Lipoxygenase metabolites of arachidonic and linoleic acids modulate the adhesion of tumor cells to endothelium via regulation of protein kinase C

Dynamic Opioid Receptor Regulation in the Periphery

Opioids serve a vital role in the current analgesic array of treatment options. They are useful in acute instances involving severe pain associated with trauma, surgery, and terminal diseases such as cancer. In the past three decades, multiple receptor isoforms and conformations have been reported throughout literature. Most of these studies conducted systemic analyses of opioid receptor function, often generalizing findings from receptor systems in central nervous tissue or exogenously expressing immortalized cell lines as common mechanisms throughout physiology. However, a culmination of innovative experimental data indicates that opioid receptor systems are differentially modulated depending on their anatomic expression profile. Importantly, opioid receptors expressed in the peripheral nervous system undergo regulation uncommon to similar receptors expressed in central nervous system tissues. This distinctive characteristic begs one to question whether peripheral opioid receptors maintain anatomically unique roles, and whether they may serve an analgesic advantage in providing pain relief without promoting addiction.

Emerging biopharmaceuticals from bioactive peptides derived from marine organisms

Biologically active natural products are spontaneous medicinal entrants, which encourage synthetic access for enhancing and supporting drug discovery and development. Marine bioactive peptides are considered as a rich source of natural products that may provide long-term health, in addition to many prophylactic and curative medicinal drug treatments. The large literature concerning marine peptides has been collected, which shows high potential of nutraceutical and therapeutic efficacy encompassing wide spectra of bioactivities against a number of infection-causing agents. Their antimicrobial, antimalarial, antitumor, antiviral, and cardioprotective actions have achieved the attention of the pharmaceutical industry toward new design of drug formulations, for treatment and prevention of several infections. However, the mechanism of action of many peptide molecules has been still untapped. So in this regard, this paper reviews several peptide compounds by which they interfere with human pathogenesis. This knowledge is one of the key tools to be understood especially for the biotransformation of biomolecules into targeted medicines. The fact that different diseases have the capability to fight at different sites inside the body can lead to a new wave of increasing the chances to produce targeted medicines.

Marine Sponges as a Drug Treasure

Marine sponges have been considered as a drug treasure house with respect to great potential regarding their secondary metabolites. Most of the studies have been conducted on sponge's derived compounds to examine its pharmacological properties. Such compounds proved to have antibacterial, antiviral, antifungal, antimalarial, antitumor, immunosuppressive, and cardiovascular activity. Although, the mode of action of many compounds by which they interfere with human pathogenesis have not been clear till now, in this review not only the capability of the medicinal substances have been examined in vitro and in vivo against serious pathogenic microbes but, the mode of actions of medicinal compounds were explained with diagrammatic illustrations. This knowledge is one of the basic components to be known especially for transforming medicinal molecules to medicines. Sponges produce a different kind of chemical substances with numerous carbon skeletons, which have been found to be the main component interfering with human pathogenesis at different sites. The fact that different diseases have the capability to fight at different sites inside the body can increase the chances to produce targeted medicines.

Metabolomic analysis of human cirrhosis, hepatocellular carcinoma, non-alcoholic fatty liver disease and non-alcoholic steatohepatitis diseases

Metabolome analysis is used to evaluate the characteristics and interactions of low molecular weight metabolites under a specific set of conditions. In cirrhosis, hepatocellular carcinoma, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatotic hepatitis (NASH) the liver does not function thoroughly due to long-term damage. Unfortunately the early detection of cirrhosis, HCC, NAFLD and NASH is a clinical problem and determining a sensitive, specific and predictive novel method based on biomarker discovery is an important task. On the other hand, metabolomics has been reported as a new and powerful technology in biomarker discovery and dynamic field that cause global comprehension of system biology. In this review, it has been collected a heterogeneous set of metabolomics published studies to discovery of biomarkers in researches to introduce diagnostic biomarkers for early detection and the choice of patient-specific therapies.

Integrated metabolomic profiling of hepatocellular carcinoma in hepatitis C cirrhosis through GC/MS and UPLC/MS-MS

BACKGROUND & AIMS

The metabolic pathway disturbances associated with hepatocellular carcinoma (HCC) remain unsatisfactorily characterized. Determination of the metabolic alterations associated with the presence of HCC can improve our understanding of the pathophysiology of this cancer and may provide opportunities for improved disease monitoring of patients at risk for HCC development. To characterize the global metabolic alterations associated with HCC arising from hepatitis C (HCV)-associated cirrhosis using an integrated non-targeted metabolomics methodology employing both gas chromatography/mass spectrometry (GC/MS) and ultrahigh-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPLC/MS-MS).

METHODS

The global serum metabolomes of 30 HCC patients, 27 hepatitis C cirrhosis disease controls and 30 healthy volunteers were characterized using a metabolomics approach that combined two metabolomics platforms, GC/MS and UPLC/MS-MS. Random forest, multivariate statistics and receiver operator characteristic analysis were performed to identify the most significantly altered metabolites in HCC patients vs. HCV-cirrhosis controls and which therefore exhibited a close association with the presence of HCC.

RESULTS

Elevated 12-hydroxyeicosatetraenoic acid (12-HETE), 15-HETE, sphingosine, γ-glutamyl oxidative stress-associated metabolites, xanthine, amino acids serine, glycine and aspartate, and acylcarnitines were strongly associated with the presence of HCC. Elevations in bile acids and dicarboxylic acids were highly correlated with cirrhosis.

CONCLUSIONS

Integrated metabolomic profiling through GC/MS and UPLC/MS-MS identified global metabolic disturbances in HCC and HCV-cirrhosis. Aberrant amino acid biosynthesis, cell turnover regulation, reactive oxygen species neutralization and eicosanoid pathways may be hallmarks of HCC. Aberrant dicarboxylic acid metabolism, enhanced bile acid metabolism and elevations in fibrinogen cleavage peptides may be signatures of cirrhosis.

