Cyclooxygenase-2 expression and function in the medullary thick ascending limb.
The medullary thick ascending limb (MTAL) metabolizes arachidonic acid (AA) via cytochrome P-450 (CyP450)- and cyclooxygenase (COX)-dependent pathways. In the present study, we demonstrated that the COX-2-selective inhibitor, NS-398, prevented tumor necrosis factor-alpha (TNF)- and phorbol myristate acetate (PMA)-mediated increases in PGE(2) production by cultured MTAL cells. Accumulation of COX-2, but not COX-1, mRNA increased when cells were challenged with TNF (1 nM) or PMA (1 microM). Pretreatment of cells for 30 min with actinomycin D (AcD, 1 microM) had little effect on COX-2 mRNA accumulation in unstimulated cells or in cells challenged with either TNF or PMA. Moreover, a posttranscriptional mechanism(s) appears to contribute significantly to COX-2 mRNA accumulation as pretreatment for 15 min with cycloheximide (CHX, 1 microM) caused a superinduction of COX-2 mRNA accumulation in unstimulated cells as well as in cells challenged with either TNF or PMA. Expression of COX-2 protein in unstimulated MTAL cells was attenuated by preincubation for 2 h with dexamethasone (Dex, 2 microM); however, Dex had little or no effect on COX-2 expression in cells challenged with either PMA or TNF. The time-dependent inhibition of 86Rb uptake by MTAL cells challenged with TNF was diminished by pretreating cells with NS-398. These data suggest that TNF-mediated induction of COX-2 protein expression accounted for the lag-time required for this cytokine to inhibit 86Rb uptake in MTAL cells.
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Department of Pharmacology, New York Medical College, Valhalla, New York 10595, USA. nick_ferreri@nymc.edu
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D000818:Animals; D002273:Carcinogens / Q000494:pharmacology; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis; D007527:Isoenzymes / Q000502:physiology*; D008138:Loop of Henle / Q000502:physiology*; D008297:Male; D009578:Nitrobenzenes / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D002273:Carcinogens; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D007527:Isoenzymes; D009578:Nitrobenzenes; D012333:RNA, Messenger; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate