Investigation of a second 15S-lipoxygenase in humans and its expression in epithelial tissues

Fatty acids and their lipid mediators in the induction of cellular apoptosis in cancer cells

The oxygenation of polyunsaturated fatty acids such as arachidonic and linoleic acid through enzymes like lipoxygenases (LOXs) are common and often leads to the production of various bioactive lipids that are important both in acute inflammation and its resolution and thus in disease progression. Amongst the several isoforms of LOX that are expressed in mammals, 15-lipoxygenase (15-LOX) has shown to be crucial in the context of inflammation. Moreover, being expressed in cells of the immune system, as well as in epithelial cells; the enzyme has been shown to crosstalk with a number of important signalling pathways. Mounting evidences from recent reports suggest that 15-LOX has anti-cancer activities which are dependent or independent of its metabolites, and is executed through several downstream pathways like cGMP, PPAR, p53, p21 and NAG-1. However, it is still unclear whether the up-regulation of 15-LOX is associated with cancer cell apoptosis. Monoamine oxidase A (MAO-A), on the other hand, is a mitochondrial flavoenzyme which is believed to be involved in the pathogenesis of atherosclerosis and inflammation and in many other neurological disorders. MAO-A has also been reported as a potential therapeutic target in different types of cancers like prostate cancer, lung cancer etc. In this review, we discussed about the role of fatty acids and their lipid mediators in cancer cell apoptosis. Here we particularly focused on the contribution of oxidative enzymes like 15-LOX and MAO-A in mediating apoptosis in lung cancer cell after fatty acid induction.

A 12-lipoxygenase-Gpr31 signaling axis is required for pancreatic organogenesis in the zebrafish

12-Lipoxygenase (12-LOX) is a key enzyme in arachidonic acid metabolism, and alongside its major product, 12-HETE, plays a key role in promoting inflammatory signaling during diabetes pathogenesis. Although 12-LOX is a proposed therapeutic target to protect pancreatic islets in the setting of diabetes, little is known about the consequences of blocking its enzymatic activity during embryonic development. Here, we have leveraged the strengths of the zebrafish-genetic manipulation and pharmacologic inhibition-to interrogate the role of 12-LOX in pancreatic development. Lipidomics analysis during zebrafish development demonstrated that 12-LOX-generated metabolites of arachidonic acid increase sharply during organogenesis stages, and that this increase is blocked by morpholino-directed depletion of 12-LOX. Furthermore, we found that either depletion or inhibition of 12-LOX impairs both exocrine pancreas growth and unexpectedly, the generation of insulin-producing β cells. We demonstrate that morpholino-mediated knockdown of GPR31, a purported G-protein-coupled receptor for 12-HETE, largely phenocopies both the depletion and the inhibition of 12-LOX. Moreover, we show that loss of GPR31 impairs pancreatic bud fusion and pancreatic duct morphogenesis. Together, these data provide new insight into the requirement of 12-LOX in pancreatic organogenesis and islet formation, and additionally provide evidence that its effects are mediated via a signaling axis that includes the 12-HETE receptor GPR31.

Preferential Generation of 15-HETE-PE Induced by IL-13 Regulates Goblet Cell Differentiation in Human Airway Epithelial Cells

Type 2-associated goblet cell hyperplasia and mucus hypersecretion are well known features of asthma. 15-Lipoxygenase-1 (15LO1) is induced by the type 2 cytokine IL-13 in human airway epithelial cells (HAECs) in vitro and is increased in fresh asthmatic HAECs ex vivo. 15LO1 generates a variety of products, including 15-hydroxyeicosatetraenoic acid (15-HETE), 15-HETE-phosphatidylethanolamine (15-HETE-PE), and 13-hydroxyoctadecadienoic acid (13-HODE). In this study, we investigated the 15LO1 metabolite profile at baseline and after IL-13 treatment, as well as its influence on goblet cell differentiation in HAECs. Primary HAECs obtained from bronchial brushings of asthmatic and healthy subjects were cultured under air-liquid interface culture supplemented with arachidonic acid and linoleic acid (10 μM each) and exposed to IL-13 for 7 days. Short interfering RNA transfection and 15LO1 inhibition were applied to suppress 15LO1 expression and activity. IL-13 stimulation induced expression of 15LO1 and preferentially generated 15-HETE-PE in vitro, both of which persisted after removal of IL-13. 15LO1 inhibition (by short interfering RNA and chemical inhibitor) decreased IL-13-induced forkhead box protein A3 (FOXA3) expression and enhanced FOXA2 expression. These changes were associated with reductions in both mucin 5AC and periostin. Exogenous 15-HETE-PE stimulation (alone) recapitulated IL-13-induced FOXA3, mucin 5AC, and periostin expression. The results of this study confirm the central importance of 15LO1 and its primary product, 15-HETE-PE, for epithelial cell remodeling in HAECs.

