Quyen Aoh - Academia.edu (original) (raw)
Papers by Quyen Aoh
Biology of the Cell, 2020
Background Information. In the yeast Saccharomyces cerevisiae, acute glucose starvation induces r... more Background Information. In the yeast Saccharomyces cerevisiae, acute glucose starvation induces rapid endocytosis followed by vacuolar degradation of many plasma membrane proteins. This process is essential for cell viability, but the regulatory mechanisms that control it remain poorly understood. Under normal growth conditions, a major regulatory decision for endocytic cargo occurs at the trans-Golgi network (TGN) where proteins can recycle back to the plasma membrane or can be recognized by TGN-localised clathrin adaptors that direct them towards the vacuole. However, glucose starvation reduces recycling and alters the localization and post-translational modification of TGN-localised clathrin adaptors. This raises the possibility that during glucose starvation endocytosed proteins are routed to the vacuole by a novel mechanism that bypasses the TGN or does not require TGN-localised clathrin adaptors. Results. Here, we investigate the role of TGN-localised clathrin adaptors in the traffic of several amino acid permeases, including Can1, during glucose starvation. We find that Can1 transits through the TGN after endocytosis in both starved and normal conditions. Can1 and other amino acid permeases require TGN-localised clathrin adaptors for maximal delivery to the vacuole. Furthermore, these permeases are actively sorted to the vacuole, because ectopically forced de-ubiquitination at the TGN results in the recycling of the Tat1 permase in starved cells. Finally, we report that the Mup1 permease requires the clathrin adaptor Gga2 for vacuolar delivery. In contrast, the clathrin adaptor protein complex AP-1 plays a minor role, potentially in retaining permeases in the TGN, but it is otherwise dispensable for vacuolar delivery. Conclusions and significance. This work elucidates one membrane trafficking pathway needed for yeast to respond to acute glucose starvation. It also reveals the functions of TGNlocalised clathrin adaptors in this process. Our results indicate that the same machinery is needed for vacuolar protein sorting at the GN in glucose starved cells as is needed in the presence of glucose. In addition, our findings provide further support for the model that the TGN is a transit point for many endocytosed proteins, and that Gga2 and AP-1 function in distinct pathways at the TGN.
Molecular Biology of the Cell, 2011
Glucose is a rich source of energy and the raw material for biomass increase. Many eukaryotic cel... more 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 ...
Molecular Biology of the Cell, 2013
Glucose is a master regulator of cell behavior in the yeast Saccharomyces cerevisiae. It acts as ... more 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...
Journal of Biological Chemistry, 2012
Background: There are multiple interacting clathrin adaptors at the trans-Golgi network and endos... more Background: There are multiple interacting clathrin adaptors at the trans-Golgi network and endosomes in yeast. Results: Autoregulation of one adaptor, Gga2, alters the temporal delay between recruitment of Gga2 and a second adaptor, Ent5, to organelles. Conclusion: The interaction between Gga2 and Ent5 is regulated by an autoregulatory sequence. Significance: This autoregulatory mechanism may ensure accurate membrane traffic in vivo. Membrane traffic is an essential process that allows protein and lipid exchange between the endocytic, lysosomal, and secretory compartments. Clathrin-mediated traffic between the trans-Golgi network and endosomes mediates responses to the environment through the sorting of biosynthetic and endocytic protein cargo. Traffic through this pathway is initiated by the controlled assembly of a clathrin-adaptor protein coat on the cytosolic surface of the originating organelle. In this process, clathrin is recruited by different adaptor proteins that act as a bridge between clathrin and the transmembrane cargo proteins to be transported. Interactions between adaptors and clathrin and between different types of adaptors lead to the formation of a densely packed protein network within the coat. A key unresolved issue is how the highly complex adaptor-clathrin interaction and adaptor-adaptor interaction landscape lead to the correct spatiotemporal assembly of the clathrin coat. Here we report the discovery of a new autoregulatory motif within the clathrin adaptor Gga2 that drives synergistic binding of Gga2 to clathrin and the adaptor Ent5. This autoregulation influences the temporal and/or spatial location of the Gga2-Ent5 interaction. We propose that this synergistic binding provides built-in regulation to ensure the correct assembly of clathrin coats. Clathrin acts in many processes, including endocytosis and transport between the trans-Golgi network (TGN) 3 and endosomes (reviewed in Ref. 1). Clathrin is a multimeric protein complex that forms a polyhedral lattice on the outer surface of some transport vesicles (2). Formation of the clathrin lattices in vivo is controlled by a class of proteins called adaptors. In both endocytosis and transport between TGN and endosomes, * This work was supported, in whole or in part, by National Institutes of Health Grants GM092741 (to M. C. D.) and GM39040 (to G. P.). This work was also supported by funds from the state of North Carolina (to M. C. D. and Q. A.
