A Second Leukotriene B₄ Receptor, Blt2: A New Therapeutic Target in Inflammation and Immunological Disorders

Leukotriene B₄ (LTB₄) is a potent chemoattractant and activator of both granulocytes and macrophages. The actions of LTB₄ appear to be mediated by a specific G protein–coupled receptor (GPCR) BLT1, originally termed BLT (Yokomizo, 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. BLT2 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 predominantly in leukocytes. Chinese hamster ovary cells expressing BLT2 exhibit LTB₄-induced chemotaxis, calcium mobilization, and pertussis toxin–insensitive inhibition of adenylyl cyclase. Several BLT1 antagonists, including U 75302, failed to inhibit LTB₄ binding to BLT2. Thus, BLT2 is a pharmacologically distinct receptor for LTB₄, and may mediate cellular functions in tissues other than leukocytes. BLT2 provides a novel target for antiinflammatory therapy and promises to expand our knowledge of LTB₄ function. The location of the gene suggests shared transcriptional regulation of these two receptors.