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Muccini AJ, Gustafson MA, Fromme JC. Structural basis for activation of Arf1 at the Golgi complex. Cell Rep 2022; 40:111282. [PMID: 36044848 PMCID: PMC9469209 DOI: 10.1016/j.celrep.2022.111282] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 07/11/2022] [Accepted: 08/05/2022] [Indexed: 11/29/2022] Open
Abstract
The Golgi complex is the central sorting station of the eukaryotic secretory pathway. Traffic through the Golgi requires activation of Arf guanosine triphosphatases that orchestrate cargo sorting and vesicle formation by recruiting an array of effector proteins. Arf activation and Golgi membrane association is controlled by large guanine nucleotide exchange factors (GEFs) possessing multiple conserved regulatory domains. Here we present cryoelectron microscopy (cryoEM) structures of full-length Gea2, the yeast paralog of the human Arf-GEF GBF1, that reveal the organization of these regulatory domains and explain how Gea2 binds to the Golgi membrane surface. We find that the GEF domain adopts two different conformations compatible with different stages of the Arf activation reaction. The structure of a Gea2-Arf1 activation intermediate suggests that the movement of the GEF domain primes Arf1 for membrane insertion upon guanosine triphosphate binding. We propose that conformational switching of Gea2 during the nucleotide exchange reaction promotes membrane insertion of Arf1. Arf1 is a GTPase that regulates Golgi trafficking by recruiting many effector proteins. Muccini et al. report cryoEM structures of the Arf1 activator Gea2, capturing Gea2 in multiple conformational states including a Gea2-Arf1 activation intermediate. The structures help explain how Gea2 activates Arf1 on the Golgi membrane surface.
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Affiliation(s)
- Arnold J Muccini
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Margaret A Gustafson
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - J Christopher Fromme
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA.
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2
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Small GTPase FoSec4-Mediated Protein Secretion Is Important for Polarized Growth, Reproduction and Pathogenicity in the Banana Fusarium Wilt Fungus Fusarium odoratissimum. J Fungi (Basel) 2022; 8:jof8080880. [PMID: 36012867 PMCID: PMC9410047 DOI: 10.3390/jof8080880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 08/15/2022] [Accepted: 08/17/2022] [Indexed: 11/18/2022] Open
Abstract
Apical secretion at hyphal tips is important for the growth and development of filamentous fungi. In this study, we analyzed the role of the Rab GTPases FoSec4 involved in the secretion of the banana wilt fungal pathogen Fusarium odoratissimum. We found that the deletion of FoSEC4 affects the activity of extracellular hydrolases and protein secretion, indicating that FoSec4 plays an important role in the regulation of protein secretion in F. odoratissimum. As a typical Rab GTPase, Sec4 participates in the Rab cycle through the conversion between the active GTP-bound state and the inactive GDP-bound state, which is regulated by guanine nucleate exchange factors (GEFs) and GTPase-activating proteins (GAPs). We further found that FoSec2 can interact with dominant-negative FoSec4 (GDP-bound and nucleotide-free form, FoSec4DN), and that FoGyp5 can interact with dominant active FoSec4 (GTP-bound and constitutively active form, FoSec4CA). We evaluated the biofunctions of FoSec4, FoSec2 and FoGyp5, and found that FoSec4 is involved in the regulation of vegetative growth, reproduction, pathogenicity and the environmental stress response of F. odoratissimum, and that FocSec2 and FoGyp5 perform biofunctions consistent with FoSec4, indicating that FoSec2 and FoGyp5 may work as the GEF and the GAP, respectively, of FoSec4 in F. odoratissimum. We further found that the amino-terminal region and Sec2 domain are essential for the biological functions of FoSec2, while the carboxyl-terminal region and Tre-2/Bub2/Cdc16 (TBC) domain are essential for the biological functions of FoGyp5. In addition, FoSec4 mainly accumulated at the hyphal tips and partially colocalized with Spitzenkörper; however, FoGyp5 accumulated at the periphery of Spitzenkörper, suggesting that FoGyp5 may recognize and inactivate FoSec4 at a specific location in hyphal tips.