BIOS, 2019
Polyglutamine diseases are a group of neurodegenerative disorders characterized by the expansion ... more Polyglutamine diseases are a group of neurodegenerative disorders characterized by the expansion of a CAG trinucleotide in a protein-coding gene. The translation of these expanded repeats leads to long polyglutamine tracts that increase the potential of the protein to aggregate itself and other proteins into the pathological amyloid conformation. Machado-Joseph disease (MJD), also known as Spinocerebellar Ataxia 3, is the second most common polyglutamine disease behind Huntington disease. In MJD, the CAG expansion occurs in the ATXN3 gene. Currently there are no FDA-approved therapies to prevent or cure MJD. However, RNA-based therapies that silence the expression of or alter the structure of the mutant protein have the potential to prevent and ameliorate the disease. Here, we will review how RNA interference (RNAi) and antisense oligonucleotides (AONs) could potentially be used to target ATXN3. These technologies could mediate allele-specific silencing of mutant ATXN3 alleles but also allele non-specific silencing for individuals without a targetable polymorphism. Both RNAi and AONs could be used to promote mRNA degradation and translational inhibition; in addition AONs may be used as splicing modulators. The evidence suggests that viral-mediated delivery of RNAi therapies may have longer term potency than liposomal-mediated delivery of RNAi or AON therapies; however, this has not been fully explored in animal models. Nevertheless, there are promising results from studies of MJD and similar neurodegenerative disorders that suggest that RNAi and AON technology may be a viable long-term treatment therapy.
Biology of the Cell, 2020
Background Information. In the yeast Saccharomyces cerevisiae, acute glucose starvation induces r... more Background Information. In the yeast Saccharomyces cerevisiae, acute glucose starvation induces rapid endocytosis followed by vacuolar degradation of many plasma membrane proteins. This process is essential for cell viability, but the regulatory mechanisms that control it remain poorly understood. Under normal growth conditions, a major regulatory decision for endocytic cargo occurs at the trans-Golgi network (TGN) where proteins can recycle back to the plasma membrane or can be recognized by TGN-localised clathrin adaptors that direct them towards the vacuole. However, glucose starvation reduces recycling and alters the localization and post-translational modification of TGN-localised clathrin adaptors. This raises the possibility that during glucose starvation endocytosed proteins are routed to the vacuole by a novel mechanism that bypasses the TGN or does not require TGN-localised clathrin adaptors. Results. Here, we investigate the role of TGN-localised clathrin adaptors in the traffic of several amino acid permeases, including Can1, during glucose starvation. We find that Can1 transits through the TGN after endocytosis in both starved and normal conditions. Can1 and other amino acid permeases require TGN-localised clathrin adaptors for maximal delivery to the vacuole. Furthermore, these permeases are actively sorted to the vacuole, because ectopically forced de-ubiquitination at the TGN results in the recycling of the Tat1 permase in starved cells. Finally, we report that the Mup1 permease requires the clathrin adaptor Gga2 for vacuolar delivery. In contrast, the clathrin adaptor protein complex AP-1 plays a minor role, potentially in retaining permeases in the TGN, but it is otherwise dispensable for vacuolar delivery. Conclusions and significance. This work elucidates one membrane trafficking pathway needed for yeast to respond to acute glucose starvation. It also reveals the functions of TGNlocalised clathrin adaptors in this process. Our results indicate that the same machinery is needed for vacuolar protein sorting at the GN in glucose starved cells as is needed in the presence of glucose. In addition, our findings provide further support for the model that the TGN is a transit point for many endocytosed proteins, and that Gga2 and AP-1 function in distinct pathways at the TGN.
