High expression of 5-lipoxygenase in normal and malignant mantle zone B lymphocytes

The role of human 5-Lipoxygenase (5-LO) in carcinogenesis - a question of canonical and non-canonical functions

5-Lipoxygenase (5-LO), a fatty acid oxygenase, is the central enzyme in leukotriene (LT) biosynthesis, potent arachidonic acid-derived lipid mediators released by innate immune cells, that control inflammatory and allergic responses. In addition, through interaction with 12- and 15-lipoxgenases, the enzyme is involved in the formation of omega-3 fatty acid-based oxylipins, which are thought to be involved in the resolution of inflammation. The expression of 5-LO is frequently deregulated in solid and liquid tumors, and there is strong evidence that the enzyme plays an important role in carcinogenesis. However, global inhibition of LT formation and signaling has not yet shown the desired success in clinical trials. Curiously, the release of 5-LO-derived lipid mediators from tumor cells is often low, and the exact mechanism by which 5-LO influences tumor cell function is poorly understood. Recent data now show that in addition to releasing oxylipins, 5-LO can also influence gene expression in a lipid mediator-independent manner. These non-canonical functions, including modulation of miRNA processing and transcription factor shuttling, most likely influence cancer cell function and the tumor microenvironment and might explain the low clinical efficacy of pharmacological strategies that previously only targeted oxylipin formation and signaling by 5-LO. This review summarizes the canonical and non-canonical functions of 5-LO with a particular focus on tumorigenesis, highlights unresolved issues, and suggests future research directions.

The mechanisms underlying alcohol-induced decreased splenic size: A network meta-analysis study

BACKGROUND

Organ weight change is widely accepted as a measure of toxicologic pathology. We and other groups have shown that excessive alcohol exposure leads to decreased spleen weight in rodents. This study explores the mechanisms underlying alcohol-induced splenic injury through a network meta-analysis.

METHODS

QIAGEN Ingenuity Pathway Analysis (IPA) and Mammalian Phenotype (MP) Ontology were used to identify alcohol-related molecules associated with the small spleen phenotype. Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and IPA bioinformatics tools were then used to analyze the biologic processes and enriched signaling pathways engaging these molecules. In addition, the "downstream effects analysis" algorithm was used to quantify alcohol's effects.

RESULTS

IPA identified 623 molecules affected by alcohol and a Venn diagram revealed that 26 of these molecules overlapped with those associated with the MP Ontology of small spleen. The 26 molecules are TGFB1, CASP8, MTOR, ESR1, CXCR4, CAMK4, NFKBIA, DRD2, BCL2, FAS, PEBP1, TRAF2, ATM, IGHM, EDNRB, MDM2, GLRA1, PRF1, TLR7, IFNG, ALOX5, FOXO1, IL15, APOE, IKBKG, and RORA. Some of the 26 molecules were also associated with the MP Ontology of abnormal white pulp and red pulp morphology of the spleen, abnormal splenic cell ratio, decreased splenocyte number, abnormal spleen physiology, increased splenocyte apoptosis, and reduced splenocyte proliferation. STRING and IPA "Core Analysis" showed that these molecules were mainly involved in pathways related to cell apoptosis, proliferation, migration, and immune responses. IPA's "Molecular Activity Predictor" tool showed that concurrent effects of activation and inhibition of these molecules led to decreased spleen size by modulating apoptosis, proliferation, and migration of splenocytes.

CONCLUSIONS

Our network meta-analysis revealed that excessive alcohol exposure can damage the spleen through a variety of molecular mechanisms, thereby affecting immune function and human health. We found that alcohol-mediated splenic atrophy is largely mediated by increased apoptosis signaling, migration of cells, and inhibition of splenocyte proliferation.

