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Sethi SC, Bharati M, Kumar Y, Yadav U, Saini H, Alam P, Komath SS. The ER-Resident Ras Inhibitor 1 (Eri1) of Candida albicans Inhibits Hyphal Morphogenesis via the Ras-Independent cAMP-PKA Pathway. ACS Infect Dis 2024. [PMID: 39119676 DOI: 10.1021/acsinfecdis.4c00175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2024]
Abstract
Ras signaling and glycosylphosphatidylinositol (GPI) biosynthesis are mutually inhibitory in S. cerevisiae (Sc). The inhibition is mediated via an interaction of yeast Ras2 with the Eri1 subunit of its GPI-N-acetylglucosaminyl transferase (GPI-GnT), the enzyme catalyzing the very first GPI biosynthetic step. In contrast, Ras signaling and GPI biosynthesis in C. albicans (Ca) are mutually activated and together control the virulence traits of the human fungal pathogen. What might be the role of Eri1 in this pathogen? The present manuscript addresses this question while simultaneously characterizing the cellular role of CaEri1. It is either nonessential or required at very low levels for cell viability in C. albicans. Severe depletion of CaEri1 results in reduced GPI biosynthesis and cell wall defects. It also produces hyperfilamentation phenotypes in Spider medium as well as in bicarbonate medium containing 5% CO2, suggesting that both the Ras-dependent and Ras-independent cAMP-PKA pathways for hyphal morphogenesis are activated in these cells. Pull-down and acceptor-photobleaching FRET experiments suggest that CaEri1 does not directly interact with CaRas1 but does so through CaGpi2, another GPI-GnT subunit. We showed previously that CaGpi2 is downstream of CaEri1 in cross talk with CaRas1 and for Ras-dependent hyphal morphogenesis. Here we show that CaEri1 is downstream of all GPI-GnT subunits in inhibiting Ras-independent filamentation. CaERI1 also participates in intersubunit transcriptional cross talk within the GPI-GnT, a feature unique to C. albicans. Virulence studies using G. mellonella larvae show that a heterozygous strain of CaERI1 is better cleared by the host and is attenuated in virulence.
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Affiliation(s)
| | - Monika Bharati
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Yatin Kumar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Usha Yadav
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Harshita Saini
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Parvez Alam
- School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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2
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Komath SS. To each its own: Mechanisms of cross-talk between GPI biosynthesis and cAMP-PKA signaling in Candida albicans versus Saccharomyces cerevisiae. J Biol Chem 2024; 300:107444. [PMID: 38838772 PMCID: PMC11294708 DOI: 10.1016/j.jbc.2024.107444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 05/24/2024] [Accepted: 05/29/2024] [Indexed: 06/07/2024] Open
Abstract
Candida albicans is an opportunistic fungal pathogen that can switch between yeast and hyphal morphologies depending on the environmental cues it receives. The switch to hyphal form is crucial for the establishment of invasive infections. The hyphal form is also characterized by the cell surface expression of hyphae-specific proteins, many of which are GPI-anchored and important determinants of its virulence. The coordination between hyphal morphogenesis and the expression of GPI-anchored proteins is made possible by an interesting cross-talk between GPI biosynthesis and the cAMP-PKA signaling cascade in the fungus; a parallel interaction is not found in its human host. On the other hand, in the nonpathogenic yeast, Saccharomyces cerevisiae, GPI biosynthesis is shut down when filamentation is activated and vice versa. This too is achieved by a cross-talk between GPI biosynthesis and cAMP-PKA signaling. How are diametrically opposite effects obtained from the cross-talk between two reasonably well-conserved pathways present ubiquitously across eukarya? This Review attempts to provide a model to explain these differences. In order to do so, it first provides an overview of the two pathways for the interested reader, highlighting the similarities and differences that are observed in C. albicans versus the well-studied S. cerevisiae model, before going on to explain how the different mechanisms of regulation are effected. While commonalities enable the development of generalized theories, it is hoped that a more nuanced approach, that takes into consideration species-specific differences, will enable organism-specific understanding of these processes and contribute to the development of targeted therapies.
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Piper-Brown E, Dresel F, Badr E, Gourlay CW. Elevated Levels of Mislocalised, Constitutive Ras Signalling Can Drive Quiescence by Uncoupling Cell-Cycle Regulation from Metabolic Homeostasis. Biomolecules 2023; 13:1619. [PMID: 38002301 PMCID: PMC10669370 DOI: 10.3390/biom13111619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 10/28/2023] [Accepted: 10/30/2023] [Indexed: 11/26/2023] Open
Abstract
The small GTPase Ras plays an important role in connecting external and internal signalling cues to cell fate in eukaryotic cells. As such, the loss of RAS regulation, localisation, or expression level can drive changes in cell behaviour and fate. Post-translational modifications and expression levels are crucial to ensure Ras localisation, regulation, function, and cell fate, exemplified by RAS mutations and gene duplications that are common in many cancers. Here, we reveal that excessive production of yeast Ras2, in which the phosphorylation-regulated serine at position 225 is replaced with alanine or glutamate, leads to its mislocalisation and constitutive activation. Rather than inducing cell death, as has been widely reported to be a consequence of constitutive Ras2 signalling in yeast, the overexpression of RAS2S225A or RAS2S225E alleles leads to slow growth, a loss of respiration, reduced stress response, and a state of quiescence. These effects are mediated via cAMP/PKA signalling and transcriptional changes, suggesting that quiescence is promoted by an uncoupling of cell-cycle regulation from metabolic homeostasis. The quiescent cell fate induced by the overexpression of RAS2S225A or RAS2S225E could be rescued by the deletion of CUP9, a suppressor of the dipeptide transporter Ptr2, or the addition of peptone, implying that a loss of metabolic control, or a failure to pass a metabolic checkpoint, is central to this altered cell fate. Our data suggest that the combination of an increased RAS2 copy number and a dominant active mutation that leads to its mislocalisation can result in growth arrest and add weight to the possibility that approaches to retarget RAS signalling could be employed to develop new therapies.