Molecular Biology of the Cell, 2011
Glucose is a rich source of energy and the raw material for biomass increase. Many eukaryotic cel... more 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 ...
Molecular Biology of the Cell, 2013
Glucose is a master regulator of cell behavior in the yeast Saccharomyces cerevisiae. It acts as ... more 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...
Journal of Biological Chemistry, 2012
Background: There are multiple interacting clathrin adaptors at the trans-Golgi network and endos... more Background: There are multiple interacting clathrin adaptors at the trans-Golgi network and endosomes in yeast. Results: Autoregulation of one adaptor, Gga2, alters the temporal delay between recruitment of Gga2 and a second adaptor, Ent5, to organelles. Conclusion: The interaction between Gga2 and Ent5 is regulated by an autoregulatory sequence. Significance: This autoregulatory mechanism may ensure accurate membrane traffic in vivo. Membrane traffic is an essential process that allows protein and lipid exchange between the endocytic, lysosomal, and secretory compartments. Clathrin-mediated traffic between the trans-Golgi network and endosomes mediates responses to the environment through the sorting of biosynthetic and endocytic protein cargo. Traffic through this pathway is initiated by the controlled assembly of a clathrin-adaptor protein coat on the cytosolic surface of the originating organelle. In this process, clathrin is recruited by different adaptor proteins that act as a bridge between clathrin and the transmembrane cargo proteins to be transported. Interactions between adaptors and clathrin and between different types of adaptors lead to the formation of a densely packed protein network within the coat. A key unresolved issue is how the highly complex adaptor-clathrin interaction and adaptor-adaptor interaction landscape lead to the correct spatiotemporal assembly of the clathrin coat. Here we report the discovery of a new autoregulatory motif within the clathrin adaptor Gga2 that drives synergistic binding of Gga2 to clathrin and the adaptor Ent5. This autoregulation influences the temporal and/or spatial location of the Gga2-Ent5 interaction. We propose that this synergistic binding provides built-in regulation to ensure the correct assembly of clathrin coats. Clathrin acts in many processes, including endocytosis and transport between the trans-Golgi network (TGN) 3 and endosomes (reviewed in Ref. 1). Clathrin is a multimeric protein complex that forms a polyhedral lattice on the outer surface of some transport vesicles (2). Formation of the clathrin lattices in vivo is controlled by a class of proteins called adaptors. In both endocytosis and transport between TGN and endosomes, * This work was supported, in whole or in part, by National Institutes of Health Grants GM092741 (to M. C. D.) and GM39040 (to G. P.). This work was also supported by funds from the state of North Carolina (to M. C. D. and Q. A.
BIOS, 2019
Polyglutamine diseases are a group of neurodegenerative disorders characterized by the expansion ... more Polyglutamine diseases are a group of neurodegenerative disorders characterized by the expansion of a CAG trinucleotide in a protein-coding gene. The translation of these expanded repeats leads to long polyglutamine tracts that increase the potential of the protein to aggregate itself and other proteins into the pathological amyloid conformation. Machado-Joseph disease (MJD), also known as Spinocerebellar Ataxia 3, is the second most common polyglutamine disease behind Huntington disease. In MJD, the CAG expansion occurs in the ATXN3 gene. Currently there are no FDA-approved therapies to prevent or cure MJD. However, RNA-based therapies that silence the expression of or alter the structure of the mutant protein have the potential to prevent and ameliorate the disease. Here, we will review how RNA interference (RNAi) and antisense oligonucleotides (AONs) could potentially be used to target ATXN3. These technologies could mediate allele-specific silencing of mutant ATXN3 alleles but also allele non-specific silencing for individuals without a targetable polymorphism. Both RNAi and AONs could be used to promote mRNA degradation and translational inhibition; in addition AONs may be used as splicing modulators. The evidence suggests that viral-mediated delivery of RNAi therapies may have longer term potency than liposomal-mediated delivery of RNAi or AON therapies; however, this has not been fully explored in animal models. Nevertheless, there are promising results from studies of MJD and similar neurodegenerative disorders that suggest that RNAi and AON technology may be a viable long-term treatment therapy.