Immunohistochemical analysis of arachidonate 5-lipoxygenase expression in B-cell lymphomas: Implication for B cell differentiation and its analogy with lymphomagenesis

Arachidonate 5-lipoxygenase (ALOX5) is a cardinal enzyme in the synthesis of leukotrienes, which are powerful immune-regulating lipid mediators. We previously reported that ALOX5 is preferentially expressed in B lymphocytes in the mantle zone of human lymphoid tissue. In the context of physiological relevance, the loss of the Alox5 gene in mice significantly impairs the development of follicular B helper T cells and antibody production. However, ALOX5 expression in B-cell lymphomas has not been investigated in detail. In this study, we examined ALOX5 expression in representative B-cell lymphomas and non-neoplastic lymphoid tissues by immunohistochemistry with a commercially available anti-ALOX5 antibody that can be used on formalin-fixed paraffin-embedded specimens. Interestingly, 22/22 cases of mantle cell lymphoma, 7/7 cases of chronic lymphocytic leukemia/small cell lymphoma, and 20/20 cases of follicular lymphoma expressed ALOX5. A small proportion of extranodal marginal zone lymphoma/mucosa-associated lymphoid tissue lymphoma or nodal marginal zone lymphoma cases were positive for ALOX5 (2/13 or 1/3, respectively). In contrast, no cases with diffuse large B-cell lymphoma, regardless of germinal center B cell (GCB) or non-GCB type, expressed ALOX5 (0/25 cases). These findings suggest that ALOX5 may be a novel marker for identifying the cell of origin of B-cell lymphoma. Further investigation is required to clarify the biological significance of ALOX5 expression in lymphoma cells.

Intrinsic 5-lipoxygenase activity regulates migration and adherence of mantle cell lymphoma cells

Human B-lymphocytes express 5-lipoxygenase (5-LOX) and 5-LOX activating protein (FLAP) and can convert arachidonic acid to leukotriene B₄. Mantle cell lymphoma (MCL) cells contain similar amounts of 5-LOX as human neutrophils but the function and mechanism of activation of 5-LOX in MCL cells, and in normal B-lymphocytes, are unclear. Here we show that the intrinsic 5-LOX pathway in the MCL cell line JeKo-1 has an essential role in migration and adherence of the cells, which are important pathophysiological characteristics of B-cell lymphoma. Incubation of JeKo-1 with the FLAP inhibitor GSK2190915 or the 5-LOX inhibitor zileuton, at a concentration below 1 μM, prior to stimulation with the chemotactic agent CXCL12, led to a significant reduction of migration. CRISPR/Cas9 mediated deletion of ALOX5 gene in JeKo-1 cells also led to a significantly decreased migration of the cells. Furthermore, 5-LOX and FLAP inhibitors markedly decreased the adherence of JeKo-1 cells to stromal cells. In comparison, these drugs had a similar effect on adherence of JeKo-1 cells as the Bruton tyrosine kinase inhibitor ibrutinib, which has a proven anti-tumour effect. These results indicate that inhibition of 5-LOX may be a novel treatment for MCL and certain other B-cell lymphomas.

Expression of CysLTR1 and 2 in Maturating Lymphocytes of Hyperplasic Tonsils Compared to Peripheral Cells in Children

Cysteinyl-leukotriene receptors 1 and 2 (CysLTR1 and 2) are related to allergic inflammatory responses. Recent studies demonstrated their role in lymphocyte division and maturation in the bone marrow. Few data are available about CysLTRs function in lymphocyte maturation in tonsils. The objectives of this study are to compare CysLTRs expression in peripheral blood lymphocytes with expression in maturating lymphocytes of hyperplasic tonsil and to check the influence of respiratory allergies in this process. Leukocytes of peripheral blood (PL) and hyperplasic tonsils of children were immunostained for CysLTR1, CysLTR2, CD3 (T cells), and CD19 (B cells) and read in flow cytometer. Lymphocyte of tonsils were divided in differentiating small cells (SC) and mitotic large cells (LC); percentage of B and T cells expressing CysLTRs was determined, and comparison was done using ANOVA and Tukey's tests. Data were analyzed as a whole and categorizing patients according the presence of allergies. Sixty children were enrolled in this study. There was a large expression of CysLTR1 and 2 in CD3+ LC, and such expression decreased progressively in SC and PL. In B cells, the highest expression of CysLTR1 and 2 was found in PL while SC showed the lowest and LC showed the intermediate expression. This pattern kept unchanged in groups of allergic and non-allergic individuals. CysLTRs seem to be involved in lymphocyte maturation that occurs in tonsils, without influence of allergies. New studies aiming the clinic treatment of tonsil hyperplasia must be targeted to the development of drugs capable of blocking both CysLTR1 and 2.

