scholarly journals Life and Death of Fungal Transporters under the Challenge of Polarity

2020 ◽  
Vol 21 (15) ◽  
pp. 5376
Author(s):  
Sofia Dimou ◽  
George Diallinas
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Cell Polarity ◽  
Secretory Pathway ◽  
Fungal Growth ◽  
Multivesicular Bodies ◽  
Present Evidence ◽  
Life And Death ◽  
Early Endosomes ◽  
Stress Signals

Eukaryotic plasma membrane (PM) transporters face critical challenges that are not widely present in prokaryotes. The two most important issues are proper subcellular traffic and targeting to the PM, and regulated endocytosis in response to physiological, developmental, or stress signals. Sorting of transporters from their site of synthesis, the endoplasmic reticulum (ER), to the PM has been long thought, but not formally shown, to occur via the conventional Golgi-dependent vesicular secretory pathway. Endocytosis of specific eukaryotic transporters has been studied more systematically and shown to involve ubiquitination, internalization, and sorting to early endosomes, followed by turnover in the multivesicular bodies (MVB)/lysosomes/vacuole system. In specific cases, internalized transporters have been shown to recycle back to the PM. However, the mechanisms of transporter forward trafficking and turnover have been overturned recently through systematic work in the model fungus Aspergillus nidulans. In this review, we present evidence that shows that transporter traffic to the PM takes place through Golgi bypass and transporter endocytosis operates via a mechanism that is distinct from that of recycling membrane cargoes essential for fungal growth. We discuss these findings in relation to adaptation to challenges imposed by cell polarity in fungi as well as in other eukaryotes and provide a rationale of why transporters and possibly other housekeeping membrane proteins ‘avoid’ routes of polar trafficking.

scholarly journals Life and Death of Fungal Transporters Under the Challenge of Polarity

2020 ◽  
Author(s):  
Sofia Dimou ◽  
George Diallinas
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Proteins ◽  
Cell Polarity ◽  
Secretory Pathway ◽  
Fungal Growth ◽  
Present Evidence ◽  
Life And Death ◽  
Early Endosomes ◽  
Stress Signals

Eukaryotic plasma membrane (PM) transporters face critical challenges that are not widely present in prokaryotes. The two most important issues are proper subcellular traffic and targeting to the PM, and regulated endocytosis in response to physiological, developmental or stress signals. Sorting of transporters from their site of synthesis, the Endoplasmic Reticulum (ER), to the PM has been long thought, but not formally shown, to occur via the conventional Golgi-dependent vesicular secretory pathway. Endocytosis of specific eukaryotic transporters has been studied more systematically and shown to involve ubiquitination, internalization, and sorting to early endosomes, followed by turnover in the MVB/lysosomes/vacuole system. In specific cases internalized transporters have been shown to recycle back to the PM. However, the mechanisms of transporter forward trafficking and turnover have been overturned recently through systematic work in the model fungus Aspergillus nidulans. In this review we present evidence that shows that transporter traffic to the PM takes place through Golgi-bypass and transporter endocytosis operates via a mechanism that is distinct from that of recycling membrane cargoes essential for fungal growth. We discuss these findings in relation to adaptation to challenges imposed by cell polarity in fungi as well as in other eukaryotes and provide a rationale why transporters and possibly other housekeeping membrane proteins ‘avoid’ routes of polar trafficking.

scholarly journals The endosomal transcriptional regulator RNF11 integrates degradation and transport of EGFR

2016 ◽  
Vol 215 (4) ◽  
pp. 543-558 ◽  
Author(s):  
Sandra Scharaw ◽  
Murat Iskar ◽  
Alessandro Ori ◽  
Gaelle Boncompain ◽  
Vibor Laketa ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Egf Receptor ◽  
Regulatory Mechanism ◽  
Transcriptional Regulator ◽  
Transport Efficiency ◽  
Early Endosomes ◽  
Epidermal Growth ◽  
Partial Degradation ◽  
Stimulation Of

