Characterization of a Mouse Second Leukotriene B4 Receptor, mBLT2

Abstract

Leukotriene B4 (LTB4) is a potent chemoattractant and activator for granulocytes and macrophages and is considered to be an inflammatory mediator. Two G-protein-coupled receptors for LTB4, BLT1 and BLT2, have been cloned from human and shown to be high and low affinity LTB4 receptors, respectively. To reveal the biological roles of BLT2 using mouse disease models, we cloned and characterized mouse BLT2. Chinese hamster ovary cells stably expressing mouse BLT2 exhibited specific binding to LTB4, LTB4-induced calcium mobilization, inhibition of adenylyl cyclase, and phosphorylation of extracellular signal-regulated kinase. We found that Compound A (4 -{[pentanoyl (phenyl) amino] methyl}-1, 1 -biphenyl-2-carboxylic acid) was a BLT2-selective agonist and induced Ca 2؉ mobilization and phosphorylation of extracellular signal-regulated kinase through BLT2, whereas it had no effect on BLT1. 12-epi LTB4 exhibited a partial agonistic activity against mBLT1 and mBLT2, whereas 6-trans-12-epi LTB4 did not. Northern blot analysis showed that mouse BLT2 is expressed highly in small intestine and skin in contrast to the ubiquitous expression of human BLT2. By in situ hybridization and the reverse transcriptase polymerase chain reaction, we demonstrated that mouse BLT2 is expressed in follicular and interfollicular keratinocytes. Compound A, LTB4, and 12-epi LTB4 all induced phosphorylation of extracellular signal-regulated kinase in primary mouse keratinocytes. Furthermore, Compound A and LTB4 induced chemotaxis in primary mouse keratinocytes. These data suggest the presence of functional BLT2 in primary keratinocytes.Leukotriene B4 (LTB4 1 ; 5[S], 12[R]-dihydroxy-6, 14-cis-8, 10-trans-eicosatetraenoic acid) (1) is biosynthesized from arachidonic acid released from membrane phospholipids by the action of cytosolic and various types of phospholipase A2s (2). Two enzymes, 5-lipoxygenase (3, 4) and LTA4 hydrolase (5, 6), are required for LTB4 biosynthesis from arachidonic acid (7,8). LTB4 is a potent proinflammatory mediator mainly synthesized by phagocytic cells, principally polymorphonuclear leukocyte and macrophage, which responds to infectious and inflammatory stimuli. LTB4 induces granulocyte migration, degranulation, superoxide generation, and adhesion to vascular endothelial cells. It plays an important role in the initial phase of the inflammatory response and is thought to be involved in a number of inflammatory diseases including psoriasis (9), bronchial asthma (10), rheumatoid arthritis (11) inflammatory bowel diseases (12), and ischemic tissue damage (13). Recently, LTB4 was shown to act as an immunomodulator by recruiting CD4ϩ early effector and CD8ϩ cytotoxic effector T-cells to inflamed tissues (14 -16), suggesting novel roles of LTB4 in immunological disorders. Thus, many BLT antagonists have been currently under development as novel antiinflammatory and anti-allergic drugs.Two types of LTB4 receptors (BLT1 and BLT2) have been isolated. BLT1 (17) and BLT2 (18 -20) are high and low affinity LTB4 receptors, respecti...

BLT2 expression improves skin integrity and protects from alterations caused by hyperglycemia in type 2 diabetes

“…Leukotriene B 4 (LTB 4 ) receptor type 2 (BLT2) is a G-protein-coupled receptor (GPCR), which binds to LTB 4 and 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT)., 5,6 It is mainly expressed in epithelial cells, such as epidermal keratinocytes 7 and intestinal epithelial cells 8 . Research on BLT2-deficient mice and studies of BLT2 antagonists have implicated the receptor in skin wound healing 7 and carcinogenesis, 9,10 as well as in the pathogenesis of arthritis 11 and bronchial asthma 12–14 .…”

12-hydroxyheptadecatrienoic acid promotes epidermal wound healing by accelerating keratinocyte migration via the BLT2 receptor

“…More recently, we identified 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT), a downstream metabolite of COX (cyclooxygenase) enzymes, as the endogenous ligand for BLT2 (Okuno et al, 2008). Mouse BLT2 is primarily expressed in epidermal keratinocytes and intestinal tissues (Iizuka et al, 2005), whereas human BLT2 is ubiquitously expressed throughout the body (Kamohara et al, 2000;Yokomizo et al, 2000b). Several lines of evidence suggest that BLT2 participates in DSS (dextran sulfate sodium)-induced colitis (Iizuka et al, 2010), carcinogenesis (Yoo et al, 2004;Hennig et al, 2008), arthritis (Shao et al, 2006), and bronchial asthma (Cho et al, 2010), but (2,4,6-trinitrobenzene sulfonic acid)-induced colitis in mouse .…”

Eicosanoids in Asthma, Allergic Inflammation, and Host Defense

“…While BLT 1 transcript is richly expressed by hematopoietic tissues, the BLT 2 transcript is expressed by skeletal muscle and ovary [82,83]. Mouse keratinocytes dominantly express BLT 2 receptors, and migrate in response to LTB 4 in vitro [84]. The fact that the distributions of the BLT receptors only partly overlap suggests that they mediate separate functions in inflammation that are cell type-and context-specific.…”