Induction of apoptosis by Trichostatin A in human breast cancer cell lines: involvement of 15-Lox-1

15-Lipoxygenase-1 (15-Lox-1) is a key enzyme mediating oxidative metabolism of polyunsaturated fatty acids and has attracted considerable interest as a potential target for the induction of apoptosis in cancer cells. Knowledge of relationship between 15-Lox-1 and histone deacetylase inhibitors is lacking in the breast cancer. This study is aimed to investigate the role of Trichostatin A (TSA) and 13(S)-HODE, as a metabolite of 15-Lox-1, in the regulation of breast cancer cell growth. The cytotoxic effect of TSA, as a potent HDAC inhibitor, was measured using MTT assay. Annexin V-FITC and PI staining were performed to detect apoptosis and cell cycle distribution using Flow cytometry. The role of 15-Lox-1 in the regulation of cell growth was assessed by 15-Lox-1 inhibitor and the level of 15-Lox-1 metabolite was measured to determine 15-Lox activity after treatment by TSA. The results demonstrated that TSA induced cell growth inhibition via 15-Lox-1, in a dose- and time-dependent manner, and subsequently accompanied by the cell cycle arrest and induction of apoptosis. Moreover, growth inhibitory effect of TSA was associated with the elevation of 15-Lox-1 metabolite (13(S)-HODE). This study provided evidences that the inhibitory effect of TSA on the breast cancer cell growth occurs via the induction of 15-Lox-1 activity and 13(S)-HODE production. Our findings underline the possible role of 15-Lox-1/13(S)-HODE pathway as a promising molecular approach for the induction of apoptosis in breast cancer cells.

15-lipoxygenase metabolites of docosahexaenoic acid inhibit prostate cancer cell proliferation and survival

A 15-LOX, it is proposed, suppresses the growth of prostate cancer in part by converting arachidonic, eicosatrienoic, and/or eicosapentaenoic acids to n-6 hydroxy metabolites. These metabolites inhibit the proliferation of PC3, LNCaP, and DU145 prostate cancer cells but only at ≥1-10 µM. We show here that the 15-LOX metabolites of docosahexaenoic acid (DHA), 17-hydroperoxy-, 17-hydroxy-, 10,17-dihydroxy-, and 7,17-dihydroxy-DHA inhibit the proliferation of these cells at ≥0.001, 0.01, 1, and 1 µM, respectively. By comparison, the corresponding 15-hydroperoxy, 15-hydroxy, 8,15-dihydroxy, and 5,15-dihydroxy metabolites of arachidonic acid as well as DHA itself require ≥10-100 µM to do this. Like DHA, the DHA metabolites a) induce PC3 cells to activate a peroxisome proliferator-activated receptor-γ (PPARγ) reporter, express syndecan-1, and become apoptotic and b) are blocked from slowing cell proliferation by pharmacological inhibition or knockdown of PPARγ or syndecan-1. The DHA metabolites thus slow prostate cancer cell proliferation by engaging the PPARγ/syndecan-1 pathway of apoptosis and thereby may contribute to the prostate cancer-suppressing effects of not only 15-LOX but also dietary DHA.

Omega-3 Fatty Acids and PPARgamma in Cancer

Omega-3 (or n-3) polyunsaturated fatty acids (PUFAs) and their metabolites are natural ligands for peroxisome proliferator receptor activator (PPAR)gamma and, due to the effects of PPARgamma on cell proliferation, survival, and differentiation, are potential anticancer agents. Dietary intake of omega-3 PUFAs has been associated with a reduced risk of certain cancers in human populations and in animal models. In vitro studies have shown that omega-3 PUFAs inhibit cell proliferation and induce apoptosis in cancer cells through various pathways but one of which involves PPARgamma activation. The differential activation of PPARgamma and PPARgamma-regulated genes by specific dietary fatty acids may be central to their distinct roles in cancer. This review summarizes studies relating PUFAs to PPARgamma and cancer and offers a new paradigm relating an n-3 PUFA through PPARgamma to the expression of the cell surface proteoglycan, syndecan-1, and to the death of cancer cells.

AmbLOXe--an epidermal lipoxygenase of the Mexican axolotl in the context of amphibian regeneration and its impact on human wound closure in vitro

OBJECTIVE

The Mexican axolotl (Ambystoma mexicanum) is a well-characterized example for intrinsic regeneration. As lipoxygenase signaling is of crucial importance to scarless mammalian wound healing, we postulated that lipoxygenases might be expressed during amphibian regeneration and they might also influence human cells under appropriate conditions. In this study we identified an amphibian lipoxygenase and evaluated its impact on human cells in an in vitro wound model.

