A Role for Tlg1p in the Transport of Proteins within the Golgi Apparatus of<i>Saccharomyces cerevisiae</i>

Coe, John G. S.; Lim, Anthony C.B.; Xu, Jing; Hong, Wanjin

doi:10.1091/mbc.10.7.2407

Cited by 55 publications

(57 citation statements)

References 75 publications

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“…In these cells the distribution of Tlg1p is reported to overlap substantially with that of Sed5p (Coe et al, 1999). Our immuno-EM studies confirm that Tlg1p is capable of reaching membranes that contain Sed5p, although we found double-labeled structures to be infrequent.…”

Section: Retrieval Of Snc1p From Early Endosomessupporting

confidence: 72%

Specific Retrieval of the Exocytic SNARE Snc1p from Early Yeast Endosomes

Lewis

Nichols

Prescianotto-Baschong

et al. 2000

MBoC

331

515

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Many endocytosed proteins in yeast travel to the vacuole, but some are recycled to the plasma membrane. We have investigated the recycling of chimeras containing green fluorescent protein (GFP) and the exocytic SNARE Snc1p. GFP-Snc1p moves from the cell surface to internal structures when Golgi function or exocytosis is blocked, suggesting continuous recycling via the Golgi. Internalization is mediated by a conserved cytoplasmic signal, whereas diversion from the vacuolar pathway requires sequences within and adjacent to the transmembrane domain. Delivery from the Golgi to the surface is also influenced by the transmembrane domain, but the requirements are much less specific. Recycling requires the syntaxins Tlg1p and Tlg2p but not Pep12p or proteins such as Vps4p and Vps5p that have been implicated in late endosome–Golgi traffic. Subtle changes to the recycling signal cause GFP-Snc1p to accumulate preferentially in punctate internal structures, although it continues to recycle to the surface. The internal GFP-Snc1p colocalizes with Tlg1p, and immunofluorescence and immunoelectron microscopy reveal structures that contain Tlg1p, Tlg2p, and Kex2p but lack Pep12p and Sec7p. We propose that these represent early endosomes in which sorting of Snc1p and late Golgi proteins occurs, and that transport can occur directly from them to the Golgi apparatus.

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Section: Retrieval Of Snc1p From Early Endosomessupporting

confidence: 72%

Specific Retrieval of the Exocytic SNARE Snc1p from Early Yeast Endosomes

Lewis

Nichols

Prescianotto-Baschong

et al. 2000

MBoC

331

515

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“…Tlg1 and Tlg2 were also tagged with YFP but on their N terminus and the plasmid carrying either functional fusion was used to transform wild-type cells together with the CFP-Atg8 chimera. As expected, Tlg1 and Tlg2 showed dispersed punctate staining that did not colocalize with CFPAtg8 (Abeliovich et al, 1998;Holthuis et al, 1998;Seron et al, 1998;Coe et al, 1999;Siniossoglou and Pelham, 2001; Figure 2B). As a control, we examined the localization of YFP-Tlg1 with CFP-Tlg2 or CFP-Snc1, a Golgi-to-plasma membrane v-SNARE.…”

supporting

confidence: 77%

Early Stages of the Secretory Pathway, but Not Endosomes, Are Required for Cvt Vesicle and Autophagosome Assembly inSaccharomyces cerevisiae

Reggiori

Wang

Nair

et al. 2004

MBoC

128

163

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The Cvt pathway is a biosynthetic transport route for a distinct subset of resident yeast vacuolar hydrolases, whereas macroautophagy is a nonspecific degradative mechanism that allows cell survival during starvation. Yet, these two vacuolar trafficking pathways share a number of identical molecular components and are morphologically very similar. For example, one of the hallmarks of both pathways is the formation of double-membrane cytosolic vesicles that sequester cargo before vacuolar delivery. The origin of the vesicle membrane has been controversial and various lines of evidence have implicated essentially all compartments of the endomembrane system. Despite the analogies between the Cvt pathway and autophagy, earlier work has suggested that the origin of the engulfing vesicle membranes is different; the endoplasmic reticulum is proposed to be required only for autophagy. In contrast, in this study we demonstrate that the endoplasmic reticulum and/or Golgi complex, but not endosomal compartments, play an important role for both yeast transport routes. Along these lines, we demonstrate that Berkeley bodies, a structure generated from the Golgi complex in sec7 cells, are immunolabeled with Atg8, a structural component of autophagosomes. Finally, we also show that none of the yeast t-SNAREs are located at the preautophagosomal structure, the presumed site of double-membrane vesicle formation. Based on our results, we propose two models for Cvt vesicle biogenesis. INTRODUCTIONThe lysosome/vacuole is the major cellular center for degradation, recycling, and storage of biological constituents. Several well-characterized transport routes are implicated in protein delivery to this organelle during normal growth conditions. These pathways are conserved among eukaryotic organisms, but work in the yeast Saccharomyces cerevisiae has had a major impact on their characterization and in the identification of the molecular machinery (Conibear and Stevens, 1998). The route called the alkaline phosphatase pathway provides a direct transport connection between the Golgi complex and the vacuole Piper et al., 1997). A second itinerary from the Golgi complex to the vacuole passes through the late endosome and is known as the carboxypeptidase Y pathway (Piper et al., 1995;Babst et al., 1998;Conibear and Stevens, 1998). These two pathways are required for the biogenesis and maintenance of vacuoles, whereas a third route, endocytosis, has a catabolic function. Endocytosis mediates the downregulation of plasma membrane proteins by delivering them via the late endosome to the vacuole for degradation (Hicke, 1999;Katzmann et al., 2002). Before reaching the late endosome, these proteins pass through the early endosome where some components are recycled back to the cell surface (Hicke et al., 1997;Prescianotto-Baschong and Riezman, 1998;Lewis et al., 2000). The carboxypeptidase Y pathway and endocytosis converge at the endosome where another route, the multivesicular body pathway, delivers both resident enzymes and substrates to the vac...