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3
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Neuman SD, Lee AR, Selegue JE, Cavanagh AT, Bashirullah A. A novel function for Rab1 and Rab11 during secretory granule maturation. J Cell Sci 2021; 134:jcs259037. [PMID: 34342349 PMCID: PMC8353522 DOI: 10.1242/jcs.259037] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 06/29/2021] [Indexed: 01/15/2023] Open
Abstract
Regulated exocytosis is an essential process whereby specific cargo proteins are secreted in a stimulus-dependent manner. Cargo-containing secretory granules are synthesized in the trans-Golgi network (TGN); after budding from the TGN, granules undergo modifications, including an increase in size. These changes occur during a poorly understood process called secretory granule maturation. Here, we leverage the Drosophila larval salivary glands as a model to characterize a novel role for Rab GTPases during granule maturation. We find that secretory granules increase in size ∼300-fold between biogenesis and release, and loss of Rab1 or Rab11 reduces granule size. Surprisingly, we find that Rab1 and Rab11 localize to secretory granule membranes. Rab11 associates with granule membranes throughout maturation, and Rab11 recruits Rab1. In turn, Rab1 associates specifically with immature granules and drives granule growth. In addition to roles in granule growth, both Rab1 and Rab11 appear to have additional functions during exocytosis; Rab11 function is necessary for exocytosis, while the presence of Rab1 on immature granules may prevent precocious exocytosis. Overall, these results highlight a new role for Rab GTPases in secretory granule maturation.
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Affiliation(s)
| | | | | | | | - Arash Bashirullah
- Division of Pharmaceutical Sciences, University of Wisconsin-Madison, Madison, WI 53705-2222, USA
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4
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LRRK2 mediated Rab8a phosphorylation promotes lipid storage. Lipids Health Dis 2018; 17:34. [PMID: 29482628 PMCID: PMC5828482 DOI: 10.1186/s12944-018-0684-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Accepted: 02/19/2018] [Indexed: 01/07/2023] Open
Abstract
Background Several mutations in leucine rich repeat kinase 2 (LRRK2) gene have been associated with pathogenesis of Parkinson’s disease (PD), a neurodegenerative disorder marked by resting tremors, and rigidity, leading to Postural instability. It has been revealed that mutations that lead to an increase of kinase activity of LRRK2 protein are significantly associated with PD pathogenesis. Recent studies have shown that some Rab GTPases, especially Rab8, serve as substrates of LRRK2 and undergo phosphorylation in its switch II domain upon interaction. Current study was performed in order to find out the effects of the phosphorylation of Rab8 and its mutants on lipid metabolism and lipid droplets growth. Methods The phosphorylation status of Rab8a was checked by phos-tag gel. Point mutant construct were generated to investigate the function of Rab8a. 3T3L1 cells were transfected with indicated plasmids and the lipid droplets were stained with Bodipy. Fluorescent microscopy experiments were performed to examine the sizes of lipid droplets. The interactions between Rab8a and Optineurin were determined by immunoprecipitation and western blot. Results Our assays demonstrated that Rab8a was phosphorylated by mutated LRRK2 that exhibits high kinase activity. Phosphorylation of Rab8a on amino acid residue T72 promoted the formation of large lipid droplets. T72D mutant of Rab8a had higher activity to promote the formation of large lipid droplets compared with wild type Rab8a, with increase in average diameter of lipid droplets from 2.10 μm to 2.46 μm. Moreover, phosphorylation of Rab8a weakened the interaction with its effector Optineurin. Conclusions Y1699C mutated LRRK2 was able to phosphorylate Rab8a and phosphorylation of Rab8a on site 72 plays important role in the fusion and enlargement of lipid droplets. Taken together, our study suggests an indirect relationship between enhanced lipid storage capacity and PD pathogenesis.
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Court H, Ahearn IM, Amoyel M, Bach EA, Philips MR. Regulation of NOTCH signaling by RAB7 and RAB8 requires carboxyl methylation by ICMT. J Cell Biol 2017; 216:4165-4182. [PMID: 29051265 PMCID: PMC5716267 DOI: 10.1083/jcb.201701053] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Revised: 08/04/2017] [Accepted: 09/12/2017] [Indexed: 01/15/2023] Open
Abstract
Isoprenylcysteine carboxyl methyltransferase (ICMT) methylesterifies C-terminal prenylcysteine residues of CaaX proteins and some RAB GTPases. Deficiency of either ICMT or NOTCH1 accelerates pancreatic neoplasia in Pdx1-Cre;LSL-KrasG12D mice, suggesting that ICMT is required for NOTCH signaling. We used Drosophila melanogaster wing vein and scutellar bristle development to screen Rab proteins predicted to be substrates for ICMT (ste14 in flies). We identified Rab7 and Rab8 as ICMT substrates that when silenced phenocopy ste14 deficiency. ICMT, RAB7, and RAB8 were all required for efficient NOTCH1 signaling in mammalian cells. Overexpression of RAB8 rescued NOTCH activation after ICMT knockdown both in U2OS cells expressing NOTCH1 and in fly wing vein development. ICMT deficiency induced mislocalization of GFP-RAB7 and GFP-RAB8 from endomembrane to cytosol, enhanced binding to RABGDI, and decreased GTP loading of RAB7 and RAB8. Deficiency of ICMT, RAB7, or RAB8 led to mislocalization and diminished processing of NOTCH1-GFP. Thus, NOTCH signaling requires ICMT in part because it requires methylated RAB7 and RAB8.