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Affiliation(s)
| | | | | | - Campbell W. Gourlay
- Kent Fungal Group, School of Biosciences, University of Kent, Canterbury CT2 7NZ, UK
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4
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Ravishankar R, Hildebrandt ER, Greenway G, Asad N, Gore S, Dore TM, Schmidt WK. Specific Disruption of Ras2 CAAX Proteolysis Alters Its Localization and Function. Microbiol Spectr 2023; 11:e0269222. [PMID: 36602340 PMCID: PMC9927470 DOI: 10.1128/spectrum.02692-22] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Many CAAX proteins, such as Ras GTPase, undergo a series of posttranslational modifications at their carboxyl terminus (i.e., cysteine prenylation, endoproteolysis of AAX, and carboxylmethylation). Some CAAX proteins, however, undergo prenylation-only modification, such as Saccharomyces cerevisiae Hsp40 Ydj1. We previously observed that altering the CAAX motif of Ydj1 from prenylation-only to canonical resulted in altered Ydj1 function and localization. Here, we investigated the effects of a reciprocal change that altered the well-characterized canonical CAAX motif of S. cerevisiae Ras2 to prenylation-only. We observed that the type of CAAX motif impacted Ras2 protein levels, localization, and function. Moreover, we observed that using a prenylation-only sequence to stage hyperactive Ras2-G19V as a farnesylated and nonproteolyzed intermediate resulted in a different phenotype relative to staging by a genetic RCE1 deletion strategy that simultaneously affected many CAAX proteins. These findings suggested that a prenylation-only CAAX motif is useful for probing the specific impact of CAAX proteolysis on Ras2 under conditions where other CAAX proteins are normally modified. We propose that our strategy could be easily applied to a wide range of CAAX proteins for examining the specific impact of CAAX proteolysis on their functions. IMPORTANCE CAAX proteins are subject to multiple posttranslational modifications: cysteine prenylation, CAAX proteolysis, and carboxylmethylation. For investigations of CAAX proteolysis, this study took the novel approach of using a proteolysis-resistant CAAX sequence to stage Saccharomyces cerevisiae Ras2 GTPase in a farnesylated and nonproteolyzed state. Our approach specifically limited the effects of disrupting CAAX proteolysis to Ras2. This represented an improvement over previous methods where CAAX proteolysis was inhibited by gene knockout, small interfering RNA knockdown, or biochemical inhibition of the Rce1 CAAX protease, which can lead to pleiotropic and unclear attribution of effects due to the action of Rce1 on multiple CAAX proteins. Our approach yielded results that demonstrated specific impacts of CAAX proteolysis on the function, localization, and other properties of Ras2, highlighting the utility of this approach for investigating the impact of CAAX proteolysis in other protein contexts.
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Affiliation(s)
- Rajani Ravishankar
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia, USA
| | - Emily R. Hildebrandt
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia, USA
| | - Grace Greenway
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia, USA
| | - Nadeem Asad
- New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - Sangram Gore
- New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - Timothy M. Dore
- New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
- Department of Chemistry, University of Georgia, Athens, Georgia, USA
| | - Walter K. Schmidt
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia, USA
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5
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Jain P, Garai P, Sethi SC, Naqvi N, Yadav B, Kumar P, Singh SL, Yadav U, Bhatnagar S, Rahul, Puri N, Muthuswami R, Komath SS. Modulation of azole sensitivity and filamentation by GPI15, encoding a subunit of the first GPI biosynthetic enzyme, in Candida albicans. Sci Rep 2019; 9:8508. [PMID: 31186458 PMCID: PMC6559964 DOI: 10.1038/s41598-019-44919-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 05/24/2019] [Indexed: 01/06/2023] Open
Abstract
Glycosylphosphatidylinositol (GPI)-anchored proteins are important for virulence of many pathogenic organisms including the human fungal pathogen, Candida albicans. GPI biosynthesis is initiated by a multi-subunit enzyme, GPI-N-acetylglucosaminyltransferase (GPI-GnT). We showed previously that two GPI-GnT subunits, encoded by CaGPI2 and CaGPI19, are mutually repressive. CaGPI19 also co-regulates CaERG11, the target of azoles while CaGPI2 controls Ras signaling and hyphal morphogenesis. Here, we investigated the role of a third subunit. We show that CaGpi15 is functionally homologous to Saccharomyces cerevisiae Gpi15. CaGPI15 is a master activator of CaGPI2 and CaGPI19. Hence, CaGPI15 mutants are azole-sensitive and hypofilamentous. Altering CaGPI19 or CaGPI2 expression in CaGPI15 mutant can elicit alterations in azole sensitivity via CaERG11 expression or hyphal morphogenesis, respectively. Thus, CaGPI2 and CaGPI19 function downstream of CaGPI15. One mode of regulation is via H3 acetylation of the respective GPI-GnT gene promoters by Rtt109. Azole sensitivity of GPI-GnT mutants is also due to decreased H3 acetylation at the CaERG11 promoter by Rtt109. Using double heterozygous mutants, we also show that CaGPI2 and CaGPI19 can independently activate CaGPI15. CaGPI15 mutant is more susceptible to killing by macrophages and epithelial cells and has reduced ability to damage either of these cell lines relative to the wild type strain, suggesting that it is attenuated in virulence.
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Affiliation(s)
- Priyanka Jain
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Pramita Garai
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | | | - Nilofer Naqvi
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Bhawna Yadav
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.,Post-doctoral Fellow, Fungal Research Group, Institute of Medical Sciences, University of Aberdeen, Aberdeen, UK
| | - Pravin Kumar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.,Research associate, National Institute of Plant Genome Research, New Delhi, 110067, India
| | - Sneh Lata Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Usha Yadav
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Shilpi Bhatnagar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Rahul
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Niti Puri
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Rohini Muthuswami
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
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6
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Komath SS, Singh SL, Pratyusha VA, Sah SK. Generating anchors only to lose them: The unusual story of glycosylphosphatidylinositol anchor biosynthesis and remodeling in yeast and fungi. IUBMB Life 2019; 70:355-383. [PMID: 29679465 DOI: 10.1002/iub.1734] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 02/16/2018] [Accepted: 02/22/2018] [Indexed: 02/06/2023]
Abstract
Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are present ubiquitously at the cell surface in all eukaryotes. They play a crucial role in the interaction of the cell with its external environment, allowing the cell to receive signals, respond to challenges, and mediate adhesion. In yeast and fungi, they also participate in the structural integrity of the cell wall and are often essential for survival. Roughly four decades after the discovery of the first GPI-APs, this review provides an overview of the insights gained from studies of the GPI biosynthetic pathway and the future challenges in the field. In particular, we focus on the biosynthetic pathway in Saccharomyces cerevisiae, which has for long been studied as a model organism. Where available, we also provide information about the GPI biosynthetic steps in other yeast/ fungi. Although the core structure of the GPI anchor is conserved across organisms, several variations are built into the biosynthetic pathway. The present Review specifically highlights these variations and their implications. There is growing evidence to suggest that several phenotypes are common to GPI deficiency and should be expected in GPI biosynthetic mutants. However, it appears that several phenotypes are unique to a specific step in the pathway and may even be species-specific. These could suggest the points at which the GPI biosynthetic pathway intersects with other important cellular pathways and could be points of regulation. They could be of particular significance in the study of pathogenic fungi and in identification of new and specific antifungal drugs/ drug targets. © 2018 IUBMB Life, 70(5):355-383, 2018.
