5-lipoxygenase mRNA and protein isoforms.

5-Lipoxygenase (5-LO) catalyses the two initial steps in the biosynthesis of leukotrienes, a group of inflammatory lipid mediators derived from arachidonic acid. An increased level of leukotrienes is associated with chronic inflammatory diseases such as asthma or atherosclerosis. In this MiniReview, we focus on recent findings regarding alternative splice variants of 5-LO with a special emphasis on two potential protein isoforms expressed in human B-lymphocytes which might be of interest as new drug targets.

MicroRNAs-novel therapeutic targets of eicosanoid signalling.

MicroRNAs (miRNAs) have emerged as important regulators in human physiological and pathological processes. We summarize the current knowledge about the role of miRNA involved in the control of inflammatory responses with a special focus on eicosanoid signalling. Cyclooxygenase 2 - the key enzyme of the prostanoid pathway - is regulated by different miRNAs such as miRNA-101, miR199a, miR26b and miR-146a. In contrast to this, the understanding of miRNA regulation on enzymes of the leukotriene biosynthesis is just at the beginning. The knowledge of miRNAs regulating enzymes of the eicosanoid pathway offers a new way for the development of new therapeutic concepts for the treatment of inflammatory diseases.

Mass spectrometry-based proteomics identifies UPF1 as a critical gene expression regulator in MonoMac 6 cells.

5-Lipoxygenase (5-LO) catalyzes the two initial steps in the biosynthesis of leukotrienes, a group of inflammatory lipid mediators derived from arachidonic acid. Recently, we have demonstrated that 5-LO mRNA expression is regulated by alternative splicing and nonsense-mediated mRNA decay (NMD). In addition to this, 5-LO protein expression was reduced on translational level in UPF1 knockdown cells, suggesting that UPF1 has a positive influence on 5-LO translation. Therefore, a mass spectrometry-based proteomics study was performed to identify compartment-specific protein expression changes upon UPF1 knockdown in differentiated and undifferentiated MM6 cells. The proteomics analysis revealed that the knockdown of UPF1 results in numerous protein changes in the microsomal fraction (~21%) but not in the cytosolic fraction (<1%). The results suggest that UPF1 is a critical gene expression regulator in a compartment-specific way. During differentiation by TGFß and calcitriol, the majority of UPF1 regulated proteins were adjusted to normal level. This indicates that the translational regulation by UPF1 can potentially be cell differentiation-dependent.

Post-transcriptional regulation of 5-lipoxygenase mRNA expression via alternative splicing and nonsense-mediated mRNA decay.

5-Lipoxygenase (5-LO) catalyzes the two initial steps in the biosynthesis of leukotrienes (LT), a group of inflammatory lipid mediators derived from arachidonic acid. Here, we investigated the regulation of 5-LO mRNA expression by alternative splicing and nonsense-mediated mRNA decay (NMD). In the present study, we report the identification of 2 truncated transcripts and 4 novel 5-LO splice variants containing premature termination codons (PTC). The characterization of one of the splice variants, 5-LOΔ3, revealed that it is a target for NMD since knockdown of the NMD factors UPF1, UPF2 and UPF3b in the human monocytic cell line Mono Mac 6 (MM6) altered the expression of 5-LOΔ3 mRNA up to 2-fold in a cell differentiation-dependent manner suggesting that cell differentiation alters the composition or function of the NMD complex. In contrast, the mature 5-LO mRNA transcript was not affected by UPF knockdown. Thus, the data suggest that the coupling of alternative splicing and NMD is involved in the regulation of 5-LO gene expression.

MicroRNA Involved in Inflammation: Control of Eicosanoid Pathway.

MicroRNAs (miRNAs) have emerged as important regulators in human physiological and pathological processes. Recent investigations implicated the involvement of miRNAs in the immune system development and function and demonstrated an unexpected new regulatory level. We summarize the current knowledge about miRNA control in the development of the immune system and discuss their role in the immune and inflammatory responses with a special focus on eicosanoid signaling.

Isothiocyanate sulforaphane inhibits protooncogenic ornithine decarboxylase activity in colorectal cancer cells via induction of the TGF-ß/Smad signaling pathway.

SCOPE: The objective of this study was to elucidate molecular mechanisms behind the antitumor activities of the isothiocyanate sulforaphane (SFN) in colorectal cancer cells. METHODS AND RESULTS: Cell growth was determined by BrdU incorporation and crystal violet staining. Protein levels were examined by Western blot analysis. Ornithine decarboxylase (ODC) activity was assayed radiometrically. Reverse transcriptase-PCR was used for measuring mRNA expression. For reporter gene assays plasmids were transfected into cells via lipofection and luciferase activity was measured luminometrically. Acetyl-histone H3 and H4 chromatin immunoprecipitation (ChIP) assays were performed followed by PCR with TGF-ß-receptor II promoter specific primers. We could show that SFN-mediated cell growth inhibition closely correlates with a dose-dependent reduction of protein expression and enzymatic activity of ODC. This effect seems to be due to reduced protein levels and transactivation activity of transcription factor c-myc, a direct regulator of ODC expression, as a consequence of SFN-induced TGF-ß/Smad signaling. The coherency of these results was further confirmed by using TGF-ß receptor kinase inhibitor SB431542, which largely abolishes inhibitory effects of SFN on both, ODC activity and cell growth. CONCLUSION: Since elevated ODC enzyme activity is associated with enhanced tumor development, SFN may be a dietary phytochemical with potential to prevent carcinogenesis.