Signaling mechanisms involved in the activation of arachidonic acid metabolism in human astrocytoma cells by Tumor necrosis factor-α : Phosphorylation of cytosolic phospholipase A2 and transactivation of cyclooxygenase-2

• Published in: Journal of neurochemistry 1999-10, Vol.73 (4), p.1641-1649
• Main Authors: HERNANDEZ, M, BAYON, Y, SANCHEZ CRESPO, M, LUISA NIETO, M
• Format: Article
• Language: English
• Subjects: Arachidonic Acid - metabolism; Astrocytoma; Biological and medical sciences; Brain Neoplasms; Cyclooxygenase 2; Cytosol - enzymology; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Neoplastic - drug effects; Humans; Isoenzymes - genetics; Isolated neuron and nerve. Neuroglia; Kinetics; Membrane Proteins; NF-kappa B - metabolism; Phospholipases A - metabolism; Phospholipases A2; Phosphorylation; Prostaglandin-Endoperoxide Synthases - genetics; Recombinant Proteins - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction - physiology; Transcriptional Activation; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha - pharmacology; Vertebrates: nervous system and sense organs
• ISSN: 0022-3042
• DOI: 10.1046/j.1471-4159.1999.0731641.x

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine that elicits cell responses by activating the mitogen-activated protein kinase (MAP kinase) cascade and transcription factors such as nuclear factor-kappaB (NF-kappaB). As these elements play a central role in the mechanisms of signaling involved in the activation of cytosolic phospholipase A2 (cPLA2) and cyclooxygenase-2 (COX-2), the effect of TNF-alpha on arachidonate (AA) metabolism in 1321N1 astrocytoma cells was assayed. TNF-alpha produced a phosphorylation of cPLA2, which was preceded by an activation of both c-Jun N-terminal kinase (JNK) and p38-MAP kinase, and this was associated with the release of [3H]AA. In contrast, TNF-alpha did not activate the extracellular signal-regulated kinase (MAP kinase) p42, nor did it elicit a mitogenic response. Analysis of [3H]AA metabolites by reverse-phase HPLC showed that all of the [3H]AA released during the first hour after TNF-alpha addition eluted as authentic AA, whereas in samples obtained at 24 h after addition of TNF-alpha, 25% of the [3H]AA had been converted into COX products as compared with only 9% in control cells. In keeping with these findings, TNF-alpha produced an increase of COX-2 expression, as judged from both RT-PCR studies and immunoblot of COX-2 protein, and a long-lasting activation of NF-kappaB. These data show that TNF-alpha produces in astrocytoma cells an early activation of both p38-MAP kinase and JNK, which is followed by the phosphorylation of cPLA2 and the release of AA. On the other hand, the activation of NF-kappaB may explain the induction of the expression of COX-2 and the delayed generation of prostanoids.