Corticosteroids inhibit anti-IgE activities of specialized proresolving mediators on B cells from asthma patients

Specialized proresolving mediators (SPMs) promote the resolution of inflammation and exert beneficial effects in animal models of chronic inflammatory diseases, including asthma. Previously, we have shown that certain SPMs reduce IgE production in B cells from healthy individuals, which has a critical role in allergic asthma. Here, we investigated the effects of SPMs on B cell IgE production in asthma patients. Peripheral blood mononuclear cells from asthma patients were treated with 17-HDHA or RvD1, and IgE levels were measured. RvD1 and 17-HDHA dampened IgE production in B cells from most asthma patients, whereas B cells from a subset of patients taking oral steroids were refractory to SPM treatment. Molecular mechanisms underlying the interaction between corticosteroids and SPMs were investigated by treating B cells from nonasthmatic donors with corticosteroids in vitro. Corticosteroids blocked the inhibitory effects of 17-HDHA and RvD1 on B cell IgE production by abolishing the suppressive activity of these mediators on IgE class switching. Corticosteroids decreased the expression of transcriptional repressor Bcl-6 as well as its suppressive activity on epsilon germline transcription. We conclude that 17-HDHA and RvD1 can reduce IgE production in asthma patients not taking high doses of steroids but that corticosteroids interfere with the ability of B cells to respond to proresolving mediators.

Lipid mediators foster the differentiation of T follicular helper cells

Lipid mediators such as leukotrienes and lipoxines broadly regulate innate and acquired immunity, and their dysfunction causes various immune-mediated disorders. We previously reported a salient feature of arachidonate 5-lipoxyganase (Alox5), which is responsible for the production of such lipid mediators, in the regulation of high affinity antibodies in vivo. The aim of this study was to determine the functional significance of Alox5-related lipid mediators during the processes of acquired humoral responses. The results of in vitro experiments using lymphocytes in tonsils and blood specimens showed that lipoxin A4 (LXA4) and leukotriene B4 (LTB4) have the capacity to differentiate naïve CD4⁺ T cells into T follicular helper (Tfh) cells, which activate naïve B cells to form germinal centers. Such a function of LXA4 was further supported by results of in vitro studies using BML-111 and BOC-2, which are an agonist and an antagonist, respectively, of FPR2 of an LXA4-specific cell-surface receptor. The results suggest that such lipid mediators have a potential role in the development of lymphoid follicles through the regulation of Tfh cell differentiation.

Expression of cysteinyl leukotriene receptor 1 and 2 (CysLTR1 and CysLTR2) in the lymphocytes of hyperplastic tonsils: comparison between allergic and nonallergic snoring children

BACKGROUND

Cysteinyl leukotriene receptor 1 and 2 (CysLTR1 and CysLTR2) are involved in allergic processes and play a role in adenotonsillar hyperplasia (AH). Clinically, only CysLTR1 may be blocked by montelukast. Our objective was to compare the expression of CysLTR1 and CysLTR2 in the B and T cells of hyperplasic tonsils of sensitized (SE) and control (NS) snoring children.

METHODS

Sixty children, 5 to 10 years of age, referred for adenotonsillectomy, were divided into SE and NS groups, according to their responses to the skin-prick test. Cells from the removed tissues were stained for CysLTR1, CysLTR2, CD19, and CD3 and counted via flow cytometry. messenger RNA (mRNA) expression of the CysLTRs genes was measured real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR).

RESULTS

The SE group showed reduced expression of the small CD3+/CysLTR1+ lymphocytes (4.6 ± 2.2 vs 6.5 ± 5.0; p = 0.04). Regarding the large lymphocytes, the SE group showed lower expression of CD3+/CysLTR1+ (40.9 ± 14.5 vs 47.6 ± 11.7; p = 0.05), CD19+/CysLTR1+ (44.6 ± 16.9 vs 54.1 ± 12.4; p = 0.01), and CD19+/CysLTR2+ (55.3 ± 11.3 vs 61.5 ± 12.6; p = 0.05) lymphocytes. Considering the total number of lymphocytes, the SE group had fewer CD3+/CysLTR1+ lymphocytes (11.1 ± 5.5 vs 13.7 ± 6.2; p = 0.04). All other cell populations exhibited reduced expression in the SE group without statistical significance. The expression of CysLTR2 was significantly higher (p < 0.05) than CysLTR1 in most studied cell populations. The mRNA expression did not show significant differences between the groups.

