Induction of interleukin-6 release by interleukin-1 in rat anterior pituitary cells in vitro: evidence for an eicosanoid-dependent mechanism.
We have reported previously that a subpopulation(s) of anterior pituitary cells released IL-6 and that this release was stimulated by interleukin-1 (IL-1) through a non-cAMP-dependent mechanism. We now report that IL-1 induces IL-6 release from anterior pituitary cells in an eicosanoid-dependent manner. Dispersed rat anterior pituitary cells were briefly prelabeled (2-3 h) with [3H]arachidonic acid (AA) to esterify the fatty acid within the lipid pool. Incubation of these prelabeled cells with 25 ng/ml IL-1 beta caused an increase only within 1-2 min in the amount of free [3H]AA detected in the extracts of the cells. During 15- to 30-min incubations, IL-1 beta (25 ng/ml) caused an increased accumulation of [3H]AA in the incubation medium which reached levels similar to those induced by 100 nM TRH. Perifused anterior pituitary cells responded to IL-1 beta (25 ng/ml) with a rapid (less than 2 min), biphasic, and reversible efflux of [3H]AA. The [3H]AA appears to have been derived from choline phospholipids, as formation of [3H]glycerophosphorylcholine was substantially increased by exposure of [3H]choline-prelabeled cells to either IL-1 alpha (171%) or IL-1 beta (236%); in addition, the complete deacylation of phosphatidylcholine suggests that other fatty acid species are liberated as a consequence of IL-1 receptor activation and, thus, may also contribute to the actions of IL-1 alpha and IL-1 beta. However, the levels of [3H]phosphorylcholine and [3H]choline were unchanged as well as those of catabolites of other lipid species. These data suggested an involvement of phospholipase-A2 (PLA2) in mediating the IL-1 induction of IL-6 release. Subsequently, we used inhibitors of the PLA2, cyclooxygenase, and lipoxygenase enzymes to investigate a possible role for the generation of AA and its subsequent enzymatic conversion in the signal transduction pathway activated by IL-1. The PLA2 inhibitor aristolochic acid (10 microM) blocked IL-1 beta-induced IL-6 release and the release of IL-6 caused by Pyrularia pubera thionin (5 micrograms/ml), a stimulator of PLA2 activity. The cyclooxygenase inhibitor indomethacin (10 microM) did not inhibit IL-1 beta-induced IL-6 release. In contrast, the general lipoxygenase inhibitor nordihydroguaiaretic acid (10 microM) and the more specific 5-lipoxygenase inhibitors AA861 and RHC5901 (both 10 microM) reduced basal and blocked IL-1 beta-induced IL-6-release.(ABSTRACT TRUNCATED AT 400 WORDS)
Spangelo
B L
BL
Department of Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
Jarvis
W D
WD
Judd
A M
AM
MacLeod
R M
RM
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D034341:Aristolochic Acids; D016227:Benzoquinones / Q000494:pharmacology; D002478:Cells, Cultured; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015777:Eicosanoids / Q000502:physiology*; D004976:Ethacrynic Acid / Q000494:pharmacology; D005260:Female; D005997:Glycerylphosphorylcholine / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000378:metabolism*; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D009637:Masoprocol / Q000494:pharmacology; D009930:Organic Chemicals; D010616:Phenanthrenes / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction
D034341:Aristolochic Acids; D016227:Benzoquinones; D016861:Cyclooxygenase Inhibitors; D015777:Eicosanoids; D007375:Interleukin-1; D015850:Interleukin-6; D016859:Lipoxygenase Inhibitors; D009930:Organic Chemicals; D010616:Phenanthrenes; C071780:RHC 5901; D016718:Arachidonic Acid; D005997:Glycerylphosphorylcholine; D009637:Masoprocol; C036837:2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone; C000228:aristolochic acid I; D010741:Phospholipases A; D054467:Phospholipases A2; D004976:Ethacrynic Acid