurobiol 2010; 70:350-9. [PMID: 20186707 DOI: 10.1002/dneu.20768] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neurotrophins are initially synthesized as larger precursors (proneurotrophins), which undergo proteolytic cleavage to yield mature forms. Although the functions of the mature neurotrophins have been well established during neural development and in the adult nervous system, roles for the proneurotrophins in developmental and injury-induced cell death, as well as in synaptic plasticity, have only recently been appreciated. Interestingly, both mature neurotrophins and proneurotrophins utilize dual-receptor complexes to mediate their actions. The mature neurotrophin coreceptors consist of the Trk receptor tyrosine kinases and p75(NTR), wherein Trk transduces survival and differentiative signaling, and p75(NTR) modulates the affinity and selectivity of Trk activation. On the other hand, proneurotrophins engage p75(NTR) and the structurally distinct coreceptor sortilin, to initiate p75(NTR)-dependent signal transduction cascade. Although the specificity of mature neurotrophins vs. proneurotrophins actions is due in part to the formation of distinct coreceptor complexes, a number of recent studies highlight how different p75(NTR)-mediated cellular actions are modulated. Here, we review emerging evidence for a novel transmembrane mechanism for ligand-specific p75(NTR) activation and several mechanisms by which p75(NTR)-dependent apoptotic and nonapoptotic responses can be selective activated.
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Affiliation(s)
- Kenneth K Teng
- Department of Medicine, Weill Cornell Medical College, New York, New York 10065, USA
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180
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Wähe A, Kasmapour B, Schmaderer C, Liebl D, Sandhoff K, Nykjaer A, Griffiths G, Gutierrez MG. Golgi-to-phagosome transport of acid sphingomyelinase and prosaposin is mediated by sortilin. J Cell Sci 2010; 123:2502-11. [PMID: 20571055 DOI: 10.1242/jcs.067686] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Sortilin, also known as neurotensin receptor 3 (NTR3), is a transmembrane protein with a dual function. It acts as a receptor for neuromediators and growth factors at the plasma membrane, but it has also been implicated in binding and transport of some lysosomal proteins. However, the role of sortilin during phagosome maturation has not been investigated before. Here, we show that in macrophages, sortilin is mainly localized in the Golgi and transported to latex-bead phagosomes (LBPs). Using live-cell imaging and electron microscopy, we found that sortilin is delivered to LBPs in a manner that depends on its cytoplasmic tail. We also show that sortilin participates in the direct delivery of acid sphingomyelinase (ASM) and prosaposin (PS) to the phagosome, bypassing fusion with lysosomal compartments. Further analysis confirmed that ASM and PS are targeted to the phagosome by sortilin in a Brefeldin-A-sensitive pathway. Analysis of primary macrophages isolated from Sort1(-/-) mice indicated that the delivery of ASM and PS, but not pro-cathepsin D, to LBPs was severely impaired. We propose a pathway mediated by sortilin by which selected lysosomal proteins are transported to the phagosome along a Golgi-dependent route during the maturation of phagosomes.
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Affiliation(s)
- Anna Wähe
- European Molecular Biology Laboratory, Postfach 102209, 69117 Heidelberg, Germany
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181
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Rogers ML, Bailey S, Matusica D, Nicholson I, Muyderman H, Pagadala PC, Neet KE, Zola H, Macardle P, Rush RA. ProNGF mediates death of Natural Killer cells through activation of the p75NTR-sortilin complex. J Neuroimmunol 2010; 226:93-103. [PMID: 20547427 DOI: 10.1016/j.jneuroim.2010.05.040] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Revised: 05/12/2010] [Accepted: 05/19/2010] [Indexed: 12/30/2022]
Abstract
The common neurotrophin receptor P75NTR, its co-receptor sortilin and ligand proNGF, have not previously been investigated in Natural Killer (NK) cell function. We found freshly isolated NK cells express sortilin but not significant amounts of P75NTR unless exposed to interleukin-12 (IL-12), or cultured in serum free conditions, suggesting this receptor is sequestered. A second messenger associated with p75NTR, neurotrophin-receptor-interacting-MAGE-homologue (NRAGE) was identified in NK cells. Cleavage resistant proNGF123 killed NK cells in the presence of IL-12 after 20h and without IL-12 in serum free conditions at 48h. This was reduced by blocking sortilin with neurotensin. We conclude that proNGF induced apoptosis of NK cells may have important implications for limiting the innate immune response.
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Affiliation(s)
- Mary-Louise Rogers
- Department of Human Physiology, School of Medicine, Flinders University, GPO Box 2100 Adelaide 5001, Australia.