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Affiliation(s)
- Helen Court
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY
| | - Ian M Ahearn
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY
| | - Marc Amoyel
- School of Cellular and Molecular Medicine, University of Bristol, Bristol, England, UK
| | - Erika A Bach
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY
| | - Mark R Philips
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY
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Correia MS, Moreiras H, Pereira FJC, Neto MV, Festas TC, Tarafder AK, Ramalho JS, Seabra MC, Barral DC. Melanin Transferred to Keratinocytes Resides in Nondegradative Endocytic Compartments. J Invest Dermatol 2017; 138:637-646. [PMID: 29074272 DOI: 10.1016/j.jid.2017.09.042] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Revised: 09/11/2017] [Accepted: 09/11/2017] [Indexed: 01/08/2023]
Abstract
Melanin transfer from melanocytes to keratinocytes and subsequent accumulation in the supranuclear region is a critical process in skin pigmentation and protection against UVR. We have previously proposed that the main mode of transfer between melanocytes and keratinocytes is through exo/endocytosis of the melanosome core, termed melanocore. In this study, we developed an in vitro uptake assay using melanocores secreted by melanocytes. We show that the uptake of melanocores, but not melanosomes, by keratinocytes is protease-activated receptor-2-dependent. Furthermore, we found that the silencing of the early endocytic regulator Rab5b, but not the late endocytic regulators Rab7a or Rab9a, significantly impairs melanocore uptake by keratinocytes. After uptake, we observed that melanin accumulates in compartments that are positive for both early and late endocytic markers. We found that melanin does not localize to either highly degradative or acidic organelles, as assessed by LysoTracker and DQ-BSA staining, despite the abundance of these types of organelles within keratinocytes. Therefore, we propose that melanocore uptake leads to storage of melanin within keratinocytes in hybrid endocytic compartments that are not highly acidic or degradative. By avoiding lysosomal degradation, these specialized endosomes may allow melanin to persist within keratinocytes for long periods.
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Affiliation(s)
- Maria S Correia
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Hugo Moreiras
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Francisco J C Pereira
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Matilde V Neto
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Tiago C Festas
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Abul K Tarafder
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - José S Ramalho
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal
| | - Miguel C Seabra
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal.
| | - Duarte C Barral
- CEDOC, Chronic Diseases Research Centre, NOVA Medical School
- Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal.
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7
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Pfeffer SR. Rab GTPases: master regulators that establish the secretory and endocytic pathways. Mol Biol Cell 2017; 28:712-715. [PMID: 28292916 PMCID: PMC5349778 DOI: 10.1091/mbc.e16-10-0737] [Citation(s) in RCA: 200] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 01/11/2017] [Accepted: 01/12/2017] [Indexed: 11/22/2022] Open
Abstract
Several of the most important discoveries in the field of membrane traffic have come from studies of Rab GTPases by Marino Zerial and Peter Novick and their colleagues. Zerial was the first to discover that Rab GTPases represent identity markers for different membrane-bound compartments, and each Rab organizes a collection of specific effectors into function-specifying membrane microdomains to carry out receptor trafficking. Novick discovered that the order (and thus polarity) of Rab GTPases along the secretory and endocytic pathways are established by their specific, cognate guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), which partner with one Rab to regulate the subsequent- and prior-acting Rabs. Such so-called Rab cascades have evolved to establish domains that contain unique Rab proteins and their cognate effectors, which drive all steps of membrane trafficking. These findings deserve much broader recognition by the biomedical research community and are highlighted here, along with open questions that require serious attention for full understanding of the molecular basis of Rab GTPase-regulated membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Suzanne R Pfeffer
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307
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8
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Abstract
Rab GTPases, the highly conserved members of Ras GTPase superfamily are central players in the vesicular trafficking. They are critically involved in intracellular trafficking pathway, beginning from formation of vesicles on donor membranes, defining trafficking specificity to facilitating vesicle docking on target membranes. Given the dynamic roles of Rabs during different stages of vesicular trafficking, mechanisms for their spatial and temporal regulation are crucial for normal cellular function. Regulation of Rab GTPase activity, localization and function has always been focused in and around the association of GDP dissociation inhibitor (GDI), Guanine nucleotide Exchange Factor (GEFs) and GTPase accelerating protein (GAP) to Rabs. However, several recent studies have highlighted the importance of different post-translational modifications in regulation of Rab activation and function. This review provides a summary of various post translational modifications (PTMs) and their significance to regulate localization and function of different Rabs.
