scholarly journals A pathway for targeting soluble misfolded proteins to the yeast vacuole.

1996 ◽  
Vol 135 (3) ◽  
pp. 623-633 ◽  
Author(s):  
E Hong ◽  
A R Davidson ◽  
C A Kaiser
Keyword(s):  
Cell Surface ◽  
Secretory Pathway ◽  
Carboxypeptidase Y ◽  
Misfolded Protein ◽  
Secreted Protein ◽  
Wild Type ◽  
Salvage Pathway ◽  
Lambda Repressor ◽  
Hybrid Proteins ◽  
Mutant Forms

We have evaluated the fate of misfolded protein domains in the Saccharomyces cerevisiae secretory pathway by fusing mutant forms of the NH2-terminal domain of lambda repressor protein to the secreted protein invertase. The hybrid protein carrying the wild-type repressor domain is mostly secreted to the cell surface, whereas hybrid proteins with amino acid substitutions that cause the repressor domain to be thermodynamically unstable are retained intracellularly. Surprisingly, the retained hybrids are found in the vacuole, where the repressor moiety is degraded by vacuolar proteases. The following observations indicate that receptor-mediated recognition of the mutant repressor domain in the Golgi lumen targets these hybrid fusions to the vacuole. (a) The invertase-repressor fusions, like wild-type invertase, behave as soluble proteins in the ER lumen. (b) Targeting to the vacuole is saturable since overexpression of the hybrids carrying mutant repressor increases the fraction of fusion protein that appears at the cell surface. (c) Finally, deletion of the VPS10 gene, which encodes the transmembrane Golgi receptor responsible for targeting carboxypeptidase Y to the vacuole, causes the mutant hybrids to be diverted to the cell surface. Together these findings suggest that yeast have a salvage pathway for degradation of nonnative luminal proteins by receptor-mediated transport to the vacuole.

scholarly journals Characterization of TPM1 disrupted yeast cells indicates an involvement of tropomyosin in directed vesicular transport.

1992 ◽  
Vol 118 (2) ◽  
pp. 285-299 ◽  
Author(s):  
H Liu ◽  
A Bretscher
Keyword(s):  
Cell Surface ◽  
Secretory Pathway ◽  
Synthetic Lethality ◽  
Vesicular Transport ◽  
Yeast Cells ◽  
Carboxypeptidase Y ◽  
Apparent Loss ◽  
Abnormal Accumulation ◽  
Late Step ◽  
Actin Cables

Disruption of the yeast tropomyosin gene TPM1 results in the apparent loss of actin cables from the cytoskeleton (Liu, H., and A. Bretscher. 1989. Cell. 57:233-242). Here we show that TPM1 disrupted cells grow slowly, show heterogeneity in cell size, have delocalized deposition of chitin, and mate poorly because of defects in both shmooing and cell fusion. The transit time of alpha-factor induced a-agglutinin secretion to the cell surface is longer than in isogenic wild-type strains, and some of the protein is mislocalized. Many of the TPM1-deleted cells contain abundant vesicles, similar in morphology to late secretory vesicles, but without an abnormal accumulation of intermediates in the delivery of either carboxypeptidase Y to the vacuole or invertase to the cell surface. Combinations of the TPM1 disruption with sec13 or sec18 mutations, which affect early steps in the secretory pathway, block vesicle accumulation, while combinations with sec1, sec4 or sec6 mutations, which affect a late step in the secretory pathway, have no effect on the vesicle accumulation. The phenotype of the TPM1 disrupted cells is very similar to that of a conditional mutation in the MYO2 gene, which encodes a myosin-like protein (Johnston, G. C., J. A. Prendergast, and R. A. Singer. 1991. J. Cell Biol. 113:539-551). The myo2-66 conditional mutation shows synthetic lethality with the TPM1 disruption, indicating that the MYO2 and TPM1 gene products may be involved in the same, or parallel function. We conclude that tropomyosin, and by inference actin cables, may facilitate directed vesicular transport of components to the correct location on the cell surface.

scholarly journals Inhibition of tyrosine sulfation in the trans-Golgi retards the transport of a constitutively secreted protein to the cell surface.