CONCLUSION

The expression of CysLTR is higher in the lymphocytes of the NS children, and CysLTR2 shows greater expression than CysLTR1 Respiratory allergies do not appear to be a stimulus for AH occurrence. Newer drugs capable of blocking both CysLTRs warrant further study.

Phosphorylation of serine 523 on 5-lipoxygenase in human B lymphocytes

The key enzyme in leukotriene (LT) biosynthesis is 5-lipoxygenase (5-LO), which is expressed in myeloid cells and in B lymphocytes. There are three phosphorylation sites on 5-LO (Ser271, Ser523 and Ser663). Protein kinase A (PKA) phosphorylates 5-LO on Ser523. In this report, we demonstrate by immunoblotting that native 5-LO in mantle B cell lymphoma (MCL) cells (Granta519, JEKO1, and Rec1) and in primary chronic B lymphocytic leukemia cells (B-CLL) is phosphorylated on Ser523. In contrast, we could not detect phosphorylation of 5-LO on Ser523 in human granulocytes or monocytes. Phosphorylated 5-LO was purified from Rec1 cells, using an ATP-agarose column, and the partially purified enzyme could be dephosphorylated with alkaline phosphatase. Incubation of Rec1 cells with 8-Br-cAMP or prostaglandin E2 stimulated phosphorylation at Ser523. Furthermore, FLAG-5LO was expressed in Rec1 cells, and the cells were cultivated in the presence of 8-Br-cAMP. The 5-LO protein from these cells was immunoprecipitated, first with anti-FLAG, followed by anti-pSer523-5-LO. The presence of 5-LO protein in the final precipitate further supported the finding that the protein recognized by the pSer523 antibody was 5-LO. Taken together, this study shows that 5-LO in B cells is phosphorylated on Ser523 and demonstrates for the first time a chemical difference between 5-LO in myeloid cells and B cells.

Advanced pancreatic adenocarcinoma: a review of current treatment strategies and developing therapies

Pancreatic adenocarcinoma is one of the deadliest solid malignancies. A large proportion of patients are diagnosed with locally advanced or metastatic disease at the time of presentation and, unfortunately, this severely limits the number of patients who can undergo surgical resection, which offers the only chance for cure. Recent therapeutic advances for patients with advanced pancreatic cancer have extended overall survival, but prognosis still remains grim. Given that traditional chemotherapy is ineffective in curing advanced pancreatic adenocarcinoma, current research is taking a multidirectional approach in the hopes of developing more effective treatments. This article reviews the major clinical trial data that is the basis for the current chemotherapy regimens used as first- and second-line treatments for advanced pancreatic adenocarcinoma. We also review the current ongoing clinical trials, which include the use of agents targeting the oncogenic network signaling of K-Ras, agents targeting the extracellular matrix, and immune therapies.

5-lipoxygenase is a direct target of miR-19a-3p and miR-125b-5p

5-Lipoxygenase (5-LO) is the key enzyme in leukotriene biosynthesis. Leukotrienes are mediators of the innate immune system and inflammatory processes, and they might also be involved in cancer development. MicroRNAs (miRNAs) are important translational regulators and have been shown to be involved in development, differentiation, and cancer. Unraveling the miRNA network is important for understanding the cellular regulation processes. We identified two new miRNAs, miR-19a-3p and miR-125b-5p, regulating 5-LO and confirmed direct interaction by reporter gene assays. Furthermore, we investigated the regulation of 5-LO by these two miRNAs in several cell types. Inhibition of both miRNAs by antagomirs during differentiation of the myeloid cell line Mono Mac 6 led to a significant increase in 5-LO protein expression. Stimulation of human T lymphocytes with PHA resulted in a strong downregulation of 5-LO mRNA expression and in the induction of miR-19a-3p. The inhibition of miR-19a-3p with an antagomir led to a significant increase in 5-LO mRNA expression in T lymphocytes. Taken together, our data reveal that miR-19a-3p and miR-125b-5p target 5-LO in a cell type- and stimulus-specific manner.