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“…Thus, the rescue mechanism by which CAPP acts is operative in the absence of the endosomal v-or t-SNAREs alone, or in combination. Deletion of either TLG gene is known to affect intracellular protein trafficking and endocytic functions to a degree and in some cell types leads to lethality (Coe et al, 1999), although conditional lethal strains bearing deletions in both genes have been reported (Holthuis et al, 1998a). In our strain background, TLG deletions have prominent effects on endocytosis, but only small effects on cell growth (Gurunathan et al, 2000).…”

Section: Discussionmentioning

confidence: 73%

“…Thus, it is likely that Tlg2, a syntaxin-like t-SNARE, and Tlg1, a SNARE light-chain, form complexes with Snc1,2 at endosomes or the trans-Golgi (TGN). Although Tlg2 has been proposed to act at early endosomes (Abeliovich et al, 1998;Seron et al, 1998), it overlaps with Tlg1, whose placement is broader and encompasses the TGN (Holthuis et al, 1998a(Holthuis et al, , 1998bCoe et al, 1999). Thus, we conjectured that Tlg1 and 2 could be partners, along with Snc1 or Snc2, in SNARE complexes relevant to endocytic functioning.…”

Section: Ceramide Treatment Enhances Tlg Assembly Into Complexes In Smentioning

confidence: 91%

“…Thus, Snc v-SNAREs confer both anterograde and retrograde transport events between the Golgi and the plasma membrane. Appropriately, their endocytic functions are likely to be dependent on two different t-SNAREs, Tlg1 and Tlg2, which are trans-Golgi and endosomal t-SNAREs involved in endosomal protein sorting (Abeliovich et al, 1998;Holthuis et al, 1998a;Seron et al, 1998;Coe et al, 1999;Abeliovich et al, 1999). This is because Snc proteins coimmunoprecipitate with the Tlg t-SNAREs (Abeliovich et al, 1998;Holthuis et al, 1998a); Snc1 ala43 is nonfunctional in their absence (Gurunathan et al, 2000); and snc tlg1 and snc tlg2 strains show synthetically enhanced phenotypes (Gurunathan et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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t-SNARE Phosphorylation Regulates Endocytosis in Yeast

Gurunathan

Marash

Weinberger

et al. 2002

MBoC

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Earlier we demonstrated that activation of a ceramide-activated protein phosphatase (CAPP) conferred normal growth and secretion to yeast lacking their complement of exocytic v-SNAREs (Snc1,2) or bearing a temperature-sensitive mutation in an exocytic t-SNARE (Sso2). CAPP activation led to Sso dephosphorylation and enhanced the assembly of t-SNAREs into functional complexes. Thus, exocytosis in yeast is modulated by t-SNARE phosphorylation. Here, we show that endocytic defects in cells lacking the v-and t-SNAREs involved in endocytosis are also rescued by CAPP activation. Yeast lacking the Tlg1 or Tlg2 t-SNAREs, the Snc v-SNAREs, or both, undergo endocytosis after phosphatase activation. CAPP activation correlated with restored uptake of FM4-64 to the vacuole, the uptake and degradation of the Ste2 receptor after mating factor treatment, and the dephosphorylation and assembly of Tlg1,2 into SNARE complexes. Activation of the phosphatase by treatment with C 2 -ceramide, VBM/ELO gene inactivation, or by the overexpression of SIT4 was sufficient to confer rescue. Finally, we found that mutation of single PKA sites in Tlg1 (Ser31 to Ala31) or Tlg2 (Ser90 to Ala90) was sufficient to restore endocytosis, but not exocytosis, to snc cells. These results suggest that endocytosis is also modulated by t-SNARE phosphorylation in vivo.

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A Role for Tlg1p in the Transport of Proteins within the Golgi Apparatus ofSaccharomyces cerevisiae

Cited by 55 publications

References 75 publications

Specific Retrieval of the Exocytic SNARE Snc1p from Early Yeast Endosomes

Specific Retrieval of the Exocytic SNARE Snc1p from Early Yeast Endosomes

Early Stages of the Secretory Pathway, but Not Endosomes, Are Required for Cvt Vesicle and Autophagosome Assembly inSaccharomyces cerevisiae

t-SNARE Phosphorylation Regulates Endocytosis in Yeast

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