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Affiliation(s)
- Swapnil Rohidas Shinde
- a Laboratory of Cell Death & Cell Survival , Centre for DNA Fingerprinting and Diagnostics (CDFD) , Nampally, Hyderabad , India.,b Graduate Studies , Manipal University , Manipal , India
| | - Subbareddy Maddika
- a Laboratory of Cell Death & Cell Survival , Centre for DNA Fingerprinting and Diagnostics (CDFD) , Nampally, Hyderabad , India
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9
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Shinde SR, Maddika S. A modification switch on a molecular switch: Phosphoregulation of Rab7 during endosome maturation. Small GTPases 2016; 7:164-7. [PMID: 27070490 DOI: 10.1080/21541248.2016.1175539] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Rab GTPases, the highly conserved members of Ras GTPase superfamily are the pivotal regulators of vesicle-mediated trafficking. Rab GTPases, each with a specific subcellular localization, exert tremendous control over various aspects of vesicular transport, identity and dynamics. Several lines of research have established that GDI, GEFs and GAPs are the critical players to orchestrate Rab GTPase activity and function. The importance of post translational modifications in Rab GTPase functional regulation is poorly or not yet been addressed except for prenylation. Our recent study has revealed a novel dephosphorylation dependent regulatory mechanism for Rab7 activity and function. We have shown the importance of PTEN mediated dephosphorylation of Rab7 on highly conserved S72 and Y183 residues, which is essential for its GDI mediated membrane targeting and further activation by GEF. In conclusion, our study highlighted the importance of a phosphorylation/dephosphorylation switch in controlling timely Rab7 localization and activity on endosomes.
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Affiliation(s)
- Swapnil Rohidas Shinde
- a Laboratory of Cell Death & Cell Survival, Centre for DNA Fingerprinting and Diagnostics (CDFD), Nampally , Hyderabad , India.,b Graduate Studies, Manipal University , Manipal , India
| | - Subbareddy Maddika
- a Laboratory of Cell Death & Cell Survival, Centre for DNA Fingerprinting and Diagnostics (CDFD), Nampally , Hyderabad , India
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10
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Abstract
Rab GTPases control intracellular membrane traffic by recruiting specific effector proteins to restricted membranes in a GTP-dependent manner. In this Cell Science at a Glance and the accompanying poster, we highlight the regulation of Rab GTPases by proteins that control their membrane association and activation state, and provide an overview of the cellular processes that are regulated by Rab GTPases and their effectors, including protein sorting, vesicle motility and vesicle tethering. We also discuss the physiological importance of Rab GTPases and provide examples of diseases caused by their dysfunctions.
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Affiliation(s)
- Yan Zhen
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, Oslo N-0379, Norway Department for Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo N-0379, Norway
| | - Harald Stenmark
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Montebello, Oslo N-0379, Norway Department for Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Montebello, Oslo N-0379, Norway
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11
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Abstract
Rab proteins represent the largest branch of the Ras-like small GTPase superfamily and there are 66 Rab genes in the human genome. They alternate between GTP- and GDP-bound states, which are facilitated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), and function as molecular switches in regulation of intracellular membrane trafficking in all eukaryotic cells. Each Rab targets to an organelle and specify a transport step along exocytic, endocytic, and recycling pathways as well as the crosstalk between these pathways. Through interactions with multiple effectors temporally, a Rab can control membrane budding and formation of transport vesicles, vesicle movement along cytoskeleton, and membrane fusion at the target compartment. The large number of Rab proteins reflects the complexity of the intracellular transport system, which is essential for the localization and function of membrane and secretory proteins such as hormones, growth factors, and their membrane receptors. As such, Rab proteins have emerged as important regulators for signal transduction, cell growth, and differentiation. Altered Rab expression and/or activity have been implicated in diseases ranging from neurological disorders, diabetes to cancer.
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Affiliation(s)
- Guangpu Li
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, 975 NE 10 Street, BRC 417, Oklahoma City, OK, 73104, USA,
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12
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Abstract
Rab GTPases are master regulators of eukaryotic endomembrane systems, particularly functioning in membrane tethering to confer the directionality of intracellular membrane trafficking. However, how exactly Rab GTPases themselves act upon membrane tethering processes has remained enigmatic. Here, we thoroughly tested seven purified Rab GTPases in human, which localize at the various representative organelles, for their capacity to support membrane tethering in vitro. Strikingly, we found that three specific human Rabs (endoplasmic reticulum/Golgi Rab2a, early endosomal Rab5a, and late endosomal/lysosomal Rab7a) strongly accelerated membrane aggregation of synthetic liposomes even in the absence of any additional components, such as classical tethers, tethering factors, and Rab effectors. This Rab-induced membrane aggregation was a reversible membrane tethering reaction that can be strictly controlled by the membrane recruitment of Rab proteins on both apposing membranes. Thus, our current reconstitution studies establish that membrane-anchored human Rab GTPases are an essential tethering factor to directly mediate membrane tethering events.