Identification of the orphan G protein-coupled receptor GPR31 as a receptor for 12-(S)-hydroxyeicosatetraenoic acid

Hydroxy fatty acids are critical lipid mediators involved in various pathophysiologic functions. We cloned and identified GPR31, a plasma membrane orphan G protein-coupled receptor that displays high affinity for the human 12-lipoxygenase-derived product 12-(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE). Thus, GPR31 is named 12-(S)-HETE receptor (12-HETER) in this study. The cloned 12-HETER demonstrated high affinity binding for 12-(S)-[(3)H]HETE (K(d) = 4.8 ± 0.12 nm). Also, 12-(S)-HETE efficiently and selectively stimulated GTPγS coupling in the membranes of 12-HETER-transfected cells (EC(50) = 0.28 ± 1.26 nm). Activating GTPγS coupling with 12-(S)-HETE proved to be both regio- and stereospecific. Also, 12-(S)-HETE/12-HETER interactions lead to activation of ERK1/2, MEK, and NFκB. Moreover, knocking down 12-HRTER specifically inhibited 12-(S)-HETE-stimulated cell invasion. Thus, 12-HETER represents the first identified high affinity receptor for the 12-(S)-HETE hydroxyl fatty acids.

Elevated dietary linoleic acid increases gastric carcinoma cell invasion and metastasis in mice

BACKGROUND

Dietary (n-6)-polyunsaturated fatty acids influence cancer development, but the mechanisms have not been well characterised in gastric carcinoma.

METHODS

We used two in vivo models to investigate the effects of these common dietary components on tumour metastasis. In a model of experimental metastasis, immunocompromised mice were fed diets containing linoleic acid (LA) at 2% (LLA), 8% (HLA) or 12% (VHLA) by weight and inoculated intraperitoneally (i.p.) with human gastric carcinoma cells (OCUM-2MD3). To model spontaneous metastasis, OCUM-2MD3 tumours were grafted onto the stomach walls of mice fed with the different diets. In in vitro assays, we investigated invasion and ERK phosphorylation of OCUM-2MD3 cells in the presence or absence of LA. Finally, we tested whether a cyclooxygenase (COX) inhibitor, indomethacin, could block peritoneal metastasis in vivo.

RESULTS

Both the HLA and VHLA groups showed increased incidence of tumour nodules (LA: 53%; HLA: 89%; VHLA: 100%; P<0.03); the VHLA group also displayed increased numbers of tumour nodules and higher total volume relative to LLA group in experimental metastasis model. Both liver invasion (78%) and metastasis to the peritoneal cavity (67%) were more frequent in VHLA group compared with the LLA group (22% and 11%, respectively; P<0.03) in spontaneous metastasis model. We also found that the invasive ability of these cells is greatly enhanced when exposed to LA in vitro. Linoleic acid also increased invasion of other scirrhous gastric carcinoma cells, OCUM-12, NUGC3 and MKN-45. Linoleic acid effect on OCUM-2MD3 cells seems to be dependent on phosphorylation of ERK. The data suggest that invasion and phosphorylation of ERK were dependent on COX. Indomethacin decreased the number of tumours and total tumour volume in both LLA and VHLA groups. Finally, COX-1, which is known to be an important enzyme in the generation of bioactive metabolites from dietary fatty acids, appears to be responsible for the increased metastatic behaviour of OCUM-2MD3 cells in the mouse model.

CONCLUSION

Dietary LA stimulates invasion and peritoneal metastasis of gastric carcinoma cells through COX-catalysed metabolism and activation of ERK, steps that compose pathway potentially amenable to therapeutic intervention.

Immunohistochemical detection of 13(R)-hydroxyoctadecadienoic acid in atherosclerotic plaques of human carotid arteries using a novel specific antibody

13-Hydroxyoctadecadienoic acid (13-HODE) is a major component of oxidized low density lipoprotein (OxLDL), which has been shown to have a crucial role in atherogenesis. Of the 13-HODE stereoisomers, 13(S)-HODE and 13(R)-HODE, little is known about the latter in contrast to the former. To detect 13(R)-HODE in atherosclerotic lesions, we prepared a mouse monoclonal antibody against 13(R)-HODE. Competitive enzyme-linked immunosorbent assay clarified the selective reaction of a clone mAb 13H1 with both free and bovine serum albumin-conjugated forms of 13(R)-HODE but not other oxidized lipids including 13(S)-HODE. Immunohistochemical analysis revealed the colocalization of 13(R)-HODE immunoreactivity with the OxLDL marker oxidized phophatidylcholine immunoreactivity in vascular endothelial cells, macrophages and migrating vascular smooth muscle cells in atherosclerotic plaques of human carotid arteries. The present results provide in vivo evidence for the formation of 13(R)-HODE in atherosclerotic lesions of carotid arteries.

Role of 12-lipoxygenase in hypoxia-induced rat pulmonary artery smooth muscle cell proliferation

The 12-lipoxygenase (12-LO) pathway of arachidonic acid metabolism stimulates cell growth and metastasis of various cancer cells and the 12-LO metabolite, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], enhances proliferation of aortic smooth muscle cells (SMCs). However, pulmonary vascular effects of 12-LO have not been previously studied. We sought evidence for a role of 12-LO and 12(S)-HETE in the development of hypoxia-induced pulmonary hypertension. We found that 12-LO gene and protein expression is elevated in lung homogenates of rats exposed to chronic hypoxia. Immunohistochemical staining with a 12-LO antibody revealed intense staining in endothelial cells of large pulmonary arteries, SMCs (and possibly endothelial cells) of medium and small-size pulmonary arteries and in alveolar walls of hypoxic lungs. 12-LO protein expression was increased in hypoxic cultured rat pulmonary artery SMCs. 12(S)-HETE at concentrations as low as 10(-5) microM stimulated proliferation of pulmonary artery SMCs. 12(S)-HETE induced ERK 1/ERK 2 phosphorylation but had no effect on p38 kinase expression as assessed by Western blotting. 12(S)-HETE-stimulated SMC proliferation was blocked by the MEK inhibitor PD-98059, but not by the p38 MAPK inhibitor SB-202190. Hypoxia (3%)-stimulated pulmonary artery SMC proliferation was blocked by both U0126, a MEK inhibitor, and baicalein, an inhibitor of 12-LO. We conclude that 12-LO and its product, 12(S)-HETE, are important intermediates in hypoxia-induced pulmonary artery SMC proliferation and may participate in hypoxia-induced pulmonary hypertension.

