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Serrano A, Basante-Bedoya MA, Bassilana M, Arkowitz RA. A live-cell ergosterol reporter for visualization of the effects of fluconazole on the human fungal pathogen Candida albicans. mBio 2023; 14:e0249323. [PMID: 38032182 PMCID: PMC10746211 DOI: 10.1128/mbio.02493-23] [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: 09/13/2023] [Accepted: 10/31/2023] [Indexed: 12/01/2023] Open
Abstract
IMPORTANCE Ergosterol is a critical membrane lipid in fungi. In Candida albicans, this essential plasma membrane amphipathic lipid is important for interactions with host cells, in particular, host immune responses. Here, we use a live-cell reporter for specifically visualizing ergosterol and show that apical enrichment of this sterol is not critical for budding and filamentous growth in this human fungal pathogen. Our results highlight that this live-cell reporter is likely to be a useful tool in the analyses of azole resistance and tolerance mechanisms, including alterations in drug targets and upregulation of efflux activities.
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Alder-Rangel A, Bailão AM, Herrera-Estrella A, Rangel AEA, Gácser A, Gasch AP, Campos CBL, Peters C, Camelim F, Verde F, Gadd GM, Braus G, Eisermann I, Quinn J, Latgé JP, Aguirre J, Bennett JW, Heitman J, Nosanchuk JD, Partida-Martínez LP, Bassilana M, Acheampong MA, Riquelme M, Feldbrügge M, Keller NP, Keyhani NO, Gunde-Cimerman N, Nascimento R, Arkowitz RA, Mouriño-Pérez RR, Naz SA, Avery SV, Basso TO, Terpitz U, Lin X, Rangel DEN. The IV International Symposium on Fungal Stress and the XIII International Fungal Biology Conference. Fungal Biol 2023; 127:1157-1179. [PMID: 37495306 PMCID: PMC11668258 DOI: 10.1016/j.funbio.2023.04.006] [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: 04/02/2023] [Accepted: 04/24/2023] [Indexed: 07/28/2023]
Abstract
For the first time, the International Symposium on Fungal Stress was joined by the XIII International Fungal Biology Conference. The International Symposium on Fungal Stress (ISFUS), always held in Brazil, is now in its fourth edition, as an event of recognized quality in the international community of mycological research. The event held in São José dos Campos, SP, Brazil, in September 2022, featured 33 renowned speakers from 12 countries, including: Austria, Brazil, France, Germany, Ghana, Hungary, México, Pakistan, Spain, Slovenia, USA, and UK. In addition to the scientific contribution of the event in bringing together national and international researchers and their work in a strategic area, it helps maintain and strengthen international cooperation for scientific development in Brazil.
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Basante-Bedoya MA, Bogliolo S, Garcia-Rodas R, Zaragoza O, Arkowitz RA, Bassilana M. Two distinct lipid transporters together regulate invasive filamentous growth in the human fungal pathogen Candida albicans. PLoS Genet 2022; 18:e1010549. [PMID: 36516161 PMCID: PMC9797089 DOI: 10.1371/journal.pgen.1010549] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 12/28/2022] [Accepted: 11/29/2022] [Indexed: 12/15/2022] Open
Abstract
Flippases transport lipids across the membrane bilayer to generate and maintain asymmetry. The human fungal pathogen Candida albicans has 5 flippases, including Drs2, which is critical for filamentous growth and phosphatidylserine (PS) distribution. Furthermore, a drs2 deletion mutant is hypersensitive to the antifungal drug fluconazole and copper ions. We show here that such a flippase mutant also has an altered distribution of phosphatidylinositol 4-phosphate [PI(4)P] and ergosterol. Analyses of additional lipid transporters, i.e. the flippases Dnf1-3, and all the oxysterol binding protein (Osh) family lipid transfer proteins, i.e. Osh2-4 and Osh7, indicate that they are not critical for filamentous growth. However, deletion of Osh4 alone, which exchanges PI(4)P for sterol, in a drs2 mutant can bypass the requirement for this flippase in invasive filamentous growth. In addition, deletion of the lipid phosphatase Sac1, which dephosphorylates PI(4)P, in a drs2 mutant results in a synthetic growth defect, suggesting that Drs2 and Sac1 function in parallel pathways. Together, our results indicate that a balance between the activities of two putative lipid transporters regulates invasive filamentous growth, via PI(4)P. In contrast, deletion of OSH4 in drs2 does not restore growth on fluconazole, nor on papuamide A, a toxin that binds PS in the outer leaflet of the plasma membrane, suggesting that Drs2 has additional role(s) in plasma membrane organization, independent of Osh4. As we show that C. albicans Drs2 localizes to different structures, including the Spitzenkörper, we investigated if a specific localization of Drs2 is critical for different functions, using a synthetic physical interaction approach to restrict/stabilize Drs2 at the Spitzenkörper. Our results suggest that the localization of Drs2 at the plasma membrane is critical for C. albicans growth on fluconazole and papuamide A, but not for invasive filamentous growth.
