Subcellular localization of ammonium transporters in Dictyostelium discoideum

Kirsten, Janet H.; Xiong, Yanhua; Davis, Carter T.; Singleton, Charles K.

doi:10.1186/1471-2121-9-71

Cited by 28 publications

(21 citation statements)

References 56 publications

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“…In order to visualise the endo-lysosomal membrane system, a fusion of mCherry with AmtA, an ammonium transporter [26, 27] that localises to all endosomes and phagosomes in Dictyostelium [26, 27], was expressed in dgat1&2 deficient cells. Interestingly, after FA supplementation no significant co-localization was observed between AmtA-mCherry and the neutral lipid structures (Fig 5B, arrowheads), implying that they are not of endosomal nature.…”

Section: Resultsmentioning

confidence: 99%

Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions

Barisch

Soldati

2017

PLoS Pathog

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During a tuberculosis infection and inside lipid-laden foamy macrophages, fatty acids (FAs) and sterols are the major energy and carbon source for Mycobacterium tuberculosis. Mycobacteria can be found both inside a vacuole and the cytosol, but how this impacts their access to lipids is not well appreciated. Lipid droplets (LDs) store FAs in form of triacylglycerols (TAGs) and are energy reservoirs of prokaryotes and eukaryotes. Using the Dictyostelium discoideum/Mycobacterium marinum infection model we showed that M. marinum accesses host LDs to build up its own intracytosolic lipid inclusions (ILIs). Here, we show that host LDs aggregate at regions of the bacteria that become exposed to the cytosol, and appear to coalesce on their hydrophobic surface leading to a transfer of diacylglycerol O-acyltransferase 2 (Dgat2)-GFP onto the bacteria. Dictyostelium knockout mutants for both Dgat enzymes are unable to generate LDs. Instead, the excess of exogenous FAs is esterified predominantly into phospholipids, inducing uncontrolled proliferation of the endoplasmic reticulum (ER). Strikingly, in absence of host LDs, M. marinum alternatively exploits these phospholipids, resulting in rapid reversal of ER-proliferation. In addition, the bacteria are unable to restrict their acquisition of lipids from the dgat1&2 double knockout leading to vast accumulation of ILIs. Recent data indicate that the presence of ILIs is one of the characteristics of dormant mycobacteria. During Dictyostelium infection, ILI formation in M. marinum is not accompanied by a significant change in intracellular growth and a reduction in metabolic activity, thus providing evidence that storage of neutral lipids does not necessarily induce dormancy.

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Section: Resultsmentioning

confidence: 99%

Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions

Barisch

Soldati

2017

PLoS Pathog

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“…Others have proposed that members of the Rh family function as NH 3 /NH 4 + sensors in determining the choice of slug vs. culmination in Dictyostelium discoideum (Kirsten et al 2005, 2008; Singleton et al 2006). We propose that oocytes have a low-affinity “sensor” that responds, directly or indirectly, to extracellular NH 3 /NH 4 + .…”

Section: Discussionmentioning

confidence: 99%

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing Xenopus oocytes to Solutions Containing NH3/NH4 +

et al. 2009

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Others have shown that exposing oocytes to high levels of NH3/NH4+ (10–20 mM) causes a paradoxical fall in intracellular pH (pHi), whereas low levels (e.g., 0.5 mM) cause little pHi change. Here we monitored pHi and extra-cellular surface pH (pHS) while exposing oocytes to 5 or 0.5 mM NH3/NH4+. We confirm that 5 mM NH3/NH4+ causes a paradoxical pHi fall (−ΔpHi ≅ 0.2), but also observe an abrupt pHS fall (−ΔpHS ≅ 0.2)—indicative of NH3 influx—followed by a slow decay. Reducing [NH3/NH4+] to 0.5 mM minimizes pHi changes but maintains pHS changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpHS at both NH3/NH4+ levels. During removal of 0.5 or 5 mM NH3/NH4+, failure of pHS to markedly overshoot bulk extracellular pH implies little NH3 efflux and, thus, little free cytosolic NH3/NH4+. A new analysis of the effects of NH3 vs. NH4+ fluxes on pHS and pHi indicates that (a) NH3 rather than NH4+ fluxes dominate pHi and pHS changes and (b) oocytes dispose of most incoming NH3. NMR studies of oocytes exposed to 15N-labeled NH3/NH4+ show no significant formation of glutamine but substantial NH3/NH4+ accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pHi and pHS demonstrate that NH3 flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane.

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“…These receptors are Ca 2+ permeable ligand-gated ion channels activated by ATP. Other transporters, such as an ammonium (NH 4 + ) transporter (AmtB, (Kirsten et al, 2008)), a homologous to the Rh protein in red blood cells (RH50, (Benghezal et al, 2001)) that could act as CO 2 transporter (Kustu and Inwood, 2006), in D. discoideum , and polyamine (TcPOT1, (Hasne et al, 2010)) and phosphate transporters (TcPHO1, (Ulrich et al, 2011)), in T. cruzi , have also been localized to the CVC.…”

Section: The Contractile Vacuolementioning

confidence: 99%

“…Furthermore, carbonic anhydrase activity was present in CV fractions and most of the acetazolamidesensitive carbonic anhydrase activity co-localized with the contractile vacuole markers (Marchesini et al, 2002). Interestingly, evidence for an ammonium (NH 4 + ) transporter (AmtB) (Kirsten et al, 2008) and a potential CO 2 transporter (RH50) (Benghezal et al, 2001) in the CVC of D. discoideum has also been provided. Although the orientation of these transporters is not known their presence suggest that NH 4 + and CO 2 could return to the cytosol once the water is eliminated by the CV discharge.…”

Section: The Contractile Vacuolementioning

confidence: 99%

New Insights into Roles of Acidocalcisomes and Contractile Vacuole Complex in Osmoregulation in Protists

Docampo

Jiménez

Lander

et al. 2013

International Review of Cell and Molecular Biology

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While free-living protists are usually subjected to hyposmotic environments, parasitic protists are also in contact with hyperosmotic habitats. Recent work in one of these parasites, Trypanosoma cruzi, has revealed that its contractile vacuole complex, which usually collects and expels excess water as a mechanism of regulatory volume decrease after hyposmotic stress, has also a role in cell shrinking when the cells are submitted to hyperosmotic stress. Trypanosomes also have an acidic calcium store rich in polyphosphate (polyP), named the acidocalcisome, which is involved in their response to osmotic stress. Here, we review newly emerging insights on the role of acidocalcisomes and the contractile vacuole complex in the cellular response to hyposmotic and hyperosmotic stresses. We also review the current state of knowledge on the composition of these organelles and their other roles in calcium homeostasis and protein trafficking.

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Subcellular localization of ammonium transporters in Dictyostelium discoideum

Cited by 28 publications

References 56 publications

Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions

Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing Xenopus oocytes to Solutions Containing NH3/NH4 +

New Insights into Roles of Acidocalcisomes and Contractile Vacuole Complex in Osmoregulation in Protists

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