CTP:phosphocholine cytidylyltransferase inhibition by ceramide via PKC-{alpha}, p38 MAPK, cPLA2, and 5-lipoxygenase

• Published in: American journal of physiology. Lung cellular and molecular physiology 2001-07, Vol.281 (1), p.108
• Main Authors: Awasthi, Shanjana, Vivekananda, Jeevalatha, Awasthi, Vibhudutta, Smith, Dolphin, King, Richard J
• Format: Article
• Language: English
• ISSN: 1040-0605; 1522-1504

Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900 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)- 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- using C 2 ceramide as a cell-penetrating sphingolipid representative of the metabolites induced by TNF- . We found that in H441 cells, as reported in other cell types, cytosolic phospholipase A 2 (cPLA 2 ) is activated by TNF- . We also observed that the inhibiting action of C 2 ceramide on CT requires protein kinase C- , p38 mitogen-activated protein kinase, and cPLA 2 . The actions of C 2 ceramide on CT activity can be duplicated by adding 2 µM lysoPC to these cells. Furthermore, we found that the effects of C 2 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 cPLA 2 by protein kinase C- and p38 mitogen-activated protein kinase. The other product of the activation of cPLA 2 , arachidonic acid, is a substrate for the synthesis of leukotrienes, which raise intracellular Ca 2+ levels and complete the activation of cPLA 2 . lung injury; pulmonary surfactant; phosphatidylcholine synthesis; leukotrienes; cytidine 5'-triphosphate; protein kinase C; mitogen-activated protein kinase; cytosolic phospholipase A 2