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Kowalewski GP, Wildeman AS, Bogliolo S, Besold AN, Bassilana M, Culotta VC. Cdc42 regulates reactive oxygen species production in the pathogenic yeast Candida albicans. J Biol Chem 2021; 297:100917. [PMID: 34181946 PMCID: PMC8329510 DOI: 10.1016/j.jbc.2021.100917] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 06/14/2021] [Accepted: 06/23/2021] [Indexed: 12/22/2022] Open
Abstract
Across eukaryotes, Rho GTPases such as Rac and Cdc42 play important roles in establishing cell polarity, which is a key feature of cell growth. In mammals and filamentous fungi, Rac targets large protein complexes containing NADPH oxidases (NOX) that produce reactive oxygen species (ROS). In comparison, Rho GTPases of unicellular eukaryotes were believed to signal cell polarity without ROS, and it was unclear whether Rho GTPases were required for ROS production in these organisms. We document here the first example of Rho GTPase-mediated post-transcriptional control of ROS in a unicellular microbe. Specifically, Cdc42 is required for ROS production by the NOX Fre8 of the opportunistic fungal pathogen Candida albicans. During morphogenesis to a hyphal form, a filamentous growth state, C. albicans FRE8 mRNA is induced, which leads to a burst in ROS. Fre8-ROS is also induced during morphogenesis when FRE8 is driven by an ectopic promoter; hence, Fre8 ROS production is in addition controlled at the post-transcriptional level. Using fluorescently tagged Fre8, we observe that the majority of the protein is associated with the vacuolar system. Interestingly, much of Fre8 in the vacuolar system appears inactive, and Fre8-induced ROS is only produced at sites near the hyphal tip, where Cdc42 is also localized during morphogenesis. We observe that Cdc42 is necessary to activate Fre8-mediated ROS production during morphogenesis. Cdc42 regulation of Fre8 occurs without the large NOX protein complexes typical of higher eukaryotes and therefore represents a novel form of ROS control by Rho GTPases.
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Puerner C, Kukhaleishvili N, Thomson D, Schaub S, Noblin X, Seminara A, Bassilana M, Arkowitz RA. Mechanical force-induced morphology changes in a human fungal pathogen. BMC Biol 2020; 18:122. [PMID: 32912212 PMCID: PMC7488538 DOI: 10.1186/s12915-020-00833-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 07/22/2020] [Indexed: 12/12/2022] Open
Abstract
Background The initial step of a number of human or plant fungal infections requires active penetration of host tissue. For example, active penetration of intestinal epithelia by Candida albicans is critical for dissemination from the gut into the bloodstream. However, little is known about how this fungal pathogen copes with resistive forces upon host cell invasion. Results In the present study, we have used PDMS micro-fabrication to probe the ability of filamentous C. albicans cells to penetrate and grow invasively in substrates of different stiffness. We show that there is a threshold for penetration that corresponds to a stiffness of ~ 200 kPa and that invasive growth within a stiff substrate is characterized by dramatic filament buckling, along with a stiffness-dependent decrease in extension rate. We observed a striking alteration in cell morphology, i.e., reduced cell compartment length and increased diameter during invasive growth, that is not due to depolarization of active Cdc42, but rather occurs at a substantial distance from the site of growth as a result of mechanical compression. Conclusions Our data reveal that in response to this compression, active Cdc42 levels are increased at the apex, whereas active Rho1 becomes depolarized, similar to that observed in membrane protrusions. Our results show that cell growth and morphology are altered during invasive growth, suggesting stiffness dictates the host cells that C. albicans can penetrate.