15(S)-Lipoxygenase-2 Mediates Arachidonic Acid-stimulated Adhesion of Human Breast Carcinoma Cells through the Activation of TAK1, MKK6, and p38 MAPK

The dietary cis-polyunsaturated fatty acid, arachidonic acid, stimulates adhesion of metastatic human breast carcinoma cells (MDA-MB-435) to the extracellular matrix, but the molecular mechanisms by which fatty acids modify the behavior of these cells are unclear. Exposure to arachidonic acid activates multiple signaling pathways. Activation of p38 mitogen-activated protein kinase (p38 MAPK) is required for increased cell adhesion to type IV collagen, and this activation is sensitive to inhibitors of lipoxygenases, suggesting a requirement for arachidonic acid metabolism. The goals of the current study were to identify the one or more key metabolites of arachidonic acid that are responsible for activation of p38 MAPK and to elucidate the upstream kinases that lead to p38 MAPK activation. High performance liquid chromatographic analysis revealed that MDA-MB-435 cells metabolize exogenous arachidonic acid predominantly to 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE). Immunoblot analysis with antibodies specific to 15(S)-lipoxygenase-1 (LOX-1) and 15(S)-lipoxygenase-2 (LOX-2) demonstrated the expression of 15-LOX-2, but not 15-LOX-1, in these tumor cells. A LOX inhibitor, nordihydroguaiaretic acid, attenuated production of 15(S)-HETE and inhibited the phosphorylation of p38 MAPK following exposure to arachidonic acid. In contrast, overexpression of LOX-2 sensitized the cells to the addition of arachidonic acid, leading to increased activation of p38 MAPK. Addition of exogenous 15(S)-HETE to MDA-MB-435 cells stimulated cell adhesion to type IV collagen and activated the p38 MAPK pathway, including the upstream kinases transforming growth factor-beta1-activated protein kinase-1 (TAK1) and MAPK kinase 6. Transfection of these cells with a dominant negative form of TAK1 blocked arachidonic acid-stimulated p38 MAPK phosphorylation. These data demonstrate that 15(S)-LOX-2 generation of 15(S)-HETE activates specific growth factor receptor-related signaling pathways, thereby initiating signal transduction events leading to increased cell adhesion to the extracellular matrix.

Marine sponges as pharmacy

Marine sponges have been considered as a gold mine during the past 50 years, with respect to the diversity of their secondary metabolites. The biological effects of new metabolites from sponges have been reported in hundreds of scientific papers, and they are reviewed here. Sponges have the potential to provide future drugs against important diseases, such as cancer, a range of viral diseases, malaria, and inflammations. Although the molecular mode of action of most metabolites is still unclear, for a substantial number of compounds the mechanisms by which they interfere with the pathogenesis of a wide range of diseases have been reported. This knowledge is one of the key factors necessary to transform bioactive compounds into medicines. Sponges produce a plethora of chemical compounds with widely varying carbon skeletons, which have been found to interfere with pathogenesis at many different points. The fact that a particular disease can be fought at different points increases the chance of developing selective drugs for specific targets.

The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina

In this work we advance the hypothesis that omega-3 (omega-3) long-chain polyunsaturated fatty acids (LCPUFAs) exhibit cytoprotective and cytotherapeutic actions contributing to a number of anti-angiogenic and neuroprotective mechanisms within the retina. omega-3 LCPUFAs may modulate metabolic processes and attenuate effects of environmental exposures that activate molecules implicated in pathogenesis of vasoproliferative and neurodegenerative retinal diseases. These processes and exposures include ischemia, chronic light exposure, oxidative stress, inflammation, cellular signaling mechanisms, and aging. A number of bioactive molecules within the retina affect, and are effected by such conditions. These molecules operate within complex systems and include compounds classified as eicosanoids, angiogenic factors, matrix metalloproteinases, reactive oxygen species, cyclic nucleotides, neurotransmitters and neuromodulators, pro-inflammatory and immunoregulatory cytokines, and inflammatory phospholipids. We discuss the relationship of LCPUFAs with these bioactivators and bioactive compounds in the context of three blinding retinal diseases of public health significance that exhibit both vascular and neural pathology. How is omega-3 LCPUFA status related to retinal structure and function? Docosahexaenoic acid (DHA), a major dietary omega-3 LCPUFA, is also a major structural lipid of retinal photoreceptor outer segment membranes. Biophysical and biochemical properties of DHA may affect photoreceptor membrane function by altering permeability, fluidity, thickness, and lipid phase properties. Tissue DHA status affects retinal cell signaling mechanisms involved in phototransduction. DHA may operate in signaling cascades to enhance activation of membrane-bound retinal proteins and may also be involved in rhodopsin regeneration. Tissue DHA insufficiency is associated with alterations in retinal function. Visual processing deficits have been ameliorated with DHA supplementation in some cases. What evidence exists to suggest that LCPUFAs modulate factors and processes implicated in diseases of the vascular and neural retina? Tissue status of LCPUFAs is modifiable by and dependent upon dietary intake. Certain LCPUFAs are selectively accreted and efficiently conserved within the neural retina. On the most basic level, omega-3 LCPUFAs influence retinal cell gene expression, cellular differentiation, and cellular survival. DHA activates a number of nuclear hormone receptors that operate as transcription factors for molecules that modulate reduction-oxidation-sensitive and proinflammatory genes; these include the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and the retinoid X receptor. In the case of PPAR-alpha, this action is thought to prevent endothelial cell dysfunction and vascular remodeling through inhibition of: vascular smooth muscle cell proliferation, inducible nitric oxide synthase production, interleukin-1 induced cyclooxygenase (COX)-2 production, and thrombin-induced endothelin 1 production. Research on model systems demonstrates that omega-3 LCPUFAs also have the capacity to affect production and activation of angiogenic growth factors, arachidonic acid (AA)-based vasoregulatory eicosanoids, and MMPs. Eicosapentaenoic acid (EPA), a substrate for DHA, is the parent fatty acid for a family of eicosanoids that have the potential to affect AA-derived eicosanoids implicated in abnormal retinal neovascularization, vascular permeability, and inflammation. EPA depresses vascular endothelial growth factor (VEGF)-specific tyrosine kinase receptor activation and expression. VEGF plays an essential role in induction of: endothelial cell migration and proliferation, microvascular permeability, endothelial cell release of metalloproteinases and interstitial collagenases, and endothelial cell tube formation. The mechanism of VEGF receptor down-regulation is believed to occur at the tyrosine kinase nuclear factor-kappa B (NFkappaB). NFkappaB is a nuclear transcription factor that up-regulates COX-2 expression, intracellular adhesion molecule, thrombin, and nitric oxide synthase. All four factors are associated with vascular instability. COX-2 drives conversion of AA to a number angiogenic and proinflammatory eicosanoids. Our general conclusion is that there is consistent evidence to suggest that omega-3 LCPUFAs may act in a protective role against ischemia-, light-, oxygen-, inflammatory-, and age-associated pathology of the vascular and neural retina.