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Affiliation(s)
- Naoki Tamura
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Joji Mima
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
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13
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Jenkins NC, Kalra RR, Dubuc A, Sivakumar W, Pedone CA, Wu X, Taylor MD, Fults DW. Genetic drivers of metastatic dissemination in sonic hedgehog medulloblastoma. Acta Neuropathol Commun 2014; 2:85. [PMID: 25059231 PMCID: PMC4149244 DOI: 10.1186/s40478-014-0085-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 07/09/2014] [Indexed: 01/31/2023] Open
Abstract
Leptomeningeal dissemination (LMD), the metastatic spread of tumor cells via the cerebrospinal fluid to the brain and spinal cord, is an ominous prognostic sign for patients with the pediatric brain tumor medulloblastoma. The need to reduce the risk of LMD has driven the development of aggressive treatment regimens, which cause disabling neurotoxic side effects in long-term survivors. Transposon-mediated mutagenesis studies in mice have revealed numerous candidate metastasis genes. Understanding how these genes drive LMD will require functional assessment using in vivo and cell culture models of medulloblastoma. We analyzed two genes that were sites of frequent transposon insertion and highly expressed in human medulloblastomas: Arnt (aryl hydrocarbon receptor nuclear translocator) and Gdi2 (GDP dissociation inhibitor 2). Here we show that ectopic expression of Arnt and Gdi2 promoted LMD in mice bearing Sonic hedgehog (Shh)-induced medulloblastomas. We overexpressed Arnt and Gdi2 in a human medulloblastoma cell line (DAOY) and an immortalized, nontransformed cell line derived from mouse granule neuron precursors (SHH-NPD) and quantified migration, invasiveness, and anchorage-independent growth, cell traits that are associated with metastatic competence in carcinomas. In SHH-NPD cells. Arnt and Gdi2 stimulated all three traits. In DAOY cells, Arnt had the same effects, but Gdi2 stimulated invasiveness only. These results support a mechanism whereby Arnt and Gdi2 cause cells to detach from the primary tumor mass by increasing cell motility and invasiveness. By conferring to tumor cells the ability to proliferate without surface attachment, Arnt and Gdi2 favor the formation of stable colonies of cells capable of seeding the leptomeninges.
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14
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Kirsten ML, Baron RA, Seabra MC, Ces O. Rab1a and Rab5a preferentially bind to binary lipid compositions with higher stored curvature elastic energy. Mol Membr Biol 2013; 30:303-14. [PMID: 23815289 DOI: 10.3109/09687688.2013.818725] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Rab proteins are a large family of GTP-binding proteins that regulate cellular membrane traffic and organelle identity. Rab proteins cycle between association with membranes and binding to RabGDI. Bound on membranes, each Rab has a very specific cellular location and it is this remarkable degree of specificity with which Rab GTPases recognize distinct subsets of intracellular membranes that forms the basis of their ability to act as key cellular regulators, determining the recruitment of downstream effectors to the correct membrane at the correct time. The molecular mechanisms controlling Rab localization remain poorly understood. Here, we present a fluorescence-based assay to investigate Rab GTPase membrane extraction and delivery by RabGDI. Using EGFP-Rab fusion proteins the amount of Rab:GDI complex obtained by GDI extraction of Rab proteins from HEK293 membranes could be determined, enabling control of complex concentration. Subsequent partitioning of the Rab GTPases into vesicles made up of artificial binary lipid mixtures showed for the first time, that the composition of the target membrane plays a key role in the localization of Rab proteins by sensing the stored curvature elastic energy in the membrane.