Stimulation of cells with epidermal growth factor (EGF) induces internalization and partial degradation of the EGF receptor (EGFR) by the endo-lysosomal pathway. For continuous cell functioning, EGFR plasma membrane levels are maintained by transporting newly synthesized EGFRs to the cell surface. The regulation of this process is largely unknown. In this study, we find that EGF stimulation specifically increases the transport efficiency of newly synthesized EGFRs from the endoplasmic reticulum to the plasma membrane. This coincides with an up-regulation of the inner coat protein complex II (COPII) components SEC23B, SEC24B, and SEC24D, which we show to be specifically required for EGFR transport. Up-regulation of these COPII components requires the transcriptional regulator RNF11, which localizes to early endosomes and appears additionally in the cell nucleus upon continuous EGF stimulation. Collectively, our work identifies a new regulatory mechanism that integrates the degradation and transport of EGFR in order to maintain its physiological levels at the plasma membrane.

Formation of chlamydospores in Gilbertella persicaria

1981 ◽  
Vol 59 (5) ◽  
pp. 908-928 ◽  
Author(s):  
Martha J. Powell ◽  
Charles E. Bracker ◽  
David J. Sternshein
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Acid Phosphatase ◽  
Light And Electron Microscopy ◽  
Multivesicular Bodies ◽  
Marker Enzyme ◽  
Transparent Layer ◽  
Thiamine Pyrophosphatase ◽  
Gilbertella Persicaria

The cytological events involved in the transformation of vegetative hyphae of the zygomycete Gilbertella persicaria (Eddy) Hesseltine into chlamydospores were studied with light and electron microscopy. Thirty hours after sporangiospores were inoculated into YPG broth, swellings appeared along the aseptate hyphae. Later, septa, traversed by plasmodesmata, delimited each end of the hyphal swellings and compartmentalized these hyphal regions as they differentiated into chlamydospores. Nonswollen regions adjacent to chlamydospores remained as isthmuses. Two additional wall layers appeared within the vegetative wall of the developing chlamydospores. An alveolate, electron-dense wall formed first, and then an electron-transparent layer containing concentrically oriented fibers formed between this layer and the plasma membrane. Rather than a mere condensation of cytoplasm, development and maturation of the multinucleate chlamydospores involved extensive cytoplasmic changes such as an increase in reserve products, lipid and glycogen, an increase and then disappearance of vacuoles, and the breakdown of many mitochondria. Underlying the plasma membrane during chlamydospore wall formation were endoplasmic reticulum, multivesicular bodies, vesicles with fibrillar contents, vesicles with electron-transparent contents, and cisternal rings containing the Golgi apparatus marker enzyme, thiamine pyrophosphatase. Acid phosphatase activity was localized cytochemically in a cisterna which enclosed mitochondria and in vacuoles which contained membrane fragments. Tightly packed membrane whorls and single membrane bounded sacs with finely granular matrices surrounding vacuoles were unique during chlamydospore development. Microbodies were rare in the mature chlamydospore, but endoplasmic reticulum was closely associated with lipid globules. As chlamydospores developed, the cytoplasm in the isthmus became highly vacuolated, lipid globules were closely associated with vacuoles, mitochondria were broken down in vacuoles, unusual membrane configurations appeared, and eventually the membranes degenerated. Unlike chlamydospores, walls of the isthmus did not thicken, but irregularly shaped appositions containing numerous channels formed at intervals on the inside of these walls. The pattern of cytoplasmic transformations during chlamydospore development is similar to events leading to the formation of zygospores and sporangiospores.

scholarly journals Ykt6 membrane-to-cytosol cycling regulates exosomal Wnt secretion

2018 ◽  
Author(s):  
Karen Linnemannstöns ◽  
Pradhipa Karuna M ◽  
Leonie Witte ◽  
Jeanette Clarissa Kittel ◽  
Adi Danieli ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Wnt Signaling ◽  
Signaling Pathways ◽  
Long Range ◽  
Protein Trafficking ◽  
Secretory Pathway ◽  
Multivesicular Bodies ◽  
Phosphorylation Sites ◽  
Wnt Proteins ◽  
C Terminus