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182
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Alexopoulos P, Kurz A, Lewczuk P, Kornhuber J, Wiltfang J, Maier W, Förstl H, Perneczky R. The sortilin-related receptor SORL1 and the amyloid cascade: a possible explanation for the concurrent elevation of CSF soluble APPalpha and APPbeta in Alzheimer's disease. Int J Geriatr Psychiatry 2010; 25:542-3. [PMID: 20391590 DOI: 10.1002/gps.2349] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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183
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SORLA/SORL1 functionally interacts with SPAK to control renal activation of Na(+)-K(+)-Cl(-) cotransporter 2. Mol Cell Biol 2010; 30:3027-37. [PMID: 20385770 DOI: 10.1128/mcb.01560-09] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Proper control of NaCl excretion in the kidney is central to bodily functions, yet many mechanisms that regulate reabsorption of sodium and chloride in the kidney remain incompletely understood. Here, we identify an important role played by the intracellular sorting receptor SORLA (sorting protein-related receptor with A-type repeats) in functional activation of renal ion transporters. We demonstrate that SORLA is expressed in epithelial cells of the thick ascending limb (TAL) of Henle's loop and that lack of receptor expression in this cell type in SORLA-deficient mice results in an inability to properly reabsorb sodium and chloride during osmotic stress. The underlying cellular defect was correlated with an inability of the TAL to phosphorylate Na(+)-K(+)-Cl(-) cotransporter 2 (NKCC2), the major sodium transporter in the distal nephron. SORLA functionally interacts with Ste-20-related proline-alanine-rich kinase (SPAK), an activator of NKCC2, and receptor deficiency is associated with missorting of SPAK. Our data suggest a novel regulatory pathway whereby intracellular trafficking of SPAK by the sorting receptor SORLA is crucial for proper NKCC2 activation and for maintenance of renal ion balance.
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184
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Serup Andersen O, Boisguerin P, Glerup S, Skeldal S, Volkmer R, Willnow TE, Nykjaer A, Andersen OM. Identification of a linear epitope in sortilin that partakes in pro-neurotrophin binding. J Biol Chem 2010; 285:12210-22. [PMID: 20159974 DOI: 10.1074/jbc.m109.062364] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Sortilin acts as a cell surface receptor for pro-neurotrophins (pro-NT) that upon complex formation with the p75 neurotrophin receptor (p75(NTR)) is able to signal neuronal cell death. Here we screened a sortilin peptide library comprising 16-mer overlapping sequences for binding of the pro-domains of nerve growth factor and brain-derived neurotrophic factor. We find that a linear surface-exposed sequence, (163)RIFRSSDFAKNF(174), constitutes an important pro-NT binding epitope in sortilin. Systematic mutational analysis revealed residues Arg(163), Phe(165), Arg(166), and Phe(170) to be critical for the interaction. Expression of a sortilin mutant in which these four amino acids were substituted by alanines disrupted pro-NT binding without affecting receptor heterodimerization with p75(NTR) or binding of ligands that selectively engages the centrally located tunnel in the beta-propeller of sortilin. We furthermore demonstrate that a peptide comprising the ligand-binding epitope can prevent pro-NT-induced apoptosis in RN22 schwannoma cells.
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Affiliation(s)
- Olga Serup Andersen
- Department of Medical Biochemistry, Membrane Receptors in Neuronal Disease (MIND) Center, University of Aarhus, OleWorms Allé, Aarhus C, Denmark
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185
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Brain-derived neurotrophic factor reduces amyloidogenic processing through control of SORLA gene expression. J Neurosci 2010; 29:15472-8. [PMID: 20007471 DOI: 10.1523/jneurosci.3960-09.2009] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Sorting protein-related receptor with A-type repeats (SORLA) is a major risk factor in cellular processes leading to Alzheimer's disease (AD). It acts as sorting receptor for the amyloid precursor protein (APP) that regulates intracellular trafficking and processing into amyloidogenic-beta peptides (A beta). Overexpression of SORLA in neurons reduces while inactivation of gene expression (as in knock-out mouse models) accelerates amyloidogenic processing and senile plaque formation. The current study aimed at identifying molecular pathways that control SORLA gene transcription in vivo and that may contribute to low levels of receptor expression in the brain of patients with AD. Using screening approaches in primary neurons, we identified brain-derived neurotrophic factor (BDNF) as a major inducer of Sorla that activates receptor gene transcription through the ERK (extracellular regulated kinase) pathway. In line with a physiological role as regulator of Sorla, expression of the receptor is significantly impaired in mouse models with genetic (Bdnf(-/-)) or disease-related loss of BDNF activity in the brain (Huntington's disease). Intriguingly, exogenous application of BDNF reduced A beta production in primary neurons and in the brain of wild-type mice in vivo, but not in animals genetically deficient for Sorla. These findings demonstrate that the beneficial effects ascribed to BDNF in APP metabolism act through induction of Sorla that encodes a negative regulator of neuronal APP processing.
