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Classical Hodgkin lymphoma (cHL) has a unique pathological feature characterized by a minority of malignant Hodgkin Reed-Sternberg (H-RS) cells surrounded by numerous inflammatory cells. Cysteinyl-leukotrienes (CysLTs) are produced by eosinophils, macrophages and mast cells in the HL tumor microenvironment. In the present study we have explored the signal transduction pathways leading to leukotriene (LT) D4 induced expression of cytokines in the Hodgkin lymphoma cell line L1236 and KM-H2. Stimulation of L1236 and KM-H2 cells with LTD4 led to a concentration- and time-dependent increase at the transcriptional level of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-8, chemokine (C-C motif) ligand 3 (CCL3) and CCL4. The expression of several transcription factors was induced upon stimulation of Hodgkin cell lines with LTD4. Among these, EGR-1 was required for cytokine production. Inhibition of EGR-1 expression using shEGR-1 transduced by lentivirus led to suppression of the expression of TNF-α and IL-6. The effect of LTD4 on the expression of transcription factors and cytokines were also blocked by the specific CysLT1 receptor antagonist zafirlukast. These results demonstrate that EGR-1 plays a critical role in LTD4-induced cytokine transcription in Hodgkin cell lines.

Lipoxygenases oxidatively metabolize polyunsaturated fatty acids to a rich spectrum of biologically active metabolites. The present study aimed at delineating the transcriptional and epigenetic mechanisms leading to 15-lipoxygenase-1 (15-LOX-1) expression in the Hodgkin lymphoma (HL) cell line L1236. Examination of the 15-LOX-1 5' promoter region demonstrated three putative binding sites for signal transducer and activator of transcription (STAT6) within the proximal 1200 base pairs relative to the start codon. Analysis by serial promoter deletions and STAT6 binding site mutations indicated that all three STAT6 binding sites are required for full activation of the 15-LOX-1 promoter. Chromatin immunoprecipitation assay demonstrated that these regions were occupied by STAT6 in L1236 (15-LOX-1 positive) but not in L428 (15-LOX-1 negative) cultured HL cells. Furthermore, DNA hypomethylation and histone hyperacetylation were detectable within the core promoter region of 15-LOX-1 only in L1236 cells but not L428 cells. Taken together, our data indicate that STAT6 activation and chromatin remodeling by DNA demethylation and histone acetylation are crucial for transcriptional activation of 15-LOX-1 in cultured HL cells. These prerequisites are fulfilled in the L1236 cell line, but not in the L428 cell line.

Objective Primary mediastinal B-cell lymphoma (PMBCL) and Hodgkin lymphoma (HL) share many biological and clinical characteristics supporting a common pathogenetic pathway. Interleukin (IL)-13 has an important pathophysiological role in HL. In this study, we asked the question of whether IL-13 is a major contributor to the observed difference in features of inflammation between HL and PMBCL. Materials and Methods Expression of IL-13 and IL-4 receptors was studied by flow cytometry, expression of a functional cysteinyl leukotriene receptor type 1 (CysLT1R) was investigated by calcium flux measurement, expression and activity of 15-lipoxygenase type 1 (15-LO-1) was determined by Western blot and reversed-phase high-performance liquid chromatography, respectively, and cytokines were quantified by Bioplex detection. Results Stimulation of the PMBCL cell line Karpas-1106P with IL-13 or IL-4 induced a proinflammatory phenotype similar to that of the HL cell line L1236. Upon interleukin stimulation of the PMBCL cell line, the cellular size increased and cells became multinucleated. Cells also expressed CysLT1R and 15-LO-1, and produced the proinflammatory eoxins. The IL-13 or IL-4 treated PMBCL cell line and the HL cell line secreted a similar set of cytokines such as IL-6, tumor necrosis factor−α, interferon-inducible protein−10, interferon-γ, and RANTES. Conclusions IL-13 or IL-4 stimulation of the PMBCL cell line Karpas-1106P induced an inflammatory phenotype that resembles that of the HL cell line. Our results suggest that the autocrine release of IL-13 in HL is one critical factor that can at least partly explain the difference in phenotype between these two lymphoma entities.

Background Arachidonic acid metabolites have been suggested to play an important role in carcinogenesis. We have recently reported that the cysteinyl leukotriene receptor 1 (CysLT 1 ) and 15-lipoxygenase-1 (15-LO-1) are expressed by the malignant Hodgkin Reed-Sternberg cells of Hodgkin lymphoma and certain Hodgkin lymphoma cell lines, and that these cells convert arachidonic acid to the novel proinflammatory eoxins. Materials and Methods The expression of the CysLT 1 receptor and 15-LO-1 was investigated in a broad range of non-Hodgkin lymphomas (NHLs) by immunohistochemistry. The functionality of the CysLT 1 receptor in primary mediastinal B-cell lymphoma (PMBCL) cell lines was studied by calcium mobilization assays. Results Primary mediastinal B-cell lymphoma was the only NHL entity showing tumor cells positive for the CysLT 1 receptor (9 of 10 tumors), and the PMBCL cell line Med-B1 expressed functional CysLT 1 receptors, responding with a robust calcium signal upon cysteinyl leukotriene challenge. Furthermore, the tumor cells in 1 of 4 T-cell—derived anaplastic large-cell lymphomas, in contrast to all other studied NHLs, strongly expressed 15-LO-1. Conclusion Among the NHL entities included in this study, the CysLT 1 receptor was exclusively expressed by the tumor cells of PMBCL. Thus, this further corroborates the pathologic overlap between PMBCL and classical Hodgkin lymphoma.

15-Lipoxygenase type 1 (15-LO), a lipid-peroxidating enzyme implicated in physiological membrane remodeling and the pathogenesis of atherosclerosis, inflammation, and carcinogenesis, is highly regulated and expressed in a tissue- and cell-type-specific fashion. It is known that interleukins (IL) 4 and 13 play important roles in transactivating the 15-LO gene. However, the fact that they only exert such effects on a few types of cells suggests additional mechanism(s) for the profile control of 15-LO expression. In the present study, we demonstrate that hyper- and hypomethylation of CpG islands in the 15-LO promoter region is intimately associated with the transcriptional repression and activation of the 15-LO gene, respectively. The 15-LO promoter was exclusively methylated in all examined cells incapable of expressing 15-LO (certain solid tumor and human lymphoma cell lines and human T lymphocytes) while unmethylated in 15-LO-competent cells (the human airway epithelial cell line A549 and human monocytes) where 15-LO expression is IL4-inducible. Inhibition of DNA methylation in L428 lymphoma cells restores IL4 inducibility to 15-LO expression. Consistent with this, the unmethylated 15-LO promoter reporter construct exhibited threefold higher activity in A549 cells compared to its methylated counterpart. Taken together, demethylation of the 15-LO promoter is a prerequisite for the gene transactivation, which contributes to tissue- and cell-type-specific regulation of 15-LO expression.