Evidence for a recycling role for Rab7 in regulating a late step in endocytosis and in retention of lysosomal enzymes in Dictyostelium discoideum.

Buczynski, Greg; Bush, John; Zhang, L; Rodriguez-Paris, Juan; Cardelli, James A.

doi:10.1091/mbc.8.7.1343

Cited by 73 publications

(70 citation statements)

References 65 publications

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“…Thus, beside homotypic fusion, syntaxin 7 could also mediate fusion of D. discoideum endosomes with vesicles carrying components necessary for their maturation, such as proteases and vacuolar ATPase. The existence of such vesicles in D. discoideum has already been suggested by the study of Rab7 mutants (48,49). Given the similarity between D. discoideum and professional phagocytes, it is likely that syntaxin 7 plays similar roles in the endo-phagosomes of mammalian phagocytes, organelles where homotypic as well as heterotypic fusions take place (50,51).…”

Section: Discussionmentioning

confidence: 89%

A Syntaxin 7 Homologue Is Present in Dictyostelium discoideum Endosomes and Controls Their Homotypic Fusion

Bogdanovic¹,

Brückert²,

Morio³

et al. 2000

Journal of Biological Chemistry

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Endo-phagocytic activity is prominent in Dictyostelium discoideum and makes it a good model organism to study the molecular organization of membrane traffic in this pathway. We have identified a syntaxin 7 homologue (26% identity and 54% similarity to human syntaxin 7) in Dictyostelium cDNA and genomic data banks. In addition to the Habc and H3 helices and the C-terminal transmembrane domain characteristic of syntaxins, this protein contains a repetitive N-terminal extension of 68 amino acids. We first showed that Dictyostelium syntaxin 7 was able to form a complex with N-ethylmaleimide-sensitive fusion protein and ␣-and ␥-soluble Nethylmaleimide-sensitive fusion protein attachment protein. Its intracellular localization was then studied by cell fractionation techniques and magnetic purification of the endocytic compartments. Most of D. discoideum syntaxin 7 is contained in endosomes. Finally, an in vitro endosome homotypic fusion assay (Laurent, O., Bruckert, F., Adessi, C., and Satre, M. (1998) J. Biol. Chem. 273, 793-799) was used to study a possible role for syntaxin 7 in this process. Purified anti-syntaxin 7 antibodies and a recombinant soluble fragment of syntaxin 7 both strongly inhibited fusion activity, indicating that this protein was necessary for endosome-endosome fusion. These results demonstrate the importance of this syntaxin 7 homologue in the early phases of Dictyostelium endo-phagocytic pathway.Intracellular membrane fusion is a complex and multistage process that requires pairing of specialized membrane proteins called SNAREs, 1 carried by both partners of the fusion reaction (1, 2). Three SNARE subfamilies, syntaxin, vesicle-associated membrane protein (VAMP)/synaptobrevin, and SNAP-25, are conserved from yeast to man (3). The structural basis of SNARE pairing is due to the characteristic presence in each SNARE of at least one ␣-helix able to adopt a coiled-coil conformation in association with other SNAREs (4, 5). In neurons, a tripartite SNARE complex is formed from four parallel ␣-helices, one contributed by the syntaxin, one by the synaptobrevin, and two by SNAP-25 (6, 7).The most diverse and currently best known SNARE family is the syntaxin family. Specific syntaxins are present in almost every compartment undergoing membrane fusion, including endocytic compartments. Yeast syntaxins are organized in a sequential manner along the endocytic pathway, with Tlg1p and Tlg2p in early endosomes (8, 9), Pep12p in the pre-vacuolar compartment (10) and Vam3p in the vacuole (11,12). A similar spatial organization is also found in Arabidopsis thaliana, where the yeast syntaxin homologues AtPep12p and AtVam3p are present on the prevacuolar and vacuolar compartments, respectively (13,14). In mammalian cells that recycle plasma membrane receptors by endocytosis, syntaxin 7 is present in early (15, 16) and late endosomes, and its activity is required for efficient transport of internalized fluid-phase marker from early to late endosomes (17). In addition, syntaxin 7 is involved in the heterotypic fusion...