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Affiliation(s)
| | - Sneh Lata Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
| | | | - Sudisht Kumar Sah
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
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7
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Jain P, Sethi SC, Pratyusha VA, Garai P, Naqvi N, Singh S, Pawar K, Puri N, Komath SS. Ras signaling activates glycosylphosphatidylinositol (GPI) anchor biosynthesis via the GPI- N-acetylglucosaminyltransferase (GPI-GnT) in Candida albicans. J Biol Chem 2018; 293:12222-12238. [PMID: 29907567 DOI: 10.1074/jbc.ra117.001225] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 04/17/2018] [Indexed: 01/08/2023] Open
Abstract
The ability of Candida albicans to switch between yeast to hyphal form is a property that is primarily associated with the invasion and virulence of this human pathogenic fungus. Several glycosylphosphatidylinositol (GPI)-anchored proteins are expressed only during hyphal morphogenesis. One of the major pathways that controls hyphal morphogenesis is the Ras-signaling pathway. We examine the cross-talk between GPI anchor biosynthesis and Ras signaling in C. albicans. We show that the first step of GPI biosynthesis is activated by Ras in C. albicans This is diametrically opposite to what is reported in Saccharomyces cerevisiae Of the two C. albicans Ras proteins, CaRas1 alone activates GPI-GnT activity; activity is further stimulated by constitutively activated CaRas1. CaRas1 localized to the cytoplasm or endoplasmic reticulum (ER) is sufficient for GPI-GnT activation. Of the six subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) that catalyze the first step of GPI biosynthesis, CaGpi2 is the key player involved in activating Ras signaling and hyphal morphogenesis. Activation of Ras signaling is independent of the catalytic competence of GPI-GnT. This too is unlike what is observed in S. cerevisiae where multiple subunits were identified as inhibiting Ras2. Fluorescence resonance energy transfer (FRET) studies indicate a specific physical interaction between CaRas1 and CaGpi2 in the ER, which would explain the ability of CaRas1 to activate GPI-GnT. CaGpi2, in turn, promotes activation of the Ras-signaling pathway and hyphal morphogenesis. The Cagpi2 mutant is also more susceptible to macrophage-mediated killing, and macrophage cells show better survival when co-cultured with Cagpi2.
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Affiliation(s)
- Priyanka Jain
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | | | | | - Pramita Garai
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Nilofer Naqvi
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Sonali Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Kalpana Pawar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Niti Puri
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
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8
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The Yeast Saccharomyces cerevisiae as a Model for Understanding RAS Proteins and their Role in Human Tumorigenesis. Cells 2018; 7:cells7020014. [PMID: 29463063 PMCID: PMC5850102 DOI: 10.3390/cells7020014] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Revised: 02/05/2018] [Accepted: 02/12/2018] [Indexed: 12/16/2022] Open
Abstract
The exploitation of the yeast Saccharomyces cerevisiae as a biological model for the investigation of complex molecular processes conserved in multicellular organisms, such as humans, has allowed fundamental biological discoveries. When comparing yeast and human proteins, it is clear that both amino acid sequences and protein functions are often very well conserved. One example of the high degree of conservation between human and yeast proteins is highlighted by the members of the RAS family. Indeed, the study of the signaling pathways regulated by RAS in yeast cells led to the discovery of properties that were often found interchangeable with RAS proto-oncogenes in human pathways, and vice versa. In this work, we performed an updated critical literature review on human and yeast RAS pathways, specifically highlighting the similarities and differences between them. Moreover, we emphasized the contribution of studying yeast RAS pathways for the understanding of human RAS and how this model organism can contribute to unveil the roles of RAS oncoproteins in the regulation of mechanisms important in the tumorigenic process, like autophagy.
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9
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Abstract
For centuries yeast species have been popular hosts for classical biotechnology processes, such as baking, brewing, and wine making, and more recently for recombinant proteins production, thanks to the advantages of unicellular organisms (i.e., ease of genetic manipulation and rapid growth) together with the ability to perform eukaryotic posttranslational modifications. Moreover, yeast cells have been used for few decades as a tool for identifying the genes and pathways involved in basic cellular processes such as the cell cycle, aging, and stress response. In the budding yeast S. cerevisiae the Ras/cAMP/PKA pathway is directly involved in the regulation of metabolism, cell growth, stress resistance, and proliferation in response to the availability of nutrients and in the adaptation to glucose, controlling cytosolic cAMP levels and consequently the cAMP-dependent protein kinase (PKA) activity. Moreover, Ras signalling has been identified in several pathogenic yeasts as a key controller for virulence, due to its involvement in yeast morphogenesis. Nowadays, yeasts are still useful for Ras-like proteins investigation, both as model organisms and as a test tube to study variants of heterologous Ras-like proteins.
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Affiliation(s)
- Renata Tisi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
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10
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Yadav B, Bhatnagar S, Ahmad MF, Jain P, Pratyusha VA, Kumar P, Komath SS. First step of glycosylphosphatidylinositol (GPI) biosynthesis cross-talks with ergosterol biosynthesis and Ras signaling in Candida albicans. J Biol Chem 2013; 289:3365-82. [PMID: 24356967 DOI: 10.1074/jbc.m113.528802] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Candida albicans is a leading cause of fungal infections worldwide. It has several glycosylphosphatidylinositol (GPI)-anchored virulence factors. Inhibiting GPI biosynthesis attenuates its virulence. Building on our previous work, we explore the interaction of GPI biosynthesis in C. albicans with ergosterol biosynthesis and hyphal morphogenesis. This study is also the first report of transcriptional co-regulation existing between two subunits of the multisubunit enzyme complex, GPI-N-acetylglucosaminyltransferase (GPI-GnT), involved in the first step of GPI anchor biosynthesis in eukaryotes. Using mutational analysis, we show that the accessory subunits, GPI2 and GPI19, of GPI-GnT exhibit opposite effects on ergosterol biosynthesis and Ras signaling (which determines hyphal morphogenesis). This is because the two subunits negatively regulate one another; GPI19 mutants show up-regulation of GPI2, whereas GPI2 mutants show up-regulation of GPI19. Two different models were examined as follows. First, the two GPI-GnT subunits independently interact with ergosterol biosynthesis and Ras signaling. Second, the two subunits mutually regulate one another and thereby regulate sterol levels and Ras signaling. Analysis of double mutants of these subunits indicates that GPI19 controls ergosterol biosynthesis through ERG11 levels, whereas GPI2 determines the filamentation by cross-talk with Ras1 signaling. Taken together, this suggests that the first step of GPI biosynthesis talks to and regulates two very important pathways in C. albicans. This could have implications for designing new antifungal strategies.
