Phosphoinositiden signalisieren Lipide, deren relative Häufigkeit schnell ändert als Reaktion auf verschiedene Reize. Dieser Artikel beschreibt eine Methode, um die Fülle der Phosphoinositiden Messung durch metabolisch Markierung von Zellen mit 3 H-myo-Inositol, gefolgt von Extraktion und Deacylierung. Extrahiert glycero-inositides werden dann durch Hochleistungs-Flüssigkeits-Chromatographie getrennt und durch Strömungs Szintillations quantifiziert.
Phosphoinositides (PtdInsPs) are essential signaling lipids responsible for recruiting specific effectors and conferring organelles with molecular identity and function. Each of the seven PtdInsPs varies in their distribution and abundance, which are tightly regulated by specific kinases and phosphatases. The abundance of PtdInsPs can change abruptly in response to various signaling events or disturbance of the regulatory machinery. To understand how these events lead to changes in the amount of PtdInsPs and their resulting impact, it is important to quantify PtdInsP levels before and after a signaling event or between control and abnormal conditions. However, due to their low abundance and similarity, quantifying the relative amounts of each PtdInsP can be challenging. This article describes a method for quantifying PtdInsP levels by metabolically labeling cells with 3H-myo-inositol, which is incorporated into PtdInsPs. Phospholipids are then precipitated and deacylated. The resulting soluble 3H-glycero-inositides are further extracted, separated by high-performance liquid chromatography (HPLC), and detected by flow scintillation. The labeling and processing of yeast samples is described in detail, as well as the instrumental setup for the HPLC and flow scintillator. Despite losing structural information regarding acyl chain content, this method is sensitive and can be optimized to concurrently quantify all seven PtdInsPs in cells.
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 activity1-3. 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. 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 membrane3,4. 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 PtdInsP3,4. Hence, misregulation of the PtdInsP regulatory machinery can perturb cell function, leading to diseases such as cancer and degenerative diseases2,5,6. To fully understand the roles and functions of PtdInsPs and their regulatory machinery, both microscopy-based and biochemical-based techniques have been developed to track and quantify PtdInsPs.
In many cases, PtdInsPs bind to their protein effectors via a specific protein domain7-9. These protein modules often retain their proper fold and lipid recognition properties when expressed separately from the entire protein. This gave rise to PtdInsP probes by fusing a specific PtdInsP-binding protein domain to a fluorescent protein (FP) like green fluorescent protein (GFP) for the subcellular detection of PtdInsPs by microscopy. Indeed, many studies have used FP-fused PtdInsP-binding protein modules to identify the localization and dynamics of specific PtdInsP species by live-cell imaging1,10. For example, the Pleckstrin homology (PH) domain of phospholipase C δ1 (PLCδ1) fused to GFP specifically recognizes the phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] on the plasma membrane, whereas tandem copies of the FYVE domain of early endosome antigen 1 (EEA1) has been employed to track phosphatidylinositol-3-phosphate (PtdIns3P) on endosomes10-13. Overall, microscopy-based techniques are great to visualize PtdInsP localization and dynamics, but there are several caveats including that PtdInsP-binding domains may also interact with additional factors other than the target PtdInsP species and that they cannot detect changes below cytosolic fluorescence of the FP-probes.
Biochemical techniques including thin-layer chromatography, mass spectrometry and radioisotope labeling can also be used to characterize and quantify the levels of each PtdInsP14-16. These methods require the isolation of lipids for the detection of cellular levels of PtdInsPs. Mass spectrometry can be used to characterize phospholipids from lipid extracts and is invaluable for determining the acyl chain composition of PtdInsPs14,17. However, mass spectrometry is mostly semi-quantitative and it remains difficult to resolve and concurrently quantify PtdInsP species of the same molecular weight14,17. In comparison, radioisotope labeling of PtdInsPs followed by high performance liquid chromatography (HPLC)-coupled flow scintillation is useful for the separation and concurrent quantification of all seven species of PtdInsPs18. The use of HPLC with a strong anion exchange (SAX) column achieves separation based on molecular weight, charge and shape, thus fractionating deacylated PtdInsPs (Gro-InsPs) even of the same molecular weight and charge. Coupling the HPLC eluent to a flow scintillator then generates radioactive-based signal peaks for each Gro-InsPs species relative to the original parent glycerol-inositol (Gro-Ins)18. This ultimately corresponds to relative levels of PtdInsPs in cells.
