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1.  Invited mini-review for thematic issue on Membrane Trafficking 
Molecular membrane biology  2010;27(8):457-461.
Membrane trafficking involves the collection of cargo into nascent transport vesicles that bud off from a donor compartment, translocate along cytoskeletal tracks, and then dock and fuse with their target membranes. Docking and fusion involve initial interaction at a distance (tethering), followed by a closer interaction that leads to pairing of vesicle SNARE proteins (v-SNAREs) with target membrane SNAREs (t-SNAREs), thereby catalyzing vesicle fusion. When tethering cannot take place, transport vesicles accumulate in the cytoplasm. Tethering is generally carried out by two broad classes of molecules: extended, coiled-coil proteins such as the so-called Golgin proteins, or multi-subunit complexes such as the Exocyst, COG or Dsl complexes. This review will focus on the most recent advances in terms of our understanding of the mechanism by which tethers carry out their roles, and new structural insights into tethering complex transactions.
doi:10.3109/09687688.2010.501765
PMCID: PMC4132666  PMID: 21067454
Membrane traffic; vesicle tethering; Rab GTPase; Golgi complex; endosomes
2.  Rab GTPase regulation of membrane identity 
Current opinion in cell biology  2013;25(4):414-419.
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.
doi:10.1016/j.ceb.2013.04.002
PMCID: PMC3729790  PMID: 23639309
3.  Golgi-associated RhoBTB3 targets Cyclin E for ubiquitylation and promotes cell cycle progression 
The Journal of Cell Biology  2013;203(2):233-250.
The Golgi protein RhoBTB3 in complex with CUL3 and RBX1 promotes Cyclin E ubiquitylation to allow its turnover during S phase and progression through the cell cycle.
Cyclin E regulates the cell cycle transition from G1 to S phase and is degraded before entry into G2 phase. Here we show that RhoBTB3, a Golgi-associated, Rho-related ATPase, regulates the S/G2 transition of the cell cycle by targeting Cyclin E for ubiquitylation. Depletion of RhoBTB3 arrested cells in S phase, triggered Golgi fragmentation, and elevated Cyclin E levels. On the Golgi, RhoBTB3 bound Cyclin E as part of a Cullin3 (CUL3)-dependent RING–E3 ubiquitin ligase complex comprised of RhoBTB3, CUL3, and RBX1. Golgi association of this complex was required for its ability to catalyze Cyclin E ubiquitylation and allow normal cell cycle progression. These experiments reveal a novel role for a Ras superfamily member in catalyzing Cyclin E turnover during S phase, as well as an unexpected, essential role for the Golgi as a ubiquitylation platform for cell cycle control.
doi:10.1083/jcb.201305158
PMCID: PMC3812982  PMID: 24145166
4.  Mutant enzymes challenge all assumptions 
eLife  2014;3:e02171.
Enzymes called Rab GTPases that carry so-called “activating” mutations may never become activated at all.
doi:10.7554/eLife.02171
PMCID: PMC3919269  PMID: 24520166
Membrane traffic; Rab GTPase; nucleotide exchange factor; Human
5.  The 5-phosphatase OCRL mediates retrograde transport of the mannose 6-phosphate receptor by regulating a Rac1-cofilin signalling module 
Human Molecular Genetics  2012;21(23):5019-5038.
Mutations in the OCRL gene encoding the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) 5-phosphatase OCRL cause Lowe syndrome (LS), which is characterized by intellectual disability, cataracts and selective proximal tubulopathy. OCRL localizes membrane-bound compartments and is implicated in intracellular transport. Comprehensive analysis of clathrin-mediated endocytosis in fibroblasts of patients with LS did not reveal any difference in trafficking of epidermal growth factor, low density lipoprotein or transferrin, compared with normal fibroblasts. However, LS fibroblasts displayed reduced mannose 6-phosphate receptor (MPR)-mediated re-uptake of the lysosomal enzyme arylsulfatase B. In addition, endosome-to-trans Golgi network (TGN) transport of MPRs was decreased significantly, leading to higher levels of cell surface MPRs and their enrichment in enlarged, retromer-positive endosomes in OCRL-depleted HeLa cells. In line with the higher steady-state concentration of MPRs in the endosomal compartment in equilibrium with the cell surface, anterograde transport of the lysosomal enzyme, cathepsin D was impaired. Wild-type OCRL counteracted accumulation of MPR in endosomes in an activity-dependent manner, suggesting that PI(4,5)P2 modulates the activity state of proteins regulated by this phosphoinositide. Indeed, we detected an increased amount of the inactive, phosphorylated form of cofilin and lower levels of the active form of PAK3 upon OCRL depletion. Levels of active Rac1 and RhoA were reduced or enhanced, respectively. Overexpression of Rac1 rescued both enhanced levels of phosphorylated cofilin and MPR accumulation in enlarged endosomes. Our data suggest that PI(4,5)P2 dephosphorylation through OCRL regulates a Rac1-cofilin signalling cascade implicated in MPR trafficking from endosomes to the TGN.