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Silva PM, Puerner C, Seminara A, Bassilana M, Arkowitz RA. Secretory Vesicle Clustering in Fungal Filamentous Cells Does Not Require Directional Growth. Cell Rep 2020; 28:2231-2245.e5. [PMID: 31433995 DOI: 10.1016/j.celrep.2019.07.062] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Revised: 04/22/2019] [Accepted: 07/18/2019] [Indexed: 11/27/2022] Open
Abstract
During symmetry breaking, the highly conserved Rho GTPase Cdc42 becomes stabilized at a defined site via an amplification process. However, little is known about how a new polarity site is established in an already asymmetric cell-a critical process in a changing environment. The human fungal pathogen Candida albicans switches from budding to filamentous growth in response to external cues, a transition controlled by Cdc42. Here, we have used optogenetic manipulation of cell polarity to reset growth in asymmetric filamentous C. albicans cells. We show that increasing the level of active Cdc42 on the plasma membrane results in disruption of the exocyst subunit Sec3 localization and a striking de novo clustering of secretory vesicles. This new cluster of secretory vesicles is highly dynamic, moving by hops and jumps, until a new growth site is established. Our results reveal that secretory vesicle clustering can occur in the absence of directional growth.
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Abstract
Morphological changes are critical for the virulence of a range of plant and human fungal pathogens.
Candida albicans is a major human fungal pathogen whose ability to switch between different morphological states is associated with its adaptability and pathogenicity. In particular,
C. albicans can switch from an oval yeast form to a filamentous hyphal form, which is characteristic of filamentous fungi. What mechanisms underlie hyphal growth and how are they affected by environmental stimuli from the host or resident microbiota? These questions are the focus of intensive research, as understanding
C. albicans hyphal growth has broad implications for cell biological and medical research.
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Weiner A, Orange F, Lacas‐Gervais S, Rechav K, Ghugtyal V, Bassilana M, Arkowitz RA. On‐site secretory vesicle delivery drives filamentous growth in the fungal pathogenCandida albicans. Cell Microbiol 2018; 21:e12963. [DOI: 10.1111/cmi.12963] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 10/02/2018] [Accepted: 10/04/2018] [Indexed: 12/31/2022]
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Wakade R, Labbaoui H, Stalder D, Arkowitz RA, Bassilana M. Overexpression of YPT6 restores invasive filamentous growth and secretory vesicle clustering in a Candida albicans arl1 mutant. Small GTPases 2017; 11:204-210. [PMID: 28960163 DOI: 10.1080/21541248.2017.1378157] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Virulence of the human fungal pathogen Candida albicans depends on the switch from budding to filamentous growth. Deletion of the Arf GTPase Arl1 results in hyphae that are shorter as well as reduced virulence. How Arl1 is regulated during hyphal growth, a process characteristic of filamentous fungi, yet absent in S. cerevisiae, is unknown. Here, we investigated the importance of the Rab6 homolog, Ypt6, in Arl1-dependent hyphal growth and determined that YPT6 overexpression specifically rescued the hyphal growth defect of an arl1 mutant, but not the converse. Furthermore, we show that deletion of ARL1 results in an alteration of the distribution of the Rab8 homolog, Sec4, in hyphal cells and that this defect is restored upon YPT6 overexpression.