METHODS

cDNA encoding for amphibian epidermal lipoxygenase (AmbLOXe) was polymerase chain reaction amplified and sequenced followed by phylogenic classification based on T-coffee alignment. Distribution of AmbLOXe was examined in various Ambystoma tissues, using polymerase chain reaction and in situ hybridization. Lipoxgenase influence was investigated using an outgrowth model of amphibian epidermal cells. Human osteosarcoma, as well as keratinocyte cell lines expressing AmbLOXe, were tested concerning in vitro wound closure in a monolayer scratch model.

RESULTS

We isolated AmbLOXe from Ambystoma limb bud blastema identified as a homologue of human epidermal lipoxygenase. Amphibian epidermal lipoxygenase is expressed in Axolotl limb blastema and in epidermal cells which show decreased cell migration and proliferation rates when treated with LOX inhibitors. Furthermore, human osteosarcoma and keratinocyte cells showed increased rates of cell migration if transfected with AmbLOXe.

CONCLUSION

In this study, AmbLOXe, a new effector of amphibian regeneration is described. In consideration of the presented data, AmbLOXe is important for amphibian epidermal cell proliferation and migration. As AmbLOXe expressing human osteosarcoma and keratinocyte cell lines showed increased rates of in vitro wound closure, an influence of amphibian mediators on human cells could be described for the first time.

Adenoviral expression of 15-lipoxygenase-1 in rabbit aortic endothelium: role in arachidonic acid-induced relaxation

Endothelium-dependent vasorelaxation of the rabbit aorta is mediated by either nitric oxide (NO) or arachidonic acid (AA) metabolites from cyclooxygenase (COX) and 15-lipoxygenase (15-LO) pathways. 15-LO-1 metabolites of AA, 11,12,15-trihydroxyeicosatrienoic acid (THETA), and 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) cause concentration-dependent relaxation. We tested the hypothesis that in the 15-LO pathway of AA metabolism, 15-LO-1 is sufficient and is the rate-limiting step in inducing relaxations in rabbit aorta. Aorta and rabbit aortic endothelial cells were treated with adenoviruses containing human 15-LO-1 cDNA (Ad-15-LO-1) or beta-galactosidase (Ad-beta-Gal). Ad-15-LO-1-transduction increased the expression of a 75-kDa protein corresponding to 15-LO-1, detected by immunoblotting with an anti-human15-LO-1 antibody, and increased the production of HEETA and THETA from [(14)C]AA. Immunohistochemical studies on Ad-15-LO-1-transduced rabbit aorta showed the presence of 15-LO-1 in endothelial cells. Ad-15-LO-1-treated aortic rings showed enhanced relaxation to AA (max 31.7 +/- 3.2%) compared with Ad-beta-Gal-treated (max 12.7 +/- 3.2%) or control nontreated rings (max 13.1 +/- 1.6%) (P < 0.01). The relaxations in Ad-15-LO-1-treated aorta were blocked by the 15-LO inhibitor cinnamyl-3,4-dihydroxy-a-cyanocinnamate. Overexpression of 15-LO-1 in the rabbit aortic endothelium is sufficient to increase the production of the vasodilatory HEETA and THETA and enhance the relaxations to AA. This confirms the role of HEETA and THETA as endothelium-derived relaxing factors.

Reticulocyte 15-Lipoxygenase-I Is Important in Acetylcholine-Induced Endothelium-Dependent Vasorelaxation in Rabbit Aorta

OBJECTIVE

Aortic 15-lipoxygenase (15-LO) metabolizes arachidonic acid (AA) to 15-hydroperoxyeicosatetraenoic acid, which is then converted to the vasodilators 15-hydroxy-11,12-epoxyeicosatrienoic acid and 11,12,15-trihydroxyeicosatrienoic acid. These metabolites contribute to endothelium-dependent relaxations of rabbit aorta to AA and acetylcholine. We investigated the identity of rabbit aortic 15-LO and studied its importance in the regulation of vascular tone.

