Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Stimulated B-lymphocytes, isolated from patients with chronic lymphocytic leukemia of B-cell type (B-CLL cells) or from human tonsils, produced similar amounts of leukotriene (LT) B4 and 5-hydroxyeicosatetraenoic acid (5-HETE) as polymorphonuclear granulocytes. Unlike intact granulocytes or monocytes, human B-lymphocytes require calcium ionophore, exogenous arachidonic acid and an oxidative environment in order to produce 5-lipoxygenase products. Several thiol-reactive compounds such as N-ethylmaleimide, methyl methanethiosulfonate, azodicarboxylic acid bis[dimethylamide] (diamide) as well as hydrogen peroxide were all found to stimulate cellular leukotriene biosynthesis. Reverse transcriptase (RT)-PCR analysis demonstrated the expression of 5-lipoxygenase, 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase mRNA in B-CLL cells. Western blot analysis demonstrated a band corresponding to the molecular size of FLAP in the B-CLL cell membrane. Furthermore, MK886, the FLAP-binding cellular leukotriene biosynthesis inhibitor, reduced both LTB4 and 5-HETE formation. Immunocytochemistry showed that 5-lipoxygenase was mainly localized in the nuclei of non-activated B-CLL cells, tonsillar B-lymphocytes and monoclonal B-cells. In contrast, neither human peripheral T-lymphocytes nor Jurkat cells were stained. These results suggest that 5-lipoxygenase and its products function in the nucleus of B-lymphocytes.
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PMID:Studies on the regulation and localization of 5-lipoxygenase in human B-lymphocytes. 755 68

Differentiation of the human monocytic cell line Mono Mac 6 with calcitriol plus transforming growth factor-beta (TGFbeta) strongly induces 5-lipoxygenase (5-LO) mRNA and protein expression. The mechanism of 5-LO mRNA induction by these agents was investigated. Analysis of mature 5-LO mRNA by reverse-transcriptase-PCR gave a 42-fold induction which was not due to alterations in 5-LO half life and which was only in part due to an induction of gene transcription. There was an up to fivefold increase in 5-LO primary transcripts by TGFbeta and calcitriol, which could be inhibited by cycloheximide. No significant effects on 5-LO transcription were observed with TGFbeta or calcitriol alone. However, treatment of the cells with either calcitriol or TGFbeta and addition of the corresponding second inducer lead to an about fourfold induction of primary transcript levels. Addition of cycloheximide together with the second inducer inhibited only the TGFbeta but not the calcitriol effects, which indicated that there is a direct stimulation of 5-LO transcription by calcitriol in the presence of TGFbeta-induced proteins. In order to investigate the effects of TGFbeta/calcitriol on 5-LO transcript, elongation and maturation, the relative changes in immature and mature 5-LO RNA species were analyzed by reverse-transcription-PCR. Analysis of exons 1-5 indicated an about threefold induction of 5-LO transcripts by calcitriol/TGFbeta, respectively. However, when exons 6-14 were determined, more pronounced increments were found (3.6-12-fold). Selective analysis of polyadenylated and spliced 5-LO mRNA species gave a 42-fold induction. The effects of both TGFbeta and calcitriol on transcript elongation and maturation were inhibited by cycloheximide. Our results show that induction of 5-LO mRNA by calcitriol and TGFbeta is due to a modest increase in 5-LO gene transcription and to the stimulation of transcript elongation and maturation.
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PMID:Calcitriol and transforming growth factor-beta upregulate 5-lipoxygenase mRNA expression by increasing gene transcription and mRNA maturation. 966 Jan 80

The liver plays a major role in metabolism and elimination of leukotrienes (LT). It produces cysteinyl leukotrienes (cLT), and cLT have been implicated in hepatocellular toxicity in several models of lipopolysaccharide (LPS)-associated liver injury. However, the liver cell types responsible for cLT production are poorly defined, and the expression of the LT-synthesis enzymes, 5-lipoxygenase (5-LO) and LTC4 synthase (LTC4-S), in liver cells has never been demonstrated. The aim of the present study was to examine the ability of rat liver cells to produce cLT by determining whether hepatocytes, Kupffer cells, and sinusoidal endothelial cells express mRNA and enzyme activities of the LT-synthesis enzymes and whether expression is altered by LPS. 5-LO mRNA was expressed in whole liver, and expression was enhanced by LPS. Cell fractionation studies demonstrated that expression was present in Kupffer cells and sinusoidal endothelial cells, but not in hepatocytes. LTC4-S mRNA was detected in whole liver, hepatocytes, and sinusoidal endothelial cells, but not in Kupffer cells. Semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) showed that LPS increased LTC4-S expression in hepatocytes by a factor of 3 (n = 3; P < .03). LTC4-S enzyme activity in the microsomal fraction of hepatocytes was also increased from 0.52 +/- 0.13 to 1.90 +/- 0.66 nmol . mg protein-1 . 5 min-1 (n = 6; P < .015) after LPS treatment. These results indicate that hepatocytes do not possess the ability for de novo synthesis of cLT from arachidonic acid, but they may actively participate in cLT production by conjugation of LTA4 with glutathione to produce LTC4. LPS enhances LTC4-S expression in hepatocytes. This intrinsic cLT production may contribute to hepatocellular injury during inflammation.
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PMID:Expression and regulation of leukotriene-synthesis enzymes in rat liver cells. 979 12

