-
International Journal of Molecular... Jul 2020Eukaryotic plasma membrane (PM) transporters face critical challenges that are not widely present in prokaryotes. The two most important issues are proper subcellular... (Review)
Review
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 . 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.
Topics: Aspergillus nidulans; Cell Membrane; Endocytosis; Endoplasmic Reticulum; Endosomes; Fungal Proteins; Gene Expression Regulation, Fungal; Golgi Apparatus; Lysosomes; Membrane Transport Proteins; Multivesicular Bodies; Protein Transport; Saccharomyces cerevisiae; Secretory Pathway; Vacuoles
PubMed: 32751072
DOI: 10.3390/ijms21155376 -
MBio Oct 2020Directional growth and tissue invasion by hyphae of the pathogenic fungus, , are disrupted by deletion of the small GTPase, Rsr1, which localizes Cdc42 and its kinase,...
Directional growth and tissue invasion by hyphae of the pathogenic fungus, , are disrupted by deletion of the small GTPase, Rsr1, which localizes Cdc42 and its kinase, Cla4, to the site of polarized growth. We investigated additional abnormalities observed in Δ hyphae, including vacuole development, cytoplasm inheritance, mitochondrial morphology, septin ring organization, nuclear division and migration, and branching frequency, which together demonstrate a fundamental role for Rsr1 in cellular organization. Rsr1 contains a C-terminal CCAAX box, which putatively undergoes both reversible palmitoylation and farnesylation for entry into the secretory pathway. We expressed variants of Rsr1 with mutated C244 or C245, or which lacked GTPase activity (Rsr1 and Rsr1), in the Δ background and compared the resulting phenotypes with those of mutants lacking Bud5 (Rsr1 GEF), Bud2 (Rsr1 GAP), or Cla4. Bud5 was required only for cell size and bud site selection in yeast, suggesting there are alternative activators for Rsr1 in hyphae. Septin ring and vacuole dynamics were restored by expression of unpalmitoylated Rsr1, which localized to endomembranes, but not by cytoplasmic Rsr1 or GTP/GDP-locked Rsr1, suggesting Rsr1 functions at intracellular membranes in addition to the plasma membrane. Rsr1 or cytoplasmic Rsr1 restored normal nuclear division but not septin ring or vacuole dynamics. Rsr1-GDP therefore plays a specific role in suppressing START, which can be signaled from the cytosol. Via differential palmitoylation and activity states, Rsr1 operates at diverse cell sites to orchestrate proper nuclear division and inheritance during constitutive polarized growth. As Δ phenocopied Δ, it is likely these functions involve Cdc42-Cla4 activity. Understanding how single eukaryotic cells self-organize to replicate and migrate is relevant to health and disease. In the fungal pathogen, , the small GTPase, Rsr1, guides the directional growth of hyphae that invade human tissue during life-threatening infections. Rsr1 is a Ras-like GTPase and a homolog of the conserved Rap1 subfamily, which directs migration in mammalian cells. Research into how this single GTPase delivers complex intracellular patterning is challenging established views of GTPase regulation, trafficking, and interaction. Here, we show that Rsr1 directly and indirectly coordinates the spatial and temporal development of key intracellular macrostructures, including septum formation and closure, vacuole dynamics, and nuclear division and segregation, as well as whole-cell morphology by determining branching patterns. Furthermore, we categorize these functions by differential Rsr1 localization and activity state and provide evidence to support the emerging view that the cytosolic pool of Ras-like GTPases is functionally active.
Topics: Candida albicans; Cytoplasm; Fungal Proteins; GTP Phosphohydrolases; Hyphae; Lipoylation; Protein Transport; Septins; Vacuoles; rab GTP-Binding Proteins
PubMed: 33051364
DOI: 10.1128/mBio.01666-20 -
MBio Dec 2021Microorganisms typically maintain cellular homeostasis despite facing large fluctuations in their surroundings. Microbes that reside on human mucosal surfaces may...
