Stimulation by vasopressin and angiotensin of phospholipid methyltransferase in isolated rat hepatocytes

Alemany, Susana; Varela, Isabel; Mato, José M.

doi:10.1016/0014-5793(81)80955-6

Cited by 39 publications

(22 citation statements)

References 24 publications

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“…PtdEtnMeTases in various tissues have been shown to be activated by such receptor agonists as catecholamines [rat reticulocytes (6,7), C6 glioma astrocytoma (8), lymphocytes (9)], lectins [lymphocytes (10), mast cells (11)], immunoglobulins [mast cells (12), leukemic basophils (13)], glucagon [hepatocytes (14)]. , vasopressin [pituitary extracts (15), hepatocytes (16)], and angiotensin [hepatocytes (16)]. This process is rapid and not dependent on cAMP synthesis.…”

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confidence: 99%

Dopamine stimulation of phosphatidylcholine (lecithin) biosynthesis in rat brain neurons.

Leprohon¹,

Blusztajn²,

Wurtman³

1983

Proc. Natl. Acad. Sci. U.S.A.

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Rat brain synaptosomes contain enzymes, phosphatidylethanolamine N-methyltransferase(s) (EC 2.1.1.17), that catalyze the methylation of endogenous phosphatidylethanolamine to form its mono-, di-, and trimethyl (i.e., phosphatidylcholine) derivatives. We observe that the activity of these enzymes is [hepatocytes (16)]. This process is rapid and not dependent on cAMP synthesis. Little information has been available on the control of PtdEtnMeTase activity within brain neurons. We report here that catecholamine neurotransmitters, especially dopamine, enhance the activities of phosph6lipid methylating enzymes in rat brain synaptosomes. METHODSPreparation of Subcellular Fractions. Male Sprague-Dawley rats (200-300 g; Charles River Breeding Laboratories) were housed under a 12-hr/12-hr light/dark schedule (lights on, 0900-2100 hr) and had free access to water and food (Charles River chow; 22% protein, 0.018% choline). The animals were decapitated at 1000 hr, and the brains were quickly dissected on ice and homogenized in 10 vol of 0.32 M sucrose in a Potter-Elvehjem homogenizer; the homogenate was then centrifuged at 1,000 x g for 15 min to remove tissue debris and nuclei. The supernatant was layered on top of 4 ml of 1.2 M sucrose and centrifuged at 165,000 X -g for 15 min in a Beckman SW 41 Ti rotor. The resulting pellet contained mitochondria; the material at the interface of the gradient (containing the synaptosomes and myelin) was diluted to obtain approximately 0.32 M sucrose, layered on top of 4 ml of 0.8 M sucrose, and centrifuged at 165,000 X g for 15 min (17). The material at the interface, containing myelin, and the pellet, shown to contain synaptosomes by electron microscopy, were collected. In some cases, the postnuclear supernatant was centrifuged at 20,000 x g for 20 min to obtain the P2 pellet (containing synaptosomes, mitochondria, and myelin). The post-P2 supernatant was centrifuged at 100,000 X g for 60 min to obtain a microsomal pellet.PtdEtnMeTase Assay. PtdEtnMeTase activity was assayed by a modification of the method described previously (4). The standard assay medium was changed to 50 mM Tris HCl, pH 7.5/5 mM MgCl2/0.2 mM EDTA/0. 1 mM ATP and tissue preparation (0.2-0.4 mg of protein) in a final volume of 120 1.l. The effect on phospholipid [3Himethyl incorporation of omitting various components of this medium was examined (see Table 1). Norepinephrine-HCI (Sigma), dopamineHCl (Sigma), haloperidol lactate (5 mg/ml, containing 1.8 mg of methylparaben and 0.2 mg of propylparaben; a gift from McNeil, Fort Washington, PA), were added to some tubes before incubation. Reactions were started by addition of 2.5 jCi of S-adenosyl[methyl-3H]methionine (New England Nuclear; 13-15 Ci/mmol; 1 Ci = 37 GBq) to a final AdoMet concentration of 1.2-1.6 ,uM. Samples were incubated for 30 min at 37TC. Reactions were stopped by addition of 3 ml of chloroform/methanol/HCI, 100:50:1 (vol/vol). Water-soluble radioactive. materials were extracted by washing the incubation mixture with two 2-ml portions of 0....

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confidence: 99%

Dopamine stimulation of phosphatidylcholine (lecithin) biosynthesis in rat brain neurons.

Leprohon¹,

Blusztajn²,

Wurtman³

1983

Proc. Natl. Acad. Sci. U.S.A.

