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Imatinib, a tyrosine kinase inhibitor (TKI) has significantly improved clinical outcome for chronic myeloid leukemia (CML) patients. However, patients develop resistance when the disease progresses to the blast phase (BP) and the mechanisms are not well understood. Here we show that BCR-ABL activates BLT2 in hematopoietic stem/progenitor cells to promote leukemogenesis and this involves the p53 signaling pathway. Compared to normal bone marrow (NBM), the mRNA and protein levels of BLT2 are significantly increased in BP-CML CD34(+) stem/progenitor cells. This is correlated with increasing BCR-ABL expression. In contrast, knockdown of BCR-ABL or inhibition of its tyrosine kinase activity decreases Blt2 protein level. BLT2 inhibition induces apoptosis, inhibits proliferation, colony formation and self-renewal capacity of CD34(+) cells from TKI-resistant BP-CML patients. Importantly, the inhibitory effects of BCR-ABL TKI on CML stem/progenitor cells are further enhanced upon combination with BLT2 inhibition. We further show that BLT2 activation selectively suppresses p53 but not Wnt or BMP-mediated luciferase activity and transcription. Our results demonstrate that BLT2 is a novel pathway activated by BCR-ABL and critically involved in the resistance of BP-CML CD34(+) stem/progenitors to TKIs treatment. Our findings suggest that BLT2 and p53 can serve as therapeutic targets for CML treatment., (Copyright © 2016 Elsevier Inc. All rights reserved.)

We investigated the role of leukotriene B(4) (LTB(4))-leukotriene receptor (BLT) signaling in preadipocyte differentiation into mature adipocytes. Blockade of BLT signaling by treatment with lipoxygenase inhibitors, a BLT antagonist, and small interfering RNAs for BLTs in human and mouse preadipocytes isolated from adipose tissues showed acceleration of differentiation into mature adipocytes. DNA microarray analysis revealed regulation of transforming growth factor, beta-induced 68 kDa (TGFBI) expression through the BLT signaling pathway during adipocyte differentiation. Knockdown of TGFBI also showed acceleration of preadipocyte differentiation. The LTB(4)-BLT signaling pathway may negatively regulate preadipocyte differentiation via induction of TGFBI expression as a rate-limiting system to control adipocyte differentiation., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The androgen receptor (AR) plays a central role in the development and progression of prostate cancer. AR expression is maintained throughout the progression of prostate cancer and is also associated with an aggressive, castration-resistant (CR) phenotype. Despite the critical roles of AR expression in prostate cancer progression, the exact signaling mechanism regulating AR expression remains unclear. In this study, we demonstrated that AR expression was increased by a low-affinity leukotriene B(4) receptor (BLT2)-linked pathway. We found that BLT2 was overexpressed in AR-positive prostate cancer cells, such as LNCaP cells, and BLT2 inhibition, using an inhibitor or siRNA knockdown, clearly attenuated AR expression and triggered apoptosis in these cells. These results suggest a role for BLT2 in AR expression and the survival of AR-positive prostate cancer cells. Moreover, we found that the NADPH oxidase family protein, Nox4, lay downstream of BLT2 and mediated the production of reactive oxygen species (ROS) and subsequent NF-κB stimulation, thereby inducing AR expression. Taken together, our results demonstrate that BLT2 plays a critical role in AR expression via a Nox4-ROS-NF-κB-linked pathway, thereby mediating the survival of AR-positive prostate cancer cells. Our findings point to BLT2 as a key regulator of AR expression and will contribute to the development of novel therapies for AR-positive prostate cancers, including androgen-responsive and CR prostate cancers., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Leukotriene B(4) (LTB(4)) is a potent chemoattractant and activator of neutrophils, macrophages and T cells. These cells are a key component of inflammation and all express BLT1, a high affinity G-protein-coupled receptor for LTB(4). However, little is known about the neuroimmune functions of BLT1. In this study, we describe a distinct role for BLT1 in the pathology of experimental autoimmune encephalomyelitis (EAE) and T(H)1/T(H)17 immune responses. BLT1 mRNA was highly upregulated in the spinal cord of EAE mice, especially during the induction phase. BLT1(-/-) mice had delayed onset and less severe symptoms of EAE than BLT1(+/+) mice. Additionally, inflammatory cells were recruited to the spinal cord of asymptomatic BLT1(+/+), but not BLT1(-/-) mice before the onset of disease. Ex vivo studies showed that both the proliferation and the production of IFN-gamma, TNF-alpha, IL-17 and IL-6 were impaired in BLT1(-/-) cells, as compared with BLT1(+/+) cells. Thus, we suggest that BLT1 exacerbates EAE by regulating the migration of inflammatory cells and T(H)1/T(H)17 immune responses. Our findings provide a novel therapeutic option for the treatment of multiple sclerosis and other T(H)17-mediated diseases., (Copyright 2010 Elsevier Inc. All rights reserved.)