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Section: Discussionmentioning

confidence: 89%

A Syntaxin 7 Homologue Is Present in Dictyostelium discoideum Endosomes and Controls Their Homotypic Fusion

Bogdanovic¹,

Brückert²,

Morio³

et al. 2000

Journal of Biological Chemistry

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“…As Dictyostelium postlysosomes constitutively exocytose their contents, we speculate that the late phase of WASH and retromer activity provides a mechanism to retrieve hydrolases before they are lost by exocytosis. Indeed, the sequential delivery and retrieval of hydrolytic enzymes during phagosome maturation is well characterized (33) and a late hydrolase retrieval step was previously proposed by others (33,58), who showed that hydrolase retention is disrupted by dominant negative Rab7-a now well-characterized regulator of the retromer (59). One of the best characterized roles for the retromer is to facilitate acid hydrolase trafficking by driving the retrograde trafficking of the cation-independent mannose-6-phosphate receptor (CI-M6PR) from lysosomes back to the trans-Golgi network (TGN) (37).…”

Section: Discussionmentioning

confidence: 98%

WASH drives early recycling from macropinosomes and phagosomes to maintain surface phagocytic receptors

Buckley

Gopaldass

Bosmani

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Macropinocytosis is an ancient mechanism that allows cells to harvest nutrients from extracellular media, which also allows immune cells to sample antigens from their surroundings. During macropinosome formation, bulk plasma membrane is internalized with all its integral proteins. It is vital for cells to salvage these proteins before degradation, but the mechanisms for sorting them are not known. Here we describe the evolutionarily conserved recruitment of the WASH (WASP and SCAR homolog) complex to both macropinosomes and phagosomes within a minute of internalization. Using Dictyostelium, we demonstrate that WASH drives protein sorting and recycling from macropinosomes and is thus essential to maintain surface receptor levels and sustain phagocytosis. WASH functionally interacts with the retromer complex at both early and late phases of macropinosome maturation, but mediates recycling via retromer-dependent and -independent pathways. WASH mutants consequently have decreased membrane levels of integrins and other surface proteins. This study reveals an important pathway enabling cells to sustain macropinocytosis without bulk degradation of plasma membrane components.phagocytosis | macropinocytosis | WASH | Dictyostelium | trafficking

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“…Interestingly, PI 3-kinases also play a role in regulating lysosome-and phagosome-homotypic fusion in Dictyostelium (Buczynski et al, 1997a;Rupper et al, 2001b), although in this latter case the product required appears to be phosphoinositide (3,4,5)-trisphosphate. PKB/Akt, in addition to the PI 3-kinases PIK1 and PIK2, regulates homotypic phagosome fusion in Dictyostelium (Rupper et al, 2001b).…”

Section: Discussionmentioning

confidence: 99%

RabD, aDictyosteliumRab14-related GTPase, regulates phagocytosis and homotypic phagosome and lysosome fusion

Harris

Cardelli

2002

Journal of Cell Science

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RabD, a Dictyostelium Rab14-related GTPase, localizes in the endo-lysosomal pathway and contractile vacuole system of membranes. Cell lines expressing dominant-negative RabD were defective in endocytosis, endosomal membrane flow and homotypic lysosome fusion. In support of a role for RabD in fusion, cells overexpressing constitutively active RabD Q67L accumulated enlarged hydrolase-rich acidic vesicles ringed with GFP-RabD, consistent with RabD directly regulating lysosome fusion. To determine whether RabD also regulated phagocytosis and/or homotypic phagosome fusion (a process stimulated by many intracellular pathogens), cells overexpressing dominant-active (RabD Q67L ) or dominant-negative (Rab N121I ) RabD were analyzed microscopically and biochemically. The rate of phagocytosis was increased twofold in RabD Q67L -expressing cells and reduced by 50% in RabD N121I -expressing cells compared with control cells. To examine the role of RabD in the formation of multiparticle phagosomes, we performed a series of pulse-chase experiments using fluorescently labeled bacteria and fluorescent latex beads. The rate of fusion of newly formed phagosomes was five times higher in the RabD Q67L -expressing cells and reduced by over 50% in RabD N121I -expressing cells as compared with control cells. GFPRabD Q67L was found to ring multiparticle spacious phagosomes, which supports a direct role for this protein in regulating fusion. Inhibition of PI 3-kinase activity, which is known to regulate phagosome fusion in the wildtype cells, reduced the rate of phagosome fusion in RabD Q67L+ cells, indicating that RabD acted upstream of or parallel with PI 3-kinase. We hypothesize that RabD and, possibly, Rab14, a related GTPase that associates with phagosomes in mammalian cells, are important regulators of homotypic phagosome and endo-lysosome fusion.

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Evidence for a recycling role for Rab7 in regulating a late step in endocytosis and in retention of lysosomal enzymes in Dictyostelium discoideum.

Cited by 73 publications

References 65 publications

A Syntaxin 7 Homologue Is Present in Dictyostelium discoideum Endosomes and Controls Their Homotypic Fusion

A Syntaxin 7 Homologue Is Present in Dictyostelium discoideum Endosomes and Controls Their Homotypic Fusion

WASH drives early recycling from macropinosomes and phagosomes to maintain surface phagocytic receptors

RabD, aDictyosteliumRab14-related GTPase, regulates phagocytosis and homotypic phagosome and lysosome fusion

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