Protein trafficking in the secretory pathway, for example the secretion of Wnt proteins, requires tight regulation. These ligands activate Wnt signaling pathways and are crucially involved in development and disease. Wnt is transported to the plasma membrane by its cargo receptor Evi, where Wnt/Evi complexes are endocytosed and sorted onto exosomes for long-range secretion. However, the trafficking steps within the endosomal compartment are not fully understood. The promiscuous SNARE Ykt6 folds into an auto-inhibiting conformation in the cytosol, but a portion associates with membranes by its farnesylated and palmitoylated C-terminus. Here, we demonstrate that membrane detachment of Ykt6 is essential for exosomal Wnt secretion. We identified conserved phosphorylation sites within the SNARE domain of Ykt6, which block Ykt6 cycling from the membrane to the cytosol. In Drosophila, Ykt6-RNAi mediated block of Wg secretion is rescued by wildtype but not phosphomimicking Ykt6. The latter accumulates at membranes, while wildtype Ykt6 regulates Wnt trafficking between the plasma membrane and multivesicular bodies. Taken together, we show that a regulatory switch in Ykt6 fine-tunes sorting of Wnts in endosomes.

scholarly journals The unconventional biogenesis of Kv7.1-KCNE1 complexes

2020 ◽  
Vol 6 (14) ◽  
pp. eaay4472 ◽  
Author(s):  
Anna Oliveras ◽  
Clara Serrano-Novillo ◽  
Cristina Moreno ◽  
Alicia de la Cruz ◽  
Carmen Valenzuela ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Secretory Pathway ◽  
Regulatory Subunit ◽  
Long Qt ◽  
Ongoing Debate ◽  
Subcellular Compartment ◽  
Ongoing Controversy ◽  
The Subject ◽  
Complex Forms

The potassium channel Kv7.1 associates with the KCNE1 regulatory subunit to trigger cardiac IKs currents. Although the Kv7.1/KCNE1 complex has received much attention, the subcellular compartment hosting the assembly is the subject of ongoing debate. Evidence suggests that the complex forms either earlier in the endoplasmic reticulum or directly at the plasma membrane. Kv7.1 and KCNE1 mutations, responsible for long QT syndromes, impair association and traffic, thereby altering IKs currents. We found that Kv7.1 and KCNE1 do not assemble in the first stages of their biogenesis. Data support an unconventional secretory pathway for Kv7.1-KCNE1 that bypasses Golgi. This route targets channels to endoplasmic reticulum–plasma membrane junctions, where Kv7.1-KCNE1 assemble. This mechanism helps to resolve the ongoing controversy about the subcellular compartment hosting the association. Our results also provide new insights into IKs channel localization at endoplasmic reticulum–plasma membrane junctions, highlighting an alternative anterograde trafficking mechanism for oligomeric ion channels.

scholarly journals ON THE THICKNESS OF THE UNIT MEMBRANE

1963 ◽  
Vol 17 (2) ◽  
pp. 413-421 ◽  
Author(s):  
Toshiyuki Yamamoto
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Electron Micrographs ◽  
Synaptic Vesicles ◽  
Multivesicular Bodies ◽  
Unit Membrane ◽  
Cell Organelles ◽  
Membrane Unit ◽  
Nuclear Membranes ◽  
Golgi Vesicles

Peak-to-peak distances between two dense lines of the unit membranes of cell organelles were measured on electron micrographs. These distances were compared with corresponding measurements on the plasma membrane and assigned a percentage value. The comparison between organelle and plasma membrane was always carried out with the same negative, in order to exclude as far as possible errors due to differences in focus or other causes. It was revealed by this study that the membranous structures of the cell can be classified into two groups, one thicker and one thinner. Unit membranes of the thicker group (synaptic vesicles, vesicles and capsules of multivesicular bodies, Golgi vesicles) were not significantly different in thickness from the plasma membrane. Unit membranes of the thinner group (mitochondria, nuclear membranes, Golgi lamellae, endoplasmic reticulum), however, were between 85 and 90 per cent of the thickness of the plasma membrane.

scholarly journals Stress-Induced Intracellular Trafficking of Corticotropin-Releasing Factor Receptors in Rat Locus Coeruleus Neurons

