scholarly journals Thrombin produces phosphorylation of cytosolic phospholipase A2 by a mitogen-activated protein kinase kinase-independent mechanism in the human astrocytoma cell line 1321N1

1997 ◽  
Vol 328 (1) ◽  
pp. 263-269 ◽  
Author(s):  
Marita HERNÁNDEZ ◽  
Yolanda BAYÓN ◽  
Mariano SÁNCHEZ CRESPO ◽  
María Luisa NIETO
Keyword(s):  
Phospholipase A2 ◽  
Map Kinase ◽  
Cell Line ◽  
Cytosolic Phospholipase A2 ◽  
Thrombin Receptor ◽  
Primary Sequence ◽  
Jun Kinase ◽  
Cytosolic Phospholipase ◽  
Astrocytoma Cell ◽  
Mitogen Activated Protein

The release of [3H]arachidonic acid was studied in the 1321N1 astrocytoma cell line upon stimulation with thrombin. The effect of thrombin was antagonized by hirudin only when both compounds were added simultaneously, which suggests activation of thrombin receptor. Evidence that the cytosolic phospholipase A2 (cPLA2) takes part in thrombin-induced arachidonate release was provided by the finding that thrombin induced retardation of the mobility of cPLA2 in SDS/polyacrylamide gels, which is a feature of the activation of cPLA2 by mitogen-activated protein (MAP) kinases. Thrombin induced activation of two members of the MAP kinase family whose consensus primary sequence appears in cPLA2, namely p42-MAP kinase and c-Jun kinase. However, the activation of c-Jun kinase preceded the phosphorylation of cPLA2 more clearly than the activation of p42-MAK kinase did. Both cPLA2 and c-Jun kinase activation were not affected by PD-98059, a specific inhibitor of MAP kinase kinases, which indeed completely blocked p42-MAP kinase shift. Heat shock, a well-known activator of c-Jun kinase, also phosphorylated cPLA2 but not p42-MAP kinase. These data indicate the existence in astrocytoma cells of a signalling pathway triggered by thrombin receptor stimulation that activates a kinase cascade acting on the Pro-Leu-Ser-Pro consensus primary sequence, activates cPLA2, and associates the release of arachidonate with nuclear signalling pathways.

scholarly journals Cytosolic phospholipase A2 is coupled to muscarinic receptors in the human astrocytoma cell line 1321N1: characterization of the transducing mechanism

1997 ◽  
Vol 323 (1) ◽  
pp. 281-287 ◽  
Author(s):  
Yolanda BAYON ◽  
Marita HERNANDEZ ◽  
Andrés ALONSO ◽  
Lucía NUÑEZ ◽  
Javier GARCIA-SANCHO ◽  
...  
Keyword(s):  
Phospholipase A2 ◽  
Cell Line ◽  
G Proteins ◽  
Muscarinic Receptors ◽  
Cytosolic Phospholipase A2 ◽  
Alternative Mechanism ◽  
Cytosolic Phospholipase ◽  
Astrocytoma Cell Line ◽  
Astrocytoma Cell ◽  
Arachidonate Release

The cholinergic agonist carbachol induced the release of arachidonic acid in the 1321N1 astrocytoma cell line, and this was blocked by atropine, suggesting the involvement of muscarinic receptors. To assess the mechanisms of signalling involved in the response to carbachol, a set of compounds characterized by eliciting responses through different mechanisms was tested. A combination of 4β-phorbol 12β-myristate 13α-acetate and thapsigargin, an inhibitor of endomembrane Ca2+-ATPase that induces a prolonged elevation of cytosolic Ca2+ concentration, induced an optimal response, suggesting at first glance that both protein kinase C (PKC) and Ca2+ mobilization were involved in the response. This was consistent with the observation that carbachol elicited Ca2+ mobilization and PKC-dependent phosphorylation of cytosolic phospholipase A2 (cPLA2; phosphatide sn-2-acylhydrolase, EC 3.1.1.4) as measured by a decrease in electrophoretic mobility. Nevertheless, the release of arachidonate induced by carbachol was unaltered in media containing decreased concentrations of Ca2+ or in the presence of neomycin, a potent inhibitor of phospholipase C which blocks phosphoinositide turnover and Ca2+ mobilization. Guanosine 5´-[γ-thio]triphosphate added to the cell-free homogenate induced both [3H]arachidonate release and cPLA2 translocation to the cell membrane fraction in the absence of Ca2+, thus suggesting the existence of an alternative mechanism of cPLA2 translocation dependent on G-proteins and independent of Ca2+ mobilization. From the combination of experiments utilizing biochemical and immunological tools the involvement of cPLA2 was ascertained. In summary, these data indicate the existence in the astrocytoma cell line 1321N1 of a pathway involving the cPLA2 which couples the release of arachidonate to the occupancy of receptors for a neurotransmitter, requires PKC activity and G-proteins and might operate in the absence of Ca2+ mobilization.

scholarly journals Effect of lipopolysaccharide on mitogen-activated protein kinases and cytosolic phospholipase A2

1995 ◽  
Vol 308 (3) ◽  
pp. 815-822 ◽  
Author(s):  
S I Fouda ◽  
T F P Molski ◽  
M S E Ashour ◽  
R I Sha′afi
Keyword(s):  
Phospholipase A2 ◽  
Map Kinase ◽  
Map Kinases ◽  
Kinase Inhibitor ◽  
Cytosolic Phospholipase A2 ◽  
Mitogen Activated Protein Kinase ◽  
Human Neutrophils ◽  
Cytosolic Phospholipase ◽  
Low Concentrations ◽  
Mitogen Activated Protein

The addition of platelet-activating factor (PAF) to human neutrophils increases phosphorylation on tyrosine residues and stimulates the activity of p42erk2 mitogen-activated protein kinase (MAP kinase). This action is rapid and transient. In contrast, p42erk2, p44erk1 and the p40hera MAP kinase isoforms are all not tyrosine phosphorylated or activated in human neutrophils stimulated with low concentrations of lipopolysaccharide (LPS) in combination with serum. In spite of this, the PAF-induced tyrosine phosphorylation and activation of the p42erk2 MAP kinase are greatly potentiated in cells pretreated with LPS. More interestingly, although low concentrations of LPS do not affect MAP kinase isoforms in these cells, they cause the phosphorylation of cytosolic phospholipase A2 (cPLA2), as evidenced by a decrease in the electrophoretic mobility of the enzyme. In addition, this stimulus-induced upward shift in the mobility of the enzyme is not inhibited by the tyrosine kinase inhibitor, genistein. Furthermore, LPS increases the release of arachidonic acid in control and PAF-stimulated human neutrophils. These observations clearly show that cPLA2 can be phosphorylated and activated by kinases other than the currently known MAP kinases. It is proposed that there are MAP kinase-dependent and -independent mechanisms for the phosphorylation of cPLA2.

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