METHODS AND RESULTS

RT-PCR using 12-lipoxygenase/15-LO specific primers resulted in a 572-bp product with a sequence identical to 15-LO-I from rabbit aorta. A RT-PCR/restriction digest strategy excluded expression of 12-lipoxygenase. Immunoblotting revealed 15-LO-I expression in rabbit endothelial and smooth muscle cells. Aortic homogenates and cytosolic fractions metabolize AA to 15(S)-hydroxyeicosatetraenoic acid and linoleic acid to 13(S)-hydroxyoctadecadienoic acid. This activity was blocked by LO inhibitors. The kinetic characteristics (Michaelis constant of aortic 15-LO is 2.2+/-0.3 micromol/L for AA and 23.5+/-3.3 micromol/L for linoleic acid) of aortic 15-LO were similar to those of the purified 15-LO-I. An antisense oligonucleotide inhibited 15-LO-I expression in rabbit aorta. Indomethacin and nitro-L-arginine-resistant relaxations to acetylcholine were inhibited by 15-LO-I antisense oligonucleotide but not by the scrambled oligonucleotide.

CONCLUSIONS

15-LO-I is expressed in rabbit aortic endothelium and is important in endothelium-dependent regulation of vascular tone.

Enzyme association with PPARγ: evidence of a new role for 15-lipoxygenase type 2

Fatty acids have historically important structural roles in contributing to epidermal barrier function and therefore cutaneous health. Their metabolism to bioactive compounds is often up-regulated in response to cutaneous toxins thus providing them with functional roles. Some metabolites of arachidonic acid, such as 15S-hydroxyeicosatetraenoic acid (HETE), also serve functional roles as direct ligands for peroxisome proliferator activated receptors (PPARs). 15S-HETE, produced by 15-lipoxygenase type 2 (15-LOX-2), is an endogenous ligand for PPARgamma. This report demonstrates epidermal keratinocyte expression of both 15-LOX-2 and PPARgamma and provides evidence for a relationship beyond that of ligand-producer and -user, namely in vivo association of the two proteins at the molecular level making the enzyme a candidate nuclear receptor coregulator. Such close physical approximation of the 15S-HETE-producing enzyme and PPARgamma could potentiate the receptor response to a short-lived ligand. 15-LOX-2 may exemplify a class of enzymatically active nuclear receptor coactivator proteins distinct from those previously described but sharing their ability to promote expression from nuclear receptor-regulated promoters.

Approaches to understanding the importance and clinical implications of peroxisome proliferator-activated receptor gamma (PPARgamma) signaling in prostate cancer

The development and maintenance of the prostate are dependent upon a complex series of interactions occurring between the epithelial and stromal tissues (Hayward and Cunha [2000]: Radiol. Clin. N. Am. 38:1-14). During the process of prostatic carcinogenesis, there are progressive changes in the interactions of the nascent tumor with its surrounding stroma and extracellular matrix. These include the development of a reactive stromal phenotype and the possible promotion, by stromal cells, of epithelial proliferation and loss of differentiated function (Hayward et al. [1996]: Ann. N. Y. Acad. Sci. 784:50-62; Grossfeld et al. [1998]: Endocr. Related Cancer 5:253-270; Rowley [1998]: Cancer Metastasis Rev. 17:411-419; Tuxhorn et al. [2002]: Clin. Cancer Res. 8:2912-2923). Many molecules play an as yet poorly defined role in establishing and maintaining a growth quiescent glandular structure in the adult. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a candidate regulator of prostatic epithelial differentiation and may play a role in restricting epithelial proliferation. PPARgamma agonists are relatively non-toxic and have been used with limited success to treat some prostate cancer patients. We would propose that a more complete understanding of PPARgamma biology, particularly in the context of appropriate stromal-epithelial and host-tumor interactions would allow for the selection of patients most likely to benefit from this line of therapy. In particular, it seems reasonable to suggest that the patients most likely to benefit may be those with relatively indolent low stage disease for whom this line of therapy could be a useful additive to watchful waiting.

Gene expression and immunolocalization of 15-lipoxygenase isozymes in the airway mucosa of smokers with chronic bronchitis