Microorganisms typically maintain cellular homeostasis despite facing large fluctuations in their surroundings. Microbes that reside on human mucosal surfaces may experience significant variations in nutrient and ion availability as well as pH. Whether the mechanisms employed by these microbial cells to sustain homeostasis directly impact on the interplay with the host's mucosae remains unclear. Here, we report that the previously uncharacterized transcription regulator in the human-associated yeast Candida albicans maintains vacuole homeostasis when the fungus faces fluctuations in nitrogen. Genome-wide identification of genes directly regulated by Zcf8p followed by fluorescence microscopy to define their subcellular localization uncovered the fungal vacuole as a top target of Zcf8p regulation. Deletion and overexpression of resulted in alterations in vacuolar morphology and luminal pH and rendered the fungus resistant or susceptible to nigericin and brefeldin A, two drugs that impair vacuole and associated functions. Furthermore, we establish that the regulator modulates C. albicans attachment to epithelial cells in a manner that depends on the status of the fungal vacuole. Our findings, therefore, suggest that fungal vacuole physiology regulation is intrinsically linked to, and shapes to a significant extent, the physical interactions that cells establish with mammalian mucosal surfaces. Candida albicans is a fungus that resides on various human mucosal surfaces. Individuals with debilitated immune systems are prone to develop C. albicans infections, which can range in severity from mucosal disease (e.g., oral thrush in AIDS patients) to life-threatening conditions (e.g., deep-seated, disseminated infections in patients undergoing organ transplants). Understanding the cellular and molecular mechanisms that this eukaryotic microbe employs to colonize different parts of the human body and to cause disease will lay the foundation for the development of novel strategies for preventing and treating C. albicans infections. This report establishes the fungal vacuole, a key organelle to the overall fungal physiology, as a key determinant of the interplay between C. albicans and mammalian mucosal surfaces.
Topics: Animals; Candida albicans; Candidiasis; Epithelial Cells; Female; Fungal Proteins; Gene Expression Regulation, Fungal; Humans; Mice; Mice, Inbred C57BL; Spores, Fungal; Transcription Factors; Vacuoles
PubMed: 34781731
DOI: 10.1128/mBio.03020-21 -
Translational Neurodegeneration May 2020Lysosomes digest extracellular material from the endocytic pathway and intracellular material from the autophagic pathway. This process is performed by the resident... (Review)
Review
BACKGROUND
Lysosomes digest extracellular material from the endocytic pathway and intracellular material from the autophagic pathway. This process is performed by the resident hydrolytic enzymes activated by the highly acidic pH within the lysosomal lumen. Lysosome pH gradients are mainly maintained by the vacuolar (H) ATPase (or V-ATPase), which pumps protons into lysosomal lumen by consuming ATP. Dysfunction of V-ATPase affects lysosomal acidification, which disrupts the clearance of substrates and leads to many disorders, including neurodegenerative diseases.
MAIN BODY
As a large multi-subunit complex, the V-ATPase is composed of an integral membrane V0 domain involved in proton translocation and a peripheral V1 domain catalyzing ATP hydrolysis. The canonical functions of V-ATPase rely on its H-pumping ability in multiple vesicle organelles to regulate endocytic traffic, protein processing and degradation, synaptic vesicle loading, and coupled transport. The other non-canonical effects of the V-ATPase that are not readily attributable to its proton-pumping activity include membrane fusion, pH sensing, amino-acid-induced activation of mTORC1, and scaffolding for protein-protein interaction. In response to various stimuli, V-ATPase complex can reversibly dissociate into V1 and V0 domains and thus close ATP-dependent proton transport. Dysregulation of pH and lysosomal dysfunction have been linked to many human diseases, including neurodegenerative disorders such as Alzheimer disease, Parkinson's disease, amyotrophic lateral sclerosis as well as neurodegenerative lysosomal storage disorders.
CONCLUSION
V-ATPase complex is a universal proton pump and plays an important role in lysosome acidification in all types of cells. Since V-ATPase dysfunction contributes to the pathogenesis of multiple neurodegenerative diseases, further understanding the mechanisms that regulate the canonical and non-canonical functions of V-ATPase will reveal molecular details of disease process and help assess V-ATPase or molecules related to its regulation as therapeutic targets.
Topics: Humans; Hydrogen-Ion Concentration; Lysosomal Storage Diseases; Lysosomes; Neurodegenerative Diseases; Vacuolar Proton-Translocating ATPases; Vacuoles
PubMed: 32393395
DOI: 10.1186/s40035-020-00196-0 -
Cell Host & Microbe Dec 2022The human pathogen Chlamydia trachomatis evades killing by IFNγ-activated mechanisms, yet how this occurs remains unclear. In this issue of Cell Host & Microbe, Walsh...
