cPLA2α gene activation by IL-1β is dependent on an upstream kinase pathway, enzymatic activation and downstream 15-lipoxygenase activity: A positive feedback loop

Abstract

Cytosolic phospholipase A2α (cPLA2α) is the most widely studied member of the Group IV PLA2 family. The enzyme is Ca2+-dependent with specificity for phospholipid substrates containing arachidonic acid. As the pinnacle of the arachidonic acid pathway, cPLA2α has a primary role in the biosynthesis of a diverse family of eicosanoid metabolites, with potent physiological, inflammatory and pathological consequences. cPLA2α activity is regulated by pro-inflammatory stimuli through pathways involving increased intracellular Ca2+ levels, phosphorylation coupled to increased enzymatic activity and de novo gene transcription. This study addresses the signal transduction pathways for protein phosphorylation and gene induction following IL-1β stimulation in human fetal lung fibroblasts. Our results utilizing both inhibitors and kinase-deficient cells demonstrate that cPLA2α is phosphorylated within 10 min of IL-1β treatment, an event requiring p38 MAPK as well as the upstream kinase, MKK3/MKK6. Inhibition of p38 MAPK also blocks the phosphorylation of a downstream, nuclear kinase, MSK-1. Our results further demonstrate that the activities of both cPLA2α and a downstream lipoxygenase (15-LOX2) are required for IL-1β-dependent induction of cPLA2α mRNA expression. Overall, these data support an MKK3/MKK6→p38 MAPK→MSK-1→cPLA2α→15-LOX2-dependent, positive feedback loop where a protein’s enzymatic activity is required to regulate its own gene induction by a pro-inflammatory stimulus.

TLR Signalling Pathways Diverge in Their Ability to Induce PGE2

“…We found that only LPS and R848 induced significant cPLA 2 phosphorylation at 30 minutes after stimulation ( Figure 4(b) ). Based on the observations in Figure 3 , it is tempting to speculate that, in our system, cPLA 2 phosphorylation may depend on MSK1 activation, as previously demonstrated in human fibroblasts stimulated with IL-1 β [ 25 , 26 ].…”

“…However only LPS, R848, PAM 3 CSK 4 , and FSL-1 also induced p38 phosphorylation and NF- κ B p65 nuclear translocation, while Poly I:C, Flagellin, and Imiquimod did not. Finally, TLR2 ligands failed to phosphorylate MSK1, a kinase downstream ERK and p38 MAPK that was described to play a role in PGE 2 production [ 25 , 26 ]. Similar activation patterns were also detected at 15 and 60 minutes after stimulation (not shown).…”

Cytosolic Phospholipase A2 Regulates TNF-Induced Production of Joint Destructive Effectors in Synoviocytes

“…It may suggest a feed-back loop from cPLA2α enzymatic activity through transcriptional regulation of the PLA2G4A gene in response to TNF in synoviocytes. Feed-back signaling where enzymatic activity of cPLA2α is required to regulate its own gene induction is previously reported in lung fibroblasts in response to IL-1β stimulation [ 9 ]. This possible auto-regulation in response to pro-inflammatory stimuli presents a potential self-reinforcing impact of inhibiting cPLA2α enzyme activity.…”

Low Molecular Weight Hyaluronan Activates Cytosolic Phospholipase A2α and Eicosanoid Production in Monocytes and Macrophages

“…3C). Various MAPKs were previously reported to take part in cPLA 2 ␣ phosphorylation (57)(58)(59). Therefore, we analyzed the phosphorylation patterns of ERK1/2, p38, JNK, and PI3K-Akt kinases after HA (100 g/ml) treatment over time.…”