Nutritional and botanical modulation of the inflammatory cascade--eicosanoids, cyclooxygenases, and lipoxygenases--as an adjunct in cancer therapy

Emerging on the horizon in cancer therapy is an expansion of the scope of treatment beyond cytotoxic approaches to include molecular management of cancer physiopathology. The goal in these integrative approaches, which extends beyond eradicating the affected cells, is to control the cancer phenotype. One key new approach appears to be modulation of the inflammatory cascade, as research is expanding that links cancer initiation, promotion, progression, angiogenesis, and metastasis to inflammatory events. This article presents a literature review of the emerging relationship between neoplasia and inflammatory eicosanoids (PGE2 and related prostaglandins), with a focus on how inhibition of their synthesizing oxidases, particularly cyclooxygenase (COX), offers anticancer actions in vitro and in vivo. Although a majority of this research emphasizes the pharmaceutical applications of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors, these agents fail to address alternate pathways available for the synthesis of proinflammatory eicosanoids. Evidence is presented that suggests the inhibition of lipoxygenase and its by-products-LTB4, 5-HETE, and 12-HETE-represents an overlooked but crucial component in complementary cancer therapies. Based on the hypothesis that natural agents capable of modulating both lipoxygenase and COX may advance the efficacy of cancer therapy, an overview and discussion is presented of dietary modifications and selected nutritional and botanical agents (notably, omega-3 fatty acids, antioxidants, boswellia, bromelain, curcumin, and quercetin) that favorably influence eicosanoid production.

Increased metastatic potential in human prostate carcinoma cells by overexpression of arachidonate 12-lipoxygenase

Arachidonate 12-lipoxygenase (LOX) converts arachidonic acid to 12(S)-hydroxyeicosatetraenoic acid (HETE), a bioactive lipid implicated in tumor angiogenesis, growth, and metastasis. Alteration in 12-LOX expression or activity has been reported in various carcinomas including prostate carcinoma. However, little is known about the impact of the altered expression or activity of 12-LOX on tumor metastasis. In the present study, we examined whether or not an increase in 12-LOX expression in human prostate carcinoma cells can modulate their metastatic potential. We report that increased expression of 12-LOX in PC-3 cells caused a significant change in cell adhesiveness, spreading, motility, and invasiveness. Specifically 12-LOX transfected PC-3 cells were more adhesive toward vitronectin, type I and IV collagen, but not to fibronectin or laminin, than cells transfected with control vector. Increased spreading on vitronectin, fibronectin, collagen type I and IV also was observed in 12-LOX transfected PC-3 cells when compared to control PC-3 cells. The increased spreading of 12-LOX transfected PC-3 cells was blocked by treatment with 12-LOX inhibitors, baicalein and CDC. 12-LOX transfected PC-3 cells were more invasive through Matrigel than cells transfected with control vector. In vivo, tumor cell invasion to surrounding muscle or fat tissues was more frequent in nude mice bearing s.c. tumors from 12-LOX transfected PC-3 cells than in those from control vector transfected cells. When injected via the tail vein into SCID mice with implanted human bone fragments, there was an increase in tumor metastasis to human bone by 12-LOX transfected PC-3 cells in comparison to control vector transfected cells. Taken together, our data suggest that an increase in 12-LOX expression enhances the metastatic potential of human prostate cancer cells.

Lung cancer chemoprevention: moving from concept to a reality

Vast numbers of individuals who have stopped smoking have already been exposed to critical amounts of tobacco combustion products and are at significant risk of developing lung cancer. If these individuals are diagnosed with regional or distant metastatic disease this condition is not typically curable with existing systemic therapy. The need for more effective tools to detect and intervene with early lung cancer detection is a pressing public health priority. A major challenge in this regard is the development of safe and effective lung cancer chemoprevention. The factors influencing the development of this new clinical tool are reviewed in the context of existing trends for lung cancer care. Existing pharmaceutical efforts have involved evaluation of existing treatments for advanced cancer or other disorders in early lung cancer. The paper describes approaches to tailor chemoprevention development specifically to the biological, pharmacological and anatomical realities of this most lethal cancer.

Growth factor-induced proliferation in corneal epithelial cells is mediated by 12(S)-HETE

PURPOSE

Previous studies in our laboratory have shown that 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a product of 12-lipoxygenase (12-LOX) activity, is the predominant metabolite formed in rabbit corneas after injury. The present study was undertaken to investigate the effects of epidermal growth factor (EGF), hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF) on 12-LOX expression and activity. We also investigated whether 12(S)-HETE mediated the growth factor-induced proliferation of corneal epithelial cells.

METHODS

Rabbit corneas were stimulated with EGF, HGF, and KGF (10 ng ml(-1)) for different times. 12-LOX activity was assayed by incubating corneal microsomal preparations with radiolabeled arachidonic acid (AA) as substrate. For inhibitor studies, the microsomes were pretreated with 12-LOX-specific inhibitors baicalein (BC) or cinnamyl 3,4-dihydroxy-(alpha)-cyanocinnamate (CDC). Lipid extracts were injected onto an Ultramex 5 microm C(18) column and radioactivity was monitored online by a Radiomatic Flo-One Beta detector. Stereochemical analysis of 12-HETE product was determined by chiral-phase HPLC. To evaluate the effects of growth factors on 12-LOX mRNA expression, mRNA was extracted at several time points (12, 24, 36, 48 hr) and subjected to real-time PCR. For 12-LOX protein expression, microsomal preparations from 24- and 48-hr incubations were analyzed by Western blot. In cell-proliferation studies, epithelial cells treated with EGF, HGF, or KGF for 24, 48, and 72 hr were measured with a CyQUANT cell-proliferation assay kit. To determine the role of growth factor-induced 12(S)-HETE synthesis on corneal epithelial cell proliferation, cells were pretreated with 12-LOX-specific inhibitors BC or CDC prior to growth-factor supplementation.