The human pathogen Chlamydia trachomatis evades killing by IFNγ-activated mechanisms, yet how this occurs remains unclear. In this issue of Cell Host & Microbe, Walsh et al. identify an IFNγ-dependent antimicrobial mechanism mediated by the host ubiquitin ligase RNF213 that is evaded by the Chlamydia effector GarD.
Topics: Humans; Vacuoles; Chlamydia trachomatis; Interferon-gamma; Ubiquitin; Chlamydia Infections; Host-Pathogen Interactions; HeLa Cells; Adenosine Triphosphatases; Ubiquitin-Protein Ligases
PubMed: 36521440
DOI: 10.1016/j.chom.2022.11.007 -
Cell Reports Jan 2021Membrane contact sites facilitate the exchange of metabolites between organelles to support interorganellar communication. The nucleus-vacuole junctions (NVJs) establish...
Membrane contact sites facilitate the exchange of metabolites between organelles to support interorganellar communication. The nucleus-vacuole junctions (NVJs) establish physical contact between the perinuclear endoplasmic reticulum (ER) and the vacuole. Although the NVJ tethers are known, how NVJ abundance and composition are controlled in response to metabolic cues remains elusive. Here, we identify the ER protein Snd3 as central factor for NVJ formation. Snd3 interacts with NVJ tethers, supports their targeting to the contacts, and is essential for NVJ formation. Upon glucose exhaustion, Snd3 relocalizes from the ER to NVJs and promotes contact expansion regulated by central glucose signaling pathways. Glucose replenishment induces the rapid dissociation of Snd3 from the NVJs, preceding the slow disassembly of the junctions. In sum, this study identifies a key factor required for formation and regulation of NVJs and provides a paradigm for metabolic control of membrane contact sites.
Topics: Cell Nucleus; Glucose; Phosphate Transport Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Signal Transduction; Vacuoles
PubMed: 33472077
DOI: 10.1016/j.celrep.2020.108637 -
Journal of Cataract and Refractive... May 2020To develop an advanced test methodology for quantification of scattered light from intraocular lenses (IOLs) and to evaluate the correlation between IOL vacuole...
PURPOSE
To develop an advanced test methodology for quantification of scattered light from intraocular lenses (IOLs) and to evaluate the correlation between IOL vacuole characteristics and measured scattered light.
SETTING
U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA.
DESIGN
Experimental and analytical study.
METHODS
Twenty-four IOLs containing vacuoles were evaluated using a digital microscopy approach for identifying and characterizing the vacuoles present. A scanning light scattering profiler (SLSP) was used to evaluate and quantify the amount of scattered light from each IOL and from a 25th control IOL without any vacuoles. A variety of IOLs and vacuoles were also modeled in a Zemax simulation of the SLSP, and the simulated scattered light was modeled.
RESULTS
The scattered light as measured with SLSP was well correlated with vacuole characteristics, specifically density and size, as measured under the digital microscope for the 24 vacuole-containing IOLs. Additional correlations were found between vacuole sizes, orientations, and the angle at which light was scattered most severely. These correlations were also present in the Zemax model.
CONCLUSIONS
Vacuole optical characteristics can be well correlated with measured scatter, demonstrating an ability to predict scattered light based solely on microscope evaluation. Furthermore, the quantitative amount of scatter predicted with Zemax simulations trended closely with the experimentally measured trends.
Topics: Humans; Lenses, Intraocular; Maryland; Scattering, Radiation; Vacuoles; Vision, Ocular
PubMed: 32358273
DOI: 10.1097/j.jcrs.0000000000000167 -
Acta Neuropathologica Communications Sep 2020In the brains of tauopathy patients, tau pathology coincides with the presence of granulovacuolar degeneration bodies (GVBs) both at the regional and cellular level.... (Review)
Review
In the brains of tauopathy patients, tau pathology coincides with the presence of granulovacuolar degeneration bodies (GVBs) both at the regional and cellular level. Recently, it was shown that intracellular tau pathology causes GVB formation in experimental models thus explaining the strong correlation between these neuropathological hallmarks in the human brain. These novel models of GVB formation provide opportunities for future research into GVB biology, but also urge reevaluation of previous post-mortem observations. Here, we review neuropathological data on GVBs in tauopathies and other neurodegenerative proteinopathies. We discuss the possibility that intracellular aggregates composed of proteins other than tau are also able to induce GVB formation. Furthermore, the potential mechanisms of GVB formation and the downstream functional implications hereof are outlined in view of the current available data. In addition, we provide guidelines for the identification of GVBs in tissue and cell models that will help to facilitate and streamline research towards the elucidation of the role of these enigmatic and understudied structures in neurodegeneration.
