title: Lipocortin-1 and the control of arachidonic acid release in cell signalling. Glucocorticoids (changed from glucorticoids) inhibit G protein-dependent activation of cPLA2 activity.
abstract: In pre-labelled A549 cells epidermal growth factor (EGF) (10 nM) stimulates the release of [5,6,8,9,11,12,14,15-3H(N)]-arachidonic acid (3H-AA) by approximately 70%. Increasing Ca2+i with thapsigargin (50 nM) stimulates 3H-AA release by approximately 120%. However, the combined use of these two agents results in a synergistic stimulation of 3H-AA release by over 700%. The EGF stimulated release is sensitive to pertussis toxin (10 ng/mL) and guanosine 5'-O-(2-thiodiphosphate) suggesting a G protein-mediated event. This is supported by the fact that the G protein activators AlF-4 and guanosine 5'-O-(2-thiotriphosphate) both stimulate 3H-AA release. The stimulation of 3H-AA release by both EGF or direct G protein activation is completely blocked following pre-treatment for 3 hr with 1 nM dexamethasone. This effect is reversed with a neutralizing antibody to lipocortin-1 (1 microgram/mL) suggesting that this protein mediates the inhibitory effects of glucocorticoids on agonist activated 3H-AA release. Thapsigargin stimulation of 3H-AA release is insensitive to dexamethasone treatment. A peptide fragment from the N-terminus of lipocortin-1-Lc13-25 (20-200 micrograms/mL) mimics the effect of glucocorticoid in suppressing both EGF and G protein activated 3H-AA release. A peptide with Me-Tyr substituting Tyr21 is much reduced in activity suggesting that the presence of this residue is essential. As peptide Lc13-25 is not derived from the Ca2+/phospholipid binding domain of the native protein then sequestration of phospholipid substrate for PLA2 remains an unlikely mechanism of action for this peptide.
authors.affiliation: Department of Biochemical Pharmacology, Medical College of St. Bartholomews Hospital, London, U.K.
authors.forename: J D
authors.initials: JD
authors.lastname: Croxtall
authors.forename: Q
authors.initials: Q
authors.lastname: Choudhury
authors.forename: H
authors.initials: H
authors.lastname: Tokumoto
authors.forename: R J
authors.initials: RJ
authors.lastname: Flower
mesh_terms: D000595:Amino Acid Sequence; D017305:Annexin A1 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology*; D016718:Arachidonic Acid / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D015398:Signal Transduction / Q000187:drug effects; D013729:Terpenes / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
chemical_list: D017305:Annexin A1; D010446:Peptide Fragments; D013729:Terpenes; D016718:Arachidonic Acid; D004815:Epidermal Growth Factor; D019284:Thapsigargin; D003907:Dexamethasone; D010741:Phospholipases A; D054467:Phospholipases A2; D019204:GTP-Binding Proteins