Abstract
The requirement of Vps34p, the sole phosphatidylinositol (PI) 3-kinase in Saccharomyces cerevisiae, for protein sorting to the vacuole in yeast has exemplified the essential role for phosphoinositides, phosphorylated derivatives of PI, in membrane trafficking. To better understand mechanisms that regulate PI 3-phosphate [PI(3)P]-mediated signaling, the role of the yeast myotubularin-related PI(3)P phosphatase Ymr1p was investigated. We found that Ymr1p and the synaptojanin-like phosphatase Sjl3p function as key regulators of the localization and levels of PI(3)P. Our data indicated that the ymr1Delta sjl3Delta double mutant aberrantly accumulated PI(3)P and demonstrated a steady-state redistribution of this lipid that leads to enrichment on the vacuolar membrane. This resulted in vacuole protein sorting defects, vacuolar fragmentation, and the misregulation of PI(3)P-specific effectors. Triple deletion of YMR1, SJL2, and SJL3 was lethal, suggesting an essential requirement for phosphatase-mediated PI(3)P regulation. Consistent with this, growth was restored to a ymr1Delta sjl2Delta sjl3Delta triple mutant by a PI(3)P-targeted Sac1p domain chimera (GFP-Sac1DeltaC-FYVE(EEA1)) that returned PI(3)P to levels comparable with wild-type cells. Together, this study demonstrated that Ymr1p, a myotubularin phosphatase family member, functions in the control of PI(3)P-dependent signaling and the maintenance of endosomal system integrity. In addition, this work defined an essential overlapping role for lipid phosphatases in the regulation of 3' phosphoinositides in yeast.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Aminopeptidases / analysis
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Aminopeptidases / metabolism
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Cytoplasm / chemistry
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Cytoplasm / physiology
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Endosomal Sorting Complexes Required for Transport
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Endosomes / chemistry
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Endosomes / physiology
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Membrane Proteins / metabolism
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Phosphatidylinositol Phosphates / metabolism*
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Phosphoric Monoester Hydrolases / classification
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Phosphoric Monoester Hydrolases / genetics
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Phosphoric Monoester Hydrolases / physiology*
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Protein Structure, Tertiary
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Protein Transport / genetics
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Protein Transport / physiology
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Protein Tyrosine Phosphatases / classification
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Protein Tyrosine Phosphatases, Non-Receptor
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Saccharomyces cerevisiae / enzymology*
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Saccharomyces cerevisiae Proteins / analysis
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Saccharomyces cerevisiae Proteins / classification
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Saccharomyces cerevisiae Proteins / genetics
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Saccharomyces cerevisiae Proteins / metabolism
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Saccharomyces cerevisiae Proteins / physiology*
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Vacuoles / chemistry
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Vacuoles / physiology
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Vesicular Transport Proteins / analysis
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Vesicular Transport Proteins / metabolism
Substances
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Endosomal Sorting Complexes Required for Transport
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Membrane Proteins
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Phosphatidylinositol Phosphates
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Saccharomyces cerevisiae Proteins
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VPS27 protein, S cerevisiae
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Vesicular Transport Proteins
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phosphatidylinositol 3-phosphate
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INP52 protein, S cerevisiae
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INP53 protein, S cerevisiae
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SAC1 protein, S cerevisiae
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Ymr1 protein, S cerevisiae
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Phosphoric Monoester Hydrolases
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Protein Tyrosine Phosphatases
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Protein Tyrosine Phosphatases, Non-Receptor
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myotubularin
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Aminopeptidases
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APE1 protein, S cerevisiae