title: Involvement of phosphatidylcholine-specific phospholipase C in thromboxane A2-induced activation of mitogen-activated protein kinase in astrocytoma cells.
abstract: Thromboxane A2 (TXA2) receptor-mediated signal transduction was investigated in 1321N1 human astrocytoma cells. 9,11-Epithio-11,12-methano-TXA2 (STA2), a TXA2 receptor agonist, induced Ca2+ mobilization and phosphoinositide hydrolysis in a concentration-dependent manner. These responses were inhibited by treatment with U73122, an inhibitor of phosphatidylinositol-specific phospholipase C, or by culturing in 0.5% fetal calf serum containing 0.5 mM dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) for 2 days. However, the dbcAMP treatment augmented the TXA2 receptor-mediated phosphorylation of mitogen-activated protein kinase (MAPK). These results were confirmed by a functional MAPK assay measuring the incorporation of 32P into the MAPK substrate peptide. The TXA2 receptor-mediated MAPK activation was inhibited by SQ29548, a TXA2 receptor antagonist, and GF109203X, an inhibitor of protein kinase C. Although U73122 did not inhibit or only slightly inhibited the activation of MAPK, D-609, an inhibitor of phosphatidylcholine-specific phospholipase C, potently attenuated the activation in a concentration-dependent manner. Furthermore, STA2 accelerated the release of [3H]choline metabolites from the cells prelabeled with [3H]choline chloride. This release was inhibited by treatment with D-609. These results suggest that phosphatidylcholine-specific phospholipase C and protein kinase C, but not phosphatidylinositol-specific phospholipase C, are involved in TXA2 receptor-mediated MAPK activation in 1321N1 human astrocytoma cells.
authors.affiliation: Department of Pharmaceutical Molecular Biology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kobayashi
authors.forename: S
authors.initials: S
authors.lastname: Honma
authors.forename: N
authors.initials: N
authors.lastname: Nakahata
authors.forename: Y
authors.initials: Y
authors.lastname: Ohizumi
mesh_terms: D002118:Calcium / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D006868:Hydrolysis; D007425:Intracellular Membranes / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D010713:Phosphatidylcholines / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D017482:Receptors, Thromboxane / Q000819:agonists / Q000502:physiology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D017482:Receptors, Thromboxane; D013928:Thromboxane A2; C037866:STA 2; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D010738:Type C Phospholipases; D002118:Calcium