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Affiliation(s)
- Bhawna Yadav
- From the School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
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11
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Belotti F, Tisi R, Paiardi C, Rigamonti M, Groppi S, Martegani E. Localization of Ras signaling complex in budding yeast. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1823:1208-16. [PMID: 22575457 DOI: 10.1016/j.bbamcr.2012.04.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Revised: 04/26/2012] [Accepted: 04/30/2012] [Indexed: 10/28/2022]
Abstract
In Saccharomyces cerevisiae, cAMP/pKA pathway plays a major role in metabolism, stress resistance and proliferation control. cAMP is produced by adenylate cyclase, which is activated both by Gpr1/Gpa2 system and Ras proteins, regulated by Cdc25/Sdc25 guanine exchange factors and Ira GTPase activator proteins. Recently, both Ras2 and Cdc25 RasGEF were reported to localize not only in plasma membrane but also in internal membranes. Here, the subcellular localization of Ras signaling complex proteins was investigated both by fluorescent tagging and by biochemical cell membrane fractionation on sucrose gradients. Although a consistent minor fraction of Ras signaling complex components was found in plasma membrane during exponential growth on glucose, Cdc25 appears to localize mainly on ER membranes, while Ira2 and Cyr1 are also significantly present on mitochondria. Moreover, PKA Tpk1 catalytic subunit overexpression induces Ira2 protein to move from mitochondria to ER membranes. These data confirm the hypothesis that different branches of Ras signaling pathways could involve different subcellular compartments, and that relocalization of Ras signaling complex components is subject to PKA control.
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Affiliation(s)
- Fiorella Belotti
- Department of Biotechnology and Biosciences, Umiversity of Milano-Bicocca, Milan, Italy
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12
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Mutual co-regulation between GPI-N-acetylglucosaminyltransferase and ergosterol biosynthesis in Candida albicans. Biochem J 2012; 443:619-25. [DOI: 10.1042/bj20120143] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A novel co-regulation exists between the first step of GPI (glycosylphosphatidylinositol) anchor biosynthesis and the rate-determining step of ergosterol biosynthesis in Candida albicans. Depleting CaGpi19p, an accessory subunit of the enzyme complex that initiates GPI biosynthesis, down-regulates ERG11, altering ergosterol levels and drug response. This effect is specific to CaGpi19p depletion and is not due to cell wall defects or GPI deficiency. Additionally, down-regulation of ERG11 down-regulates CaGPI19 and GPI biosynthesis.
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13
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Jin T, Ding Q, Huang H, Xu D, Jiang Y, Zhou B, Li Z, Jiang X, He J, Liu W, Zhang Y, Pan Y, Wang Z, Thomas WG, Chen Y. PAQR10 and PAQR11 mediate Ras signaling in the Golgi apparatus. Cell Res 2012; 22:661-76. [PMID: 21968647 PMCID: PMC3317553 DOI: 10.1038/cr.2011.161] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Revised: 07/07/2011] [Accepted: 08/11/2011] [Indexed: 02/05/2023] Open
Abstract
Ras plays a pivotal role in many cellular activities, and its subcellular compartmentalization provides spatial and temporal selectivity. Here we report a mode of spatial regulation of Ras signaling in the Golgi apparatus by two highly homologous proteins PAQR10 and PAQR11 of the progestin and AdipoQ receptors family. PAQR10 and PAQR11 are exclusively localized in the Golgi apparatus. Overexpression of PAQR10/PAQR11 stimulates basal and EGF-induced ERK phosphorylation and increases the expression of ERK target genes in a dose-dependent manner. Overexpression of PAQR10/PAQR11 markedly elevates Golgi localization of HRas, NRas and KRas4A, but not KRas4B. PAQR10 and PAQR11 can also interact with HRas, NRas and KRas4A, but not KRas4B. The increased Ras protein at the Golgi apparatus by overexpression of PAQR10/PAQR11 is in an active state. Consistently, knockdown of PAQR10 and PAQR11 reduces EGF-stimulated ERK phosphorylation and Ras activation at the Golgi apparatus. Intriguingly, PAQR10 and PAQR11 are able to interact with RasGRP1, a guanine nucleotide exchange protein of Ras, and increase Golgi localization of RasGRP1. The C1 domain of RasGRP1 is both necessary and sufficient for the interaction of RasGRP1 with PAQR10/PAQR11. The simulation of ERK phosphorylation by overexpressed PAQR10/PAQR11 is abrogated by downregulation of RasGRP1. Furthermore, differentiation of PC12 cells is significantly enhanced by overexpression of PAQR10/PAQR11. Collectively, this study uncovers a new paradigm of spatial regulation of Ras signaling in the Golgi apparatus by PAQR10 and PAQR11.
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Affiliation(s)
- Ting Jin
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Qiurong Ding
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Heng Huang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Daqian Xu
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yuhui Jiang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ben Zhou
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Zhenghu Li
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Xiaomeng Jiang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jing He
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Weizhong Liu
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yixuan Zhang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yi Pan
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Zhenzhen Wang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Walter G Thomas
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia
| | - Yan Chen
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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14
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15
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Victoria GS, Kumar P, Komath SS. The Candida albicans homologue of PIG-P, CaGpi19p: gene dosage and role in growth and filamentation. Microbiology (Reading) 2010; 156:3041-3051. [DOI: 10.1099/mic.0.039628-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glycosylphosphatidyl inositol (GPI)-anchored proteins in Candida albicans are responsible for a vast range of functions, and deletions in certain GPI-anchored proteins severely reduce adhesion and virulence of this organism. In addition, completely modified GPIs are necessary for virulence. GPI anchor biosynthesis is essential for viability and starts with the transfer of N-acetylglucosamine to phosphatidylinositol. This step is catalysed by a multi-subunit complex, GPI–N-acetylglucosaminyltransferase (GPI–GnT). In this, the first report to our knowledge on a subunit of the Candida GPI–GnT complex, we show that CaGpi19p is the functional equivalent of the Saccharomyces cerevisiae Gpi19p. An N-terminal truncation mutant of CaGpi19p functionally complements a conditionally lethal S. cerevisiae gpi19 mutant. Further, we constructed a conditional null mutant of CaGPI19 by disrupting one allele and placing the remaining copy under the control of the MET3 promoter. Repression leads to growth defects, cell wall biogenesis aberrations, azole sensitivity and hyperfilamention. In addition, there is a noticeable gene dosage effect, with the heterozygote also displaying intermediate degrees of most phenotypes. The mutants also displayed a reduced susceptibility to the antifungal agent amphotericin B. Collectively, the results suggest that CaGPI19 is required for normal morphology and cell wall architecture.