RESULTS

Stimulation with EGF, HGF, or KGF for 12 hr induced 12-LOX mRNA expression in rabbit corneal epithelial cells. This gene induction was followed by an increase in protein expression at 24 and 48 hr and a marked increase in 12(S)-HETE synthesis when compared to untreated controls. At 24-hr incubations, KGF showed a greater capacity than did EGF and HGF to stimulate microsomal 12-LOX activity, while at 48 hr 12(S)-HETE synthesis was significantly greater in EGF-treated cells as compared to that of HGF- and KGF-treated cells. Pretreatment with 12-LOX inhibitors blocked the growth factor-induced increase in 12(S)-HETE synthesis. Stimulation with growth factors or 12(S)-HETE for 24, 48, and 72hr produced a significant increase in corneal epithelial proliferation, which was partially inhibited by pretreatment of cells with 12-LOX-specific inhibitors.

CONCLUSION

These findings suggest that EGF, HGF, and KGF stimulate 12(S)-HETE production in rabbit corneal epithelial cells through gene induction of 12-LOX. Furthermore, 12(S)-HETE may play a role in regulating epithelial cell proliferation and the rate of corneal re-epithelialization following an injury.

Mechanisms and applications of non-steroidal anti-inflammatory drugs in the chemoprevention of cancer

Biological and chemical irritants can be the cause of irritation in a variety of organ sites. It is becoming well understood that chronic irritation in any form can initiate and accelerate the cancer process in these same organs. This understanding comes in part from the many epidemiologic studies which point out that chronic inflammation correlates with increased risk of developing cancer in that organ which is affected. One of the hallmarks of chronic irritation is the increased activity in the arachidonic acid pathway which provides many of the necessary inflammatory biochemical mediators to this process. Arachidonic acid metabolism diverges down two main pathways, the cyclooxygenase (COX) and the lipoxygenase (LOX) pathways. The COX pathway leads to prostaglandin and thromboxane production and the LOX pathway leads to the leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs). These classes of inflammatory molecules exert profound biological effects which enhance the development and progression of human cancers. A large number of synthetic drugs and natural products have been discovered that block many of these key pathways. Much experimental evidence in animals has shown that inhibition of the key enzymes which drive these pathways can, in fact, prevent, slow or reverse the cancer process. The data are convincing in a number of organ sites including colon, breast, lung, bladder and skin. More recently, double-blinded randomize clinical trials in humans have shown the prevention of colonic polyps by anti-inflammatory agents. These studies have primarily used non-steroidal anti-inflammatory drugs (NSAIDS) which block the COX pathways. Recent preclinical studies indicate that the LOX pathway also may be an important target for cancer prevention strategy. The expression of high levels of these enzymes in cancerous tissues make them an obvious first target for cancer prevention strategies. As newer more specific drugs are developed with few adverse effects this important prevention strategy may become a reality.

Association between E-cadherin expression by human colon, bladder and breast cancer cells and the 13-HODE:15-HETE ratio. A possible role of their metastatic potential

The relationship between 15(S)-HETE and 13(S)-HODE from different human tumor cells exposed to n-6 and n-3 essential fatty acids (EFAs) and E-cadherin expression was studied. Colon cancer cells (HRT-18) exposed to gamma linoleic acid (18:3n-6, GLA) and eicosapentaenoic (20:5n-3, EPA) (50microM) showed an increased expression of E-cadherin. Breast cancer (MCF-7) exposed to EPA showed an increment whereas GLA had no effect on E-cadherin expression. No expression of E-cadherin was observed for urothelial cancer (T-24) after GLA or EPA treatment. Significant levels of 15(S)-HETE and 13(S)-HODE were detected after GLA or EPA treatment for all tumor lines. E-cadherin expression was inversely proportional to the 13(S)-HODE:15(S)-HETE ratio when cells were pretreated with GLA or EPA. Nevertheless, the liberation of these metabolites seems to be independent of the E-cadherin expression. The increase in the13(S)-HODE:15(S)-HETE correlates to a decrease in the expression of E-cadherin. Both factors may play a role in metastasis development.

Inhibition of peroxisome proliferator-activated receptor (PPAR)-mediated keratinocyte differentiation by lipoxygenase inhibitors

Lipoxygenase (LOX) metabolites from arachidonic acid and linoleic acid have been implicated in atherosclerosis, inflammation, keratinocyte differentiation and tumour progression. We previously showed that peroxisome proliferator-activated receptors (PPARs) play a role in keratinocyte differentiation and that the PPARalpha ligand 8S-hydroxyeicosatetraenoic acid is important in this process. We hypothesized that blocking LOX activity would block PPAR-mediated keratinocyte differentiation. Three LOX inhibitors, nordihydroguaiaretic acid, quercetin and morin, were studied for their effects on primary keratinocyte differentiation and PPAR activity. All three LOX inhibitors blocked calcium-induced expression of the differentiation marker keratin 1. In addition, activity of a PPAR-responsive element was inhibited in the presence of all three inhibitors, and this effect was mediated primarily through PPARalpha and PPARgamma. LOX inhibitors decreased the activity of a chimaeric PPAR-Gal4-ligand-binding domain reporter system and this effect was reversed by addition of PPAR ligands. Ligand-binding studies revealed that the LOX inhibitors bind directly to PPARs and demonstrate a novel mechanism for these inhibitors in altering PPAR-mediated gene expression.

