Phosphatidylinositol transfer protein dictates the rate of inositol trisphosphate production by promoting the synthesis of PIP2
| Autor: | Andrew Ball, Emer Cunningham, Shamshad Cockcroft, Geraint M.H. Thomas, Ian Hiles |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Phosphatidylinositol 4
5-Diphosphate GTP' Inositol Phosphates Molecular Sequence Data Coenzymes Phospholipase C beta HL-60 Cells Phospholipase Biology Phosphatidylinositols General Biochemistry Genetics and Molecular Biology Substrate Specificity chemistry.chemical_compound Phosphatidylinositol Phosphates GTP-Binding Proteins Phosphoinositide phospholipase C Animals Humans Inositol Phosphatidylinositol Phospholipid Transfer Proteins Phosphatidylinositol transfer protein DNA Primers Agricultural and Biological Sciences(all) Base Sequence Biochemistry Genetics and Molecular Biology(all) Membrane Proteins Inositol trisphosphate Cell biology Rats Isoenzymes chemistry Biochemistry Type C Phospholipases Signal transduction General Agricultural and Biological Sciences Carrier Proteins Signal Transduction |
| Zdroj: | Current biology : CB. 5(7) |
| ISSN: | 0960-9822 |
| Popis: | Background: Phosphatidylinositol transfer protein (PI-TP), which has the ability to transfer phosphatidylinositol (PI) from one membrane compartment to another, is required in the inositol lipid signalling pathway through phospholipase C– β (PLC– β ) that is regulated by GTP-binding protein(s) in response to extracellular signals. Here, we test the hypothesis that the principal role of PI-TP is to couple sites of lipid hydrolysis to sites of synthesis, and so to replenish depleted substrate for PLC– β . Results We have designed an experimental protocol that takes advantage of the different rates of release of endogenous PI-TP and PLC- β from HL60 cells permeabilized with streptolysin O. We have examined the kinetics of stimulated inositol lipid hydrolysis in cells depleted of PI-TP, but not of endogenous PLC- β , in the presence and absence of exogenous PI-TP. Linear time-courses were observed in the absence of any added protein, and the rate was accelerated by PI-TP using either guanosine 5′[ γ -thio]-triphosphate (GTP γ S) or the receptor-directed agonist fMetLeuPhe as activators. In addition, depletion from the cells of both PI-TP and PLC- β isoforms by extended permeabilization (40 minutes) allowed us to control the levels of PLC– β present in the cells. Once again, PI-TP increased the rates of reactions. To identify whether the role of PI-TP was to make available the substrate phosphatidylinositol bisphosphate (PIP 2 ) for the PLC, we examined the synthesis of PIP 2 in cells depleted of PI-TP. We found that PI-TP was essential for the synthesis of PIP 2 . Conclusion The predicted function of PI-TP in inositol lipid signalling is the provision of substrate for PLC– β from intracellular sites where PI is synthesized. We propose that PI-TP is in fact a co-factor in inositol lipid signalling and acts by interacting with the inositol lipid kinases. We hypothesize that the preferred substrate for PLC– β is not the lipid that is resident in the membrane but that provided through PI-TP. |
| Databáze: | OpenAIRE |
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