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186
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Preservation of cortical sortilin protein levels in MCI and Alzheimer's disease. Neurosci Lett 2010; 471:129-33. [PMID: 20085800 DOI: 10.1016/j.neulet.2010.01.023] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2009] [Revised: 01/11/2010] [Accepted: 01/13/2010] [Indexed: 01/01/2023]
Abstract
The nerve growth factor (NGF) precursor protein proNGF is the predominant NGF moiety found in the human neocortex and exhibits pro-apoptotic properties when bound to the p75(NTR) neurotrophin receptor in the presence of sortilin, a Vps10p domain trafficking protein. Recently studies have shown that proNGF levels increase in the cortex of people who died with early stage Alzheimer's disease (AD) or with mild cognitive impairment (MCI), a putative prodromal AD stage. In contrast, cortical levels of the high-affinity, pro-survival NGF receptor TrkA are reduced in AD despite stable levels of p75(NTR). These data suggest a stoichiometric shift in proNGF and its receptors which favors proNGF binding of p75(NTR). Whether cortical levels of sortilin are altered during the progression of AD remains unknown. Therefore, we measured sortilin protein levels in postmortem superior frontal and superior temporal cortical tissues derived from Religious Orders Study subjects clinically diagnosed antemortem with no cognitive impairment (NCI), MCI or AD. No changes in frontal or temporal cortical sortilin protein levels occurred across the clinical groups. There was no association between sortilin levels and antemortem cognitive test scores. However, there was a positive association between temporal cortex sortilin levels and severity of neuropathology by Braak and NIA-Reagan diagnoses. The stability of cortical sortilin levels in the face of stable p75(NTR), increased proNGF, and reduced TrkA levels may favor pro-apoptotic proNGF:p75(NTR):sortilin trimeric interactions within the cortex during the earliest stages of AD. These findings are relevant to the development of NGF drug therapy for the treatment of dementia.
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187
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Yano H, Torkin R, Martin LA, Chao MV, Teng KK. Proneurotrophin-3 is a neuronal apoptotic ligand: evidence for retrograde-directed cell killing. J Neurosci 2009; 29:14790-802. [PMID: 19940174 PMCID: PMC2824605 DOI: 10.1523/jneurosci.2059-09.2009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 09/01/2009] [Accepted: 10/13/2009] [Indexed: 12/20/2022] Open
Abstract
Although mature neurotrophins are well described trophic factors that elicit retrograde survival signaling, the precursor forms of neurotrophins (i.e., proneurotrophins) can function as high-affinity apoptotic ligands for selected neural populations. An outstanding question is whether target-derived proneurotrophins might affect neuronal survival/death decisions through a retrograde transport mechanism. Since neurotrophin-3 (NT-3) is highly expressed in non-neural tissues that receive peripheral innervation, we investigated the localized actions of its precursor (proNT-3) on sympathetic neurons in the present study. Pharmacological inhibition of intracellular furin proteinase activity in 293T cells resulted in proNT-3 release instead of mature NT-3, whereas membrane depolarization in cerebellar granule neurons stimulated endogenous proNT-3 secretion, suggesting that proNT-3 is an inducible bona fide ligand in the nervous system. Our data also indicate that recombinant proNT-3 induced sympathetic neuron death that is p75(NTR)- and sortilin-dependent, with hallmark features of apoptosis including JNK (c-Jun N-terminal kinase) activation and nuclear fragmentation. Using compartmentalized culture systems that segregate neuronal cell bodies from axons, proNT-3, acting within the distal axon compartment, elicited sympathetic neuron death and overrode the survival-promoting actions of NGF. Together, these results raise the intriguing possibility that dysregulation of proneurotrophin processing/release by innervated targets can be deleterious to the neurons projecting to these sites.
