scholarly journals Multiple C-terminal serine phosphorylation accompanies both protein kinase C-dependent and -independent activation of cytosolic 85 kDa phospholipase A2 in macrophages

1997 ◽  
Vol 325 (2) ◽  
pp. 405-410 ◽  
Author(s):  
Jonny WIJKANDER ◽  
Karin GEWERT ◽  
Ulf SVENSSON ◽  
Elisabeth HOLST ◽  
Roger SUNDLER
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Phospholipase A2 ◽  
Phorbol Ester ◽  
Serine Phosphorylation ◽  
Mitogen Activated Protein Kinase ◽  
Phosphorylation Sites ◽  
Kinase C ◽  
Extracellular Signal ◽  
Mitogen Activated Protein

Exposure of mouse macrophages to either phorbol ester or certain bacteria was previously shown to cause increased phosphorylation of the cytosolic 85 kDa phospholipase A2 as well as a stable increase in its catalytic activity. We have now attempted to map the major phosphorylation sites on the enzyme in such cells. Phosphorylation occurred on serine residues without a detectable increase in either phosphothreonine or phosphotyrosine. After CNBr cleavage five fragments showed increased 32P labelling. Among those the most heavily labelled fragment was identified as the most C-terminal (residues 698–749), containing six serine residues. This was true whether phorbol ester or bacteria, causing protein kinase C-independent phospholipase A2 activation, was used as stimulus. The heavy phosphorylation of the most C-terminal fragment and an analysis of tryptic peptides derived from it suggested that more than one of the six serine residues became phosphorylated. Smaller increases also occurred in other CNBr-cleaved fragments from the C-terminal part of the protein, including that carrying Ser-505, a known target of the mitogen-activated protein kinase ERK-2 (extracellular-signal regulated kinase). Dexamethasone treatment (1–100 nM for 20 h), which was earlier shown to dose-dependently down-regulate the 85 kDa phospholipase A2 and its activation by phorbol ester and zymosan, was here shown also to counteract the protein kinase C-independent activation and arachidonate release elicited by bacteria. It remains to be determined whether all phosphorylation sites are equally affected under those conditions.

scholarly journals Inhibition of mitogen-activated protein kinase kinase does not impair primary activation of human platelets

1996 ◽  
Vol 318 (1) ◽  
pp. 207-212 ◽  
Author(s):  
Angelika G. BÖRSCH-HAUBOLD ◽  
Ruth M. KRAMER ◽  
Steve P WATSON
Keyword(s):  
Arachidonic Acid ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Phorbol Ester ◽  
Substrate Inhibition ◽  
Human Platelets ◽  
Mitogen Activated Protein Kinase ◽  
Ionophore A23187 ◽  
Kinase C ◽  
Mitogen Activated Protein

Mitogen-activated protein kinases (MAPKs), a family of protein serine/threonine kinases regulating cell growth and differentiation, are activated by a dual-specificity kinase through phosphorylation at threonine and tyrosine. We used a recently described selective inhibitor of the p42/p44mapk-activating enzyme, PD 98059 [2-(2´-amino-3´-methoxyphenyl)-oxanaphthalen-4-one], to investigate the role of the p42/p44mapk pathway in human platelets. PD 98059 inhibited p42/p44mapk activation in thrombin-, collagen- and phorbol ester-stimulated platelets, as determined from in-gel renaturation kinase assays, with an IC50 of approx. 5 µM (thrombin stimulation). It also prevented activation of MAPK kinase, which was measured in whole-cell lysates with glutathione S-transferase/p42mapk fusion protein (GST–MAPK) as substrate. Inhibition of p42/p44mapk did not affect platelet responses to thrombin or collagen such as aggregation, 5-hydroxytryptamine release and protein kinase C activation. In addition, PD 98059 did not interfere with release of arachidonic acid, a response mediated by cytosolic phospholipase A2 (cPLA2), or with cPLA2 phosphorylation. This suggests that platelet cPLA2 is not regulated by p42/p44mapk after stimulation with physiological agonists. In contrast, phorbol ester-induced phosphorylation of cPLA2 and potentiation of arachidonic acid release stimulated by Ca2+ ionophore A23187 were inhibited by PD 98059, indicating that p42/p44mapk phosphorylates cPLA2 after activation of protein kinase C by the non-physiological tumour promoter.

scholarly journals Diacylglycerol generated by exogenous phospholipase C activates the mitogen-activated protein kinase pathway independent of Ras- and phorbol ester-sensitive protein kinase C: dependence on protein kinase C-ζ

