Take our Survey

Reference: Sbrissa D, et al. (2007) Core protein machinery for mammalian phosphatidylinositol 3,5-bisphosphate synthesis and turnover that regulates the progression of endosomal transport. Novel Sac phosphatase joins the ArPIKfyve-PIKfyve complex. J Biol Chem 282(33):23878-91

Reference Help

Abstract


Perturbations in PtdIns(3,5)P(2) synthesizing enzymes result in enlarged endocytic organelles from yeast to humans, indicating evolutionary conserved function of PtdIns(3,5)P(2) in endosome-related events. This is reinforced by the structural and functional homology of yeast Vac14 and hVac14 (ArPIKfyve), which activate yeast and mammalian PtdIns(3,5)P(2)-producing enzymes, Fab1 and PIKfyve, respectively. In yeast, PtdIns(3,5)P(2)-specific phosphatase, Fig4, in association with Vac14, turns over PtdIns(3,5)P(2) but whether such a mechanism operates in mammalian cells and what the identity of mammalian Fig4 may be, are unknown. Here we have identified and characterized Sac3, a Sac domain phosphatase, as the Fig4 mammalian counterpart. Endogenous Sac3, a widespread 97-kDa protein, formed a stable ternary complex with ArPIKfyve and PIKfyve. Concordantly, Sac3 cofractionated and colocalized with ArPIKfyve and PIKfyve. The intrinsic Sac3(WT) phosphatase activity preferably hydrolyzed PtdIns(3,5)P(2) in vitro although the other D-5-phosphorylated polyphosphoinositides were also substrates. Ablation of endogenous Sac3 by siRNAs elevated PtdIns(3,5)P(2) in (32)P-labeled HEK293 cells. Ectopically expressed Sac3(WT) in COS cells colocalized with, and dilated EEA1-positive endosomes, consistent with the PtdIns(3,5)P(2) requirement in early endosome dynamics. In vitro reconstitution of carrier vesicle formation from donor early endosomes revealed a gain of function upon Sac3 loss, whereas PIKfyve or ArPIKfyve protein depletion produced a loss of function. These data demonstrate a coupling between the machinery for PtdIns(3,5)P(2) synthesis and turnover achieved through a physical assembly of PIKfyve, ArPIKfyve and Sac3. We suggest that the tight regulation in PtdIns(3,5)P(2) homeostasis is mechanistically linked to early endosome dynamics in the course of cargo transport.

Reference Type
Journal Article
Authors
Sbrissa D, Ikonomov OC, Fu Z, Ijuin T, Gruenberg J, Takenawa T, Shisheva A
Primary Lit For
Additional Lit For
Review For

Interaction Annotations


Increase the total number of rows showing on this page by using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table; click on the small "i" buttons located within a cell for an annotation to view further details about experiment type and any other genes involved in the interaction.

Interactor Interactor Type Assay Annotation Action Modification Phenotype Source Reference

Gene Ontology Annotations


Increase the total number of rows showing on this page using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table.

Gene Gene Ontology Term Qualifier Aspect Method Evidence Source Assigned On Annotation Extension Reference

Phenotype Annotations


Increase the total number of rows showing on this page using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table; click on the small "i" buttons located within a cell for an annotation to view further details.

Gene Phenotype Experiment Type Mutant Information Strain Background Chemical Details Reference

Regulation Annotations


Increase the total number of rows displayed on this page using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; to filter the table by a specific experiment type, type a keyword into the Filter box (for example, “microarray”); download this table as a .txt file using the Download button or click Analyze to further view and analyze the list of target genes using GO Term Finder, GO Slim Mapper, SPELL, or YeastMine.

Regulator Target Experiment Assay Construct Conditions Strain Background Reference