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Labbaoui H, Bogliolo S, Ghugtyal V, Solis NV, Filler SG, Arkowitz RA, Bassilana M. Role of Arf GTPases in fungal morphogenesis and virulence. PLoS Pathog 2017; 13:e1006205. [PMID: 28192532 PMCID: PMC5325608 DOI: 10.1371/journal.ppat.1006205] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 02/24/2017] [Accepted: 01/29/2017] [Indexed: 12/30/2022] Open
Abstract
Virulence of the human fungal pathogen Candida albicans depends on the switch from budding to filamentous growth, which requires sustained membrane traffic and polarized growth. In many organisms, small GTPases of the Arf (ADP-ribosylation factor) family regulate membrane/protein trafficking, yet little is known about their role in fungal filamentous growth. To investigate these GTPases in C. albicans, we generated loss of function mutants in all 3 Arf proteins, Arf1-Arf3, and 2 Arf-like proteins, Arl1 and Arl3. Our results indicate that of these proteins, Arf2 is required for viability and sensitivity to antifungal drugs. Repressible ARF2 expression results in defects in filamentous growth, cell wall integrity and virulence, likely due to alteration of the Golgi. Arl1 is also required for invasive filamentous growth and, although arl1/arl1 cells can initiate hyphal growth, hyphae are substantially shorter than that of the wild-type, due to the inability of this mutant to maintain hyphal growth at a single site. We show that this defect does not result from an alteration of phospholipid distribution and is unlikely to result from the sole Golgin Imh1 mislocalization, as Imh1 is not required for invasive filamentous growth. Rather, our results suggest that the arl1/arl1 hyphal growth defect results from increased secretion in this mutant. Strikingly, the arl1/arl1 mutant is drastically reduced in virulence during oropharyngeal candidiasis. Together, our results highlight the importance of Arl1 and Arf2 as key regulators of hyphal growth and virulence in C. albicans and identify a unique function of Arl1 in secretion.
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Arkowitz RA, Bassilana M. Regulation of hyphal morphogenesis by Ras and Rho small GTPases. FUNGAL BIOL REV 2015. [DOI: 10.1016/j.fbr.2015.02.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Corvest V, Bogliolo S, Follette P, Arkowitz RA, Bassilana M. Spatiotemporal regulation of Rho1 and Cdc42 activity duringCandida albicansfilamentous growth. Mol Microbiol 2013; 89:626-48. [DOI: 10.1111/mmi.12302] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/18/2013] [Indexed: 01/02/2023]
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Vernay A, Schaub S, Guillas I, Bassilana M, Arkowitz RA. A steep phosphoinositide bis-phosphate gradient forms during fungal filamentous growth. ACTA ACUST UNITED AC 2012; 198:711-30. [PMID: 22891265 PMCID: PMC3514036 DOI: 10.1083/jcb.201203099] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
A gradient of PI(4,5)P2 formed by phospholipid synthesis, diffusion,
and regulated turnover is crucial for filamentous growth. Membrane lipids have been implicated in many critical cellular processes, yet
little is known about the role of asymmetric lipid distribution in cell
morphogenesis. The phosphoinositide bis-phosphate PI(4,5)P2 is
essential for polarized growth in a range of organisms. Although an asymmetric
distribution of this phospholipid has been observed in some cells, long-range
gradients of PI(4,5)P2 have not been observed. Here, we show that in
the human pathogenic fungus Candida albicans a steep,
long-range gradient of PI(4,5)P2 occurs concomitant with emergence of
the hyphal filament. Both sufficient PI(4)P synthesis and the actin cytoskeleton
are necessary for this steep PI(4,5)P2 gradient. In contrast, neither
microtubules nor asymmetrically localized mRNAs are critical. Our results
indicate that a gradient of PI(4,5)P2, crucial for filamentous
growth, is generated and maintained by the filament tip–localized
PI(4)P-5-kinase Mss4 and clearing of this lipid at the back of the cell.
Furthermore, we propose that slow membrane diffusion of PI(4,5)P2
contributes to the maintenance of such a gradient.
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Arkowitz RA, Bassilana M. Polarized growth in fungi: symmetry breaking and hyphal formation. Semin Cell Dev Biol 2011; 22:806-15. [PMID: 21906692 DOI: 10.1016/j.semcdb.2011.08.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Revised: 08/16/2011] [Accepted: 08/18/2011] [Indexed: 01/12/2023]
Abstract
Cell shape is a critical determinant for function. The baker's yeast Saccharomyces cerevisiae changes shape in response to its environment, growing by budding in rich nutrients, forming invasive pseudohyphal filaments in nutrient poor conditions and pear shaped shmoos for growth towards a partner during mating. The human opportunistic pathogen Candida albicans can switch from budding to hyphal growth, in response to numerous environmental stimuli to colonize and invade its host. Hyphal growth, typical of filamentous fungi, is not observed in S. cerevisiae. A number of internal cues regulate when and where yeast cells break symmetry leading to polarized growth and ultimately distinct cell shapes. This review discusses how cells break symmetry using the yeast S. cerevisiae paradigm and how polarized growth is initiated and maintained to result in dramatic morphological changes during C. albicans hyphal growth.
