PHOSPHATIDYLINOSITOL TRANSFER PROTEIN DICTATES THE RATE OF INOSITOL TRISPHOSPHATE PRODUCTION BY PROMOTING THE SYNTHESIS OF PIP2

被引：140

作者：

CUNNINGHAM, E

THOMAS, GMH

BALL, A

HILES, I

COCKCROFT, S

机构：

[1] UNIV LONDON UNIV COLL, DEPT PHYSIOL, LONDON WC1E 6JJ, ENGLAND

[2] UCL, SCH MED, LUDWIG INST CANC RES, LONDON W1P 8BT, ENGLAND

来源：

CURRENT BIOLOGY | 1995年 / 5卷 / 07期

基金：

英国惠康基金; 英国医学研究理事会;

关键词：

D O I：

10.1016/S0960-9822(95)00154-0

中图分类号：

Q5 [生物化学]; Q7 [分子生物学];

学科分类号：

071010 ; 081704 ;

摘要：

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-beta (PLC-beta) 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-beta. Results: We have designed an experimental protocol that takes advantage of the different rates of release of endogenous PI-TP and PLC-beta 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-beta, 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'[gamma-thio]-triphosphate (GTP gamma S) or the receptor-directed agonist fMetLeuPhe as activators. In addition, depletion from the cells of both PI-TP and PLC-beta isoforms by extended permeabilization (40 minutes) allowed us to control the levels of PLC-beta 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 (PIP2) for the PLC, we examined the synthesis of PIP2 in cells depleted of PI-TP. We found that PI-TP was essential for the synthesis of PIP2. Conclusions: The predicted function of PI-TP in inositol lipid signalling is the provision of substrate for PLC-beta 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-beta is not the lipid that is resident in the membrane but that provided through PI-TP.

引用

页码：775 / 783

页数：9

共 38 条

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