Topics: Animals; Brain; Cytoplasmic Granules; Humans; Inclusion Bodies; Neurons; Tauopathies; Vacuoles
PubMed: 32883341
DOI: 10.1186/s40478-020-00996-5 -
Hong Kong Medical Journal = Xianggang... Feb 2023This study evaluated the arched bridge and vacuole signs, which constitute morphological patterns of lung sparing in coronavirus disease 2019 (COVID-19), then examined...
Chest computed tomography analysis of lung sparing morphology: differentiation of COVID-19 pneumonia from influenza pneumonia and bacterial pneumonia using the arched bridge and vacuole signs.
INTRODUCTION
This study evaluated the arched bridge and vacuole signs, which constitute morphological patterns of lung sparing in coronavirus disease 2019 (COVID-19), then examined whether these signs could be used to differentiate COVID-19 pneumonia from influenza pneumonia or bacterial pneumonia.
METHODS
In total, 187 patients were included: 66 patients with COVID-19 pneumonia, 50 patients with influenza pneumonia and positive computed tomography findings, and 71 patients with bacterial pneumonia and positive computed tomography findings. Images were independently reviewed by two radiologists. The incidences of the arched bridge sign and/or vacuole sign were compared among the COVID-19 pneumonia, influenza pneumonia, and bacterial pneumonia groups.
RESULTS
The arched bridge sign was much more common among patients with COVID-19 pneumonia (42/66, 63.6%) than among patients with influenza pneumonia (4/50, 8.0%; P<0.001) or bacterial pneumonia (4/71, 5.6%; P<0.001). The vacuole sign was also much more common among patients with COVID-19 pneumonia (14/66, 21.2%) than among patients with influenza pneumonia (1/50, 2.0%; P=0.005) or bacterial pneumonia (1/71, 1.4%; P<0.001). The signs occurred together in 11 (16.7%) patients with COVID-19 pneumonia, but they did not occur together in patients with influenza pneumonia or bacterial pneumonia. The arched bridge and vacuole signs predicted COVID-19 pneumonia with respective specificities of 93.4% and 98.4%.
CONCLUSION
The arched bridge and vacuole signs are much more common in patients with COVID-19 pneumonia and can help differentiate COVID-19 pneumonia from influenza and bacterial pneumonia.
Topics: Humans; COVID-19; Influenza, Human; Vacuoles; SARS-CoV-2; Retrospective Studies; Lung; Tomography, X-Ray Computed; Pneumonia, Bacterial
PubMed: 36810239
DOI: 10.12809/hkmj219291 -
Cells Sep 2022Arsenic (As) is a toxic metalloid for all living organisms and can cause serious harm to humans. Arsenic is also toxic to plants. To alleviate As toxicity, all living... (Review)
Review
Arsenic (As) is a toxic metalloid for all living organisms and can cause serious harm to humans. Arsenic is also toxic to plants. To alleviate As toxicity, all living organisms (from prokaryotes to higher plants) have evolved comprehensive mechanisms to reduce cytosolic As concentration through the set of As transporters localized at the plasma and tonoplast membranes, which operate either in arsenite As(III) extrusion out of cells (via ArsB, ACR3, and aquaporins) or by sequestering arsenic into vacuoles (by ABC transporters). In addition, a special arsenate resistance mechanism found in some bacterial systems has evolved in an As hyperaccumulating fern , which involves transforming arsenate As(V) to an As(V) phosphoglycerate derivative by a glyceraldehyde 3-phosphate dehydrogenase and transporting this complex by an efflux transporter. In the present review, we summarize the evolution of these arsenic resistance mechanisms from prokaryotes to eukaryotes and discuss future approaches that could be utilized to better understand and improve As resistance mechanisms in plants.
Topics: Arsenates; Arsenic; Bacteria; Membrane Transport Proteins; Pteris; Vacuoles
PubMed: 36078150
DOI: 10.3390/cells11172741