doi:10.1093/hmg/dds343
PMCID: PMC3490508  PMID: 22907655
6.  Hopping rim to rim through the Golgi 
eLife  2013;2:e00903.
A novel approach based on tracking the fate of proteins that become ‘stapled’ to the walls of the Golgi yields insights into the long-sought mechanism of transport through this organelle.
doi:10.7554/eLife.00903
PMCID: PMC3679515  PMID: 23795298
Golgi; Traffic; Membrane; Cell biology; Human
7.  Cholesterol Accumulation Sequesters Rab9 and Disrupts Late Endosome Function in NPC1-deficient Cells* 
The Journal of biological chemistry  2006;281(26):17890-17899.
Niemann-Pick type C disease is an autosomal recessive disorder that leads to massive accumulation of cholesterol and glycosphingolipids in late endosomes and lysosomes. To understand how cholesterol accumulation influences late endosome function, we investigated the effect of elevated cholesterol on Rab9-dependent export of mannose 6-phosphate receptors from this compartment. Endogenous Rab9 levels were elevated 1.8-fold in Niemann-Pick type C cells relative to wild type cells, and its half-life increased 1.6-fold, suggesting that Rab9 accumulation is caused by impaired protein turnover. Reduced Rab9 degradation was accompaniedby stabilization on endosome membranes, as shown by a reduction in the capacity of Rab9 for guanine nucleotide dissociation inhibitor-mediated extraction from Niemann-Pick type C membranes. Cholesterol appeared to stabilize Rab9 directly, as liposomes loaded with prenylated Rab9 showed decreased extractability with increasing cholesterol content. Rab9 is likely sequestered in an inactive form on Niemann-Pick type C membranes, as cation-dependent man-nose 6-phosphate receptorswere missorted to the lysosome for degradation, a process that was reversed by overexpression of GFP-tagged Rab9. In addition to using primary fibroblasts isolated from Niemann-Pick type C patients, RNA interference was utilized to recapitulate the disease phenotype in cultured cells, greatly facilitating the analysis of cholesterol accumulation and late endosome function. We conclude that cholesterol contributes directly to the sequestration of Rab9 on Niemann-Pick type C cell membranes, which in turn, disrupts mannose 6-phosphate receptor trafficking.
doi:10.1074/jbc.M601679200
PMCID: PMC3650718  PMID: 16644737
8.  Entry at the trans-Face of the Golgi 
The trans-Golgi network (TGN) receives a select set of proteins from the endocytic pathway—about 5% of total plasma membrane glycoproteins (Duncan and Kornfeld 1988). Proteins that are delivered include mannose 6-phosphate receptors (MPRs), TGN46, sortilin, and various toxins that hitchhike a ride backward through the secretory pathway to intoxicate cells after they exit into the cytoplasm from the endoplasmic reticulum (ER). This article will review work on the molecular players that drive protein transport from the endocytic pathway to the TGN. Distinct requirements have revealed multiple routes for retrograde transport; in addition, the existence of multiple, potential coat proteins and/or cargo adaptors imply that multiple vesicular transfers are likely involved. Several comprehensive reviews have appeared recently and should be sought for additional details (Bonifacino and Rojas 2006; Johannes and Popoff 2008).
Proteins such as mannose 6-phosphate receptors and sortilin move to the trans-Golgi network following endocytosis. The retrograde pathways are more complex than expected, requiring numerous adaptor proteins and multiple vesicle transport steps.
doi:10.1101/cshperspect.a005272
PMCID: PMC3039930  PMID: 21421921
9.  GCC185 plays independent roles in Golgi structure maintenance and AP-1–mediated vesicle tethering 
The Journal of Cell Biology  2011;194(5):779-787.
Two distinct domains of GCC185 function in maintaining Golgi structure or in binding to AP-1 to tether retrograde transport vesicles en route to the Golgi.