Radiolabeling of PtdInsPs and HPLC-coupled flow scintillation is a useful tool to investigate the regulation and function of phosphatidylinositol 3,5-bisphosphate [PtdIns(3,5)P2], a PtdInsP that only constitutes ~0.1-0.3% of PtdIns16,19,20. Synthesis of PtdIns(3,5)P2 is performed by the PtdIns3P 5-kinase called Fab1 in yeast and PIKfyve in mammals21. This reaction is counteracted by a PtdIns(3,5)P2 5-phosphatase called Fig4 in yeast or mFig4/Sac3 in mammals22-24. Interestingly, both PIKfyve/Fab1 and mFig4/Fig4/Sac3 exist in a single complex and are regulated by the scaffolding adaptor protein, Vac14 in yeast or mVac14/ArPIKfyve in mammals25,26. In VAC14-deleted yeast cells, Fab1 does not function efficiently leading to a 90% decrease in PtdIns(3,5)P2 levels27,28. On the other hand, Atg18 is a PtdIns(3,5)P2 effector protein that may control vacuolar fission 29. Atg18 is also a negative regulator of PtdIns(3,5)P2 since the deletion of its gene, ATG18, causes a 10 to 20-fold increase in PtdIns(3,5)P2 levels29,30. Overall, changes in the levels of PtdIns(3,5)P2 severely impacts the function of the yeast vacuole and the mammalian lysosomes, consequently affecting processes such as membrane trafficking, phagosome maturation, autophagy and ion transport 6,19,21,31.
This article describes the process of radioisotope labeling of PtdInsPs with 3H-myo-inositol in yeast to detect the relative levels of PtdIns(3,5)P2 in wild-type, vac14Δ and atg18Δ yeast strains. Using this as an example, the resolving capabilities of HPLC for the separation of individual PtdInsPs as well as the sensitivity of flow scintillation for detection of trace amount of 3H-myo-inositol is shown. We also elaborate on how one might optimize the methodology for labeling and separating 3H-labelled PtdInsPs from mammalian cells, whose samples tend to be more complex since these cells possess all seven PtdInsP species.
Dieser Artikel beschreibt die experimentelle Protokoll erforderlich, um Zellebenen PtdnsPs durch HPLC-gekoppelten Strömungs Szintillations aus Hefe zu quantifizieren. Die Methodik ermöglicht die metabolische Markierung von PtdInsPs mit 3 H- myo-Inositol, gefolgt von Lipid Aufarbeitung und Extraktion von wasserlöslichen 3 H-Gro-InsPs, HPLC-Fraktionierung und Analyse. Mit dieser Methode können die relativen Mengen an PtdInsPs in Zellen unter verschiedenen Bedingungen quantifiziert werden…
The authors have nothing to disclose.
C.Y.H. was supported by an Ontario Graduate Scholarship from the Government of Ontario. This article was made possible by funding held by R.J.B. from the Natural Sciences and Engineering Research Council, the Canada Research Chairs Program and Ryerson University.