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Vauchelles R, Stalder D, Botton T, Arkowitz RA, Bassilana M. Rac1 dynamics in the human opportunistic fungal pathogen Candida albicans. PLoS One 2010; 5:e15400. [PMID: 21060846 PMCID: PMC2965673 DOI: 10.1371/journal.pone.0015400] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 09/08/2010] [Indexed: 02/07/2023] Open
Abstract
The small Rho G-protein Rac1 is highly conserved from fungi to humans, with approximately 65% overall sequence identity in Candida albicans. As observed with human Rac1, we show that C. albicans Rac1 can accumulate in the nucleus, and fluorescence recovery after photobleaching (FRAP) together with fluorescence loss in photobleaching (FLIP) studies indicate that this Rho G-protein undergoes nucleo-cytoplasmic shuttling. Analyses of different chimeras revealed that nuclear accumulation of C. albicans Rac1 requires the NLS-motifs at its carboxyl-terminus, which are blocked by prenylation of the adjacent cysteine residue. Furthermore, we show that C. albicans Rac1 dynamics, both at the plasma membrane and in the nucleus, are dependent on its activation state and in particular that the inactive form accumulates faster in the nucleus. Heterologous expression of human Rac1 in C. albicans also results in nuclear accumulation, yet accumulation is more rapid than that of C. albicans Rac1. Taken together our results indicate that Rac1 nuclear accumulation is an inherent property of this G-protein and suggest that the requirements for its nucleo-cytoplasmic shuttling are conserved from fungi to humans.
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Hope H, Schmauch C, Arkowitz RA, Bassilana M. The Candida albicans ELMO homologue functions together with Rac1 and Dck1, upstream of the MAP Kinase Cek1, in invasive filamentous growth. Mol Microbiol 2010; 76:1572-90. [PMID: 20444104 DOI: 10.1111/j.1365-2958.2010.07186.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Regulation of Rho G-proteins is critical for cytoskeletal organization and cell morphology in all eukaryotes. In the human opportunistic pathogen Candida albicans, Rac1 and its activator Dck1, a member of the CED5, Dock180, myoblast city family of guanine nucleotide exchange factors, are required for the budding to filamentous transition during invasive growth. We show that Lmo1, a protein with similarity to human ELMO1, is necessary for invasive filamentous growth, similar to Rac1 and Dck1. Furthermore, Rac1, Dck1 and Lmo1 are required for cell wall integrity, as the deletion mutants are sensitive to cell wall perturbing agents, but not to oxidative or osmotic stresses. The region of Lmo1 encompassing the ELMO and PH-like domains is sufficient for its function. Both Rac1 and Dck1 can bind Lmo1. Overexpression of a number of protein kinases in the rac1, dck1 and lmo1 deletion mutants indicates that Rac1, Dck1 and Lmo1 function upstream of the mitogen-activated protein kinases Cek1 and Mkc1, linking invasive filamentous growth to cell wall integrity. We conclude that the requirement of ELMO/CED12 family members for Rac1 function is conserved from fungi to humans.
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Hope H, Bogliolo S, Arkowitz RA, Bassilana M. Activation of Rac1 by the guanine nucleotide exchange factor Dck1 is required for invasive filamentous growth in the pathogen Candida albicans. Mol Biol Cell 2008; 19:3638-51. [PMID: 18579689 DOI: 10.1091/mbc.e07-12-1272] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Rho G proteins and their regulators are critical for cytoskeleton organization and cell morphology in all eukaryotes. In the opportunistic pathogen Candida albicans, the Rho G proteins Cdc42 and Rac1 are required for the switch from budding to filamentous growth in response to different stimuli. We show that Dck1, a protein with homology to the Ced-5, Dock180, myoblast city family of guanine nucleotide exchange factors, is necessary for filamentous growth in solid media, similar to Rac1. Our results indicate that Dck1 and Rac1 do not function in the same pathway as the transcription factor Czf1, which is also required for embedded filamentous growth. The conserved catalytic region of Dck1 is required for such filamentous growth, and in vitro this region directly binds a Rac1 mutant, which mimics the nucleotide-free state. In vivo overexpression of a constitutively active Rac1 mutant, but not wild-type Rac1, in a dck1 deletion mutant restores filamentous growth. These results indicate that the Dock180 guanine nucleotide exchange factor homologue, Dck1 activates Rac1 during invasive filamentous growth. We conclude that specific exchange factors, together with the G proteins they activate, are required for morphological changes in response to different stimuli.
