Table 1.
Abundance, location, measurement, and roles of PPI lipids in eukaryotic cells
| Lipid | Abundance | Distribution | Assays for measurement | Cellular role |
|---|---|---|---|---|
| Phosphatidylinositol (a.k.a. PI, PtdIns) | ∼80 mol% of total cellular PPIs | Abundant in ER but potentially all membranes | TLC, HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium | Precursor for PI(3)P and PI(4)P |
| Phosphatidylinositol 4-phosphate (a.k.a. PI (4)P, PtdIns4P, PI4P) | ∼2–5 mol% of total cellular PPI | PM, endosomes, trans-Golgi | TLC, HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium, immunofluorescence, fluorescent biosensor (P4M) | Precursor for PI(4,5) P2, recruitment of clathrin adaptors, lipid binding to OSBP, ORP, CERT, FAPP2. |
| Phosphatidylinositol 3-phosphate (a.k.a. PI (3)P, PtdIns3P, PI3P) | ∼0.2–0.5 mol % of total cellular PPI | Early endosomes | TLC, [3H] or [32P] radiolabeling to equilibrium, fluorescent biosensors (FYVE) | Involved in endocytic vesicle fusion and trafficking, autophagy |
| Phosphatidylinositol 5-phosphate (a.k.a. PI (5)P, PtdIns5P, PI5P) | ∼0.01 mol% of total cellular PPI | PM, endosomes, nuclear envelope | TLC, [3H] or [32P] radiolabeling to equilibrium | Stress signal, apoptosis, Akt/ mTOR signal pathway |
| Phosphatidylinositol 4,5-bisphosphate (a.k. a. PI(4,5)P2, PtdIns4,5P2, PI4,5P2, ‘PIP2’) | 2–5 mol% of total PPI | PM, recycling endosomes, lysosomes | TLC, HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium, immunofluorescence, genetically encoded fluorescent biosensor (PH domain from PLCδ1 for PM labeling), ion channel currents. | Intimately involved in key PM events, including regulation of endo- and exocytosis, phagocytosis, cell motility, signal transduction, and ion channel function |
| Phosphatidylinositol 3,4-bisphosphate (a.k. a. PI(3,4)P2, PtdIns3,4P2, PI3,4P2) | <0.1mol% of total PPI | PM, early endosomes | TLC, HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium, immunofluorescence, genetically encoded fluorescent biosensor (TAPP1 PH domain) | PI3K/Akt signaling pathway, clathrin-coated vesicle maturation, endocytic trafficking |
| Phosphatidylinositol 3,5-bisphosphate (a.k. a. PI(3,5)P2, PtdIns3,5P2, PI3,5P2) | <∼2 mol% of total PPI | Late endosomes and Lysosomes | TLC, HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium, immunofluorescence, genetically encoded fluorescent biosensor (Fyve) | Protein sorting at the late endosomes/ multivesicular bodies |
| Phosphatidylinositol 3,4,5 trisphosphate (a. k.a. PI(3,4,5)P3, PtdIns3,4,5P3, PI3,4,5P3, PIP3) | <0.05% of total PPI | PM, some endocytic compartments | Thin layer chromatography (TLC), HPLC-MS/MS, [3H] or [32P] radiolabeling to equilibrium, immunofluorescence, genetically encoded fluorescent biosensor (AKT, BTK biosensors). | Cell proliferation and cell survival, cytoskeleton dynamics, cell motility, membrane trafficking and apoptosis |
Abbreviations: ER, endoplasmic reticulum; HPLC, High-pressure liquid chromatography; MS, mass spectrometry; PM, plasma membrane; PPI, Polyphosphoinositides; TLC, Thin layer chromatography.