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Affiliation(s)
- Hiroko Yano
- Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, New York 10016
| | - Risa Torkin
- Department of Medicine, Weill Cornell Medical College, New York, New York 10065, and
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
| | - Laura Andrés Martin
- Department of Medicine, Weill Cornell Medical College, New York, New York 10065, and
| | - Moses V. Chao
- Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, New York 10016
| | - Kenneth K. Teng
- Department of Medicine, Weill Cornell Medical College, New York, New York 10065, and
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Thiele CJ, Li Z, McKee AE. On Trk--the TrkB signal transduction pathway is an increasingly important target in cancer biology. Clin Cancer Res 2009; 15:5962-7. [PMID: 19755385 DOI: 10.1158/1078-0432.ccr-08-0651] [Citation(s) in RCA: 174] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
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.
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Affiliation(s)
- Carol J Thiele
- Cell and Molecular Biology Section, Pediatric Oncology Branch, Center for Cancer Research, CRC, NCI, Bethesda, Maryland 20892, USA.
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189
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Koharudin LMI, Furey W, Liu H, Liu YJ, Gronenborn AM. The phox domain of sorting nexin 5 lacks phosphatidylinositol 3-phosphate (PtdIns(3)P) specificity and preferentially binds to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). J Biol Chem 2009; 284:23697-707. [PMID: 19553671 PMCID: PMC2749144 DOI: 10.1074/jbc.m109.008995] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 06/08/2009] [Indexed: 11/06/2022] Open
Abstract
Subcellular retrograde transport of cargo receptors from endosomes to the trans-Golgi network is critically involved in a broad range of physiological and pathological processes and highly regulated by a genetically conserved heteropentameric complex, termed retromer. Among the retromer components identified in mammals, sorting nexin 5 and 1 (SNX5; SNX1) have recently been found to interact, possibly controlling the membrane binding specificity of the complex. To elucidate how the unique sequence features of the SNX5 phox domain (SNX5-PX) influence retrograde transport, we have determined the SNX5-PX structure by NMR and x-ray crystallography at 1.5 A resolution. Although the core fold of SNX5-PX resembles that of other known PX domains, we found novel structural features exclusive to SNX5-PX. It is most noteworthy that in SNX5-PX, a long helical hairpin is added to the core formed by a new alpha2'-helix and a much longer alpha3-helix. This results in a significantly altered overall shape of the protein. In addition, the unique double PXXP motif is tightly packed against the rest of the protein, rendering this part of the structure compact, occluding parts of the putative phosphatidylinositol (PtdIns) binding pocket. The PtdIns binding and specificity of SNX5-PX was evaluated by NMR titrations with eight different PtdIns and revealed that SNX5-PX preferentially and specifically binds to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)). The distinct structural and PtdIns binding characteristics of SNX5-PX impart specific properties on SNX5, influencing retromer-mediated regulation of retrograde trafficking of transmembrane cargo receptors.
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Affiliation(s)
| | - William Furey
- Pharmacology and Chemical Biology
- the Biocrystallography Laboratory, Veterans Affairs Medical Center, Pittsburgh, Pennsylvania 15240
| | | | - Yong-Jian Liu
- Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260 and
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190
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Saftig P, Klumperman J. Lysosome biogenesis and lysosomal membrane proteins: trafficking meets function. Nat Rev Mol Cell Biol 2009; 10:623-35. [PMID: 19672277 DOI: 10.1038/nrm2745] [Citation(s) in RCA: 1162] [Impact Index Per Article: 77.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lysosomes are the primary catabolic compartments of eukaryotic cells. They degrade extracellular material that has been internalized by endocytosis and intracellular components that have been sequestered by autophagy. In addition, specialized cells contain lysosome-related organelles that store and secrete proteins for cell-type-specific functions. The functioning of a healthy cell is dependent on the proper targeting of newly synthesized lysosomal proteins. Accumulating evidence suggests that there are multiple lysosomal delivery pathways that together allow the regulated and sequential deposition of lysosomal components. The importance of lysosomal trafficking pathways is emphasized by recent findings that reveal new roles for lysosomal membrane proteins in cellular physiology and in an increasing number of diseases that are characterized by defects in lysosome biogenesis.
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Affiliation(s)
- Paul Saftig
- Department of Biochemistry, Christian-Albrechts University, Kiel, Germany.