The leukotriene B(4) receptor (BLTR) is a seven-transmembrane chemoattractant receptor that is important in pro-inflammatory responses. We have produced the first widely applicable monoclonal antibodies against the human BLTR and confirmed the antibody specificity using flow cytometric analysis of three different cell lines stably expressing the recombinant receptor. The antibodies did not cross-react with the recently cloned second LTB(4) receptor, BLTR2, or the Cys LT1 and Cys LT2 receptors. Functional analysis in combination with two-color flow cytometry showed that the BLTR antibodies bind to cells that are activated by LTB(4). The antibodies were shown to recognize BLTR in cell ELISA and immunocytochemistry. Endogenous expression of BLTR in CD15-positive blood leukocytes and in differentiated HL-60 cells was also demonstrated with the antibodies., (Copyright 2000 Academic Press.)

The genomic region containing the genes encoding the first leukotriene B(4) receptor, BLTR, as well as the recently cloned second leukotriene B(4)-activated receptor, BLTR2, was mapped by (a) sequence analysis of a human bacterial artificial chromosome (BAC) library containing a 15-kb segment corresponding to chromosome 14q11. 2-12 where the BLTR/BLTR2 genes were previously shown to be located, together with (b) sequence analysis of 83 expressed sequence tags (ESTs) from this region. The BLTR gene includes four different 5' untranslated regions (UTRs) and a mutual acceptor site for the exon containing the intronless open reading frame. The BLTR2 gene is intronless and overlapped by a 5' UTR splice version of BLTR and, on the reverse strand, of the apoptosis-related CIDE-B gene. This indicates a complex posttranscriptional gene regulation. Further adding to the complexity of the region is evidence of a fourth putative and novel gene, most homologous to the rat adenylyl cyclase IV gene., (Copyright 2000 Academic Press.)

By homology screening using BLAST searches of expressed sequence tags (ESTs), we have found a previously unidentified cDNA encoding a putative seven-transmembrane receptor with highest similarity to the leukotriene B(4) receptor, BLTR. Analysis of calcium flow in transfected cells, along with sequence analysis, revealed that the EST encoded a functionally inactive protein, lacking the segment corresponding to the C-terminal part of the putative receptor protein. The missing segment was obtained by PCR amplification of a human leukocyte cDNA library and ligated to the truncated EST cDNA. The novel cDNA encodes a full-length receptor with 39% identity to the previously cloned BLTR. Studies of intracellular calcium flow of transfected HeLa cells exposed to various leukotrienes showed that also the novel BLTR-like receptor can be activated by leukotriene B(4), and it is therefore tentatively named BLTR2., (Copyright 2000 Academic Press.)

Leukotriene B(4) (LTB(4)), which is an arachidonic acid metabolite produced by the 5-lipoxygenase pathway and a well-characterized chemical mediator of inflammation, has been proposed to be an immune response modulator. Here we showed the constitutive expression of the LTB(4) receptor (LTB(4)R) in resting and activated T cells. We found that the LTB(4)R antagonist inhibited T cell proliferation induced by Con A, immobilized anti-CD3 mAb, or IL-2. This inhibitory effect was abolished by addition of LTB(4)R agonist. The LTB(4)R antagonist inhibited IL-2, IFN-gamma, and IL-4 production by anti-CD3-stimulated T cells and also inhibited IL-12-induced IFN-gamma production. Moreover, the LTB(4)R antagonist exerted an additive inhibitory effect to FK506 on T cell proliferation. These results suggest that LTB(4) is intrinsically involved in T cell activation to upregulate cytokine production and proliferation, and thus the LTB(4)R antagonist might be useful as an immunosuppressive agent., (Copyright 1999 Academic Press.)

Leukotriene B(4) (LTB(4)) is a potent chemoattractant for neutrophils and eosinophils. cDNAs for LTB(4) receptor (BLT) have been cloned from human, mouse, and guinea pig. Here we report the isolation of BLT from rat genomic library. Rat BLT consists of 351 amino acids with homologies of 80.2, 93.2, and 71.6%, to human, mouse, and guinea pig BLT, respectively. When expressed in human embryonic kidney (HEK)-293 cells, rat BLT showed a specific and high-affinity binding to LTB(4) with a Kd value of 0.68 nM (mean, n = 3). Northern blot analysis showed that BLT is exclusively expressed in polymorphonuclear leukocytes. Furthermore, the expression of BLT was high in proteosepeptone-activated peritoneal macrophages, while the resident macrophages did not show significant expression. The present results suggest important roles of LTB(4) in macrophage recruitment and activation., (Copyright 1999 Academic Press.)