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Affiliation(s)
| | - Pravin Kumar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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16
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Manandhar SP, Hildebrandt ER, Jacobsen WH, Santangelo GM, Schmidt WK. Chemical inhibition of CaaX protease activity disrupts yeast Ras localization. Yeast 2010; 27:327-43. [PMID: 20162532 DOI: 10.1002/yea.1756] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Proteins possessing a C-terminal CaaX motif, such as the Ras GTPases, undergo extensive post-translational modification that includes attachment of an isoprenoid lipid, proteolytic processing and carboxylmethylation. Inhibition of the enzymes involved in these processes is considered a cancer-therapeutic strategy. We previously identified nine in vitro inhibitors of the yeast CaaX protease Rce1p in a chemical library screen (Manandhar et al., 2007). Here, we demonstrate that these agents disrupt the normal plasma membrane distribution of yeast GFP-Ras reporters in a manner that pharmacologically phenocopies effects observed upon genetic loss of CaaX protease function. Consistent with Rce1p being the in vivo target of the inhibitors, we observe that compound-induced delocalization is suppressed by increasing the gene dosage of RCE1. Moreover, we observe that Rce1p biochemical activity associated with inhibitor-treated cells is inversely correlated with compound dose. Genetic loss of CaaX proteolysis results in mistargeting of GFP-Ras2p to subcellular foci that are positive for the endoplasmic reticulum marker Sec63p. Pharmacological inhibition of CaaX protease activity also delocalizes GFP-Ras2p to foci, but these foci are not as strongly positive for Sec63p. Lastly, we demonstrate that heterologously expressed human Rce1p can mediate proper targeting of yeast Ras and that its activity can also be perturbed by some of the above inhibitors. Together, these results indicate that disrupting the proteolytic modification of Ras GTPases impacts their in vivo trafficking.
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Affiliation(s)
- Surya P Manandhar
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA
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17
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Backert S, Kenny B, Gerhard R, Tegtmeyer N, Brandt S. PKA-mediated phosphorylation of EPEC-Tir at serine residues 434 and 463: A novel pathway in regulating Rac1 GTPase function. Cell Signal 2010; 21:462-9. [PMID: 19091303 DOI: 10.1016/j.cellsig.2008.11.013] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Accepted: 11/15/2008] [Indexed: 01/29/2023]
Abstract
Type-III or type-IV secretion systems of many Gram-negative bacterial pathogens inject effector proteins into host cells that modulate cellular functions in their favour. A preferred target of these effectors is the actin-cytoskeleton as shown by studies using the gastric pathogens Helicobacter pylori (H. pylori) and enteropathogenic Escherichia coli (EPEC). We recently developed a co-infection approach to study effector protein function and molecular mechanisms by which they highjack cellular signalling cascades. This is exemplified by our observation that EPEC profoundly blocks H. pylori-induced epithelial cell scattering and elongation, a disease-related event requiring the activity of small Rho GTPase Rac1. While this suppressive effect is dependent on the effector protein Tir and the outer-membrane protein Intimin, it unexpectedly revealed evidence for Tir-signalling independent of phosphorylation of Tir at tyrosine residues 454 and 474. Instead, our studies revealed a previously unidentified function for protein kinase A (PKA)-mediated phosphorylation of Tir at serine residues 434 and 463. We demonstrated that EPEC infection activates PKA for Tir phosphorylation. Activated PKA then phosphorylates Rac1 at its serine residue 71 associated with reduced GTP-load and inhibited cell elongation. Phosphorylation of Rho GTPases such as Rac1 might be an interesting novel strategy in microbial pathogenesis.
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Affiliation(s)
- Steffen Backert
- University College Dublin; School of Biomolecular and Biomedical Sciences; Dublin, Ireland
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18
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Abstract
The mitogen-activated protein kinase (MAPK) pathway provides cells with the means to interpret external signal cues or conditions, and respond accordingly. This cascade regulates many cell functions such as differentiation, proliferation and migration. Through modulation of both the amplitude and duration of MAPK signalling, cells can control their responses to the multiple activators of the pathway. In addition, recent work has highlighted the importance of the cellular compartment from which the signalling occurs. Cells have developed intricate systems that enable them to localise MAPK components to specific subcellular domains in response to a particular stimulus. Consequently, different factors can activate the same kinase in separate locations. Crucial to this ability are molecular scaffolds, which act as signalling modules for MAPKs, confining them to the desired compartment. The participation of the MAPK network in fundamental physiological processes, such as cell proliferation and inflammation, and the derangement of the homeostasis that occurs in disease processes, renders MAPK a highly desirable target for therapeutic intervention. As we enhance our comprehension of scaffolds and other regulatory molecules, novel targets for drug design may be discovered that will afford selective and specific MAPK modulation.
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Affiliation(s)
- M D Brown
- Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
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19
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Orlean P, Menon AK. Thematic review series: lipid posttranslational modifications. GPI anchoring of protein in yeast and mammalian cells, or: how we learned to stop worrying and love glycophospholipids. J Lipid Res 2007; 48:993-1011. [PMID: 17361015 DOI: 10.1194/jlr.r700002-jlr200] [Citation(s) in RCA: 273] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycosylphosphatidylinositol (GPI) anchoring of cell surface proteins is the most complex and metabolically expensive of the lipid posttranslational modifications described to date. The GPI anchor is synthesized via a membrane-bound multistep pathway in the endoplasmic reticulum (ER) requiring >20 gene products. The pathway is initiated on the cytoplasmic side of the ER and completed in the ER lumen, necessitating flipping of a glycolipid intermediate across the membrane. The completed GPI anchor is attached to proteins that have been translocated across the ER membrane and that display a GPI signal anchor sequence at the C terminus. GPI proteins transit the secretory pathway to the cell surface; in yeast, many become covalently attached to the cell wall. Genes encoding proteins involved in all but one of the predicted steps in the assembly of the GPI precursor glycolipid and its transfer to protein in mammals and yeast have now been identified. Most of these genes encode polytopic membrane proteins, some of which are organized in complexes. The steps in GPI assembly, and the enzymes that carry them out, are highly conserved. GPI biosynthesis is essential for viability in yeast and for embryonic development in mammals. In this review, we describe the biosynthesis of mammalian and yeast GPIs, their transfer to protein, and their subsequent processing.