GCC185 is a long coiled-coil protein localized to the trans-Golgi network (TGN) that functions in maintaining Golgi structure and tethering mannose 6-phosphate receptor (MPR)–containing transport vesicles en route to the Golgi. We report the identification of two distinct domains of GCC185 needed either for Golgi structure maintenance or transport vesicle tethering, demonstrating the independence of these two functions. The domain needed for vesicle tethering binds to the clathrin adaptor AP-1, and cells depleted of GCC185 accumulate MPRs in transport vesicles that are AP-1 decorated. This study supports a previously proposed role of AP-1 in retrograde transport of MPRs from late endosomes to the Golgi and indicates that docking may involve the interaction of vesicle-associated AP-1 protein with the TGN-associated tethering protein GCC185.
doi:10.1083/jcb.201104019
PMCID: PMC3171126  PMID: 21875948
10.  Recent advances in understanding Golgi biogenesis 
The Golgi complex is a central processing station for proteins traversing the secretory pathway, yet we are still learning how this compartment is constructed and how cargo moves through it. Recent experiments suggest a key role for Ras-like Rab GTPases and provide important new ideas for how the Golgi may function.
doi:10.3410/B2-32
PMCID: PMC2897732  PMID: 20625450
11.  Multiple routes of protein transport from endosomes to the trans Golgi network 
FEBS letters  2009;583(23):3811-3816.
Proteins use multiple routes for transport from endosomes to the Golgi complex. Shiga and cholera toxins and TGN38/46 are routed from early and recycling endosomes, while mannose 6-phosphate receptors are routed from late endosomes. The identification of distinct molecular requirements for each of these pathways makes it clear that mammalian cells have evolved more complex targeting mechanisms and routes than previously anticipated.
doi:10.1016/j.febslet.2009.10.075
PMCID: PMC2787657  PMID: 19879268
endosome; Golgi; Rab GTPase; mannose 6-phosphate receptors; Shiga and cholera toxins
12.  Unconventional secretion by autophagosome exocytosis 
The Journal of Cell Biology  2010;188(4):451-452.
In this issue, Duran et al. (2010. J. Cell Biol. doi: 10.1083/jcb.200911154) and Manjithaya et al. (2010. J. Cell Biol. doi: 10.1083/jcb.200911149) use yeast genetics to reveal a role for autophagosome intermediates in the unconventional secretion of an acyl coenzyme A (CoA)–binding protein that lacks an endoplasmic reticulum signal sequence. Medium-chain acyl CoAs are also required and may be important for substrate routing to this pathway.
doi:10.1083/jcb.201001121
PMCID: PMC2828920  PMID: 20156968
13.  Association of β-1,3-N-acetylglucosaminyltransferase 1 and β-1,4-galactosyltransferase 1, trans-Golgi enzymes involved in coupled poly-N-acetyllactosamine synthesis 
Glycobiology  2009;19(6):655-664.
Poly-N-acetyllactosamine (polyLacNAc) is a linear carbohydrate polymer composed of alternating N-acetylglucosamine and galactose residues involved in cellular functions ranging from differentiation to metastasis. PolyLacNAc also serves as a scaffold on which other oligosaccharides such as sialyl Lewis X are displayed. The polymerization of the alternating N-acetylglucosamine and galactose residues is catalyzed by the successive action of UDP-GlcNAc:βGal β-1,3-N-acetylglucosaminyltransferase 1 (B3GNT1) and UDP-Gal:βGlcNAc β-1,4-galactosyltransferase, polypeptide 1 (B4GALT1), respectively. The functional association between these two glycosyltransferases led us to investigate whether the enzymes also associate physically. We show that B3GNT1 and B4GALT1 colocalize by immunofluorescence microscopy, interact by coimmunoprecipitation, and affect each other's subcellular localization when one of the two proteins is artificially retained in the endoplasmic reticulum. These results demonstrate that B3GNT1 and B4GALT1 physically associate in vitro and in cultured cells, providing insight into possible mechanisms for regulation of polyLacNAc production.
doi:10.1093/glycob/cwp035
PMCID: PMC2682609  PMID: 19261593
endoplasmic reticulum; enzyme complexes; glycosyltransferase; Golgi complex; poly-N-acetyllactosamine
14.  RhoBTB3: A Rho GTPase-family ATPase required for endosome to Golgi transport 
Cell  2009;137(5):938-948.