The novel anticancer agent JNJ-26854165 induces cell death through inhibition of cholesterol transport and degradation of ABCA1

JNJ-26854165 (serdemetan) has previously been reported to inhibit the function of the E3 ligase human double minute 2, and we initially sought to characterize its activity in models of mantle cell lymphoma (MCL) and multiple myeloma (MM). Serdemetan induced a dose-dependent inhibition of proliferation in both wild-type (wt) and mutant (mut) p53 cell lines, with IC50 values from 0.25 to 3 μM/l, in association with an S phase cell cycle arrest. Caspase-3 activation was primarily seen in wtp53-bearing cells but also occurred in mutp53-bearing cells, albeit to a lesser extent. 293T cells treated with JNJ-26854165 and serdemetan-resistant fibroblasts displayed accumulation of cholesterol within endosomes, a phenotype reminiscent of that seen in the ATP-binding cassette subfamily A member-1 (ABCA1) cholesterol transport disorder, Tangiers disease. MM and MCL cells had decreased cholesterol efflux and electron microscopy demonstrated the accumulation of lipid whorls, confirming the lysosomal storage disease phenotype. JNJ-26854165 induced induction of cholesterol regulatory genes, sterol regulatory element-binding transcription factor-1 and -2, liver X receptors α and β, along with increased expression of Niemann-Pick disease type-C1 and -C2. However, JNJ-26854165 induced enhanced ABCA1 turnover despite enhancing transcription. Finally, ABCA1 depletion resulted in enhanced sensitivity to JNJ-26854165. Overall, these findings support the hypothesis that serdemetan functions in part by inhibiting cholesterol transport and that this pathway is a potential new target for the treatment of MCL and MM.

Cancer-produced metabolites of 5-lipoxygenase induce tumor-evoked regulatory B cells via peroxisome proliferator-activated receptor α

Breast cancer cells facilitate distant metastasis through the induction of immunosuppressive regulatory B cells, designated tBregs. We report in this study that, to do this, breast cancer cells produce metabolites of the 5-lipoxygenase pathway such as leukotriene B4 to activate the peroxisome proliferator-activated receptor α (PPARα) in B cells. Inactivation of leukotriene B4 signaling or genetic deficiency of PPARα in B cells blocks the generation of tBregs and thereby abrogates lung metastasis in mice with established breast cancer. Thus, in addition to eliciting fatty acid oxidation and metabolic signals, PPARα initiates programs required for differentiation of tBregs. We propose that PPARα in B cells and/or tumor 5-lipoxygenase pathways represents new targets for pharmacological control of tBreg-mediated cancer escape.

Cysteinyl leukotriene receptors in tonsillar B- and T-lymphocytes from children with obstructive sleep apnea

OBJECTIVES

Cysteinyl leukotrienes have been implicated in the pathogenesis of adenotonsillar hypertrophy in children with obstructive sleep apnea (OSA). This study aimed to quantify the expression of cysteinyl leukotriene receptors (CysLT(1), CysLT(2)) by tonsillar lymphocyte subpopulations from children with OSA and to make comparisons to lymphocyte subpopulations from control subjects with recurrent tonsillitis (RT).

METHODS

Tonsillar tissue from children with OSA or RT was studied for CysLT(1) and CysLT(2) expression by RT-PCR, flow cytometry (FC), and immunofluorescence.

RESULTS

Ten children with OSA and 10 control subjects were recruited. In OSA participants, CysLT(1)+ fraction of small-size CD19+ B-lymphocytes was similar to the CysLT(1)+ CD3+ T-lymphocytes fraction (FC: 36.5 [16.5-55.4] vs. 14 [2.8-22.1]) (p>0.05) and higher than the CysLT(1)+ moderate/large-size CD19+ B-lymphocytes fraction (6.6 [1.5-14.4]) (p<0.01). Similar trends were recognized for CysLT(2). CysLT(1) and CysLT(2) immunoreactivity was detected by immunofluorescence in the tonsillar mantle zones (small B-lymphocytes) and the extrafollicular areas (T-lymphocytes). Compared to subjects with RT, children with OSA had significantly higher expression of CysLT(1) in small-size CD19+ B-lymphocytes (FC) and in CD3+ T-lymphocytes (RT-PCR and FC) (p<0.05).