Protein kinase C as a molecular target for cancer prevention by selenocompounds

Selenium is a very effective cancer-preventive agent, suppressing tumor promotion and early stages of tumor progression. However, the mechanisms by which selenium exerts these cancer-preventive actions are not known. Protein kinase C (PKC) is a receptor for certain tumor promoters and also plays a crucial role in events related to tumor progression. Therefore, it is not only a potential target for the cancer-preventive activity of selenium, but also it has the structural basis for interaction with selenium. Redox-active selenocompounds can inactivate PKC, particularly the Ca(2+)-dependent isozymes, by reacting with the critical cysteine-rich regions present within the catalytic domain while, in some cases, also reacting with the cysteine residues present within the zinc-fingers of the regulatory domain. The selenoprotein thioredoxin reductase (TR), acting through thioredoxin, reverses the inactivation of PKC induced by selenometabolites. Furthermore, TR, through a direct interaction involving its selenosulfur center with the zinc-thiolates of PKC, can reverse the redox modification of this kinase induced by selenometabolites. Thus the selenometabolite-induced toxicity is reversed by a selenoprotein, and therefore an interrelationship exists between these two mechanisms of selenium actions. Moreover, this also explains how a resistance to selenium develops in advanced tumor cells probably due to an overexpression of functional TR. Selenium-induced inactivation of PKC may, at least in part, be responsible for the selenium-induced inhibition of tumor promotion, cell growth, invasion, and metastasis, as well as for the induction of apoptosis.

Regulation of tumor angiogenesis by dietary fatty acids and eicosanoids

Angiogenesis is a prerequisite for tumor growth and metastasis. Vascular endothelial cell proliferation, migration, and capillary formation are stimulated by angiogenic growth factors, which include the proteins vascular endothelial growth factor, basic fibroblast growth factor, and transforming growth factor-beta, and eicosanoids synthesized from n-6 fatty acids. Clinical studies have shown that angiogenesis in solid tumors relates to a poor prognosis and, in premalignant lesions, indicates potential for cancerous transformation. High-fat, n-6 fatty acid-rich diets were associated with a relatively poor prognosis in breast cancer patients; in a nude mouse model the same diet enhanced breast cancer progression, whereas n-3 fatty acids exerted suppressive effects that were associated with impaired angiogenesis. Lipoxygenase and cyclooxygenase products of n-6 fatty acid metabolism are angiogenic in in vitro assays. This activity is blocked by pharmacological inhibitors of eicosanoid biosynthesis, and one, indomethacin, suppressed n-6 fatty acid-stimulated murine mammary carcinoma growth and metastasis and tumor vascularization. Review of the experimental data suggests that selective inhibitors of eicosanoid-synthesizing enzymes and dietary intervention with n-3 fatty acids merit clinical evaluation as adjuvant therapy and chemopreventive agents.

Autocrine motility factor (neuroleukin, phosphohexose isomerase) induces cell movement through 12-lipoxygenase-dependent tyrosine phosphorylation and serine dephosphorylation events

Autocrine motility factor (AMF) is one of the motility cytokines regulating tumor cell migration, therefore identification of the signaling pathway coupled with it has critical importance. Previous studies revealed several elements of this pathway predominated by lipoxygenase-PKC activations but the role for tyrosine kinases remained questionable. Motility cytokines frequently have mitogenic effect as well, producing activation of overlapping signaling pathways therefore we have used B16a melanoma cells as models where AMF has exclusive motility effect. Our studies revealed that in B16a cells AMF initiated rapid (1-5 min) activation of the protein tyrosine kinase (PTK) cascade inducing phosphorylation of 179, 125, 95 and 40/37 kD proteins which was mediated by upstream cyclo- and lipoxygenases. The phosphorylated proteins were localized to the cortical actin-stress fiber attachment zones in situ by confocal microscopy. On the other hand, AMF receptor activation induced significant decrease in overall serine-phosphorylation level of cellular proteins accompanied by serine phosphorylation of 200, 90, 78 and 65 kd proteins. The decrease in serine phosphorylation was independent of PTKs, PKC as well as cyclo- and lipoxygenases. However, AMF induced robust translocation of PKCalpha to the stress fibers and cortical actin suggesting a critical role for this kinase in the generation of the motility signal. Based on the significant decrease in serine phosphorylation after AMF stimulus in B16a cells we postulated the involvement of putative serine/threonine phosphatase(s) upstream lipoxygenase and activation of the protein tyrosine kinase cascade downstream cyclo- and lipoxygenase(s) in the previously identified autocrine motility signal.

Prostate Cancer - Old Problems and New Approaches. (Part II. Diagnostic and Prognostic Markers, Pathology and Biological Aspects)

Diagnostic and prognostic markers for prostatic cancer (PCa) include conventional protein markers (e.g., PAP, PSA, PSMA, PIP, OA-519, Ki-67, PCNA, TF, collagenase, and TIMP 1), angiogenesis indicator (e.g., factor VIII), neuroendocrine differentiation status, adhesion molecules (E-cadherin, integrin), bone matrix degrading products (e.g., ICPT), as well as molecular markers (e.g., PSA, PSMA, p53, 12-LOX, and MSI). Currently, only PSA is used clinically for early diagnosis and monitoring of PCa. The histological differential diagnosis of prostatic adenocarcinoma includes normal tissues such as Cowper's gland, paraganglion tissue and seminal vesicle or ejaculatory duct as well as pathological conditions such as atypical adenomatous hyperplasia, atrophy, basal cell hyperplasia and sclerosing adenosis. A common PCa is characterized by a remarkable heterogeneity in terms of its differentiation, microscopic growth patterns and biological aggressiveness. Most PCa are multifocal with signi ficant variations in tumor grade between anatomically separated tumor foci. The Gleason grading system which recognizes five major grades defined by patterns of neoplastic growth has gained almost uniform acceptance. In predicting the biologic behavior of PCa clinical and pathological stages are used as the major prognostic indicators. Among the cell proliferation and death regulators androgens are critical survival factors for normal prostate epithelial cells as well as for the androgen-dependent human prostatic cancer cells. The androgen ablation has been shown to increase the apoptotic index in prostatic cancer patients and castration also promotes apoptotic death of human prostate carcinoma grown in mice. The progression of PCa, similarly to other malignancies, is a multistep process, accompanied by genetic and epigenetic changes, involving phenomenons as adhesion, invasion and angiogenesis (without prostate specific features).

