CTP:phosphocholine cytidylyltransferase inhibition by ceramide via PKC-alpha, p38 MAPK, cPLA2, and 5-lipoxygenase.
In a companion paper (Vivekananda J, Smith D, and King RJ. Am J Physiol Lung Cell Mol Physiol 281: L98-L107, 2001), we demonstrated that tumor necrosis factor (TNF)-alpha inhibited the activity of CTP:phosphocholine cytidylyltransferase (CT), the rate-limiting enzyme in the de novo synthesis of phosphatidylcholine (PC), and that its actions were likely exerted through a metabolite of sphingomyelin. In this paper, we explore the signaling pathway employed by TNF-alpha using C2 ceramide as a cell-penetrating sphingolipid representative of the metabolites induced by TNF-alpha. We found that in H441 cells, as reported in other cell types, cytosolic phospholipase A2 (cPLA2) is activated by TNF-alpha. We also observed that the inhibiting action of C2 ceramide on CT requires protein kinase C-alpha, p38 mitogen-activated protein kinase, and cPLA2. The actions of C2 ceramide on CT activity can be duplicated by adding 2 microM lysoPC to these cells. Furthermore, we found that the effects of C2 ceramide are dependent on 5-lipoxygenase but that cyclooxygenase II is unimportant. We hypothesize that CT activity is inhibited by the lysoPC generated as a consequence of the activation of cPLA2 by protein kinase C-alpha and p38 mitogen-activated protein kinase. The other product of the activation of cPLA2, arachidonic acid, is a substrate for the synthesis of leukotrienes, which raise intracellular Ca2+ levels and complete the activation of cPLA2.
Awasthi
S
S
Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA.
Vivekananda
J
J
Awasthi
V
V
Smith
D
D
King
R J
RJ
D001094:Arachidonate 5-Lipoxygenase / Q000502:physiology*; D002518:Ceramides / Q000378:metabolism / Q000494:pharmacology*; D019916:Choline-Phosphate Cytidylyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051546:Cyclooxygenase 2; D003600:Cytosol / Q000378:metabolism*; D015777:Eicosanoids / Q000502:physiology; D005799:Genes, Dominant; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015289:Leukotrienes / Q000096:biosynthesis / Q000502:physiology; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D010713:Phosphatidylcholines / Q000096:biosynthesis; D010741:Phospholipases A / Q000502:physiology*; D054467:Phospholipases A2; D010766:Phosphorylation / Q000187:drug effects; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051571:Protein Kinase C-alpha; D015398:Signal Transduction / Q000502:physiology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases
D002518:Ceramides; D015777:Eicosanoids; D007527:Isoenzymes; D015289:Leukotrienes; D008244:Lysophosphatidylcholines; D008565:Membrane Proteins; D010710:Phosphates; D010713:Phosphatidylcholines; D014409:Tumor Necrosis Factor-alpha; D001094:Arachidonate 5-Lipoxygenase; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D019916:Choline-Phosphate Cytidylyltransferase; D010741:Phospholipases A; D054467:Phospholipases A2