CONCLUSIONS

Increased expression of leukotriene receptors by immunologically active tonsillar areas in children with OSA is a potential therapeutic target for pediatric sleep apnea.

5-oxo-ETE is a major oxidative stress-induced arachidonate metabolite in B lymphocytes

B lymphocytes convert arachidonic acid (AA) to the 5-lipoxygenase products leukotriene B4 (LTB4) and 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) when subjected to oxidative stress. 5-HETE has little biological activity, but can be oxidized by a selective dehydrogenase in some cells to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), a potent eosinophil chemoattractant. We found that CESS cells, a B lymphocyte cell line, convert AA to 5-oxo-ETE and this is selectively stimulated by oxidative stress. In the presence of H2O2, 5-oxo-ETE is a major AA metabolite in these cells (5-oxo-ETE≈5-HETE>LTB4). The cyclooxygenase product 12-hydroxy-5,8,10-heptadecatrienoic acid is also formed, but is not affected by H2O2. Diamide had effects similar to those of H2O2 and both substances had similar effects on human tonsillar B cells. H2O2 also stimulated 5-oxo-ETE formation from its direct precursor 5-HETE in tonsillar B and CESS cells, and this was inhibited by the glutathione reductase inhibitor carmustine. H2O2 concomitantly induced rapid increases in GSSG and NADP+ and reductions in GSH and NADPH. We conclude that oxidative stress stimulates 5-oxo-ETE synthesis in B lymphocytes by two mechanisms: activation of 5-lipoxygenase and increased oxidation of 5-HETE by NADP+-dependent 5-hydroxyeicosanoid dehydrogenase. B lymphocyte-derived 5-oxo-ETE could contribute to eosinophilic inflammation in asthma and other allergic diseases.

5-Lipoxygenase-deficient mice infected with Borrelia burgdorferi develop persistent arthritis

The enzyme 5-lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid into the leukotrienes, which are critical regulators of inflammation and inflammatory diseases, such as asthma and arthritis. Although leukotrienes are present in the synovial fluid of Lyme disease patients, their role in the development of Lyme arthritis has not been determined. In the current study, we used a murine model of Lyme arthritis to investigate the role 5-LO products might have in the development of this inflammatory disease. After infection of Lyme arthritis-susceptible C3H/HeJ mice with Borrelia burgdorferi, mRNA expression of 5-LO and 5-LO-activating protein was induced in the joints, and the 5-LO product leukotriene B(4) was produced. Using C3H 5-LO-deficient mice, we demonstrated that 5-LO activity was not necessary for the induction of Lyme arthritis, but that its deficiency resulted in earlier joint swelling and an inability to resolve arthritis as demonstrated by sustained arthritis pathology through day 60 postinfection. Although production of anti-Borrelia IgG was decreased in 5-LO-deficient mice, bacterial clearance from the joints was unaffected. Phagocytosis of B. burgdorferi and efferocytosis of apoptotic neutrophils was defective in macrophages from 5-LO-deficient mice, and uptake of opsonized spirochetes by neutrophils was reduced. These results demonstrate that products of the 5-LO metabolic pathway are not required for the development of disease in all models of arthritis and that caution should be used when targeting 5-LO as therapy for inflammatory diseases.

Arachidonate 5-lipoxygenase establishes adaptive humoral immunity by controlling primary B cells and their cognate T-cell help

In this study, we report the unique role of arachidonate 5-lipoxygenase (Alox5) in the regulation of specific humoral immune responses. We previously reported an L22 monoclonal antibody with which human primary resting B cells in the mantle zones of lymphoid follicles are well-defined. Proteomics analyses enabled identification of an L22 antigen as Alox5, which was highly expressed by naive and memory B cells surrounding germinal centers. Cellular growth of mantle cell lymphoma cells also seemed to depend on Alox5. Alox5(-/-) mice exhibited weak antibody responses specific to foreign antigens at the initial and recall phases. This was probably attributable to the low number of follicular and memory B cells and the functional loss of interleukin-21-mediated responses of follicular B cells. Moreover, Alox5(-/-) mice could not fully foster the development of follicular B helper T (Tfh) cells even after immunization with foreign antigens. Further experiments indicated that Alox5 affected mortality in experimentally induced enterocolitis in germ-prone circumstances, indicating that Alox5 would endow immunologic milieu. Our results illustrate the novel role of Alox5 in adaptive humoral immunity by managing primary B cells and Tfh cells in vivo.

