DDM-PGE₂-mediated cytoprotection in renal epithelial cells by a thromboxane A₂ receptor coupled to NF-κB

The present studies were conducted to determine the pharmacological nature of a cytoprotective 11-deoxy-16,16-dimethyl-PGE₂ (DDM-PGE₂) receptor in LLC-PK₁ cells. DDM-PGE₂-mediated cytoprotection against 2,3,5- (trisglutathion-S-yl)hydroquinone (TGHQ)-mediated cytotoxicity can be reproduced using thromboxane A₂ (TXA₂) receptor (TP) agonists (U46619 and IBOP), and the cytoprotective response to DDM-PGE₂ and TP agonists is inhibited by TP antagonists (SQ-29,548 and ISAP). Western blot analysis using an antipeptide antibody against the human platelet TP receptor (55 kDa) identified a particulate associated 54-kDa protein. DDMPGE₂-mediated 12-O-tetradecanoyl phorbol-13-acetate (TPA) responsive element (TRE) binding activity is not inhibited by cyclooxygenase inhibitors (aspirin and indomethacin) or a TXA₂ synthase inhibitor (sulfasalazine), suggesting that the biological response to DDM-PGE₂ is not dependent on de novo TXA₂ biosynthesis. Peak DDM-PGE₂- and U46619-mediated TRE binding activity and nuclear factor-κB (NF-κB) binding activity are inhibited by SQ-29,548. The full cytoprotective response to DDM-PGE₂ requires an 8-h pulse with agonist. DDM-PGE₂-mediated TRE and NF-κB binding activity remain elevated in the presence of agonist and rapidly decay following agonist washout, suggesting a direct correlation between DDM-PGE₂-mediated cytoprotection and persistent DNA binding activities. TPA, a protein kinase C activator, induces cytoprotection and a persistent increase of NF-κB binding activity. DDM-PGE₂-mediated cytoprotection and NF-κB binding activity but not TRE binding activity are inhibited by sulfasalazine. We conclude that the DDM- PGE₂ receptor is a TP receptor and that the cytoprotective response may be mediated in part by NF-κB.