Summary
Rho GTPases are key regulators of the actin-based cytoskeleton; Rab GTPases are key regulators of membrane traffic. We report here that the atypical Rho GTPase family member, RhoBTB3, binds directly to Rab9 GTPase, and functions with Rab9 in protein transport from endosomes to the trans Golgi network. Gene replacement experiments show that RhoBTB3 function in cultured cells requires both RhoBTB3’s N-terminal, Rho-related domain, and C-terminal sequences that are important for Rab9 interaction.9 Biochemical analysis reveals that RhoBTB3 binds and hydrolyzes ATP rather than GTP. Rab9 binding opens the auto-inhibited RhoBTB3 protein to permit maximal ATP hydroysis. Because RhoBTB3 interacts with TIP47 on membranes, we propose that it may function to release this cargo selection protein from vesicles to permit their efficient docking and fusion at the Golgi.
doi:10.1016/j.cell.2009.03.043
PMCID: PMC2801561  PMID: 19490898
15.  Journeys through the Golgi—taking stock in a new era 
The Journal of Cell Biology  2009;187(4):449-453.
The Golgi apparatus is essential for protein sorting and transport. Many researchers have long been fascinated with the form and function of this organelle. Yet, despite decades of scrutiny, the mechanisms by which proteins are transported across the Golgi remain controversial. At a recent meeting, many prominent Golgi researchers assembled to critically evaluate the core issues in the field. This report presents the outcome of their discussions and highlights the key open questions that will help guide the field into a new era.
doi:10.1083/jcb.200909011
PMCID: PMC2779233  PMID: 19948493
16.  Recent advances in understanding Golgi biogenesis 
The Golgi complex is a central processing station for proteins traversing the secretory pathway, yet we are still learning how this compartment is constructed and how cargo moves through it. Recent experiments suggest a key role for Ras-like Rab GTPases and provide important new ideas for how the Golgi may function.
doi:10.3410/B2-32
PMCID: PMC2897732  PMID: 20625450
17.  Multiple Rab GTPase Binding Sites in GCC185 Suggest a Model for Vesicle Tethering at the Trans-Golgi 
Molecular Biology of the Cell  2009;20(1):209-217.
GCC185, a trans-Golgi network-localized protein predicted to assume a long, coiled-coil structure, is required for Rab9-dependent recycling of mannose 6-phosphate receptors (MPRs) to the Golgi and for microtubule nucleation at the Golgi via CLASP proteins. GCC185 localizes to the Golgi by cooperative interaction with Rab6 and Arl1 GTPases at adjacent sites near its C terminus. We show here by yeast two-hybrid and direct biochemical tests that GCC185 contains at least four additional binding sites for as many as 14 different Rab GTPases across its entire length. A central coiled-coil domain contains a specific Rab9 binding site, and functional assays indicate that this domain is important for MPR recycling to the Golgi complex. N-Terminal coiled-coils are also required for GCC185 function as determined by plasmid rescue after GCC185 depletion by using small interfering RNA in cultured cells. Golgi-Rab binding sites may permit GCC185 to contribute to stacking and lateral interactions of Golgi cisternae as well as help it function as a vesicle tether.
doi:10.1091/mbc.E08-07-0740
PMCID: PMC2613123  PMID: 18946081
18.  A syntaxin 10–SNARE complex distinguishes two distinct transport routes from endosomes to the trans-Golgi in human cells 
The Journal of Cell Biology  2008;180(1):159-172.
Mannose 6-phosphate receptors (MPRs) are transported from endosomes to the Golgi after delivering lysosomal enzymes to the endocytic pathway. This process requires Rab9 guanosine triphosphatase (GTPase) and the putative tether GCC185. We show in human cells that a soluble NSF attachment protein receptor (SNARE) complex comprised of syntaxin 10 (STX10), STX16, Vti1a, and VAMP3 is required for this MPR transport but not for the STX6-dependent transport of TGN46 or cholera toxin from early endosomes to the Golgi. Depletion of STX10 leads to MPR missorting and hypersecretion of hexosaminidase. Mouse and rat cells lack STX10 and, thus, must use a different target membrane SNARE for this process. GCC185 binds directly to STX16 and is competed by Rab6. These data support a model in which the GCC185 tether helps Rab9-bearing transport vesicles deliver their cargo to the trans-Golgi and suggest that Rab GTPases can regulate SNARE–tether interactions. Importantly, our data provide a clear molecular distinction between the transport of MPRs and TGN46 to the trans-Golgi.
doi:10.1083/jcb.200707136
PMCID: PMC2213607  PMID: 18195106
19.  Dual GTPase regulation of the GCC185 Golgin: Communication between adjacent Rab6 and Arl1 binding sites 
Cell  2008;132(2):286-298.
Summary
GCC185 is a large coiled coil protein at the trans Golgi network that is required for receipt of transport vesicles inbound from late endosomes, and for anchoring non-centrosomal microtubules that emanate from the Golgi. Here we demonstrate that recruitment of GCC185 to the Golgi is mediated by two Golgi-localized small GTPases of the Rab and Arl families. GCC185 binds Rab6 and mutation of residues needed for Rab binding abolishes Golgi localization. The crystal structure of Rab6 bound to the GCC185 Rab binding domain reveals that Rab6 recognizes a two-fold symmetric surface on a coiled coil immediately adjacent to a C-terminal GRIP domain. Unexpectedly, Rab6 binding promotes association of Arl1 with the GRIP domain. We present a structure-derived model for dual GTPase membrane attachment that highlights the potential ability of Rab GTPases to reach binding partners at a significant distance from the membrane via their unstructured and membrane-anchored, hypervariable domains.
doi:10.1016/j.cell.2007.11.048
PMCID: PMC2344137  PMID: 18243103
20.  Clues to Neuro-Degeneration in Niemann-Pick Type C Disease from Global Gene Expression Profiling 
PLoS ONE  2006;1(1):e19.
Background
Niemann-Pick Type C (NPC) disease is a neurodegenerative disease that is characterized by the accumulation of cholesterol and glycosphingolipids in the late endocytic pathway. The majority of NPC cases are due to mutations in the NPC1 gene. The precise function of this gene is not yet known.
Methodology/Principal Findings
Using cDNA microarrays, we analyzed the genome-wide expression patterns of human fibroblasts homozygous for the I1061T NPC1 mutation that is characterized by a severe defect in the intracellular processing of low density lipoprotein-derived cholesterol. A distinct gene expression profile was identified in NPC fibroblasts from different individuals when compared with fibroblasts isolated from normal subjects. As expected, NPC1 mutant cells displayed an inappropriate homeostatic response to accumulated intracellular cholesterol. In addition, a number of striking parallels were observed between NPC disease and Alzheimer's disease.
Conclusions/Significance
Many genes involved in the trafficking and processing of amyloid precursor protein and the microtubule binding protein, tau, were more highly expressed. Numerous genes important for membrane traffic and the cellular regulation of calcium, metals and other ions were upregulated. Finally, NPC fibroblasts exhibited a gene expression profile indicative of oxidative stress. These changes are likely contributors to the pathophysiology of Niemann-Pick Type C disease.
doi:10.1371/journal.pone.0000019
PMCID: PMC1762405  PMID: 17183645
21.  TIP47 is a key effector for Rab9 localization 
The Journal of Cell Biology  2006;173(6):917-926.
The human genome encodes ∼70 Rab GTPases that localize to the surfaces of distinct membrane compartments. To investigate the mechanism of Rab localization, chimeras containing heterologous Rab hypervariable domains were generated, and their ability to bind seven Rab effectors was quantified. Two chimeras could bind effectors for two distinctly localized Rabs; a Rab5/9 hybrid bound both Rab5 and Rab9 effectors, and a Rab1/9 hybrid bound to certain Rab1 and Rab9 effectors. These unusual chimeras permitted a test of the importance of effector binding for Rab localization. In both cases, changing the cellular concentration of a key Rab9 effector, which is called tail-interacting protein of 47 kD, moved a fraction of the proteins from their parental Rab localization to that of Rab9. Thus, relative concentrations of certain competing effectors could determine a chimera's localization. These data confirm the importance of effector interactions for Rab9 localization, and support a model in which effector proteins rely on Rabs as much as Rabs rely on effectors to achieve their correct steady state localizations.
doi:10.1083/jcb.200510010
PMCID: PMC2063917  PMID: 16769818
22.  A Functional Role for the GCC185 Golgin in Mannose 6-Phosphate Receptor Recycling 
Molecular Biology of the Cell  2006;17(10):4353-4363.