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Affiliation(s)
- Peter Orlean
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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20
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Pittet M, Conzelmann A. Biosynthesis and function of GPI proteins in the yeast Saccharomyces cerevisiae. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:405-20. [PMID: 16859984 DOI: 10.1016/j.bbalip.2006.05.015] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Revised: 05/20/2006] [Accepted: 05/22/2006] [Indexed: 11/28/2022]
Abstract
Like most other eukaryotes, Saccharomyces cerevisiae harbors a GPI anchoring machinery and uses it to attach proteins to membranes. While a few GPI proteins reside permanently at the plasma membrane, a majority of them gets further processed and is integrated into the cell wall by a covalent attachment to cell wall glucans. The GPI biosynthetic pathway is necessary for growth and survival of yeast cells. The GPI lipids are synthesized in the ER and added onto proteins by a pathway comprising 12 steps, carried out by 23 gene products, 19 of which are essential. Some of the estimated 60 GPI proteins predicted from the genome sequence serve enzymatic functions required for the biosynthesis and the continuous shape adaptations of the cell wall, others seem to be structural elements of the cell wall and yet others mediate cell adhesion. Because of its genetic tractability S. cerevisiae is an attractive model organism not only for studying GPI biosynthesis in general, but equally for investigating the intracellular transport of GPI proteins and the peculiar role of GPI anchoring in the elaboration of fungal cell walls.
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Affiliation(s)
- Martine Pittet
- Department of Medicine, Division of Biochemistry, Chemin du Musée 5, CH-1700 Fribourg, Switzerland
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21
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Tsai FM, Shyu RY, Jiang SY. RIG1 suppresses Ras activation and induces cellular apoptosis at the Golgi apparatus. Cell Signal 2006; 19:989-99. [PMID: 17196792 DOI: 10.1016/j.cellsig.2006.11.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Revised: 11/16/2006] [Accepted: 11/16/2006] [Indexed: 10/23/2022]
Abstract
Retinoid-inducible gene 1 encodes RIG1 is a growth regulator, which inhibits the pathways of the RAS/mitogen-activated protein kinases by suppressing the activation of RAS. Confocal microscopic analysis demonstrated that RIG1 is localized in the endoplasmic reticulum (ER) and Golgi apparatus in HtTA cervical cancer cells. Carboxyterminal-deleted RIG1 targeted to the Golgi or ER was constructed and validated. The activation of HRAS was inhibited by 25.1% or 81.4% in cells cotransfected with wild-type or Golgi-targeted RIG1, respectively. Expression of wild-type or Golgi-targeted RIG1 for 24 h induced cellular apoptosis in HtTA cells, as assessed by MTT assay, the release of lactate dehydrogenase, and chromatin condensation. In contrast, ER-targeted RIG1 and carboxyterminal-deleted RIG1 (RIG1DeltaC) exhibited no activity. Caspase-2, -3, and -9 were activated following the expression of wild-type and Golgi-targeted RIG1. Although the caspase-3 inhibitor Z-DEVD-FMK partially or completely reversed the cell death induced by wild-type or Golgi-targeted RIG1, it did not prevent the anti-RAS effect of RIG1. In conclusion, the proapoptotic and anti-RAS activities of RIG1 are primarily associated with the Golgi localization of the protein. The proapoptotic activities of RIG1 are mediated through the activation of caspase-2 and -3 and are independent of its effect on RAS.
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Affiliation(s)
- Fu-Ming Tsai
- Graduate Institute of Life Sciences, National Defense Medical Center, and Department of Medical Education and Research, Buddhist Tzu Chi General Hospital, 289 Jianguo Road, Xindian City, Taipei, Taiwan, ROC
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22
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Kastenmayer JP, Ni L, Chu A, Kitchen LE, Au WC, Yang H, Carter CD, Wheeler D, Davis RW, Boeke JD, Snyder MA, Basrai MA. Functional genomics of genes with small open reading frames (sORFs) in S. cerevisiae. Genome Res 2006; 16:365-73. [PMID: 16510898 PMCID: PMC1415214 DOI: 10.1101/gr.4355406] [Citation(s) in RCA: 157] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Genes with small open reading frames (sORFs; <100 amino acids) represent an untapped source of important biology. sORFs largely escaped analysis because they were difficult to predict computationally and less likely to be targeted by genetic screens. Thus, the substantial number of sORFs and their potential importance have only recently become clear. To investigate sORF function, we undertook the first functional studies of sORFs in any system, using the model eukaryote Saccharomyces cerevisiae. Based on independent experimental approaches and computational analyses, evidence exists for 299 sORFs in the S. cerevisiae genome, representing approximately 5% of the annotated ORFs. We determined that a similar percentage of sORFs are annotated in other eukaryotes, including humans, and 184 of the S. cerevisiae sORFs exhibit similarity with ORFs in other organisms. To investigate sORF function, we constructed a collection of gene-deletion mutants of 140 newly identified sORFs, each of which contains a strain-specific "molecular barcode," bringing the total number of sORF deletion strains to 247. Phenotypic analyses of the new gene-deletion strains identified 22 sORFs required for haploid growth, growth at high temperature, growth in the presence of a nonfermentable carbon source, or growth in the presence of DNA damage and replication-arrest agents. We provide a collection of sORF deletion strains that can be integrated into the existing deletion collection as a resource for the yeast community for elucidating gene function. Moreover, our analyses of the S. cerevisiae sORFs establish that sORFs are conserved across eukaryotes and have important biological functions.
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Affiliation(s)
- James P Kastenmayer
- Genetics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20889, USA
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23
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Abstract
The Ras GTPases act as binary switches for signal transduction pathways that are important for growth regulation and tumorigenesis. Despite the biochemical simplicity of this switch, Ras proteins control multiple pathways, and the functions of the four mammalian Ras proteins are not overlapping. This raises an important question--how does a Ras protein selectively regulate a particular activity? One recently emerging model suggests that a single Ras protein can control different functions by acting in distinct cellular compartments. A critical test of this model is to identify pathways that are selectively controlled by Ras when it is localized to a particular compartment. A recent study has examined Ras signaling in the fission yeast Schizosaccharomyces pombe, which expresses only one Ras protein that controls two separate evolutionarily conserved pathways. This study demonstrates that whereas Ras localized to the plasma membrane selectively regulates a MAP kinase pathway to mediate mating pheromone signaling, Ras localized to the endomembrane activates a Cdc42 pathway to mediate cell polarity and protein trafficking. This study has provided unambiguous evidence for compartmentalized signaling of Ras.