Associations of PKC isoforms with the cytoskeleton of B16F10 melanoma cells

Although PKC plays a major role in regulating the morphology and function of the cytoskeleton, little is known about in situ associations of specific isoforms with the cytoskeleton. We demonstrate that seven PKC isoforms are expressed in B16F10 melanoma cells and show different levels of induction by serum. Using cell cytoskeleton preparations (CSKs), confocal microscopy, and immunocytochemistry, all isoforms show specific patterns of localization to focal contact-like structures (alpha, delta), very small cytoplasmic granules/vesicles (all isoforms), dense ordered arrays of small granules in the perinuclear region (alpha, delta), granules/vesicles associated with a homogeneous framework in the cytoplasm adjacent to the nucleus (gamma), or irregular-shaped patches of granules at or near the nuclear perimeter (eta, theta). In addition, several isoforms are present as cytoplasmic granules/ vesicles in linear or curvilinear arrays (alpha, delta, epsilon, theta). When isoform localization is examined using 3.7% formaldehyde or methanol:acetone, the patterns of localization in CSKs are often difficult or impossible to detect, and many are described here for the first time. Double-labeling experiments with CSK demonstrate that PKC actin co-localizes with punctate alpha-rich particles above the nucleus, granules of epsilon throughout the cytoplasm, and with theta in irregular-shaped aggregates associated with the nucleus. Vimentin co-localizes with perinuclear granules of delta and beta(2), and alpha-tubulin co-localizes with theta in structures at or near the nuclear surface and in microtubules associated with the microtubule organizing center (MTOC). In summary, the present study demonstrates that seven PKC isoforms are endogenously expressed in B16F10 melanoma cells. These isoforms show various levels of induction by serum and specific patterns of association with various components of the detergent-resistant cell cytoskeleton.

Eicosanoid activation of extracellular signal-regulated kinase1/2 in human epidermoid carcinoma cells

12(S)-Hydroxyeicosatetraenoic acid (12(S)-HETE), a 12-lipoxygenase metabolite of arachidonic acid, has multiple effects on tumor and endothelial cells, including stimulation of invasion and angiogenesis. However, the signaling mechanisms controlling these physiological processes are poorly understood. In a human epidermoid carcinoma cell line (i.e. A431), 12(S)-HETE activates extracellular signal-regulated kinases 1/2 (ERK1/2), which is mediated by upstream kinases MEK and Raf. 12(S)-HETE stimulates phosphorylation of phospholipase Cgamma1 and activity of protein kinase Calpha (PKCalpha). In addition, independent of PKC 12(S)-HETE increases tyrosine phosphorylation of Shc, and Grb2, stimulates association between Shc and Src, and increases the activity of Ras, via Src family kinases. Furthermore, at low (10-100 nm) concentrations 12(S)-HETE counteracts epidermal growth factor-stimulated activation of ERK1/2 via stimulating protein tyrosine phosphatases. We also present evidence that 12(S)-HETE stimulates ERK1/2 via G proteins and that A431 cells have multiple binding sites for 12(S)-HETE. Finally, inhibition of 12-lipoxygenase induced apoptosis of A431 cells, which was reversed by addition of exogenous 12(S)-HETE. Collectively we demonstrate that the activation of ERK1/2 by 12(S)-HETE may be regulated by multiple receptors triggering PKC-dependent and PKC-independent pathways in A431 cells.

Potential use of lipoxygenase inhibitors for cancer chemoprevention

Increasing evidence suggests that lipoxygenase (LO)-catalysed metabolites have a profound influence on the development and progression of human cancers. Compared with normal tissues, significantly elevated levels of LO products have been found in breast tumours, colon cancers, lung, skin and prostate cancers, as well as in cells from patients with both acute and chronic leukaemias. LO-mediated products elicit diverse biological activities needed for neoplastic cell growth, influencing growth factor and transcription factor activation, oncogene induction, stimulation of tumour cell adhesion and regulation of apoptotic cell death. Agents that block LO catalytic activity may be effective in preventing cancer by interfering with signalling events needed for tumour growth. In the past ten years, pharmaceuticals agents that specifically inhibit the 5-LO metabolic pathway have been developed to treat inflammatory diseases such as asthma, arthritis and psoriasis. Some of these compounds possess anti-oxidant properties and may be effective in preventing cancer by blocking free radical-induced genetic damage or by preventing the metabolic activation of carcinogens. Other compounds may work by negatively modulating DNA synthesis. Pharmacological profiles of potential chemopreventive agents are compiled from enzyme assays, in vitro testing (e.g., cell proliferation inhibition in human cancer cells) and in vivo animal carcinogenesis models (e.g., N-methyl-N-nitrosourea-induced rat mammary cancer, benzo(a)pyrene-induced lung tumours in strain A/J mice and hormone-induced prostate tumours in rats). In this way, compounds are identified for chemoprevention trials in human subjects. Based on currently available data, it is expected that the prevention of lung and prostate cancer will be initially studied in human trials of LO inhibitors.

Effects of mutant p53 expression on human 15-lipoxygenase-promoter activity and murine 12/15-lipoxygenase gene expression: evidence that 15-lipoxygenase is a mutator gene

Human 15-lipoxygenase (h15-LO) is present on chromosome 17p13.3 in close proximity to the tumor-suppressor gene, p53. 15-LO is implicated in antiinflammation, membrane remodeling, and cancer development/metastasis. The murine BALB/c embryo fibroblast cell line, (10)1val, expresses p53 in mutant (mt) conformation when grown at 39 degrees C and in wild-type conformation when grown at 32 degrees C. Transfection of h15-LO promoter constructs (driving luciferase reporter) into (10)1val cells and into p53-deficient (10)1 cells resulted in a marked increase in h15-LO promoter activity in (10)1val cells at 39 degrees C, but not at 32 degrees C, or as compared with (10)1 cells. Transfection of h15-LO promoter deletion constructs, however, resulted in total loss of activity in both cell types at 32 degrees C and 39 degrees C. Cotransfection of (10)1 cells with h15-LO promoter (driving luciferase reporter) along with increasing levels of a mt p53 expression vector demonstrated dose-dependent capacity of mt p53 to induce 15-LO promoter activity. No effect was observed with wild-type p53. In contrast to h15-LO promoter activity, (10)1val cells had significantly lower levels of endogenous (murine) 12/15-LO (mouse analog of h15-LO) mRNA and protein when grown at 39 degrees C compared with cells grown at 32 degrees C. Our data support the hypothesis that loss of a tumor-suppressor gene (p53), or "gain-of-function activities" resulting from the expression of its mutant forms, regulates 15-LO promoter activity in man and in mouse, albeit in directionally opposite manners. The studies define a direct link between 15-LO activity and an established tumor-suppressor gene located in close chromosomal proximity.