Endocrinology ◽  
2007 ◽  
Vol 149 (1) ◽  
pp. 122-130 ◽  
Author(s):  
Beverly A. S. Reyes ◽  
Rita J. Valentino ◽  
Elisabeth J. Van Bockstaele
Keyword(s):  
Plasma Membrane ◽  
Golgi Apparatus ◽  
Locus Coeruleus ◽  
Intracellular Trafficking ◽  
Corticotropin Releasing Factor ◽  
Cellular Trafficking ◽  
Multivesicular Bodies ◽  
Swim Stress ◽  
Early Endosomes ◽  
Crf1 Antagonist

Corticotropin-releasing factor (CRF) activates locus coeruleus (LC)-norepinephrine neurons during stress. Previous stress or CRF administration attenuates the magnitude of this response by decreasing postsynaptic sensitivity to CRF. Here we describe the fate of CRF receptors (CRFr) in LC neurons after stress. Rats were exposed to swim stress or handling and perfused 1 or 24 h later. Sections through the LC were processed for immunogold-silver labeling of CRFr. CRFr in LC dendrites was present on the plasma membrane and within the cytoplasm. In control rats, the ratio of cytoplasmic to total dendritic labeling was 0.55 ± 0.01. Swim stress increased this ratio to 0.77 ± 0.01 and 0.80 ± 0.02 at 1 and 24 h after stress, respectively. Internalized CRFr was associated with different organelles at different times after stress. At 1 h after stress, CRFr was often associated with early endosomes in dendrites and perikarya. By 24 h, more CRFr was associated with multivesicular bodies, suggesting that some of the internalized receptor is targeted for degradation. In perikarya, more internalized CRFr was associated with Golgi apparatus 24 vs. 1 h after stress. This is suggestive of changes in CRFr synthesis. Alternatively, this may indicate communication between multivesicular bodies and Golgi apparatus in the process of recycling. Administration of the selective CRF1 antagonist, antalarmin, before swim stress attenuated CRFr internalization. The present demonstration of stress-induced internalization of CRFr in LC neurons provides evidence that CRF is released in the LC during swim stress to activate this system and initiate cellular trafficking of the receptor that determines subsequent sensitivity of LC neurons to CRF.

scholarly journals Role of the Transmembrane Domain of Marburg Virus Surface Protein GP in Assembly of the Viral Envelope

2007 ◽  
Vol 81 (8) ◽  
pp. 3942-3948 ◽  
Author(s):  
Eva Mittler ◽  
Larissa Kolesnikova ◽  
Thomas Strecker ◽  
Wolfgang Garten ◽  
Stephan Becker
Keyword(s):  
Plasma Membrane ◽  
Secretory Pathway ◽  
Matrix Protein ◽  
Transmembrane Domain ◽  
Transmembrane Protein ◽  
Marburg Virus ◽  
Viral Envelope ◽  
Major Protein ◽  
Multivesicular Bodies ◽  
Virus Surface

ABSTRACT The major protein constituents of the filoviral envelope are the matrix protein VP40 and the surface transmembrane protein GP. While VP40 is recruited to the sites of budding via the late retrograde endosomal transport route, GP is suggested to be transported via the classical secretory pathway involving the endoplasmic reticulum, Golgi apparatus, and trans-Golgi network until it reaches the plasma membrane where most filoviral budding takes place. Since both transport routes target the plasma membrane, it was thought that GP and VP40 join there to form the viral envelope. However, it was recently shown that, upon coexpression of both proteins, GP is partially recruited into peripheral VP40-enriched multivesicular bodies, which contained markers of the late endosome. Accumulation of GP and VP40 in this compartment was presumed to play an important role in the formation of the filoviral envelope. Using a domain-swapping approach, we were able to show that the transmembrane domain of GP was essential and sufficient for (i) partial recruitment of chimeric glycoproteins into VP40-enriched multivesicular bodies and (ii) incorporation into virus-like particles (VLPs) that were released upon expression of VP40. Only those chimeric glycoproteins which were targeted to VP40-enriched endosomal multivesicular bodies were subsequently recruited into VLPs. These data show that the transmembrane domain of GP is critical for the mixing of VP40 and GP in multivesicular bodies and incorporation of GP into the viral envelope. Results further suggest that trapping of GP in the VP40-enriched late endosomal compartment is important for the formation of the viral envelope.

scholarly journals Assembly of influenza hemagglutinin trimers and its role in intracellular transport.