Increased expression of 5-lipoxygenase (5LO) in pulmonary artery endothelial cells (PAECs) has been observed in disease states such as pulmonary hypertension and allergen challenge. To understand the function of endothelial 5LO, we examined the expression of this enzyme in normally cultured human PAECs and its characteristics when overexpressed. A small amount of 5LO message and protein was detected by reverse-transcriptase-mediated PCR (RT-PCR) and Western blotting in PAECs. Sequencing of the RT-PCR products that overlapped the entire coding region of 5LO mRNA indicated that the sequence of PAEC 5LO was identical with that of leucocyte 5LO. Incubation of the PAECs with A23187 and arachidonic acid led to a small production of 5-hydroxyeicosatetraenoic acid (5-HETE) (46-98 pmol/4x10(6) cells) but no leukotrienes. Overexpression of 5LO in PAECs by adenovirus-mediated gene transfer revealed that the enzyme was localized in the nucleus. Incubation of the transduced cells with A23187 (5 microM) caused the production of both 5LO products and downstream leukotrienes. The proportions of the produced leukotriene A(4) (LTA(4)) hydrolates (sum of 6-trans-LTB(4) and 12-epi-6-trans-LTB(4)), LTB(4) and cysteinyl leukotriene were approx. 17:14:10. cGMP production in the 5LO-transduced PAECs was decreased by 33+/-14% on stimulation with A23187. These results show that cultured PAECs express a minimal amount of 5LO, which can generate some 5-HETE, but not leukotrienes. However, increased expression of 5LO in PAECs can lead to the production of all downstream leukotrienes, which could potentially cause endothelial dysfunction in the pulmonary vasculature.
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PMID:Expression of 5-lipoxygenase in pulmonary artery endothelial cells. 1177 98

The 5-lipoxygenase (5-LOX) pathway is critical for pancreatic cancer cell growth and escape from apoptosis. Inhibition of 5-LOX blocks proliferation and induces apoptosis in human pancreatic cancer cells. However, the expression of 5-LOX and its downstream signaling pathway have not been investigated in human pancreatic adenocarcinoma. Reverse transcriptase-polymerase chain reaction revealed expression of 5-LOX mRNA in all pancreatic cancer cell lines tested including, PANC-1, AsPC-1, and MiaPaCa2 cells, but not in normal pancreatic ductal cells. The expression of 5-LOX protein in pancreatic cancer cell lines was demonstrated by Western blotting. Finally, 5-LOX up-regulation in human pancreatic cancer tissues was verified by intense positive staining in cancer cells by immunohistochemistry. Staining for the 5-LOX protein was particularly evident in the ductal components of the more differentiated tumors but not in ductal cells in normal pancreatic tissues from cadaver donors. Immunohistochemistry also revealed strong staining of cancer tissues with an antibody to the receptor of the downstream 5-LOX metabolite, leukotriene B(4). The current study demonstrated marked expression of 5-LOX and the leukotriene B(4) receptor in human pancreatic cancer tissues. These findings provide further evidence of up-regulation of this pathway in pancreatic cancer and that LOX inhibitors are likely to be valuable in the treatment of this dreadful disease.
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PMID:5-Lipoxygenase and leukotriene B(4) receptor are expressed in human pancreatic cancers but not in pancreatic ducts in normal tissue. 1216 67