1988 ◽  
Vol 107 (5) ◽  
pp. 1655-1667 ◽  
Author(s):  
E Friederich ◽  
H J Fritz ◽  
W B Huttner
Keyword(s):  
Cell Surface ◽  
Intracellular Transport ◽  
Secretory Protein ◽  
Reversible Inhibitor ◽  
Secreted Protein ◽  
Half Time ◽  
Wild Type ◽  
Tyrosine Sulfation ◽  
L Cell ◽  
Cell Clones

The effect of tyrosine sulfation on the transport of a constitutively secreted protein, yolk protein 2 (YP2) of Drosophila melanogaster, to the cell surface was investigated after expression of YP2 in mouse fibroblasts. Inhibition of YP2 sulfation was achieved by two distinct approaches. First, the single site of sulfation in YP2, tyrosine 172, was changed to phenylalanine by oligonucleotide-directed mutagenesis. Second, L cell clones stably expressing YP2 were treated with chlorate, a reversible inhibitor of sulfation. Pulse-chase experiments with transfected L cell clones showed that the half-time of transport from the rough endoplasmic reticulum to the cell surface of the unsulfated mutant YP2 and the unsulfated wild-type YP2 produced in the presence of chlorate was 15-18 min slower than that of the sulfated wild-type YP2. Control experiments indicated (a) that the tyrosine to phenylalanine change itself did not affect YP2 transport, (b) that the retardation of YP2 transport by chlorate occurred only with sulfatable but not with unsulfatable YP2, (c) that the transport difference between wild-type and mutant YP2 was not due to the level of YP2 expression, and (d) that transport of the endogenous secretory protein fibronectin was the same in L cell clones expressing wild-type and mutant YP2. Since the half-time of transport of wild-type YP2 from the intracellular site of sulfation, the trans-Golgi, to the cell surface was found to be 10 min, the 15-18-min retardation seen upon inhibition of tyrosine sulfation reflected a two- to threefold increase in the half-time of trans-Golgi to cell surface transport, which was most probably caused by an increased residence time of unsulfated YP2 in the trans-Golgi. The results demonstrate a role of tyrosine sulfation in the intracellular transport of a constitutively secreted protein.

scholarly journals Signal transduction by Fc gamma RIII (CD16) is mediated through the gamma chain.

1992 ◽  
Vol 175 (5) ◽  
pp. 1381-1390 ◽  
Author(s):  
U Wirthmueller ◽  
T Kurosaki ◽  
M S Murakami ◽  
J V Ravetch
Keyword(s):  
Signal Transduction ◽  
Cell Surface ◽  
Cell Activation ◽  
Receptor Activation ◽  
Alpha Subunit ◽  
Wild Type ◽  
Cytoplasmic Domains ◽  
Gamma Chain ◽  
Glycosyl Phosphatidylinositol ◽  
Mutant Forms

To determine the functional role of the two isoforms of Fc gamma RIII (CD16) (IIIA, IIIB), the signal transduction capabilities of wild-type and mutant forms of these receptors were analyzed in transfected lymphoid, myeloid, and fibroblastic cell lines. Functional reconstitution of receptor signalling was observed in hematopoietic T and mast cells, and was absent in nonhematopoietic (CHO) cells. Fc gamma RIIIA, a hetero-oligomeric receptor composed of a ligand-binding subunit alpha and dimeric gamma chains, generated both proximal and distal responses in Jurkat and P815 cells, typical of what is seen in natural killer cells and macrophages upon receptor activation. In contrast, Fc gamma RIIIB, which is normally attached to the cell surface via a glycosyl-phosphatidylinositol anchor, was incapable of transducing signals. After crosslinking, Fc gamma RIIIA signalling was dependent only upon the gamma chain. Fc gamma RIIIA chimeras in which the alpha subunit transmembrane and cytoplasmic domains were substituted with the corresponding gamma chain sequences functioned as well as wild-type hetero-oligomeric receptors. These data indicate that the ability of the Fc gamma RIIIA complex to activate the appropriate pathways for cell activation is cell-type restricted and independent of the transmembrane and cytoplasmic domains of the alpha subunit. The presence of the gamma chain is responsible for the assembly of, as well as the signal transduction by, the functional cell surface complex.

scholarly journals Proper Folding and Endoplasmic Reticulum to Golgi Transport of Tyrosinase Are Induced by Its Substrates, DOPA and Tyrosine

2000 ◽  
Vol 276 (15) ◽  
pp. 11933-11938 ◽  
Author(s):  
Ruth Halaban ◽  
Elaine Cheng ◽  
Sherri Svedine ◽  
Rebecca Aron ◽  
Daniel N. Hebert
Keyword(s):  
Endoplasmic Reticulum ◽  
Melanoma Cells ◽  
Proteolytic Degradation ◽  
Misfolded Protein ◽  
Antigenic Peptides ◽  
Wild Type ◽  
Native Form ◽  
Golgi Transport ◽  
Cellular Immune ◽  
Mutant Forms

