title: An enzymatic cascade of Rab5 effectors regulates phosphoinositide turnover in the endocytic pathway.
abstract: Generation and turnover of phosphoinositides (PIs) must be coordinated in a spatial- and temporal-restricted manner. The small GTPase Rab5 interacts with two PI 3-kinases, Vps34 and PI3Kbeta, suggesting that it regulates the production of 3-PIs at various stages of the early endocytic pathway. Here, we discovered that Rab5 also interacts directly with PI 5- and PI 4-phosphatases and stimulates their activity. Rab5 regulates the production of phosphatidylinositol 3-phosphate (PtdIns[3]P) through a dual mechanism, by directly phosphorylating phosphatidylinositol via Vps34 and by a hierarchical enzymatic cascade of phosphoinositide-3-kinasebeta (PI3Kbeta), PI 5-, and PI 4-phosphatases. The functional importance of such an enzymatic pathway is demonstrated by the inhibition of transferrin uptake upon silencing of PI 4-phosphatase and studies in weeble mutant mice, where deficiency of PI 4-phosphatase causes an increase of PtdIns(3,4)P2 and a reduction in PtdIns(3)P. Activation of PI 3-kinase at the plasma membrane is accompanied by the recruitment of Rab5, PI 4-, and PI 5-phosphatases to the cell cortex. Our data provide the first evidence for a dual role of a Rab GTPase in regulating both generation and turnover of PIs via PI kinases and phosphatases to coordinate signaling functions with organelle homeostasis.
authors.affiliation: Max-Planck Institute of Molecular Cell Biology and Genetics, 01307, Dresden, Germany.
authors.forename: Hye-Won
authors.initials: HW
authors.lastname: Shin
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Hayashi
authors.forename: Savvas
authors.initials: S
authors.lastname: Christoforidis
authors.forename: Sandra
authors.initials: S
authors.lastname: Lacas-Gervais
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hoepfner
authors.forename: Markus R
authors.initials: MR
authors.lastname: Wenk
authors.forename: Jan
authors.initials: J
authors.lastname: Modregger
authors.forename: Sandrine
authors.initials: S
authors.lastname: Uttenweiler-Joseph
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilm
authors.forename: Arne
authors.initials: A
authors.lastname: Nystuen
authors.forename: Wayne N
authors.initials: WN
authors.lastname: Frankel
authors.forename: Michele
authors.initials: M
authors.lastname: Solimena
authors.forename: Pietro
authors.initials: P
authors.lastname: De Camilli
authors.forename: Marino
authors.initials: M
authors.lastname: Zerial
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002384:Catalysis; D002451:Cell Compartmentation; D002846:Chromatography, Affinity; D015536:Down-Regulation / Q000235:genetics; D004705:Endocytosis; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D044967:Serum; D014168:Transferrin / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D014168:Transferrin; C055525:phosphatidylinositol 3-phosphate; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases; D020696:rab5 GTP-Binding Proteins