1-Butanol | Biobasic | BC1800 | Reagent grade |
Ammonium phosphate dibasic | Bioshop | APD001 | ACS grade |
Ammonium sulfate | Biobasic | ADB0060 | Ultra Pure grade |
Autosampler | Agilent | G1329B | Agilent 1260 infinity series |
Biotin | Sigma | B4501 | |
Boric acid | Biobasic | BB0044 | Molecular biology grade |
Calcium Chloride | Biobasic | CT1330 | Ahydrous, industrial grade |
Calcium pantothenate | Sigma | C8731 | |
Copper(II) sulfate | Sigma | 451657 | Anhydrous |
D-Glucose | Biobasic | GB0219 | Anhydrous, biotech grade |
Dulbecco's modification of Eagle's Medium | Life | 11995-065 | With 4.5 g/L glucose, 110 mg/L pyruate, L-glutamine |
Dulbecco's modification of Eagle's Medium | MP biomedicals | 0916429 | With 4.5 g/L glucose, without L-gluatmine, without inositol |
EDTA | Biobasic | EB0107 | Acid free, ultra pure grade |
Ethyl ether | Caledon labs | 1/10/4700 | Anhydrous, reagent grade |
Ethyl formate | Sigma | 112682 | Reagent grade |
Fetal bovine serum | Wisent | 080-450 | US origin, premium quality, heat inactivated |
Fetal Bovine Serum, Dialyzed | Life | 26400044 | US origin |
FlowLogic U | LabLogic Systems Ltd | SG-BXX-05 | Scintillation fluid for flow scintillation |
Folic acid | Biobasic | FB0466 | USP grade |
HEPES buffer solution | Life | 15630080 | 1 M solution |
Inositol, Myo-[2-3H(N)] | Perkin Elmer | NET114005MC | 9:1 ethanol to water |
Insulin-Transferrin-Selenium-Ethanolamine | Life | 51500056 | 100x solution |
Iron(III) chloride | Sigma | 157740 | Reagent grade |
Laura – Chromatography data collection and analysis software | LabLogic Systems Ltd | Version 4.2.1.18 | Flow scintillator software |
L-glutamine | Sigma | G7513 | 200 mM, solution, sterile-filtered, BioXtra, suitable for cell culture |
Magnesium Chloride | Sigma | M8266 | Anhydrous |
Manganese sulfate | Biobasic | MB0334 | Monohydrate, ACS grade |
Methanol | Caledon labs | 6701-7-40 | HPLC Grade |
Methylamine solution | Sigma | 426466 | 40% (v/v) |
Monopotassium phosphate | Biobasic | PB0445 | Anhydrous, ACS grade |
Nicotinic acid | Biobasic | NB0660 | Reagent grade |
OpenLAB CSD ChemStation | Agilent | Rev. C.01.03 | HPLC software |
p-aminobenzoic acid (PABA) | Bioshop | PAB001.100 | Free acid |
Penicillin-Streptomycin | Sigma | P4333 | 100X, liquid, stabilized, sterile-filtered, cell culture tested |
Perchloric acid | Sigma | 244252 | ACS reagent, 70% |
PhenoSpher SAX column | Phenomenex | 00G-315-E0 | 5µm, 80Å, 250 x 4.6 mm |
Phosphoric acid | Caledon labs | 1/29/8425 | Reagent grade |
Potassium Chloride | Biobasic | PB0440 | ACS grade |
Potassium iodide | Biobasic | PB0443 | ACS grade |
Pyridoxine hydrochloride | Sigma | P9755 | |
Quaternary pump | Agilent | G1311C | Agilent 1260 infinity series |
Riboflavin | Bioshop | RIB333.100 | USP grade |
Sodium Chloride | Biobasic | DB0483 | Biotech grade |
Sodium molybdate | Sigma | 243655 | |
Thermostatted Column Compartment | Agilent | G1316A | Agilent 1260 infinity series |
Thiamine hydrochloride | Sigma | T4625 | Reagent grade; make solution of 0.02% (w/v), forms a suspension. mix and freeze aliquots |
Ultima Gold | Perkin Elmer | 6013321 | Scintillation coctail for liquid scintillation counting |
Zinc sulfate | Biobasic | ZB2906 | Heptahydrate, reagent grade |
β-RAM 4 | IN/US systems | Model 4 | Flow scintillator – 500 µL flow cell; alternative Radiomatic Flow Scintillator Analyser by Perkin Elmer |