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Affiliation(s)
- Eric C. Chang
- Baylor College of Medicine; Department of Molecular and Cell Biology; The Breast Center; Houston, Texas
- Correspondence to: Eric C. Chang; Baylor College of Medicine; Baylor Plaza, BCM 600; Department of Molecular and Cell Biology; The Breast Center; Houston, Texas, 77030; Tel.: 713-798-3519; Fax: 713-798-1462; /Mark R. Philips; New York University School of Medicine; 550 1st Avenue; Departments of Medicine, Cell Biology and Pharmacology; New York, New York 10016, USA; Tel.: 212.263.7404;
| | - Mark R. Philips
- New York University School of Medicine; Department of Medicine, Cell Biology and Pharmacology; New York, New York
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24
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Abstract
Signal transduction down the Ras/MAPK pathway, including that critical to T cell activation, proliferation, and differentiation, has been generally considered to occur at the plasma membrane. It is now clear that the plasma membrane does not represent the only platform for Ras/MAPK signaling. Moreover, the plasma membrane itself is no longer considered a uniform structure but rather a patchwork of microdomains that can compartmentalize signaling. Signaling on internal membranes was first recognized on endosomes. Genetically encoded fluorescent probes for signaling events such as GTP/GDP exchange on Ras have revealed signaling on a variety of intracellular membranes, including the Golgi apparatus. In fibroblasts, Ras is activated on the plasma membrane and Golgi with distinct kinetics. The pathway by which Golgi-associated Ras becomes activated involves PLCgamma and RasGRP1 and may also require retrograde trafficking of Ras from the plasma membrane to the Golgi as a consequence of depalmitoylation. Thus, the Ras/MAPK pathway represents a clear example of compartmentalized signaling.
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Affiliation(s)
- Adam Mor
- Department of Medicine, New York University Medical Center, New York, NY 10016-6402, USA.
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25
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Onken B, Wiener H, Philips MR, Chang EC. Compartmentalized signaling of Ras in fission yeast. Proc Natl Acad Sci U S A 2006; 103:9045-50. [PMID: 16754851 PMCID: PMC1482563 DOI: 10.1073/pnas.0603318103] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Compartment-specific Ras signaling is an emerging paradigm that may explain the multiplex outputs from a single GTPase. The fission yeast, Schizosaccharomyces pombe, affords a simple system in which to study Ras signaling because it has a single Ras protein, Ras1, that regulates two distinct pathways: one that controls mating through a Byr2-mitogen-activated protein kinase cascade and one that signals through Scd1-Cdc42 to maintain elongated cell morphology. We generated Ras1 mutants that are restricted to either the endomembrane or the plasma membrane. Protein binding studies showed that each could interact with the effectors of both pathways. However, when examined in ras1 null cells, endomembrane-restricted Ras1 supported morphology but not mating, and, conversely, plasma membrane-restricted Ras1 supported mating but did not signal to Scd1-Cdc42. These observations provide a striking demonstration of compartment-specific Ras signaling and indicate that spatial specificity in the Ras pathway is evolutionarily conserved.
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Affiliation(s)
- Brian Onken
- *Department of Molecular and Cell Biology, The Breast Center, Baylor College of Medicine, 1 Baylor Plaza, BCM 600, Houston, TX 77030; and
| | - Heidi Wiener
- Department of Medicine, Cell Biology, and Pharmacology, New York University School of Medicine, 550 1st Avenue, New York, NY 10016
| | - Mark R. Philips
- Department of Medicine, Cell Biology, and Pharmacology, New York University School of Medicine, 550 1st Avenue, New York, NY 10016
- To whom correspondence may be addressed. E-mail:
or
| | - Eric C. Chang
- *Department of Molecular and Cell Biology, The Breast Center, Baylor College of Medicine, 1 Baylor Plaza, BCM 600, Houston, TX 77030; and
- To whom correspondence may be addressed. E-mail:
or
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26
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Wang G, Deschenes RJ. Plasma membrane localization of Ras requires class C Vps proteins and functional mitochondria in Saccharomyces cerevisiae. Mol Cell Biol 2006; 26:3243-55. [PMID: 16581797 PMCID: PMC1446948 DOI: 10.1128/mcb.26.8.3243-3255.2006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ras proteins are synthesized as cytosolic precursors, but then undergo posttranslational lipid addition, membrane association, and subcellular targeting to the plasma membrane. Although the enzymes responsible for farnesyl and palmitoyl lipid addition have been described, the mechanism by which these modifications contribute to the subcellular localization of Ras is not known. Following addition of the farnesyl group, Ras associates with the endoplasmic reticulum (ER), where palmitoylation occurs in Saccharomyces cerevisiae. The subsequent translocation of Ras from the ER to the plasma membrane does not require the classical secretory pathway or a functional Golgi apparatus. Vesicular and nonvesicular transport pathways for Ras proteins have been proposed, but the pathway is not known. Here we describe a genetic screen designed to identify mutants defective in Ras trafficking in S. cerevisiae. The screen implicates, for the first time, the class C VPS complex in Ras trafficking. Vps proteins are best characterized for their role in endosome and vacuole membrane fusion. However, the role of the class C Vps complex in Ras trafficking is distinct from its role in endosome and vacuole vesicle fusion, as a mitochondrial involvement was uncovered. Disruption of class C VPS genes results in mitochondrial defects and an accumulation of Ras proteins on mitochondrial membranes. Ras also fractionates with mitochondria in wild-type cells, where it is detected on the outer mitochondrial membrane by virtue of its sensitivity to protease treatment. These results point to a previously uncharacterized role of mitochondria in the subcellular trafficking of Ras proteins.
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Affiliation(s)
- Geng Wang
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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27
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Newman HA, Romeo MJ, Lewis SE, Yan BC, Orlean P, Levin DE. Gpi19, the Saccharomyces cerevisiae homologue of mammalian PIG-P, is a subunit of the initial enzyme for glycosylphosphatidylinositol anchor biosynthesis. EUKARYOTIC CELL 2006; 4:1801-7. [PMID: 16278447 PMCID: PMC1287868 DOI: 10.1128/ec.4.11.1801-1807.2005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Glycosylphosphatidylinositols (GPIs) are attached to the C termini of some glycosylated secretory proteins, serving as membrane anchors for many of those on the cell surface. Biosynthesis of GPIs is initiated by the transfer of N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to phosphatidylinositol. This reaction is carried out at the endoplasmic reticulum (ER) by an enzyme complex called GPI-N-acetylglucosaminyltransferase (GPI-GlcNAc transferase). The human enzyme has six known subunits, at least four of which, GPI1, PIG-A, PIG-C, and PIG-H, have functional homologs in the budding yeast Saccharomyces cerevisiae. The uncharacterized yeast gene YDR437w encodes a protein with some sequence similarity to human PIG-P, a fifth subunit of the GPI-GlcNAc transferase. Here we show that Ydr437w is a small but essential subunit of the yeast GPI-GlcNAc transferase, and we designate its gene GPI19. Similar to other mutants in the yeast enzyme, temperature-sensitive gpi19 mutants display cell wall defects and hyperactive Ras phenotypes. The Gpi19 protein associates with the yeast GPI-GlcNAc transferase in vivo, as judged by coimmuneprecipitation with the Gpi2 subunit. Moreover, conditional gpi19 mutants are defective for GPI-GlcNAc transferase activity in vitro. Finally, we present evidence for the topology of Gpi19 within the ER membrane.
