Plasma membrane to vacuole traffic induced by glucose starvation requires Gga2‐dependent sorting at thetrans‐Golgi network (original) (raw)
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Glucose regulates clathrin adaptors at the trans-Golgi network and endosomes
Molecular Biology of the Cell, 2011
Glucose is a rich source of energy and the raw material for biomass increase. Many eukaryotic cells remodel their physiology in the presence and absence of glucose. The yeast Saccharomyces cerevisiae undergoes changes in transcription, translation, metabolism, and cell polarity in response to glucose availability. Upon glucose starvation, translation initiation and cell polarity are immediately inhibited, and then gradually recover. In this paper, we provide evidence that, as in cell polarity and translation, traffic at the trans-Golgi network (TGN) and endosomes is regulated by glucose via an unknown mechanism that depends on protein kinase A (PKA). Upon glucose withdrawal, clathrin adaptors exhibit a biphasic change in localization: they initially delocalize from the membrane within minutes and later partially recover onto membranes. Additionally, the removal of glucose induces changes in posttranslational modifications of adaptors. Ras and Gpr1 signaling pathways, which converge ...
2020
Eukaryotic cells adapt their metabolism to the extracellular environment. Downregulation of surface cargo proteins in response to nutrient stress reduces the burden of anabolic processes whilst elevating catabolic production in the lysosome. We use yeast to show that glucose starvation triggers a transcriptional response that simultaneously increases internalisation from the plasma membrane whilst supressing recycling from endosomes back to the surface. Nuclear export of the Mig1 transcriptional repressor in response to glucose starvation increases levels of the Yap1801/02 clathrin adaptors, which is sufficient to increase cargo internalisation. We also show Gpa1, which coordinates endosomal lipid homeostasis, is required for surface recycling of cargo. Nuclear translocation of Mig1 increases GPA2 levels and inhibits recycling, potentially by diverting Gpa1 to the surface and interfering with its endosomal role in recycling. Finally, we show glucose starvation results in transcriptional upregulation of many eisosomal factors, which serve to sequester a portion of nutrient transporters to persist the starvation period and maximise nutrient uptake upon return to replete conditions. This latter mechanism provides a physiological benefit for cells to rapidly recover from glucose starvation. Collectively, this remodelling of the surface protein landscape during glucose starvation calibrates metabolism to available nutrients.
Membrane Trafficking in the Yeast Saccharomyces cerevisiae Model
The yeast Saccharomyces cerevisiae is one of the best characterized eukaryotic models. The secretory pathway was the first trafficking pathway clearly understood mainly thanks to the work done in the laboratory of Randy Schekman in the 1980s. They have isolated yeast sec mutants unable to secrete an extracellular enzyme and these SEC genes were identified as encoding key effectors of the secretory machinery. For this work, the 2013 Nobel Prize in Physiology and Medicine has been awarded to Randy Schekman; the prize is shared with James Rothman and Thomas Südhof. Here, we present the different trafficking pathways of yeast S. cerevisiae. At the Golgi apparatus newly synthesized proteins are sorted between those transported to the plasma membrane (PM), or the external medium, via the exocytosis or secretory pathway (SEC), and those targeted to the vacuole either through endosomes (vacuolar protein sorting or VPS pathway) or directly (alkaline phosphatase or ALP pathway). Plasma membrane proteins can be internalized by endocytosis (END) and transported to endosomes where they are sorted between those targeted for vacuolar degradation and those redirected to the Golgi (recycling or RCY pathway). Studies in yeast S. cerevisiae allowed the identification of most of the known effectors, protein complexes, and trafficking pathways in eukaryotic cells, and most of them are conserved among eukaryotes.