15-lipoxygenase (15-LO) has been implicated in the inflammation of chronic bronchitis (CB), but it is unclear which of its isoforms, 15-LOa or 15-LOb, is primarily involved. To detect 15-LO gene (mRNA) and protein expression, we have applied in situ hybridization (ISH) and immunohistochemistry (IHC), respectively, to bronchial biopsies obtained from 7 healthy nonsmokers (HNS), 5 healthy smokers (HS), and 8 smokers with CB, and additionally include the airways of lungs resected from 11 asymptomatic smokers (AS) and 11 smokers with CB. Compared with HNS, biopsies in CB demonstrated increased numbers of 15-LOa mRNA+ cells (median: HNS = 31.3/mm(2) versus CB = 84.9/mm(2), P < 0.01) and protein+ cells (HNS = 2.9/mm(2) versus CB = 32.1/mm(2), P < 0.01). The HS group also showed a significant increase in protein+ cells (HNS = 2.9/mm(2) versus HS = 14/mm(2), P < 0.05). In the resected airways, 15-LOa protein+ cells in the submucosal glands of the CB group were more numerous than in the AS group (AS = 33/mm(2) versus CB = 208/mm(2); P < 0.001). 15-LOa mRNA+ and protein+ cells consistently outnumbered 15-LOb by approximately 7- and 5-fold, respectively (P < 0.01). Quantitative reverse transcriptase polymerase chain reaction of complementary biopsies confirmed the increased levels of 15-LOa in CB compared with that in either HNS or HS (P < 0.05). There was no difference between the subject groups with respect to 15-LOb expression. The numbers of cells expressing mRNA for 15-LOa in CB showed a positive association with those expressing interleukin (IL)-4 mRNA (r = 0.80; P < 0.01). We conclude that the upregulation of 15-LO activity in the airways of HS and of smokers with CB primarily involves the 15-LOa isoform: the functional consequences of its association the upregulation of IL-4 in chronic bronchitis requires further study.

15-Lipoxygenase-2 expression in benign and neoplastic sebaceous glands and other cutaneous adnexa

15-Lipoxygenase-2 has a limited tissue distribution in epithelial tissues, with mRNA detected in skin, cornea, lung, and prostate. It was originally cloned from human hair rootlets. In this study the distribution of 15-lipoxygenase-2 was characterized in human skin using immunohistochemistry and in situ hybridization. Strong uniform 15-lipoxygenase-2 in situ hybridization (n = 6) and immunostaining (n = 16) were observed in benign cutaneous sebaceous glands, with expression in differentiated secretory cells. Strong 15-lipoxygenase-2 immunostaining was also observed in secretory cells of apocrine and eccrine glands. Variable reduced immunostaining was observed in skin-derived sebaceous neoplasms (n = 8). In the eyelid, Meibomian glands were uniformly negative for 15-lipoxygenase-2 in all cases examined (n = 9), and sebaceous carcinomas apparently derived from Meibomian glands were also negative (n = 12). The mechanisms responsible for differential expression in cutaneous sebaceous vs eyelid Meibomian glands remain to be established. In epidermis, positive immunostaining was observed in the basal cell layer in normal skin, whereas five examined basal cell carcinomas were negative. Thus, the strongest 15-lipoxygenase-2 expression is in the androgen regulated secretory cells of sebaceous, apocrine, and eccrine glands. This compares with the prostate, in which 15-lipoxygenase-2 is expressed in differentiated prostate secretory cells (and reduced in the majority of prostate adenocarcinomas). The product of 15-lipoxygenase-2, 15-hydroxyeicosatetraenoic acid, may be a ligand for the nuclear receptor peroxisome proliferator activated receptor-gamma, which is expressed in sebocytes, and contribute to secretory differentiation in androgen regulated tissues such as prostate and sebaceous glands.

A Gene Cluster Encoding Human Epidermis-type Lipoxygenases at Chromosome 17p13.1: Cloning, Physical Mapping, and Expression

Epidermis-type lipoxygenases, a distinct subclass within the multigene family of mammalian lipoxygenases (LOX), comprise recently discovered novel isoenzymes isolated from human and mouse skin including human 15-LOX-2, human and mouse 12R-LOX, mouse 8S-LOX, and mouse e-LOX-3. We have isolated the human homologue of mouse e-LOX-3. The cDNA of 3362 bp encodes a 711-amino-acid protein displaying 89% sequence identity with the mouse protein and exhibiting the same unusual structural feature, i.e., an extra segment of 41 amino acids, which can be located beyond the N-terminal beta-barrel domain at the surface of the C-terminal catalytic domain. The gene encoding e-LOX-3, ALOXE3, was found to be part of a gene cluster of approximately 100 kb on human chromosome 17p13.1 containing in addition the 12R-LOX gene, ALOX12B, the 15-LOX-2 gene, ALOX15B, and a novel 15-LOX pseudogene, ALOX15P. ALOXE3 and ALOX12B are arranged in a head-to-tail fashion separated by 8.5 kb. The genes are split into 15 exons and 14 introns spanning 22 and 15 kb, respectively. ALOX15P was found on the opposite DNA strand directly adjacent to the 3'-untranslated region of ALOX12B. ALOX15B is located in the same orientation 25 kb downstream of ALOX12B, and is composed of 14 exons and 13 introns spanning a total of 9.7 kb of genomic sequence. RT-PCR analysis demonstrated a predominant expression of ALOXE3, ALOX12B, and ALOX15B in skin.