A second leukotriene B-4 receptor, BLT2: A new therapeutic target in inflammation and immunological disorders

Leukotriene B-4 (LTB4) is a potent chemoattractant and activator of both gr anulocytes and macrophages. The actions of LTB4 appear to be mediated by a specific G protein-coupled receptor (GPCR) BLT1, originally termed BLT (Yok omizo, T., T. Izumi, K. Chang, Y, Takuwa, and T. Shimizu. 1997. Nature. 387 :620-624). Here, we report the molecular cloning of a novel GPCR for LTB4, designated BLT2, which binds LTB4 with a Kd value of 23 nM compared with 1. 1 nM for BLT1, but still efficiently transduces intracellular signaling. BL T2 is highly homologous to BLT1, with an amino acid identity of 45.2%, and Its open reading frame is located in the promoter region of the BLT1 gene. BLT2 is expressed ubiquitously, in contrast to BLT1, which is expressed pre dominantly in leukocytes. Chinese hamster ovary cells expressing BLT2 exhib it LTB4-induced chemotaxis, calcium mobilization, and pertussis toxin-insen sitive inhibition of adenylyl cyclase. Several BLT1 antagonists, including U 75302, failed to inhibit LTB4 binding to BLT2. Thus, BLT2 is a pharmacolo gically distinct receptor for LTB4, and may mediate cellular functions in t issues other than leukocytes. BLT2 provides a novel target for antiinflamma tory therapy and promises to expand our knowledge of LTB4 function. The loc ation of the gene suggests shared transcriptional regulation of these two r eceptors.