IDENTIFICATION OF A HUMAN ENTEROCYTE LIPOXIN A(4) RECEPTOR THAT IS REGULATED BY INTERLEUKIN (IL)-13 AND INTERFERON-GAMMA AND INHIBITS TUMOR-NECROSIS-FACTOR ALPHA-INDUCED IL-8 RELEASE

Epithelial cells of the alimentary tract play a central role in mucosa l immunophysiology. Pathogens and/or agonists that interact with mucos al surfaces often elicit epithelial responses that upregulate inflamma tion. Therefore, it was of interest to explore potential epithelial ta rgeted antiinflammatory signals. Here we identified and sequenced a hu man enterocyte lipoxin (LX) A(4) [5(S),6(R),15(S)-trihydroxy-7,9,13-tr ans-11-cis eicosatetraenoic acid] receptor, and demonstrate that trans cription of this receptor was controlled by cytokines, of which lympho cyte-derived interleukin (IL)-13 aid interferon gamma were the most po tent. When lipoxins and LXA(4) stable analogs were evaluated for enter ocyte functional as well as immune responses, lipoxins sharply inhibit ed TNF-alpha-induced IL-8 release but did lot alter either barrier fun ction or agonist-stimulated chloride secretion. 15R/S-methyl-LXA(4) an d 16-phenoxy-LXA(4) each attenuated (IC50 similar to 10 nM) IL-8 relea se. Cyclooxygenase (COX) II is emerging as an important component in w ound healing and proliferation in intestinal epithelia and when acetyl ated by acetylsalicylic acid (aspirin) initiates the biosynthesis of a LXA(4) receptor ligand. We therefore determined whether colonic cell Lines (HT-29 C1.19A, Caco-2, or T84) express the COX II isozyme. Resul ts for RT-PCR and Western blot analysis showed that COX I as well as a n IL-1 beta- and TNF-alpha-inducible COX II are expressed in HT-29 C1. 19A. In addition, aspirin-treated enterocytes generated 15R-HETE, a pr ecursor of 15-epi-LXA(4) biosynthesis, whose potent bioactions were mi micked by the stable analog 15R/S-methyl-LXA(4). Taken together, these results identify an endogenous pathway for downregulating mucosal inf lammatory events and suggest a potential therapeutic benefit for LXA(4 ) stable analogs.