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Affiliation(s)
- Marie L Kirsten
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK
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15
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Cabrera M, Ungermann C. Guanine nucleotide exchange factors (GEFs) have a critical but not exclusive role in organelle localization of Rab GTPases. J Biol Chem 2013; 288:28704-12. [PMID: 23979137 DOI: 10.1074/jbc.m113.488213] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Membrane fusion at eukaryotic organelles is initiated by Rab GTPases and tethering factors. Rabs in their GDP-bound form are kept soluble in the cytoplasm by the GDP dissociation inhibitor (GDI) chaperone. Guanine nucleotide exchange factors (GEFs) are found at organelles and are critical for Rab function. Here, we surveyed the overall role of GEFs in Rab localization. We show that GEFs, but none of the proposed GDI displacement factors, are essential for the correct membrane localization of yeast Rabs. In the absence of the GEF, Rabs lost their primary localization to the target organelle. Several Rabs, such as vacuolar Ypt7, were found at the endoplasmic reticulum and thus were still membrane-bound. Surprisingly, a Ypt7 mutant that undergoes facilitated nucleotide exchange localized to vacuoles independently of its GEF Mon1-Ccz1 and rescued vacuole morphology. In contrast, wild-type Ypt7 required its GEF for localization and to counteract the extraction by GDI. Our data agree with the emerging model that GEFs are critical for Rab localization but raise the possibility that additional factors can contribute to this process.
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Affiliation(s)
- Margarita Cabrera
- From the Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
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16
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Rab27a and melanosomes: a model to investigate the membrane targeting of Rabs. Biochem Soc Trans 2013; 40:1383-8. [PMID: 23176485 DOI: 10.1042/bst20120200] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Rab proteins constitute the largest family within the Ras superfamily of small GTPases (>60 in mammals) and are essential regulators of transport between intracellular organelles. Key to this activity is their targeting to specific compartments within the cell. However, although great strides have been made over the last 25 years in assigning functions to individual Rabs and identifying their downstream effectors, the mechanism(s) regulating their targeting to specific subcellular membranes remains less well understood. In the present paper, we review the evidence supporting the proposed mechanisms of Rab targeting and highlight insights into this process provided by studies of Rab27a.
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Abstract
Rab GTPases are master regulators of membrane traffic. By binding to distinct sets of effector proteins, Rabs catalyse the formation of function-specifying membrane microdomains. They are delivered to membranes by a protein named GDI (guanine-nucleotide-dissociation inhibitor) and are stabilized there after nucleotide exchange by effector binding. In the present mini-review, I discuss what we know about how Rab GTPases are delivered to the correct membrane-bound compartments and how Rab GTPase cascades order Rabs within the secretory and endocytic pathways. Finally, I describe how Rab cascades may establish the distinct compartments of the Golgi complex to permit ordered processing, sorting and secretion of secretory cargoes.
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18
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Pfeffer SR. Rab GTPase regulation of membrane identity. Curr Opin Cell Biol 2013; 25:414-9. [PMID: 23639309 DOI: 10.1016/j.ceb.2013.04.002] [Citation(s) in RCA: 263] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 03/25/2013] [Accepted: 04/05/2013] [Indexed: 11/15/2022]
Abstract
A fundamental question in cell biology is how cells determine membrane compartment identity and the directionality with which cargoes pass through the secretory and endocytic pathways. The discovery of so-called 'Rab cascades' provides a satisfying molecular mechanism that helps to resolve this paradox. One Rab GTPase has the ability to template the localization of the subsequent acting Rab GTPase along a given transport pathway. Thus, in addition to determining compartment identity and functionality, Rab GTPases are likely able to order the events of membrane trafficking. This review will highlight recent advances in our understanding of Rabs and Rab cascades.
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Affiliation(s)
- Suzanne R Pfeffer
- Department of Biochemistry, Stanford University School of Medicine, 279 Campus Drive B400, Stanford, CA 94305-5307, USA.
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Tsvetanova NG. The secretory pathway in control of endoplasmic reticulum homeostasis. Small GTPases 2012; 4:28-33. [PMID: 23235440 DOI: 10.4161/sgtp.22599] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In eukaryotic cells, proteins and membranes are transported between successive compartments by vesicle trafficking. Since precise protein localization is crucial for a range of cellular functions, it is not surprising that vesicle trafficking plays a role in many processes, including cell division, signaling, development, and even gene expression. We recently found evidence that the yeast secretory pathway directly regulates the dynamics of a key cell survival process, the unfolded protein response (UPR). UPR activation requires the processing of the transcription factor encoding RNA HAC1. We showed that the small yeast GTPase Ypt1, which regulates endoplasmic reticulum-to-Golgi trafficking, associates with and controls the RNA stability of unspliced HAC1 under normal growth conditions. Other small GTPases of the Ypt family also interacted with the unprocessed RNA. Here we speculate about the possible mechanism behind this novel secretory pathway-dependent regulation of endoplasmic reticulum homeostasis.
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Affiliation(s)
- Nikoleta G Tsvetanova
- Department of Psychiatry, University of California at San Francisco, San Francisco, CA, USA.
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Abstract
Despite over two decades of research, the mechanism of Rab targeting to specific intracellular membranes is still not completely understood. Present evidence suggests that the original hypothesis that the message for targeting resides solely in the hypervariable C-terminus is incorrect, and a second mechanism involving a GDF [GDI (guanine-nucleotide-dissociation inhibitor) displacement factor] to disrupt stable Rab–GDI complexes has only been shown to apply in one case, despite the need for targeting over 60 human Rab proteins. Evidence for the involvement of Rab–effector interactions has only been presented for a few cases or in a very specific context. There is mounting evidence that GEFs (guanine-nucleotide-exchange factors) are essential for membrane targeting, although contributions from additional factors are likely to be of importance, at least in specific cases.
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Posttranslational modifications of Rab GTPases help their insertion into membranes. Proc Natl Acad Sci U S A 2012; 109:5555-6. [PMID: 22451945 DOI: 10.1073/pnas.1202494109] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Posttranslational modifications of Rab proteins cause effective displacement of GDP dissociation inhibitor. Proc Natl Acad Sci U S A 2012; 109:5621-6. [PMID: 22411835 DOI: 10.1073/pnas.1121161109] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Intracellular vesicular trafficking is regulated by approximately 60 members of the Rab subfamily of small Ras-like GDP/GTP binding proteins. Rab proteins cycle between inactive and active states as well as between cytosolic and membrane bound forms. Membrane extraction/delivery and cytosolic distribution of Rabs is mediated by interaction with the protein GDP dissociation inhibitor (GDI) that binds to prenylated inactive (GDP-bound) Rab proteins. Because the Rab:GDP:GDI complex is of high affinity, the question arises of how GDI can be displaced efficiently from Rab protein in order to allow the necessary recruitment of the Rab to its specific target membrane. While there is strong evidence that DrrA, as a bacterially encoded GDP/GTP exchange factor, contributes to this event, we show here that posttranslational modifications of Rabs can also modulate the affinity for GDI and thus cause effective displacement of GDI from Rab:GDI complexes. These activities have been found associated with the phosphocholination and adenylylation activities of the enzymes AnkX and DrrA/SidM, respectively, from the pathogenic bacterium Legionella pneumophila. Both modifications occur after spontaneous dissociation of Rab:GDI complexes within their natural equilibrium. Therefore, the effective GDI displacement that is observed is caused by inhibition of reformation of Rab:GDI complexes. Interestingly, in contrast to adenylylation by DrrA, AnkX can covalently modify inactive Rabs with high catalytic efficiency even when GDP is bound to the GTPase and hence can inhibit binding of GDI to Rab:GDP complexes. We therefore speculate that human cells could employ similar mechanisms in the absence of infection to effectively displace Rabs from GDI.
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Lachance V, Cartier A, Génier S, Munger S, Germain P, Labrecque P, Parent JL. Regulation of β2-adrenergic receptor maturation and anterograde trafficking by an interaction with Rab geranylgeranyltransferase: modulation of Rab geranylgeranylation by the receptor. J Biol Chem 2011; 286:40802-13. [PMID: 21990357 DOI: 10.1074/jbc.m111.267815] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Previous reports by us and others demonstrated that G protein-coupled receptors interact functionally with Rab GTPases. Here, we show that the β(2)-adrenergic receptor (β(2)AR) interacts with the Rab geranylgeranyltransferase α-subunit (RGGTA). Confocal microscopy showed that β(2)AR co-localizes with RGGTA in intracellular compartments and at the plasma membrane. Site-directed mutagenesis revealed that RGGTA binds to the L(339)L(340) motif in the β(2)AR C terminus known to be involved in the transport of the receptor from the endoplasmic reticulum to the cell surface. Modulation of the cellular levels of RGGTA protein by overexpression or siRNA-mediated knockdown of the endogenous protein demonstrated that RGGTA has a positive role in the maturation and anterograde trafficking of the β(2)AR, which requires the interaction of RGGTA with the β(2)AR L(339)L(340) motif. Furthermore, the β(2)AR modulates the geranylgeranylation of Rab6a, Rab8a, and Rab11a, but not of other Rab proteins tested in this study. Regulation of Rab geranylgeranylation by the β(2)AR was dependent on the RGGTA-interacting L(339)L(340) motif. Interestingly, a RGGTA-Y107F mutant was unable to regulate Rab geranylgeranylation but still promoted β(2)AR maturation, suggesting that RGGTA may have functions independent of Rab geranylgeranylation. We demonstrate for the first time an interaction between a transmembrane receptor and RGGTA which regulates the maturation and anterograde transport of the receptor, as well as geranylgeranylation of Rab GTPases.
