A novel hepatointestinal leukotriene B-4 receptor - Cloning and functionalcharacterization

Leukotriene B-4 (LTB4) is a product of eicosanoid metabolism and acts as an extremely potent chemotactic mediator for inflammation, LTB4 exerts positi ve effects on the immigration and activation of leukocytes. These effects s uggest an involvement of LTB4 in several diseases: inflammatory bowel disea se, psoriasis, arthritis, and asthma. LTB4 elicits actions through interact ion with one or more cell surface receptors that lead to chemotaxis and inf lammation, One leukotriene B-4 receptor-has been recently identified (LTB4- R1). In this report we describe cloning of a cDNA encoding a novel 358-amin o acid receptor (LTB4-R2) that possesses seven membrane-spanning domains an d is homologous (42%) and genetically linked to LTB4-R1. Expression of LTB4 -R2 is broad but highest in liver, intestine, spleen, and kidney. In radiol igand 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. Radioli gand competition assays revealed high affinities of the receptor for LTB4 a nd 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-am inopropylamide, 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 Cy sLT1-selective antagonists montelukast and zafirlukast. LTB, functionally m obilized intracellular calcium and inhibited forskolin-stimulated cAMP prod uction in 293 cells. The discovery of this new receptor should aid in furth er understanding the roles of LTB, in pathologies in these tissues and may provide a tool in identification of specific antagonists/ agonists for pote ntial therapeutic treatments.