1997 ◽  
Vol 323 (3) ◽  
pp. 693-699 ◽  
Author(s):  
Marc C. M. van DIJK ◽  
Francisco J. G. MURIANA ◽  
Paul C. J. van der HOEVEN ◽  
John de WIDT ◽  
Dick SCHAAP ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Growth Factor ◽  
Protein Kinase ◽  
Phospholipase C ◽  
Phorbol Ester ◽  
Mitogen Activated Protein Kinase ◽  
Mapk Activation ◽  
Kinase C ◽  
Mitogen Activated Protein ◽  
Pkc Ζ

The role of diacylglycerol (DG) formation from phosphatidylcholine in mitogenic signal transduction is poorly understood. We have generated this lipid at the plasma membrane by treating Rat-1 fibroblasts with bacterial phosphatidylcholine-specific phospholipase C (PC-PLC). This treatment leads to activation of mitogen-activated protein kinase (MAPK). However, unlike platelet-derived growth factor (PDGF) or epidermal growth factor (EGF), PC-PLC fails to activate Ras and to induce DNA synthesis, and activates MAPK only transiently (< 45 min). Down-regulation of protein kinase C (PKC) -α, -Δ and -ε isotypes has little or no effect on MAPK activation by either PC-PLC or growth factors. However, Ro 31-8220, a highly selective inhibitor of all PKC isotypes, including atypical PKC-ζ but not Raf-1, blocks MAPK activation by PDGF and PC-PLC, but not that by EGF, suggesting that atypical PKC mediates the PDGF and PC-PLC signal. In line with this, PKC-ζ is activated by PC-PLC and PDGF, but not by EGF, as shown by a kinase assay in vitro, using biotinylated ε-peptide as a substrate. Furthermore, dominant-negative PKC-ζ inhibits, while (wild-type) PKC-ζ overexpression enhances MAPK activation by PDGF and PC-PLC. The results suggest that DG generated by PC-PLC can activate the MAPK pathway independent of Ras and phorbol-ester-sensitive PKC but, instead, via PKC-ζ.

scholarly journals Activation of the Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Pathway by Conventional, Novel, and Atypical Protein Kinase C Isotypes

1998 ◽  
Vol 18 (2) ◽  
pp. 790-798 ◽  
Author(s):  
Dorothee C. Schönwasser ◽  
Richard M. Marais ◽  
Christopher J. Marshall ◽  
Peter J. Parker
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Mapk Cascade ◽  
Mitogen Activated Protein Kinase ◽  
Extracellular Signal Regulated Kinase ◽  
Erk Mapk ◽  
Kinase C ◽  
Extracellular Signal ◽  
Mitogen Activated Protein ◽  
Stimulation Of

ABSTRACT Phorbol ester treatment of quiescent Swiss 3T3 cells leads to cell proliferation, a response thought to be mediated by protein kinase C (PKC), the major cellular receptor for this class of agents. We demonstrate here that this proliferation is dependent on the activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) cascade. It is shown that dominant-negative PKC-α inhibits stimulation of the ERK/MAPK pathway by phorbol esters in Cos-7 cells, demonstrating a role for PKC in this activation. To assess the potential specificity of PKC isotypes mediating this process, constitutively active mutants of six PKC isotypes (α, β1, δ, ɛ, η, and ζ) were employed. Transient transfection of these PKC mutants into Cos-7 cells showed that members of all three groups of PKC (conventional, novel, and atypical) are able to activate p42 MAPK as well as its immediate upstream activator, the MAPK/ERK kinase MEK-1. At the level of Raf, the kinase that phosphorylates MEK-1, the activation cascade diverges; while conventional and novel PKCs (isotypes α and η) are potent activators of c-Raf1, atypical PKC-ζ cannot increase c-Raf1 activity, stimulating MEK by an independent mechanism. Stimulation of c-Raf1 by PKC-α and PKC-η was abrogated for RafCAAX, which is a membrane-localized, partially active form of c-Raf1. We further established that activation of Raf is independent of phosphorylation at serine residues 259 and 499. In addition to activation, we describe a novel Raf desensitization induced by PKC-α, which acts to prevent further Raf stimulation by growth factors. The results thus demonstrate a necessary role for PKC and p42 MAPK activation in 12-O-tetradecanoylphorbol-13-acetate induced mitogenesis and provide evidence for multiple PKC controls acting on this MAPK cascade.

Sign in / Sign up

Export Citation Format

Share Document