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191
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Hermey G. The Vps10p-domain receptor family. Cell Mol Life Sci 2009; 66:2677-89. [PMID: 19434368 PMCID: PMC11115710 DOI: 10.1007/s00018-009-0043-1] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 04/21/2009] [Accepted: 04/21/2009] [Indexed: 12/24/2022]
Abstract
The family of mammalian type-I transmembrane receptors containing a Vps10p domain contains five members, Sortilin, SorCS1, SorCS2, SorCS3, and SorLA. The common characteristic of these receptors is an N-terminal Vps10p domain, which either represents the only module of the luminal/extracellular moiety or is combined with additional domains. Family members play roles in protein transport and signal transduction. The individual receptors bind and internalize a variety of ligands, such as neuropeptides and trophic factors, and Sortilin and SorLA mediate trans-Golgi network-to-endosome sorting. Their prominent neuronal expression, several of the identified ligands, and recent results support the notion that members of this receptor family have important functions in neurogenesis, plasticity-related processes, and functional maintenance of the nervous system. For instance, it has been demonstrated that Sortilin partakes in the transduction of proapoptotic effects, and there is converging biochemical and genetic evidence that implies that SorLA is an Alzheimer's disease risk factor.
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Affiliation(s)
- Guido Hermey
- Institute of Molecular and Cellular Cognition, Zentrum für Molekulare Neurobiologie Hamburg, Hamburg, Germany.
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192
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Sequence and structural analysis of the Asp-box motif and Asp-box beta-propellers; a widespread propeller-type characteristic of the Vps10 domain family and several glycoside hydrolase families. BMC STRUCTURAL BIOLOGY 2009; 9:46. [PMID: 19594936 PMCID: PMC2716378 DOI: 10.1186/1472-6807-9-46] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Accepted: 07/13/2009] [Indexed: 11/25/2022]
Abstract
Background The Asp-box is a short sequence and structure motif that folds as a well-defined β-hairpin. It is present in different folds, but occurs most prominently as repeats in β-propellers. Asp-box β-propellers are known to be characteristically irregular and to occur in many medically important proteins, most of which are glycosidase enzymes, but they are otherwise not well characterized and are only rarely treated as a distinct β-propeller family. We have analyzed the sequence, structure, function and occurrence of the Asp-box and s-Asp-box -a related shorter variant, and provide a comprehensive classification and computational analysis of the Asp-box β-propeller family. Results We find that all conserved residues of the Asp-box support its structure, whereas the residues in variable positions are generally used for other purposes. The Asp-box clearly has a structural role in β-propellers and is highly unlikely to be involved in ligand binding. Sequence analysis of the Asp-box β-propeller family reveals it to be very widespread especially in bacteria and suggests a wide functional range. Disregarding the Asp-boxes, sequence conservation of the propeller blades is very low, but a distinct pattern of residues with specific properties have been identified. Interestingly, Asp-boxes are occasionally found very close to other propeller-associated repeats in extensive mixed-motif stretches, which strongly suggests the existence of a novel class of hybrid β-propellers. Structural analysis reveals that the top and bottom faces of Asp-box β-propellers have striking and consistently different loop properties; the bottom is structurally conserved whereas the top shows great structural variation. Interestingly, only the top face is used for functional purposes in known structures. A structural analysis of the 10-bladed β-propeller fold, which has so far only been observed in the Asp-box family, reveals that the inner strands of the blades are unusually far apart, which explains the surprisingly large diameter of the central tunnel of sortilin. Conclusion We have provided new insight into the structure and function of the Asp-box motif and of Asp-box β-propellers, and expect that the classification and analysis presented here will prove helpful in interpreting future data on Asp-box proteins in general and on Asp-box β-propellers in particular.
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Abstract
PURPOSE OF REVIEW Over the past few years, apolipoprotein E (ApoE) receptors, also known as LDL receptor-related proteins, have distinguished themselves as functionally diverse signaling receptors with pivotal roles not only in the vascular system but also in the nervous system and during development. RECENT FINDINGS The expanding roles of ApoE receptors for cellular signal transduction at the same time transcend and integrate their lipid transport roles into a larger biological and clinical context. ApoE receptors are essential for the development of the nervous system, the regulation of synaptic plasticity, neuroprotection and the innervation of the muscle. They also regulate the metabolism of the amyloid precursor protein on multiple levels, implicating them in the pathogenesis of Alzheimer's disease. SUMMARY ApoE, a common ligand for all members of the evolutionarily ancient LDL receptor gene family, is the major genetic modifier of the age of onset of Alzheimer's disease. The underlying molecular mechanisms remain shrouded in mystery, but the numerous critical functions of ApoE receptors within and outside the nervous system that have recently emerged make it likely that these multifunctional signal modulators participate in Alzheimer's disease pathogenesis. This review attempts to summarize the most recent and relevant findings in this area.
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Affiliation(s)
- Joachim Herz
- Department of Molecular Genetics, UT Southwestern, Dallas, Texas 75390-9046, USA.
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