Possible Involvement of Mitogen‐Activated Protein Kinase in Phospholipase D Activation Induced by H₂O₂, but Not by Carbachol, in Rat Pheochromocytoma PC12 Cells

Abstract

Abstract:We have previously reported that hydrogen peroxide (H202) induced a considerable increase of phospholipase D (PLD) activity and phosphorylation of mitogen-activated protein (MAP) kinase in P012 cells. H202-induced PLD activation and MAP kinase phosphorylation were dose-dependently inhibited by a specific MAP kinase kinase inhibitor, PD 098059. In contrast, carbacholmediated PLD activation was not inhibited by the PD 098059 pretreatment whereas MAP kinase phosphorylation was prevented. These findings indicated that MAP kinase is implicated in the PLD activation induced by H202, but not by carbachol. In the present study, H202 also caused a marked release of oleic acid (OA) from membrane phospholipids in P012 cells. As we have previously shown that OA stimulates PLD activity in P012 cells, the mechanism of H202-induced fatty acid liberation and its relation to PLD activation were investigated. Pretreatment of the cells with methylarachidonyl fluorophosphonate (MAFP), a phospholipase A2 (PLA2) inhibitor, almost completely prevented the release of [ 3H]OAby H 202 treatment. From the preferential release of OA and sensitivity to other PLA2 inhibitors, the involvement of a Ca 2~-independent cytosolic PLA 2-type enzyme was suggested. In contrast to OA release, MAFP did not inhibit PLD activation by H202. The inhibitory profile of the OA release by PD 098059 did not show any correlation with that of MAP kinase. These results lead us to suggest that H202-induced PLD activation may be mediated by MAP kinase and also that H202-mediated OA release, which would be catalyzed by a Ca 2~-independentcytosolic PLA 2-like enzyme, is not linked to the PLD activation in P012 cells. Key Words: Hydrogen peroxide-Mitogenactivated protein kinase-Phospholipase D-Oleic acid-Phospholipase A2-P012 cells.

α-Synuclein Affects the MAPK Pathway and Accelerates Cell Death

“…Since oxidative stress caused by hydrogen peroxide activates p38 MAPK and SAPK/JNK (56 -58), ␣-synuclein might block this reaction and disrupt equilibration of the MAPK pathway, thereby causing cell death. ␣-and ␤-synuclein are known to inhibit phospholipase D activity in vitro (59), which is intimately related to ERK1/2 function (60,61). Considering this along with our own results, ␣-synuclein might bind to a number of molecules in order to regulate signal transduction.…”

Phospholipase D2 Activity Suppresses Hydrogen Peroxide‐Induced Apoptosis in PC12 Cells

“…Ito et al. (1998) reported that ERK was involved in PLD activation induced by H 2 O 2 , whereas Rizzo et al (1999) reported that PLD is the upstream signal protein in the activation of the ERK pathway. We investigated whether ERK is the upstream signal protein or downstream target of PLD.…”

Implication of Phospholipase D2 in Oxidant-induced Phosphoinositide 3-Kinase Signaling via Pyk2 Activation in PC12 Cells

“…Proteins were separated as described for Western blot analysis. (14,15,17). These observations lead us to assume that tyrosine phosphorylation of PLD2 expressed in this cell may regulate its activity.…”

“…A number of studies have demonstrated that hydrogen peroxide (H 2 O 2 ) stimulates phospholipase D (PLD), 1 which generates phosphatidic acid (PA), a second messenger in various types of cell, such as endothelial cells (10,11), fibroblasts (12,13), PC12 cells (14 -17), vascular smooth muscle cells (18), and leukemia L1210 cells (19). As the mechanisms underlying the oxidant-induced PLD activation, various factors including protein-tyrosine kinase (10,11,13,14), protein kinase C (PKC) (13,16,19), and mitogen-activated protein kinase (15,17) have been proposed. Direct or indirect tyrosine phosphorylation has been thought to be involved in PLD activation in response to H 2 O 2 exposure.…”