Tyrosinase is essential for pigmentation and is a source of tumor-derived antigenic peptides and cellular immune response. Wild type tyrosinase in melanoma cells and certain albino mutants in untransformed melanocytes are targeted to proteolytic degradation by the 26 S proteasome due to retention of the misfolded protein in the endoplasmic reticulum and its subsequent retranslocation to the cytosol. Here, we demonstrate that the substrates DOPA and tyrosine induced in melanoma cells a transition of misfolded wild type tyrosinase to the native form that is resistant to proteolysis, competent to exit the endoplasmic reticulum, and able to produce melanin. Because the enzymatic activity of tyrosinase is induced by DOPA, we propose that proper folding of the wild type protein, just like mutant forms, is tightly linked to its catalytic state. Loss of pigmentation, therefore, in tyrosinase-positive melanoma cells is a consequence of tumor-induced metabolic changes that suppress tyrosinase activity and DOPA production within these cells.

scholarly journals The ankyrin repeat-containing protein Akr1p is required for the endocytosis of yeast pheromone receptors.

1997 ◽  
Vol 8 (7) ◽  
pp. 1317-1327 ◽  
Author(s):  
S A Givan ◽  
G F Sprague
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Surface ◽  
Hybrid System ◽  
Secretory Pathway ◽  
Cytoplasmic Tail ◽  
Ankyrin Repeat ◽  
Wild Type ◽  
Delta Cells ◽  
Type Receptor ◽  
Two Hybrid

The Saccharomyces cerevisiae a-factor receptor (Ste3p) requires its C-terminal cytoplasmic tail for endocytosis. Wild-type receptor is delivered to the cell surface via the secretory pathway but remains there only briefly before being internalized and delivered to the vacuole for degradation. Receptors lacking all or part of the cytoplasmic tail are not subject to this constitutive endocytosis. We used the cytoplasmic tail of Ste3p as bait in the two-hybrid system in an effort to identify other proteins involved in endocytosis. One protein identified was Akr1p, an ankyrin repeat-containing protein. We applied three criteria to demonstrate that Akr1p is involved in the constitutive endocytosis of Ste3p. First, when receptor synthesis is shut off, akr1 delta cells retain the ability to mate longer than do AKR1 cells. Second, Ste3p half-life is increased by greater than 5-fold in akr1 delta cells compared with AKR1 cells. Third, after a pulse of synthesis, newly synthesized receptor remains at the cell surface in akr1 delta mutants, whereas it is rapidly internalized in AKR1 cells. Specifically, in akr1 delta mutants, newly synthesized receptor is accessible to exogenous protease, and by indirect immunofluorescence, the receptor is located at the cell surface. akr1 delta cells are also defective for endocytosis of the alpha-factor receptor (Ste2p). Despite the block to constitutive endocytosis exhibited by akr1 delta cells, they are competent to carry out ligand-mediated endocytosis of Ste3p. In contrast, akr1 delta cells cannot carry out ligand-mediated endocytosis of Ste2p. We discuss the implications for Akr1p function in endocytosis and suggest a link to the regulation of ADP-ribosylation proteins (Arf proteins).

scholarly journals The effects of clathrin inactivation on localization of Kex2 protease are independent of the TGN localization signal in the cytosolic tail of Kex2p.

1996 ◽  
Vol 7 (11) ◽  
pp. 1667-1677 ◽  
Author(s):  
K Redding ◽  
M Seeger ◽  
G S Payne ◽  
R S Fuller
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Heavy Chain ◽  
Intracellular Transport ◽  
Chain Gene ◽  
Wild Type ◽  
Clathrin Heavy Chain ◽  
Localization Signal ◽  
Mutant Forms ◽  
Kex2 Protease