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Bassilana M, Arkowitz RA. Rac1 and Cdc42 have different roles in Candida albicans development. EUKARYOTIC CELL 2006; 5:321-9. [PMID: 16467473 PMCID: PMC1405900 DOI: 10.1128/ec.5.2.321-329.2006] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We investigated the role of the highly conserved G protein Rac1 in the opportunistic pathogen Candida albicans. We identified and disrupted RAC1 and show here that, in contrast to CDC42, it is not necessary for viability or serum-induced hyphal growth but is essential for filamentous growth when cells are embedded in a matrix. Rac1 is localized to the plasma membrane, yet its distribution is more homogenous than that of Cdc42, with no enrichment at the tips of either buds or hyphae. In addition, fluorescence recovery after photobleaching results indicate that Rac1 and Cdc42 have different dynamics at the membrane. Furthermore, overexpression of Rac1 does not complement Cdc42 function, and conversely, overexpression of Cdc42 does not complement Rac1 function. Thus, Rac1 and Cdc42, although highly similar to one another, have different roles in C. albicans development.
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Bassilana M, Hopkins J, Arkowitz RA. Regulation of the Cdc42/Cdc24 GTPase module during Candida albicans hyphal growth. EUKARYOTIC CELL 2005; 4:588-603. [PMID: 15755921 PMCID: PMC1087799 DOI: 10.1128/ec.4.3.588-603.2005] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Rho G protein Cdc42 and its exchange factor Cdc24 are required for hyphal growth of the human fungal pathogen Candida albicans. Previously, we reported that strains ectopically expressing Cdc24 or Cdc42 are unable to form hyphae in response to serum. Here we investigated the role of these two proteins in hyphal growth, using quantitative real-time PCR to measure induction of hypha-specific genes together with time lapse microscopy. Expression of the hypha-specific genes examined depends on the cyclic AMP-dependent protein kinase A pathway culminating in the Efg1 and Tec1 transcription factors. We show that strains with reduced levels of CDC24 or CDC42 transcripts induce hypha-specific genes yet cannot maintain their expression in response to serum. Furthermore, in serum these mutants form elongated buds compared to the wild type and mutant budding cells, as observed by time lapse microscopy. Using Cdc24 fused to green fluorescent protein, we also show that Cdc24 is recruited to and persists at the germ tube tip during hyphal growth. Altogether these data demonstrate that the Cdc24/Cdc42 GTPase module is required for maintenance of hyphal growth. In addition, overexpression studies indicate that specific levels of Cdc24 and Cdc42 are important for invasive hyphal growth. In response to serum, CDC24 transcript levels increase transiently in a Tec1-dependent fashion, as do the G-protein RHO3 and the Rho1 GTPase activating protein BEM2 transcript levels. These results suggest that a positive feedback loop between Cdc24 and Tec1 contributes to an increase in active Cdc42 at the tip of the germ tube which is important for hypha formation.
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Bassilana M, Blyth J, Arkowitz RA. Cdc24, the GDP-GTP exchange factor for Cdc42, is required for invasive hyphal growth of Candida albicans. EUKARYOTIC CELL 2003; 2:9-18. [PMID: 12582118 PMCID: PMC141177 DOI: 10.1128/ec.2.1.9-18.2003] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans, the most common human fungal pathogen, is particularly problematic for immunocompromised individuals. The reversible transition of this fungal pathogen to a filamentous form that invades host tissue is important for its virulence. Although different signaling pathways such as a mitogen-activated protein kinase and a protein kinase A cascade are critical for this morphological transition, the function of polarity establishment proteins in this process has not been determined. We examined the role of four different polarity establishment proteins in C. albicans invasive growth and virulence by using strains in which one copy of each gene was deleted and the other copy expressed behind the regulatable promoter MET3. Strikingly, mutants with ectopic expression of either the Rho G-protein Cdc42 or its exchange factor Cdc24 are unable to form invasive hyphal filaments and germ tubes in response to serum or elevated temperature and yet grow normally as a budding yeast. Furthermore, these mutants are avirulent in a mouse model for systemic infection. This function of the Cdc42 GTPase module is not simply a general feature of polarity establishment proteins. Mutants with ectopic expression of the SH3 domain containing protein Bem1 or the Ras-like G-protein Bud1 can grow in an invasive fashion and are virulent in mice, albeit with reduced efficiency. These results indicate that a specific regulation of Cdc24/Cdc42 activity is required for invasive hyphal growth and suggest that these proteins are required for pathogenicity of C. albicans.
