A novel hepatointestinal leukotriene B4 receptor -: Cloning and functional characterization

Leukotriene B-4 (LTB4) is a product of eicosanoid metabolism and acts as an extremely potent chemotactic mediator for inflammation, LTB4 exerts positive effects on the immigration and activation of leukocytes. These effects suggest an involvement of LTB4 in several diseases: inflammatory bowel disease, psoriasis, arthritis, and asthma. LTB4 elicits actions through interaction with one or more cell surface receptors that lead to chemotaxis and inflammation, One leukotriene B-4 receptor-has been recently identified (LTB4-R1). In this report we describe cloning of a cDNA encoding a novel 358-amino acid receptor (LTB4-R2) that possesses seven membrane-spanning domains and is homologous (42%) and genetically linked to LTB4-R1. Expression of LTB4-R2 is broad but highest in liver, intestine, spleen, and kidney. In radioligand binding assays, membranes prepared from COS-7 cells transfected with LTB4-R2 cDNA displayed high affinity (K-d = 0.17 nM) for [H-3]LTB4. Radioligand competition assays revealed high affinities of the receptor for LTB4 and LTB5, and 20-hydroxy-LTB4, and intermediate affinities for 15(5)HETE and 12-oxo-ETE. Three LTB, receptor antagonistst 14,15-dehydro-LTB4, LTB4-3-aminopropylamide, and U-75302, had high affinity for LTB4-R1 but not for LTB4-R2. No apparent affinity binding for the receptors was detected for the CysLT1-selective antagonists montelukast and zafirlukast. LTB, functionally mobilized intracellular calcium and inhibited forskolin-stimulated cAMP production in 293 cells. The discovery of this new receptor should aid in further understanding the roles of LTB, in pathologies in these tissues and may provide a tool in identification of specific antagonists/ agonists for potential therapeutic treatments.