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Affiliation(s)
- Véronik Lachance
- Service de Rhumatologie, Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, the Centre de Recherche Clinique Étienne-Le Bel, and the Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4
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Wu YW, Oesterlin LK, Tan KT, Waldmann H, Alexandrov K, Goody RS. Membrane targeting mechanism of Rab GTPases elucidated by semisynthetic protein probes. Nat Chem Biol 2010; 6:534-40. [PMID: 20512138 DOI: 10.1038/nchembio.386] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Accepted: 05/30/2010] [Indexed: 12/31/2022]
Abstract
Post-translationally isoprenylated proteins represent major hubs in most membrane-connected signaling networks. GDP dissociation inhibitors (GDIs) are molecular chaperones that shuttle geranylgeranylated GTPases between membranes and the cytosol. Despite numerous studies, the mechanism of targeted membrane delivery of GTPases remains unknown. Here we have combined chemical synthesis and expressed protein ligation to generate fluorescent lipidated RabGTPase-based sensor molecules. Using these protein probes, we have demonstrated that RabGDI and the related Rab escort protein REP show a three-order-of-magnitude greater affinity for GDP-bound Rab GTPase than for the GTP-bound state. Combined with a relatively high dissociation rate of the Rab-GDI complex, this would enable guanine nucleotide exchange factors (GEFs) to efficiently dissociate the complex and promote membrane attachment of the GTPase. The findings suggest strongly that GEFs are necessary and sufficient for membrane targeting of GTPases and that the previously proposed GDI displacement factors (GDFs) are not thermodynamically required for this process.
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Affiliation(s)
- Yao-Wen Wu
- Department of Physical Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
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Bahk JD, Bang WY, Heo JB. Plant PRA plays an important role in intracellular vesicular trafficking between compartments as GDF. PLANT SIGNALING & BEHAVIOR 2009; 4:1094-1095. [PMID: 20009555 PMCID: PMC2819524 DOI: 10.4161/psb.4.11.9828] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Accepted: 08/17/2009] [Indexed: 05/28/2023]
Abstract
Rab GTPases like Ras-related monomeric GTPases are well known to regulate intracellular vesicle trafficking by cycling between membrane-bound and cytosolic states. The functions of these proteins are controlled by upstream regulators and downstream effectors. Ypt/Rabs transmit signals to downstream effectors in a GTP-dependent manner. GDP-bound Rab proteins are extracted from their target membrane by cytosolic proteins known as GDP dissociation inhibitors (GDIs), and the Rab GTPase is recruited to the membrane compartment following dissociation from the GDI by GDI displacement factor (GDF). Now, we're going to discuss the role of plant PRA concerted with Rab and GDI proteins by recycling Rab between membrane and cytosol for intracellular trafficking of cargo proteins.
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Affiliation(s)
- Jeong Dong Bahk
- Division of Applied Life Science (BK21-EBNCRC), Graduate School of Gyeongsang National University, Jinju, Korea.
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Minimal membrane docking requirements revealed by reconstitution of Rab GTPase-dependent membrane fusion from purified components. Proc Natl Acad Sci U S A 2009; 106:17626-33. [PMID: 19826089 DOI: 10.1073/pnas.0903801106] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Rab GTPases and their effectors mediate docking, the initial contact of intracellular membranes preceding bilayer fusion. However, it has been unclear whether Rab proteins and effectors are sufficient for intermembrane interactions. We have recently reported reconstituted membrane fusion that requires yeast vacuolar SNAREs, lipids, and the homotypic fusion and vacuole protein sorting (HOPS)/class C Vps complex, an effector and guanine nucleotide exchange factor for the yeast vacuolar Rab GTPase Ypt7p. We now report reconstitution of lysis-free membrane fusion that requires purified GTP-bound Ypt7p, HOPS complex, vacuolar SNAREs, ATP hydrolysis, and the SNARE disassembly catalysts Sec17p and Sec18p. We use this reconstituted system to show that SNAREs and Sec17p/Sec18p, and Ypt7p and the HOPS complex, are required for stable intermembrane interactions and that the three vacuolar Q-SNAREs are sufficient for these interactions.
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Rab GTPases as coordinators of vesicle traffic. Nat Rev Mol Cell Biol 2009. [DOI: 10.1038/nrm2728 and 5410=5410-- pmza] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Stenmark H. Rab GTPases as coordinators of vesicle traffic. Nat Rev Mol Cell Biol 2009. [DOI: 10.1038/nrm2728 and 6285=8708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Stenmark H. Rab GTPases as coordinators of vesicle traffic. Nat Rev Mol Cell Biol 2009. [DOI: 10.1038/nrm2728 order by 1-- gjxv] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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