Energy metabolism regulates clathrin adaptors at thetrans-Golgi network and endosomes
Molecular Biology of the Cell, 2013
Glucose is a master regulator of cell behavior in the yeast Saccharomyces cerevisiae. It acts as both a metabolic substrate and a potent regulator of intracellular signaling cascades. Glucose starvation induces the transient delocalization and then partial relocalization of clathrin adaptors at the trans-Golgi network and endosomes. Although these localization responses are known to depend on the protein kinase A (PKA) signaling pathway, the molecular mechanism of this regulation is unknown. Here we demonstrate that PKA and the AMP-regulated kinase regulate adaptor localization through changes in energy metabolism. We show that genetic and chemical manipulation of intracellular ATP levels cause corresponding changes in adaptor localization. In permeabilized cells, exogenous ATP is sufficient to induce adaptor localization. Furthermore, we reveal distinct energy-dependent steps in adaptor localization: a step that requires the ADP-ribosylation factor ARF, an ATP-dependent step that r...
Endosomal sorting of GLUT4 and Gap1 is conserved between yeast and insulin-sensitive cells
Journal of Cell Science, 2013
The insulin-regulated trafficking of the facilitative glucose transporter GLUT4 in fat and muscle cells and the nitrogen-regulated trafficking of the general amino acid permease Gap1 in the yeast Saccharomyces cerevisiae share several common features: Both Gap1 and GLUT4 are nutrient transporters that are mobilised to the cell surface from an intracellular store in response to an environmental cue; both are polytopic membrane proteins harboring amino acid targeting motifs in their carboxy-terminal tails that are required for their regulated trafficking; ubiquitination of both Gap1 and GLUT4 plays an important role in their regulated trafficking, as do the ubiquitin-binding GGA (Golgi-localised, γ-ear-containing, ARF-binding) adaptor proteins. Here, we find that when expressed heterologously in yeast, human GLUT4 is subject to nitrogen-regulated trafficking in a ubiquitin-dependent manner similar to Gap1. In addition, by expressing a GLUT4/Gap1 chimeric protein in adipocytes we show ...
Ubiquitin Is Required for Sorting to the Vacuole of the Yeast General Amino Acid Permease, Gap1
In yeast, ubiquitin plays a central role in proteolysis of a multitude of proteins and serves also as a signal for endocytosis of many plasma membrane proteins. We showed previously that ubiquitination of the general amino acid permease (Gap1) is essential to its endocytosis followed by vacuolar degradation. These processes occur when NH4 , a preferential source of nitrogen, is added to cells growing on proline or urea, i.e. less favored nitrogen sources. In this study, we show that Gap1 is ubiquitinated on two lysine residues in the cytosolic N terminus (positions 9 and 16). A mutant Gap1 in which both lysines are mutated (Gap1K9K16) remains fully stable at the plasma membrane after NH4 addition. Furthermore, each of the two lysines harbors a polyubiquitin chain in which ubiquitin is linked to the lysine 63 of the preceding ubiquitin. The Gap1K9 and Gap1K16 mutants, in which a single lysine is mutated, are downregulated in response to NH4 although more slowly. In proline-grown cells lacking Npr1, a protein kinase involved in the control of Gap1 trafficking, newly synthesized Gap1 is sorted from the Golgi to the vacuole without passing through the plasma membrane (accompanying article, De Craene, J.-O., Soetens, O., and Andre´ , B. (2001) J. Biol. Chem. 276, 43939–43948). We show here that ubiquitination of Gap1 is also required for this direct sorting to the vacuole. In an npr1 mutant, neosynthesized Gap1K9K16 is rerouted to and accumulates at the plasma membrane. Finally, Bul1 and Bul2, two proteins interacting with Npi1/Rsp5, are essential to ubiquitination and down-regulation of cell-surface Gap1, as well as to sorting of neosynthesized Gap1 to the vacuole, as occurs in an npr1 mutant. Our results reveal a novel role of ubiquitin in the control of Gap1 trafficking, i.e. direct sorting from the late secretory pathway to the vacuole. This result reinforces the growing evidence that ubiquitin plays an important role not only in internalization of plasma membrane proteins but also in their sorting in the endosomes and/or trans-Golgi.