Mannose 6-phosphate receptors (MPRs) deliver newly synthesized lysosomal enzymes to endosomes and then recycle to the Golgi. MPR recycling requires Rab9 GTPase; Rab9 recruits the cytosolic adaptor TIP47 and enhances its ability to bind to MPR cytoplasmic domains during transport vesicle formation. Rab9-bearing vesicles then fuse with the trans-Golgi network (TGN) in living cells, but nothing is known about how these vesicles identify and dock with their target. We show here that GCC185, a member of the Golgin family of putative tethering proteins, is a Rab9 effector that is required for MPR recycling from endosomes to the TGN in living cells, and in vitro. GCC185 does not rely on Rab9 for its TGN localization; depletion of GCC185 slightly alters the Golgi ribbon but does not interfere with Golgi function. Loss of GCC185 triggers enhanced degradation of mannose 6-phosphate receptors and enhanced secretion of hexosaminidase. These data assign a specific pathway to an interesting, TGN-localized protein and suggest that GCC185 may participate in the docking of late endosome-derived, Rab9-bearing transport vesicles at the TGN.
doi:10.1091/mbc.E06-02-0153
PMCID: PMC1635343  PMID: 16885419
23.  Rab9 GTPase Regulates Late Endosome Size and Requires Effector Interaction for Its Stability 
Molecular Biology of the Cell  2004;15(12):5420-5430.
Rab9 GTPase resides in a late endosome microdomain together with mannose 6-phosphate receptors (MPRs) and the tail-interacting protein of 47 kDa (TIP47). To explore the importance of Rab9 for microdomain establishment, we depleted the protein from cultured cells. Rab9 depletion decreased late endosome size and reduced the numbers of multilamellar and dense-tubule–containing late endosomes/lysosomes, but not multivesicular endosomes. The remaining late endosomes and lysosomes were more tightly clustered near the nucleus, implicating Rab9 in endosome localization. Cells displayed increased surface MPRs and lysosome-associated membrane protein 1. In addition, cells showed increased MPR synthesis in conjunction with MPR missorting to the lysosome. Surprisingly, Rab9 stability on late endosomes required interaction with TIP47. Rabs are thought of as independent, prenylated entities that reside either on membranes or in cytosol, bound to GDP dissociation inhibitor. These data show that Rab9 stability is strongly influenced by a specific effector interaction. Moreover, Rab9 and the proteins with which it interacts seem critical for the maintenance of specific late endocytic compartments and endosome/lysosome localization.
doi:10.1091/mbc.E04-08-0747
PMCID: PMC532021  PMID: 15456905
24.  Visualization of Rab9-mediated vesicle transport from endosomes to the trans-Golgi in living cells 
The Journal of Cell Biology  2002;156(3):511-518.
Mannose 6-phosphate receptors (MPRs) are transported from endosomes to the trans-Golgi via a transport process that requires the Rab9 GTPase and the cargo adaptor TIP47. We have generated green fluorescent protein variants of Rab9 and determined their localization in cultured cells. Rab9 is localized primarily in late endosomes and is readily distinguished from the trans-Golgi marker galactosyltransferase. Coexpression of fluorescent Rab9 and Rab7 revealed that these two late endosome Rabs occupy distinct domains within late endosome membranes. Cation-independent mannose 6-phosphate receptors are enriched in the Rab9 domain relative to the Rab7 domain. TIP47 is likely to be present in this domain because it colocalizes with the receptors in fixed cells, and a TIP47 mutant disrupted endosome morphology and sequestered MPRs intracellularly. Rab9 is present on endosomes that display bidirectional microtubule-dependent motility. Rab9-positive transport vesicles fuse with the trans-Golgi network as followed by video microscopy of live cells. These data provide the first indication that Rab9-mediated endosome to trans-Golgi transport can use a vesicle (rather than a tubular) intermediate. Our data suggest that Rab9 remains vesicle associated until docking with the Golgi complex and is rapidly removed concomitant with or just after membrane fusion.
doi:10.1083/jcb.200109030
PMCID: PMC2173336  PMID: 11827983
endosome; Rab9; Golgi complex; Rab7; TIP47
25.  Constructing a Golgi complex 
The Journal of Cell Biology  2001;155(6):873-876.
In this issue, Short et al. report the discovery of a protein named Golgin-45 that is located on the surface of the middle (or medial) cisternae of the Golgi complex. Depletion of this protein disrupts the Golgi complex and leads to the return of a resident, lumenal, medial Golgi enzyme to the endoplasmic reticulum. These findings suggest that Golgin-45 serves as a linchpin for the maintenance of Golgi complex structure, and offer hints as to the mechanisms by which the polarized Golgi complex is constructed.
doi:10.1083/jcb.200109095
PMCID: PMC2150916  PMID: 11739400

Results 1-25 (27)