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Affiliation(s)
- Heather A Newman
- Department of Biochemistry & Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21205-2179, USA
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28
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Abstract
Eukaryotic cells possess an exquisitely interwoven and fine-tuned series of signal transduction mechanisms with which to sense and respond to the ubiquitous fermentable carbon source glucose. The budding yeast Saccharomyces cerevisiae has proven to be a fertile model system with which to identify glucose signaling factors, determine the relevant functional and physical interrelationships, and characterize the corresponding metabolic, transcriptomic, and proteomic readouts. The early events in glucose signaling appear to require both extracellular sensing by transmembrane proteins and intracellular sensing by G proteins. Intermediate steps involve cAMP-dependent stimulation of protein kinase A (PKA) as well as one or more redundant PKA-independent pathways. The final steps are mediated by a relatively small collection of transcriptional regulators that collaborate closely to maximize the cellular rates of energy generation and growth. Understanding the nuclear events in this process may necessitate the further elaboration of a new model for eukaryotic gene regulation, called "reverse recruitment." An essential feature of this idea is that fine-structure mapping of nuclear architecture will be required to understand the reception of regulatory signals that emanate from the plasma membrane and cytoplasm. Completion of this task should result in a much improved understanding of eukaryotic growth, differentiation, and carcinogenesis.
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Affiliation(s)
- George M Santangelo
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS 39406-5018, USA.
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29
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Abstract
Ras GTPases are universal molecular switches that act as kinetic timers of signal transduction events. They are post-translationally modified by the addition of lipid groups to their hypervariable carboxyl termini, which plug the proteins to membranes and influence their dynamic sorting and trafficking. For the past twenty years, the plasma membrane has been considered to be the predominant platform from which Ras operates. Recent work using live-cell imaging and novel probes to visualize where and when Ras is active has supported this long-held belief. However, an equally fascinating aspect of these imaging studies has been the discovery of dynamic Ras activity, as well as distinct signal output, from intracellular organelles. Activation of Ras on the Golgi exhibits kinetics different from Ras activation on the plasma membrane, and compartmentalized Ras signalling seems particularly prominent in lymphocytes. However, data on the spatial and temporal regulation of Ras activity has frequently differed depending on the nature of the probe, the cell type and the stimulus. Nevertheless, because Ras traffics through endomembranes en route to the plasma membrane, it seems likely that Ras can signal from such compartments. The burning question in this field concerns the significance of this observation for endogenous Ras signalling output.
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Affiliation(s)
- Simon A Walker
- Laboratory of Molecular Signalling, The Babraham Institute, Babraham Research Campus, Babraham, Cambridge, CB2 4AT, UK
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30
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Murakami Y, Siripanyaphinyo U, Hong Y, Tashima Y, Maeda Y, Kinoshita T. The initial enzyme for glycosylphosphatidylinositol biosynthesis requires PIG-Y, a seventh component. Mol Biol Cell 2005; 16:5236-46. [PMID: 16162815 PMCID: PMC1266422 DOI: 10.1091/mbc.e05-08-0743] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Biosynthesis of glycosylphosphatidylinositol (GPI) is initiated by an unusually complex GPI-N-acetylglucosaminyltransferase (GPI-GnT) consisting of at least six proteins. Here, we report that human GPI-GnT requires another component, termed PIG-Y, a 71 amino acid protein with two transmembrane domains. The Burkitt lymphoma cell line Daudi, severely defective in the surface expression of GPI-anchored proteins, was a null mutant of PIG-Y. A complex of six components was formed without PIG-Y. PIG-Y appeared to be directly associated with PIG-A, implying that PIG-Y is the key molecule that regulates GPI-GnT activity by binding directly to the catalytic subunit PIG-A. PIG-Y is probably homologous to yeast Eri1p, a component of GPI-GnT. We did not obtain evidence for a functional linkage between GPI-GnT and ras GTPases in mammalian cells as has been reported for yeast cells. A single transcript encoded PIG-Y and, to its 5' side, another protein PreY that has homologues in a wide range of organisms and is characterized by a conserved domain termed DUF343. These two proteins are translated from one mRNA by leaky scanning of the PreY initiation site.
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Affiliation(s)
- Yoshiko Murakami
- Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
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31
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Abstract
A new study shows that Ras2 regulates GPI-anchor synthesis in the ER. Reciprocally, the targeted enzyme GPI-GlcNAc transferase regulates Ras2 signal output. This novel intersection of Ras2 signaling and an ER-localized protein complex has interesting implications for Ras function.
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Affiliation(s)
- John F Hancock
- Institute for Molecular Bioscience, University of Queensland Brisbane 4072, Australia
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32
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Sobering AK, Watanabe R, Romeo MJ, Yan BC, Specht CA, Orlean P, Riezman H, Levin DE. Yeast Ras regulates the complex that catalyzes the first step in GPI-anchor biosynthesis at the ER. Cell 2004; 117:637-48. [PMID: 15163411 DOI: 10.1016/j.cell.2004.05.003] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2004] [Revised: 04/12/2004] [Accepted: 04/12/2004] [Indexed: 10/26/2022]
Abstract
The yeast ERI1 gene encodes a small ER-localized protein that associates in vivo with GTP bound Ras2 in an effector loop-dependent manner. We showed previously that loss of Eri1 function results in hyperactive Ras phenotypes. Here, we demonstrate that Eri1 is a component of the GPI-GlcNAc transferase (GPI-GnT) complex in the ER, which catalyzes transfer of GlcNAc from UDP-GlcNAc to an acceptor phosphatidylinositol, the first step in the production of GPI-anchors for cell surface proteins. We also show that GTP bound Ras2 associates with the GPI-GnT complex in vivo and inhibits its activity, indicating that yeast Ras uses the ER as a signaling platform from which to negatively regulate the GPI-GnT. We propose that diminished GPI-anchor protein production contributes to hyperactive Ras phenotypes.
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Affiliation(s)
- Andrew K Sobering
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, MD 21205, USA
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33
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Current awareness on yeast. Yeast 2003; 20:1309-16. [PMID: 14664230 DOI: 10.1002/yea.951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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