Localization of Kex2 protease (Kex2p) to the yeast trans-Golgi network (TGN) requires a TGN localization signal (TLS) in the Kex2p C-terminal cytosolic tail. Mutation of the TLS accelerates transport of Kex2p to the vacuole by an intracellular (SEC1-independent) pathway. In contrast, inactivation of the clathrin heavy-chain gene CHC1 results in transport of Kex2p and other Golgi membrane proteins to the cell surface. Here, the relationship of the two localization defects was assessed by examining the effects of a temperature-sensitive CHC1 allele on trafficking of wild-type (WT) and TLS mutant forms of Kex2p. Inactivation of clathrin by shifting chc1-ts cells to 37 degrees C caused WT and TLS mutant forms of Kex2p to behave identically. All forms of Kex2p appeared at the plasma membrane within 30-60 min of the temperature shift. TLS mutant forms of Kex2p were stabilized, their half-lives increasing to that of wild-type Kex2p. After inactivation of clathrin heavy chain, vacuolar protease-dependent degradation of all forms of Kex2p was blocked by a sec1 mutation, which is required for secretory vesicle fusion to the plasma membrane, indicating that transport to the cell surface was required for degradation by vacuolar proteolysis. Finally, after clathrin inactivation, all forms of Kex2p were degraded in part by a vacuolar protease-independent pathway. After inactivation of both chc1-ts and sec1-ts, Kex2 was degraded exclusively by this pathway. We conclude that the effects of clathrin inactivation on Kex2p localization are independent of the Kex2p C-terminal cytosolic tail. Although these results neither prove nor rule out a direct interaction between the Kex2 TLS and a clathrin-dependent structure, they do imply that clathrin is required for the intracellular transport of Kex2p TLS mutants to the vacuole.

scholarly journals Yos9p and Hrd1p mediate ER retention of misfolded proteins for ER-associated degradation

2012 ◽  
Vol 23 (7) ◽  
pp. 1283-1293 ◽  
Author(s):  
Toshiaki Izawa ◽  
Hiroyuki Nagai ◽  
Toshiya Endo ◽  
Shuh-ichi Nishikawa
Keyword(s):  
Fusion Proteins ◽  
Secretory Pathway ◽  
Early Stage ◽  
Misfolded Proteins ◽  
Carboxypeptidase Y ◽  
Misfolded Protein ◽  
Er Retention ◽  
Hsp70 Chaperone ◽  
Degradation Step ◽  
Glycan Degradation

The endoplasmic reticulum (ER) has an elaborate quality control system, which retains misfolded proteins and targets them to ER-associated protein degradation (ERAD). To analyze sorting between ER retention and ER exit to the secretory pathway, we constructed fusion proteins containing both folded carboxypeptidase Y (CPY) and misfolded mutant CPY (CPY*) units. Although the luminal Hsp70 chaperone BiP interacts with the fusion proteins containing CPY* with similar efficiency, a lectin-like ERAD factor Yos9p binds to them with different efficiency. Correlation between efficiency of Yos9p interactions and ERAD of these fusion proteins indicates that Yos9p but not BiP functions in the retention of misfolded proteins for ERAD. Yos9p targets a CPY*-containing ERAD substrate to Hrd1p E3 ligase, thereby causing ER retention of the misfolded protein. This ER retention is independent of the glycan degradation signal on the misfolded protein and operates even when proteasomal degradation is inhibited. These results collectively indicate that Yos9p and Hrd1p mediate ER retention of misfolded proteins in the early stage of ERAD, which constitutes a process separable from the later degradation step.

scholarly journals The beta 4 subunit cytoplasmic domain mediates the interaction of alpha 6 beta 4 integrin with the cytoskeleton of hemidesmosomes.

1993 ◽  
Vol 4 (9) ◽  
pp. 871-884 ◽  
Author(s):  
L Spinardi ◽  
Y L Ren ◽  
R Sanders ◽  
F G Giancotti
Keyword(s):  
Cell Surface ◽  
Cytoplasmic Domain ◽  
Wild Type ◽  
Type Iii ◽  
Amino Acid Region ◽  
C Terminus ◽  
Mutant Forms ◽  
Terminal Pair ◽  
Acid Region