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“…All animals had free access to food and water. Hepatocytes were isolated as in [5,7]. Isolated hepatocytes were then shaken in stoppered 20ml vials at 37°C in the presence of glucose as in [5,7], Cells were stimulated after 30 min prein~ubation.…”

Section: Methodsmentioning

confidence: 99%

“…At various times after the addition of EGF the hepatocytes were poured into precooled centrifuge tubes a rd immediately centrifuged at 100 x g for 20s. The supernatant was then discarded and the pellet was homogenized and phospholipid methyltransferase assayed as in [5,7]. EGF was a generous gift of Dr Ira Pastan, NIH.…”

Section: Methodsmentioning

confidence: 99%

Stimulation by epidermal growth factor of phospholipid methyltransferase in isolated rat hepatocytes

1983

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Epidermal growth factor produces a time-and dose-dependent activation of phospholipid methyltransferase activity in hepatocytes isolated from juvenile and mature hepatectomized rats. This treatment however has no effect with hepatocytes isolated from mature or laparotomized rats. Dansylcadaverine (50cM), an inhibitor of receptor-mediated internali~tion of epidermal growth factor, has no effect on basal phospholipid methyltransferase but inhibits the stimulation of this enzyme by epidermal growth factor.These results indicate a possible role of phospholipid methylation during liver proliferation.~hospholipid methyIation Epidermal growth factor Hepatocyte Liver regeneration

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“…After this report, investigators examined the possibility that enzymatic methylation of phospholipids plays a role in the transduction of receptormediated signals through the membranes of a variety of cells (2). In addition to agents such as f-agonists (3), benzodiazepine (4), dopamine (5), concanavalin A (6), and IgE antibody (7), several peptide hormones have been shown to alter phospholipid methylation, including glucagon (8), vasopressin (9), angiotensin (10), bradykinin (11), and nerve growth factor (12). This process is rapid and has been localized to a stimulation of plasma membrane methyltransferase activity in certain systems (13).…”

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confidence: 99%

Insulin stimulation of phospholipid methylation in isolated rat adipocyte plasma membranes.

Kelly¹,

Kiechle²,

Jarett³

1984

Proc. Natl. Acad. Sci. U.S.A.

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Partially purified plasma membranes prepared from rat adipocytes contain N-methyltraitsferase(s) that utilize(s) S-adenosyl-L-methionine to synthesize phosphatidylcholine from phosphatidylethanolamine. The incorporation of[3H]methyl from S-adenosyl-L-[methyl-3H]methionine into plasma membrane phospholipids was linear with incubatiop time and plasma membrane protein concentration and was inhibited in a dose-dependent manner by both S-adenosyl-L-homocysteine and 3-deazadenosine. The addition of insulin to plasma membranes stimulated the methylation of endogenous phosphatidylethanolamine, as evidenced by an increase in the levels of phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine. The effect of insulin was rapid and concentration-dependent, with 100 microunits/ml providing near maximal stimulation. The incorporation of [3H]methyl into phospholipids of control and insulin-stimulated plasma membranes was enhanced by the addition of exogenous methyltransferase substrates phosphatidylethanolamine, phosphatidyl-N-monomethylethanolamine, and phosphatidyl-N,N-dimethylethanolamine. The stimulatory effect of insulin on adipocyte plasma membrane phospholipid methylation may have a physiological role in insulin action.The conversion by methylation of phosphatidylethanolamine to phosphatidylcholine was first reported in rat liver microsomes by Bremer and Greenberg (1). After this report, investigators examined the possibility that enzymatic methylation of phospholipids plays a role in the transduction of receptormediated signals through the membranes of a variety of cells (2). In addition to agents such as f-agonists (3), benzodiazepine (4), dopamine (5), concanavalin A (6), and IgE antibody (7), several peptide hormones have been shown to alter phospholipid methylation, including glucagon (8), vasopressin (9), angiotensin (10), bradykinin (11), and nerve growth factor (12). This process is rapid and has been localized to a stimulation of plasma membrane methyltransferase activity in certain systems (13).The activity of phospholipid methyltransferases in liver endoplasmic reticulum of alloxan-treated diabetic rats is reduced as compared to control (14), suggesting that insulin may induce the opposite effect, or increase phospholipid methylation. However, no direct evidence has been reported to date to support the hypothesis that insulin, after binding to its receptor, alters phospholipid methylation. We report here that partially purified plasma membranes prepared from rat adipocytes contain a phosphatidylethanolamine methyltransferase (PtdEtn MeTase) system and that insulin stimulates this enzyme system in a concentration-dependent manner. The effects of insulin were rapid and were observed as early as 15 sec after the addition of the hormone. MATERIALS AND METHODSMaterials. Male Sprague-Dawley rats (120 g) were obtained from Ace Animals (Boyertown, PA). Collagenase, albumin (fraction V), L-a-phosphatidylethanolamine (type III), L-a-phosphatidyl-N-monomethylethano...

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Stimulation by vasopressin and angiotensin of phospholipid methyltransferase in isolated rat hepatocytes

Cited by 39 publications

References 24 publications

Dopamine stimulation of phosphatidylcholine (lecithin) biosynthesis in rat brain neurons.

Dopamine stimulation of phosphatidylcholine (lecithin) biosynthesis in rat brain neurons.

Stimulation by epidermal growth factor of phospholipid methyltransferase in isolated rat hepatocytes

Insulin stimulation of phospholipid methylation in isolated rat adipocyte plasma membranes.

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