Cpla(2)Alpha Gene Activation By Il-1 Beta Is Dependent On An Upstream Kinase Pathway, Enzymatic Activation And Downstream 15-Lipoxygenase Activity: A Positive Feedback Loop

Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is the most widely studied member of the Group IV PIA(2) family. The enzyme is Ca2+-dependent with specificity for phospholipid substrates containing arachidonic acid. As the pinnacle of the arachidonic acid pathway, cPLA(2)alpha has a primary role in the biosynthesis of a diverse family of eicosanoid metabolites, with potent physiological, inflammatory and pathological consequences. cPLA(2)alpha 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-1 beta stimulation in human fetal lung fibroblasts. Our results utilizing both inhibitors and kinase-deficient cells demonstrate that cPLA(2)alpha is phosphorylated within 10 min of IL-1 beta 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 cPLA(2)alpha and a downstream lipoxygenase (15-LOX2) are required for IL-1 beta-dependent induction of cPLA(2)alpha mRNA expression. Overall, these data support an MKK3/MKK6 -> p38 MAPK -> MSK-1 -> cPLA(2)alpha -> 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. (C) 2011 Elsevier Inc. All rights reserved.