1986 ◽  
Vol 103 (4) ◽  
pp. 1179-1191 ◽  
Author(s):  
C S Copeland ◽  
R W Doms ◽  
E M Bolzau ◽  
R G Webster ◽  
A Helenius
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Golgi Complex ◽  
Intracellular Transport ◽  
Secretory Pathway ◽  
Quaternary Structure ◽  
Subunit Interactions ◽  
Oligomer Formation ◽  
Influenza Hemagglutinin ◽  
Triton X

The hemagglutinin (HA) of influenza virus is a homotrimeric integral membrane glycoprotein. It is cotranslationally inserted into the endoplasmic reticulum as a precursor called HA0 and transported to the cell surface via the Golgi complex. We have, in this study, investigated the kinetics and cellular location of the assembly reaction that results in HA0 trimerization. Three independent criteria were used for determining the formation of quaternary structure: the appearance of an epitope recognized by trimer-specific monoclonal antibodies; the acquisition of trypsin resistance, a characteristic of trimers; and the formation of stable complexes which cosedimented with the mature HA0 trimer (9S20,w) in sucrose gradients containing Triton X-100. The results showed that oligomer formation is a posttranslational event, occurring with a half time of approximately 7.5 min after completion of synthesis. Assembly occurs in the endoplasmic reticulum, followed almost immediately by transport to the Golgi complex. A stabilization event in trimer structure occurs when HA0 leaves the Golgi complex or reaches the plasma membrane. Approximately 10% of the newly synthesized HA0 formed aberrant trimers which were not transported from the endoplasmic reticulum to the Golgi complex or the plasma membrane. Taken together the results suggested that formation of correctly folded quaternary structure constitutes a key event regulating the transport of the protein out of the endoplasmic reticulum. Further changes in subunit interactions occur as the trimers move along the secretory pathway.

scholarly journals Intracellular Trafficking of a Palmitoylated Membrane-Associated Protein Component of Enveloped Vaccinia Virus

2003 ◽  
Vol 77 (16) ◽  
pp. 9008-9019 ◽  
Author(s):  
Matloob Husain ◽  
Bernard Moss
Keyword(s):  
Plasma Membrane ◽  
Vaccinia Virus ◽  
Intracellular Trafficking ◽  
Plasma Membranes ◽  
Secretory Pathway ◽  
Fluorescent Protein ◽  
Dominant Negative ◽  
Coated Pits ◽  
Early Endosomes ◽  
Green Fluorescent

ABSTRACT The F13L protein of vaccinia virus, an essential and abundant palmitoylated peripheral membrane component of intra- and extracellular enveloped virions, associates with Golgi, endosomal, and plasma membranes in the presence or absence of other viral proteins. In the present study, the trafficking of a fully functional F13L-green fluorescent protein (GFP) chimera in transfected and productively infected cells was analyzed using specific markers and inhibitors. We found that Sar1H79G, a trans-dominant-negative protein inhibitor of cargo transport from the endoplasmic reticulum, had no apparent effect on the intracellular distribution of F13L-GFP, suggesting that the initial membrane localization occurs at a downstream compartment of the secretory pathway. Recycling of F13L-GFP from the plasma membrane was demonstrated by partial colocalization with FM4-64, a fluorescent membrane marker of endocytosis. Punctate F13L-GFP fluorescence overlapped with clathrin and Texas red-conjugated transferrin, suggesting that endocytosis occurred via clathrin-coated pits. The inhibitory effects of chlorpromazine and trans-dominant-negative forms of dynamin and Eps15 protein on the recycling of F13L-GFP provided further evidence for clathrin-mediated endocytosis. In addition, the F13L protein was specifically coimmunoprecipitated with α-adaptin, a component of the AP-2 complex that interacts with Eps15. Nocodazole and wortmannin perturbed the intracellular trafficking of F13L-GFP, consistent with its entry into late and early endosomes through the secretory and endocytic pathways, respectively. The recycling pathway described here provides a mechanism for the reutilization of the F13L protein following its deposition in the plasma membrane during the exocytosis of enveloped virions.

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