Changing phosphoinositides “on the fly”: how trafficking vesicles avoid an identity crisis

Abstract

Joining an antagonistic phosphoinositide (PtdInsP) kinase and phosphatase into a single protein complex may regulate rapid and local PtdInsP changes. This may be important for processes such as membrane fission that require a specific PtdInsP and that are innately local and rapid. Such a complex could couple vesicle formation, with erasing of the identity of the donor organelle from the vesicle prior to its fusion with target organelles, thus preventing organelle identity intermixing. Coordinating signals are postulated to switch the relative activities of the kinase and phosphatase in a spatio-temporal manner that matches membrane fission events. The discovery of two such complexes supports this hypothesis. One regulates the interconversion of phosphatidylinositol and PtdIns(3)P by joining the Vps34 PtdIns 3-kinase and the myotubularin 3-phosphatases. The other regulates the interconversion between PtdIns(3)P and PtdIns(3,5)P(2) through the Fab1/PIKfyve kinase and the Fig4/mFig4 phosphatase. These lipids are essential components of the endosomal identity code.

Spatial and temporal integration of signalling networks regulating pollen tube growth

“…PtdIns(4,5)P 2 is involved in clathrin-mediated endocytosis (Brearley, 2008;Konig et al, 2008;Botelho, 2009) and reorganization of the actin cytoskeleton (Staiger, 2000;Meijer and Munnik, 2003;Staiger and Blanchoin, 2006). PtdIns(4,5)P 2 is synthesized via phosphorylation of PtdIns4P by phosphatidylinositol-4-phosphate 5-kinase (PI4P5K), and its hydrolysis by phospholipase C (PLC) produces diacylglycerol (DAG) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3 ].…”

Radiolabeling and Quantification of Cellular Levels of Phosphoinositides by High Performance Liquid Chromatography-coupled Flow Scintillation

“…It provides the experimental details for labeling yeast cells with 3 H-myo-inositol, extracting and deacylating lipids and an HPLC-elution protocol to fractionate and quantify deacylated PtdInsPs. Please note that labeling, deacylation, resolution and quantification of PtdInsPs in mammalian cells require optimization and longer HPLC-elution profiles.…”

“…Phosphoinositides (PtdInsPs) are important signaling phospholipids that help regulate a variety of cellular functions, including signal transduction, membrane trafficking and gene expression, which then modulate higher-order cell behavior such as cell division, organelle identity and metabolic activity [1][2][3] . There are seven species of PtdInsPs that are derived from the phosphorylation of the 3, 4, and/or 5 positions of the inositol head group of phosphatidylinositol (PtdIns), the parent phospholipid.…”

“…There are seven species of PtdInsPs that are derived from the phosphorylation of the 3, 4, and/or 5 positions of the inositol head group of phosphatidylinositol (PtdIns), the parent phospholipid. Importantly, the seven PtdInsPs are unequally distributed and the local concentration of each PtdInsP species can increase or decrease at specific subcellular sites where they bind to a distinct set of protein effectors, which together permits each PtdInsP to control the identity and function of its host membrane 3,4 . In addition, the levels of each PtdInsP need to be tightly controlled since this can significantly impact the signal intensityproduced by a PtdInsP.…”

“…In addition, the levels of each PtdInsP need to be tightly controlled since this can significantly impact the signal intensityproduced by a PtdInsP. The localization and levels of each PtdInsP depends on the targeting and activity of numerous lipid kinases, phosphatases and phospholipases that mediate the synthesis and turnover of each PtdInsP 3,4 . Hence, misregulation of the PtdInsP regulatory machinery can perturb cell function, leading to diseases such as cancer and degenerative diseases 2,5,6 .…”