Phosphoinositides serve crucial roles in cell physiology, ranging from cell signalling to membrane traffic. Among the seven eukaryotic phosphoinositides the best studied species is phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2), which is concentrated at the plasma membrane where, among other functions, it is required for the nucleation of endocytic clathrin-coated pits. No phosphatidylinositol other than PI(4,5)P2 has been implicated in clathrin-mediated endocytosis, whereas the subsequent endosomal stages of the endocytic pathway are dominated by phosphatidylinositol-3-phosphates(PI(3)P). How phosphatidylinositol conversion from PI(4,5)P2-positive endocytic intermediates to PI(3)P-containing endosomes is achieved is unclear. Here we show that formation of phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2) by class II phosphatidylinositol-3-kinase C2α (PI(3)K C2α) spatiotemporally controls clathrin-mediated endocytosis. Depletion of PI(3,4)P2 or PI(3)K C2α impairs the maturation of late-stage clathrin-coated pits before fission. Timed formation of PI(3,4)P2 by PI(3)K C2α is required for selective enrichment of the BAR domain protein SNX9 at late-stage endocytic intermediates. These findings provide a mechanistic framework for the role of PI(3,4)P2 in endocytosis and unravel a novel discrete function of PI(3,4)P2 in a central cell physiological process.
"The class III PI3 kinase VPS-34 may play a major role in producing PtdIns3P on sealed phagosomes, as both MTM-1 and PIKI-1 are released at this stage. Human class II PI3 kinase C2α is reported to control clathrin-mediated endocytosis by generating Pt- dIns(3,4)P 2 (Posor et al., 2013). In our study, however, 2xFYVE but not TAPP1, a PtdIns(3,4)P 2 reporter, is readily seen on phagosomes and abrogated by loss of PIKI-1. "
The Journal of Cell Biology 08/2015; 210(3):485-502. DOI:10.1083/jcb.201501038 · 9.83 Impact Factor
"Whether the enzyme is indeed able to directly generate these products is as yet debated. Classical experiments with HPLC-based analytical methods identify PtdIns(3)P as the most abundant, if not exclusive, PI3K-C2a product   . In agreement, cells lacking PI3K-C2a do not evidence general changes in PtdIns(3,4)P 2 that can be detected by HLPC analysis. "
"Enhanced tocopherol delivery to membranes may be required in cells at risk for tocopherol depletion, such as in epithelial duct cells of secretory glands or airway ciliated epithelial cells exposed to high levels of oxygen, in which the hTAPs are abundantly expressed , . Enrichment of αT, αTP, or PI3P/PI4P at specific sites may also contribute to the αT-mediated increase of hexosaminidase secretion in rat mast cells , and/or determine the identity of vesicles required for intracellular trafficking . It is noteworthy that the related Saccharomyes cerevisiae SEC14p mediates vesicle formation and secretion from endosomes and the trans-Golgi Network (TGN) to the vacuole , and it can be speculated that the lumen of the epithelial ducts represents a cellular space that is homologous to the yeast vacuole. "
[Show abstract][Hide abstract] ABSTRACT: The vitamin E derivative, alpha-tocopheryl phosphate (αTP), is detectable in cultured cells, plasma and tissues in small amounts, suggesting the existence of enzyme(s) with α-tocopherol (αT) kinase activity. Here, we characterize the production of αTP from αT and [γ-32P]-ATP in primary human coronary artery smooth muscle cells (HCA-SMC) using separation by thin layer chromatography (TLC) and subsequent analysis by Ultra Performance Liquid Chromatography (UPLC). In addition to αT, although to a lower amount, also γT is phosphorylated. In THP-1 monocytes, γTP inhibits cell proliferation and reduces CD36 scavenger receptor expression more potently than αTP. Both αTP and γTP activate the promoter of the human vascular endothelial growth factor (VEGF) gene with similar potency, whereas αT and γT had no significant effect. The recombinant human tocopherol associated protein 1 (hTAP1, hSEC14L2) binds both αT and αTP and stimulates phosphorylation of αT possibly by facilitating its transport and presentation to a putative αT kinase. Recombinant hTAP1 reduces the in vitro activity of the phosphatidylinositol-3-kinase gamma (PI3Kγ) indicating the formation of a stalled/inactive hTAP1/PI3Kγ heterodimer. The addition of αT, βT, γT, δT or αTP differentially stimulates PI3Kγ, suggesting facilitated egress of sequestered PI from hTAP1 to the enzyme. It is suggested that the continuous competitive exchange of different lipophilic ligands in hTAPs with cell enzymes and membranes may be a way to make these lipophiles more accessible as substrates for enzymes and as components of specific membrane domains.
PLoS ONE 07/2014; 9(7):e101550. DOI:10.1371/journal.pone.0101550 · 3.23 Impact Factor
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