Protein profiling of plasma membranes defines aberrant signaling pathways in mantle cell lymphoma

We used shotgun proteomics to identify plasma membrane and lipid raft proteins purified from B cells obtained from mantle cell lymphoma (MCL) patients in leukemic phase. Bioinformatics identified 111 transmembrane proteins, some of which were profiled in primary MCL cases, MCL-derived cell lines, and normal B cells using RT-PCR and Western blotting. Several transmembrane proteins, including CD27, CD70, and CD31 (PECAM-1), were overexpressed when compared with normal B cells. CD70 was up-regulated (>10-fold) in three of five MCL patients along with its cognate receptor CD27, which was up-regulated (4-9-fold) in five of five patients, suggesting that MCL cells may undergo autocrine stimulation via this signaling pathway. Activated calpain I and protein kinase C betaII were also detected in the plasma membranes, suggesting that these proteins are constitutively active in MCL. Protein kinase C betaII has been associated with lipid rafts, and shotgun proteomics/protein profiling revealed that key lipid raft proteins, raftlin (four of five patients) and CSK (C-terminal Src kinase)-binding protein (Cbp)/phosphoprotein associated with glycosphingolipid-enriched microdomains (PAG) (four of four patients) were down-regulated in MCL. Levels of other known lipid raft proteins, such as Lyn kinase and flotillin 1, were similar to normal B cells. However, 5-lipoxygenase (5-LO), a key enzyme in leukotriene biosynthesis, was associated with lipid rafts and was up-regulated approximately 7-fold in MCL compared with normal B cells. Significantly inhibitors of 5-LO activity (AA861) and 5-LO-activating protein (FLAP) (MK886, its activating enzyme) induced apoptosis in MCL cell lines and primary chronic lymphocytic leukemia cells, indicating an important role for the leukotriene biosynthetic pathway in MCL and other B cell malignancies. Thus, using shotgun proteomics and mRNA and protein expression profiling we identified a subset of known and unknown transmembrane proteins with aberrant expression in MCL plasma membranes. These proteins may play a role in the pathology of the disease and are potential therapeutic targets in MCL.

Expression of 5-lipoxygenase and 15-lipoxygenase in rheumatoid arthritis synovium and effects of intraarticular glucocorticoids

Introduction

It was previously shown that lipoxygenase (LO) pathways are important in the rheumatoid arthritis (RA) inflammatory process and that synovial fluid from RA patients contains high amounts of leukotrienes. We therefore aimed to investigate the 5-LO and 15-LO-1 expression pattern in RA and ostheoarthritis (OA) synovial tissue and to study the effect of intraarticular glucocorticoid (GC) therapy on enzyme expression.

Methods

Expression of LOs was evaluated by immunohistochemistry in RA and OA synovial biopsies. Cellular localization of these enzymes was analyzed by double immunofluorescence. In synovial biopsies from 11 RA patients, 5-LO and 15-LO-1 expression was evaluated before and after triamcinolone hexacetonide knee injection and assessed by image analysis to quantify their expression. We also investigated the presence of 15-LO-1 by immunohistochemistry in synovial fluid (SF) cells as well as their ability to form 15-hydroxyeicosatetraenoic acid (15-HETE) following treatment with arachidonic acid (AA).

Results

5-LO and 15-LO-1 are present in RA and OA synovium, with 5-LO being mostly expressed in lining and sublining macrophages, neutrophils and mast cells and 15-LO-1 mainly in lining macrophages, fibroblasts and sublining endothelial cells. Intraarticular GC treatment resulted in a significant suppression of 5-LO expression, but did not influence the 15-LO-1 enzyme significantly. Also, SF cells express a functional 15-LO-1 and produce 15-HETE when challenged with AA.

Conclusions

These data demonstrate that local therapy with GC decreases 5-LO expression in RA synovium and offer an additional possible mechanism for the efficiency of intraarticular adjuvant therapy in RA.