The alpha 6 beta 4 integrin is structurally distinct from all the other known integrins because the cytoplasmic domain of beta 4 is unusually large and contains four type III fibronectin-like modules toward its C-terminus. To examine the function of the beta 4 cytoplasmic tail, we have expressed full-length and truncated human beta 4 cDNAs in rat bladder epithelial 804G cells, which form hemidesmosome-like adhesions in vitro. The cDNA encoded wild-type beta 4 subunit associated with endogenous alpha 6 and was recruited at the cell surface within hemidesmosome-like adhesions. A recombinant form of beta 4, lacking almost the entire cytoplasmic domain associated with alpha 6, reached the cell surface but remained diffusely distributed. A beta 4 molecule lacking almost the entire extracellular portion did not associate with alpha 6 but was correctly targeted to the hemidesmosome-like adhesions. Thus, the cytoplasmic portion of beta 4 contains sequences that are required and may be sufficient for the assembly of the alpha 6 beta 4 integrin into hemidesmosomes. To localize these sequences we examined the properties of additional mutant forms of beta 4. A truncated beta 4 subunit, lacking the most C-terminal pair of type III fibronectin homology domains, was incorporated into hemidesmosome-like adhesions, but another recombinant beta 4 molecule, lacking both pairs of type III fibronectin repeats, was not. Finally a recombinant beta 4 molecule, which was created by adjoining the region of the cytoplasmic domain including all type III repeats to the transmembrane segment, was efficiently recruited in hemidesmosome-like adhesions. Taken together these results suggest that the assembly of the alpha 6 beta 4 integrin into hemidesmosomes is mediated by a 303-amino acid region of beta 4 tail that comprises the first pair of type III fibronectin repeats and the segment between the second and third repeats. These data imply a function of a specific segment of the beta 4 cytoplasmic domain in interaction with cytoskeletal components of hemidesmosomes.

scholarly journals The Protein Tyrosine Phosphatase PTP1B Is Required for Efficient Delivery of N-Cadherin to the Cell Surface

2010 ◽  
Vol 21 (8) ◽  
pp. 1387-1397 ◽  
Author(s):  
Mariana V. Hernández ◽  
Diana P. Wehrendt ◽  
Carlos O. Arregui
Keyword(s):  
Cell Surface ◽  
Secretory Pathway ◽  
Tyrosine Phosphatase ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
P120 Catenin ◽  
Efficient Delivery ◽  
Kinetics Of ◽  
Higher Sensitivity ◽  
Endoglycosidase H

PTP1B bound to mature N-cadherin promotes the association of β-catenin into the complex, the stable expression of the complex at cell surface, and cadherin-mediated adhesion. Here we show that PTP1B is also required for N-cadherin precursor trafficking through early stages of the secretory pathway. This function does not require association of PTP1B with the precursor. In PTP1B null cells, the N-cadherin precursor showed higher sensitivity to endoglycosidase H than in cells reconstituted with the wild-type enzyme. It also showed slower kinetics of ER-to-Golgi translocation and processing. Trafficking of the viral stomatitis vesicular glycoprotein, VSV-G, however, revealed no differences between PTP1B null and reconstituted cells. N-cadherin precursor complexes contained similar levels of α- and β-catenin regardless of PTP1B expression. In contrast, the associated p120 catenin (p120) was significantly reduced in absence of PTP1B expression. An N-cadherin precursor construct defective in p120 binding, and expressed in PTP1B reconstituted cells, showed higher sensitivity to endoglycosidase H and slower kinetics of processing than the wild-type precursor. Our results suggest that PTP1B promotes the association of p120 to the N-cadherin precursor, facilitating the trafficking of the complex from the ER to the Golgi complex.

scholarly journals Investigation of the Stability of Yeast rad52 Mutant Proteins Uncovers Post-translational and Transcriptional Regulation of Rad52p

Genetics ◽  
2003 ◽  
Vol 163 (1) ◽  
pp. 91-101 ◽  
Author(s):  
Erin N Asleson ◽  
Dennis M Livingston
Keyword(s):  
Half Life ◽  
Translational Regulation ◽  
Cellular Level ◽  
Missense Mutations ◽  
Wild Type ◽  
Mutant Proteins ◽  
Gal1 Promoter ◽  
Rad52 Protein ◽  
The Stability ◽  
Mutant Forms

Abstract We investigated the stability of the Saccharomyces cerevisiae Rad52 protein to learn how a cell controls its quantity and longevity. We measured the cellular levels of wild-type and mutant forms of Rad52p when expressed from the RAD52 promoter and the half-lives of the various forms of Rad52p when expressed from the GAL1 promoter. The wild-type protein has a half-life of 15 min. rad52 mutations variably affect the cellular levels of the protein products, and these levels correlate with the measured half-lives. While missense mutations in the N terminus of the protein drastically reduce the cellular levels of the mutant proteins, two mutations—one a deletion of amino acids 210-327 and the other a missense mutation of residue 235—increase the cellular level and half-life more than twofold. These results suggest that Rad52p is subject to post-translational regulation. Proteasomal mutations have no effect on Rad52p half-life but increase the amount of RAD52 message. In contrast to Rad52p, the half-life of Rad51p is >2 hr, and RAD51 expression is unaffected by proteasomal mutations. These differences between Rad52p and Rad51p suggest differential regulation of two proteins that interact in recombinational repair.

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