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Bassilana M, Damiano E, Leblanc G. Kinetic properties of sodium-proton antiport in Escherichia coli membrane vesicles: effects of imposed electrical potential, proton gradient, and internal pH. Biochemistry 2002; 23:5288-94. [DOI: 10.1021/bi00317a029] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Gwizdek C, Leblanc G, Bassilana M. Proteolytic mapping and substrate protection of the Escherichia coli melibiose permease. Biochemistry 1997; 36:8522-9. [PMID: 9214297 DOI: 10.1021/bi970312n] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The topology and substrate-induced conformational change(s) of the Na+ (Li+ or H+)-melibiose cotransporter (MelB) of Escherichia coli were investigated by limited protease digestion. To facilitate these analyses, MelB was epitope-tagged both at its carboxyl-terminus and at its amino-terminus. Limited digestion with different proteases indicates that the cytoplasmic loops connecting transmembrane domains 4-5, 6-7, and 10-11 together with the carboxyl-terminus of MelB are exposed in the cytoplasm. In contrast, periplasmic loops are highly resistant to all the proteases examined, including nonspecific proteases such as proteinase K and thermolysin. The effect of Na+ or Li+ and/or melibiose on the rate of protease digestion of the cytoplasmic loops was also analyzed. The rate of protease digestion of loop 4-5 is specifically reduced, by approximately 3-fold, by the presence of Na+ or Li+. These results suggest that loop 4-5 is near or part of the cation binding site. Moreover, the presence of both melibiose and either Na+ or Li+ further reduced the rate of protease digestion of this loop 4-5 by up to 9-fold, although no protection from protease digestion was observed when melibiose was added alone. The increase in resistance to proteases observed in the presence of the cation alone or the cation plus melibiose suggests that the interaction of the two cosubstrate with MelB results in change(s) of MelB conformation.
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Bassilana M, Gwizdek C. In vivo membrane assembly of the E.coli polytopic protein, melibiose permease, occurs via a Sec-independent process which requires the protonmotive force. EMBO J 1996. [DOI: 10.1002/j.1460-2075.1996.tb00905.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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Bassilana M, Gwizdek C. In vivo membrane assembly of the E.coli polytopic protein, melibiose permease, occurs via a Sec-independent process which requires the protonmotive force. EMBO J 1996; 15:5202-8. [PMID: 8895565 PMCID: PMC452264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
To investigate the mechanism of polytopic membrane protein insertion in Escherichia coli, we have examined the protein and energy requirements for in vivo membrane assembly of the prototypic 12 transmembrane domain sugar co-transporter, melibiose permease (MelB). MelB membrane assembly was analyzed both kinetically, by pulse labeling experiments, and functionally by measuring the activity of the inserted permease. Strikingly, the rate of MelB membrane assembly is decreased approximately 4-fold upon dissipation of the transmembrane electrochemical proton gradient, delta(mu)H+, indicative of a strong requirement for delta(mu)H+. Interestingly, selective dissipation of either the electrical (delta(psi)) or the chemical (delta(pH)) component of delta(mu)H+ demonstrates that either form of energy is required for MelB membrane assembly. In contrast, MelB membrane assembly does not require SecA, SecY or SecE, all three proteins which are strictly required for protein translocation. Neither the rate of MelB membrane assembly nor the amount of functional permease is affected by inactivation or depletion of these Sec proteins. These results strongly suggest that polytopic membrane proteins such as MelB insert into the cytoplasmic membrane by a mechanism fundamentally different from protein translocation.
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Arkowitz RA, Bassilana M. Protein translocation in Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1197:311-43. [PMID: 7819269 DOI: 10.1016/0304-4157(94)90012-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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