Evidence for a single pool of <i>myo</i>‐inositol in hormone‐responsive WRK‐1 cells

Monaco, Marie E.; Moldover, Nancy H.

doi:10.1002/jcb.240590208

Cited by 2 publications

(2 citation statements)

References 17 publications

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“…Thus, newly synthesized PtdIns is not preferentially relocalized to a hormone-responsive pool but rather generally distributed throughout the cell. These results are in agreement with our previous findings that the phosphoinositide cycle is not closed with respect to Ins, since exogenous Ins and that derived from hormone-induced hydrolysis of Ins lipids exist in the same intracellular pool [Monaco and Moldover, 1995].…”

Section: Discussionsupporting

confidence: 93%

Organization of the receptor-mediated phosphoinositide cycle: Relationship between receptor occupancy and accession of phosphatidylinositol

Monaco

Moldover

1997

J. Cell. Biochem.

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We have previously reported the existence of separate hormone-responsive and -unresponsive pools of inositol phospholipids in WRK-1 cells. In order to further explore this concept, we have performed experiments to examine the relationship between the plasma membrane receptor and the pool of phosphatidylinositol (Ptdlns) that is metabolized in response to hormonal stimulation. The results support the following conclusions. 1) The amount of Ptdlns metabolized in WRK-1 cells in response to vasopressin is proportional to the number of receptors occupied; neither prolonged activation with nor readdition of submaximal concentration of vasopressin induced the same degree of Ptdlns metabolism as maximal concentration of vasopressin. 2) Dissociation of cytoskeletal structures by incubation with cytochalasin D did not alter the amount of Ptdlns accessed during hormonal stimulation. 3) Accession of Ptdlns from internal membranes does not depend on internalization and recycling of the receptor; cells incubated in potassium-free medium failed to internalize receptor-ligand complexes, yet they accessed the same amount of Ptdlns in response to vasopressin as did control cells. 4) Golgi-mediated phosphatidylinositol transport is not involved in hormone-stimulated phosphoinositide turnover, since brefeldin A, which interferes with Golgi-mediated transport processes, had no effect on the amount of Ptdlns accessed during vasopressin stimulation. 5) Phosphoinositide breakdown and compensatory resynthesis is not a closed process; newly synthesized Ptdlns is not preferentially localized to a hormone-responsive pool but is generally redistributed between responsive and unresponsive pools.

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Section: Discussionsupporting

confidence: 93%

Organization of the receptor-mediated phosphoinositide cycle: Relationship between receptor occupancy and accession of phosphatidylinositol

Monaco

Moldover

1997

J. Cell. Biochem.

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“…However, the latter, synthetic phase of the cycle, namely the conversion of CDP-DG to PtdIns, does not require the continued presence of hormone (Monaco and Adelson, 1991), and does not appear to be compartmentalized in the manner of the hydrolytic phase of the cycle; exogenously added inositol is able to be utilized as a substrate for the PtdIns synthase (Monaco and Moldover, 1995).…”

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confidence: 97%

Analysis of hormone‐stimulated phosphatidylinositol synthesis

Monaco

Moldover

Walden

2002

Journal Cellular Physiology

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Agonist-stimulated phosphoinositide turnover is accompanied by compensatory resynthesis of these lipids. Several lines of evidence suggest that resynthesis of phosphatidylinositol (PtdIns) involves phosphorylation of diacylglycerol (DG) (salvage pathway) rather than acylation of glycerol phosphate (de novo pathway), although a contribution from the de novo pathway has not been ruled out. To determine the relative contribution of the de novo and salvage pathways in stimulated PtdIns resynthesis, an inhibitor of de novo synthesis (Triacsin C) was incubated simultaneously with the hormone agonist. Results indicate that at early times (90 min), hormone-stimulated PtdIns synthesis proceeds predominantly via the salvage pathway, although some de novo synthesis is also taking place. At later times (24 h), stimulated synthesis is solely via the de novo pathway. Increasing cellular DG content by either adding exogenous DG or treating cells with bacterial phospholipase C (bPLC) results in deacylation of the DG rather than phosphorylation; however, inhibition of this deacylation fails to stimulate phosphorylation by DG kinase (DGK), suggesting channeling of the DG substrate between PLC and DG kinase. Receptor activation is not required for activation of DGK, since treatment with a calcium ionophore induces the same Triacsin C-insensitive PtdIns synthesis. Depletion of the polyphosphoinositide pools by treatment with wortmannin prevents both hormone and A23187-induced polyphosphoinositide hydrolysis; however, A23187 is still able to induce hydrolysis of PtdIns and subsequent compensatory resynthesis. The inability of R59949 to inhibit either hormone-induced or ionophore-induced PtdIns resynthesis suggests that the alpha isoform is not involved; however, its possible that the channeling phenomenon prevents the inhibitor from gaining access to the diacylglycerol kinase enzyme. Further study will be required to determine which isoform catalyzes hormone-induced resynthesis of PtdIns.

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Evidence for a single pool of myo‐inositol in hormone‐responsive WRK‐1 cells

Cited by 2 publications

References 17 publications

Organization of the receptor-mediated phosphoinositide cycle: Relationship between receptor occupancy and accession of phosphatidylinositol

Organization of the receptor-mediated phosphoinositide cycle: Relationship between receptor occupancy and accession of phosphatidylinositol

Analysis of hormone‐stimulated phosphatidylinositol synthesis

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