Proliferation of fibroblasts is vital for adequate wound healing but is probably also involved in different hyperproliferative disorders such as atherosclerosis and cancer. The regeneration of tissue usually starts with coagulation, involving release of mitogenic and inflammatory factors from activated platelets. This study focuses on the role of eicosanoids in the proliferative effects of platelets on human fibroblasts. We show that the phospholipase A (2) inhibitor 7,7-dimethyl-5,8-eicosadienoic acid (DMDA), the combined cyclooxygenase (COX) and lipoxygenase (LOX) inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA) and the LOX inhibitor 5,8,11-eicosatriynoic acid (ETI) block the platelet-induced proliferation of serum starved subconfluent human fibroblasts. Anti-proliferative effects were also obtained by specific inhibition of 5-LOX with 5,6-dehydro arachidonic acid (5,6-dAA), whereas the 12-LOX inhibitor cinnamyl-3,4-dihydroxy- a -cyanocinnamate (CDC) did not affect the platelet-stimulated growth of fibroblasts. The expression of 5-LOX was analyzed by reverse-transcriptase-mediated PCR (RT-PCR), Western blotting and HPLC. 5-LOX message and protein was detected in fibroblasts but not in platelets. Incubation with platelets markedly increased, already after one hour, the expression of 5-LOX in the fibroblast culture. The increased 5-LOX activity was associated with an elevated level of the 5-LOX metabolite 5-hydroxyeicosatetraenoic acid (5-HETE) reaching its maximum after 1 - 2 hours of co-incubation of fibroblasts and platelets. The 5-HETE production was reduced by the inhibitors DMDA, ETYA and ETI. In conclusion, this study suggests that platelet-stimulated proliferation of fibroblasts is mediated by an increased 5-LOX activity, which supports recent findings indicating a crucial role for this enzyme in proliferative disorders such as atherosclerosis.
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PMID:Platelet-induced growth of human fibroblasts is associated with an increased expression of 5-lipoxygenase. 1708 Feb 23

Leukotrienes (LTs), metabolites of arachidonic acid through 5-lipoxygenase (5-LOX), have been known to play a role in leukocyte recruitment. However, the contribution of LTB4 to liver microcirculatory dysfunction during endotoxemia remains unknown. LTB4 receptor (BLT1) has been identified as a high-affinity receptor specific for LTB4. The present study was conducted to examine the roles of LTB4 and BLT1 in hepatic microcirculatory dysfunction elicited by LPS in mice. The number of leukocytes adhering to the endothelial cells of the hepatic microvessels and perfused sinusoids was determined 4 h after the administration of LPS (0.3 mg/kg, i.v.) to male C57Bl6 mice by in vivo microscopy. A 5-LOX synthase inhibitor, AA-861 (10 or 100 mg/kg, s.c.), was administered 30 min before LPS injection. BLT1 knockout mice were used to investigate whether LPS-induced hepatic microcirculatory dysfunction is mediated by BLT1 signaling. The expression of 5-LOX, intercellular adhesion molecule (ICAM) 1, and TNF-[alpha] in the liver was measured by real-time reverse-transcriptase-polymerase chain reaction. The administration of LPS caused significant accumulation of leukocyte adhesion to the hepatic microvessels and reduced sinusoidal perfusion when compared with saline-treated mice. The hepatic microcirculatory dysfunction elicited by LPS was minimized in mice pretreated with AA-861 or in BLT1 knockout mice. This was associated with the suppression of hepatic expression of 5-LOX, ICAM-1, and TNF-[alpha]. These findings suggest that the LTB4/BLT1 pathway mediates hepatic microcirculatory dysfunction by enhanced expression of ICAM-1 and TNF-[alpha] in a murine model of endotoxemia.
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PMID:Leukotriene B4/leukotriene B4 receptor pathway is involved in hepatic microcirculatory dysfunction elicited by endotoxin. 1800 32

Inflammatory diseases are major health concerns affecting millions of people worldwide. Aspilia africana has been used for centuries by many African communities in the treatment of a wide range of health conditions, including inflammatory diseases, osteoporosis, rheumatic pains, and wounds. Analysis of the phytochemical composition of A. africana indicated that the plant is rich in a broad range of secondary metabolites, including flavonoids, alkaloids, tannins, saponins, terpenoids, sterols, phenolic compounds, and glycosides. This explains the efficacy of the plant in treating inflammation-related diseases, as well as several other health conditions affecting different African communities. The mechanisms of action of the anti-inflammatory phytochemical compounds in A. africana include inhibition of a number of physiological processes involved in the inflammatory process and synthesis or action of proinflammatory enzymes. The phytochemicals enhance anti-inflammatory biological responses such as inhibition of a number of chemical mediators including histamine, prostanoids and kinins, 5-lipoxygenase. and cyclooxygenase and activation of phosphodiesterase and transcriptase. Currently used anti-inflammatory medications are associated with several disadvantages such as drug toxicity and iatrogenic reactions, thereby complicating the treatment process. The adverse effects related to the use of these conventional synthetic drugs have been the driving force behind consideration of natural remedies, and efforts are being made toward the development of anti-inflammatory agents based on natural extracts. A. africana is rich in secondary metabolites, and its use as a traditional medicine for treating inflammatory diseases has been validated through in vitro and in vivo studies. Therefore, the plant could be further explored for potential development of novel anti-inflammatory therapeutics.
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PMID:Ethnopharmacological Potential of Aspilia africana for the Treatment of Inflammatory Diseases. 3273 88