Leukotriene binding, signaling, and analysis of HIV coreceptor function inmouse and human leukotriene B-4 receptor-transfected cells

The mouse leukotriene B-4 receptor (m-BLTR) gene was cloned. Membrane fract ions of human embryonic kidney 293 cells stably expressing m-BLTR demonstra ted a high affinity and specific binding for leukotriene B-4 (LTB4, K-d = 0 .24 +/- 0.03 nM). In competition binding experiments, LTB4 was the most pot ent competitor (K-i = 0.23 +/- 0.05 nM) followed by 20-hydroxy-LTB4 (K-i = 1.1 +/- 0.2 mu M) and by 6-trans-12-epi-LTB4 and LTD4 (K-i > 1 mu M). In st ably transfected Chinese hamster ovary cells, LTB4 inhibited forskolin-acti vated cAMP production and induced an increase of intracellular calcium, sug gesting that this receptor is coupled to G(i)- and G(o)-like proteins. In X enopus laevis melanophores transiently expressing m-BLTR, LTB4 induced the aggregation of pigment granules, confirming the inhibition of cAMP producti on induced by LTB4. BLT receptors share significant sequence homology with chemokine receptors (CCR5 and CXCR4) that act as human immunodeficiency vir us (HIV) coreceptors. However, among the 16 HIV/SIV strains tested, the hum an BLT receptor did not act as a coreceptor for virus entry into CD4-expres sing cells based on infection and cell-cell fusion assays. In 5-lipoxygenas e-deficient mice, the absence of leukotriene B-4 biosynthesis did not detec tably alter m-BLT receptor binding in membranes obtained from glycogen-elic ited neutrophils. Isolation of the m-BLTR gene will form the basis of futur e experiments to elucidate the selective role of LTB4, as opposed to cystei nyl-leukotrienes, in murine models of inflammation.