12-hydroxy-5Z, 8Z, 10E, 14Z, eicosatetraenoic acid (12-HETE) stimulates cAMP production in normal human fibroblasts

We report here that the 12-lipoxygenase metabolite of arachidonic acid, 12-hydroxy-5Z, 8Z, 10E, 14Z, eicosatetraenoic acid (12-HETE), stimulates cAMP production in human fibroblasts among various cultured cell lines tested. Although 12-HETE seemed to stimulate the phospholipase C (PLC)-protein kinase C (PKC) system, inhibitors against PLC and PKC did not reduce the cAMP production induced by 12-HETE, indicating that the activation of PLC-PKC system is not positively coupled with the stimulation of cAMP production. On the other hand, the cAMP production induced by 12-HETE was dependent on the Ca2+/calmodulin system in the cells. The results suggest that 12-HETE specifically stimulates Ca2+/calmodulin-dependent adenylyl cyclase to increase cAMP level in the fibroblasts.

H-7 stimulates desmosome formation and inhibits growth in KB oral carcinoma cells

Protein kinase inhibitor H-7 was reported to stimulate desmosome formation in normal keratinocytes and to inhibit proliferation of neural cell lines. In the present study, the effects of this inhibitor on adhesion and growth of KB human oral carcinoma cells were investigated. H-7 was found to enhance desmosome assembly, as evidenced by an increased punctate labeling for the major desmosomal markers. Immunogold labeling confirmed the formation of desmosomes both at the cell surface and in the cytoplasm. In order to assess cell proliferation and possible correlation with adhesion, confluent cultures were treated and both adherert and detached cell fractions were counted. Under serum-free conditions, H-7 significantly reduced cell detachment. In contrast, EGF stimulated cell detachment, and this effect was abolished when cells were simultaneously treated with both EGF and H-7. Total cell counts were also significantly reduced by H-7, both in the presence and absence of EGF. Using the TUNEL technique, labeled cells were increased after H-7 treatment, thus implicating protein kinase inhibition in cell death. These results indicate that H-7 inhibits growth and stimulates adhesion of KB carcinoma cells.

The role of protein glycosylation inhibitors in the prevention of metastasis and therapy of cancer

Oligosaccharide moieties of cell-surface glycoproteins are thought to be involved in recognition events during cancer metastasis and invasion. Swainsonine, an inhibitor of the Golgi alpha-mannosidase II, has been shown to block pulmonary colonization by tumor cells and stimulate components of the immune system. Swainsonine also abrogates much of the toxicity of chemotherapeutic agents and stimulates bone marrow hematopoietic progenitor cells, suggesting additional therapeutic applications. We are currently characterizing the ability of swainsonine to modify cell growth in human and murine bone marrow progenitor cells. Furthermore, we are examining crucial steps in metastasis that depend upon cell surface molecules that play a role in cell-matrix interactions. Our work shows that tumor cell adhesion to collagen IV in vitro is rapidly stimulated by cis-polyunsaturated fatty acids and is dependent on protein kinase C activity. We are investigating the hypothesis that integrins are critical components of this adhesion and are examining potential signal transduction pathways that lead to the modulation of cell adhesion.

The importance of linoleic acid metabolites in cancer metastasis and in the synthesis and actions of 13-HODE

Large scale human epidemiological studies indicate that high intakes of linoleic acid protect against the development of cancer. One mechanism may be the generation of 13-HODE from linoleic acid. 13-HODE prevents cell adhesion to endothelial cells and can inhibit cancer metastasis. 13-HODE synthesis is enhanced by cyclic AMP. Gamma-linolenic acid, a desaturated metabolite of linoleic acid, causes substantial stimulation of 13-HODE synthesis. A fall in gamma-linolenic acid synthesis with age may be related to the age-related fall in 13-HODE formation.

Role of protein kinase C and phosphatases in 12(S)-HETE-induced tumor cell cytoskeletal reorganization

Adherent B16 amelanotic melanoma (B16a) cells exposed to fatty acid 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, demonstrated a gradual dissolution of stress fibers and bundling-together of vimentin. The 12(S)-HETE effects on tumor cell cytoskeleton appeared 5 min after treatment, became prominent approximately 15 min following stimulation, and generally disappeared by 30 min. Simultaneous treatment of cells with 12(S)-HETE and okadaic acid (OA) prevented disappearance of the 12(S)-HETE effects by 30 min. Quantitative double immunoblotting of actin and vimentin indicated that actin, but not vimentin, underwent a time-related depolymerization. On the other hand, enhanced phosphorylation of vimentin but not of actin was observed after 12(S)-HETE treatment. 12(S)-HETE-enhanced vimentin phosphorylation was abolished by protein kinase C (PKC) inhibitor calphostin C, thus suggesting the involvement of PKC.

Arachidonate initiated protein kinase C activation regulates HeLa cell spreading on a gelatin substrate by inducing F-actin formation and exocytotic upregulation of beta 1 integrin

HeLa cell spreading on a gelatin substrate requires the activation of protein kinase C (PKC), which occurs as a result of cell-attachment-induced activation of phospholipase A2 (PLA2) to produce arachidonic acid (AA) and metabolism of AA by lipoxyginase (LOX). The present study examines how PKC activation affects the actin- and microtubule-based cytoskeletal machinery to facilitate HeLa cell spreading on gelatin. Cell spreading on gelatin is contingent on PKC induction of both actin polymerization and microtubule-facilitated exocytosis, which is based on the following observations. There is an increase in the relative content of filamentous (F)-actin during HeLa cell spreading, and treating HeLa cells with PKC-activating phorbol esters such as 12-O-tetradecanoyl phorbol 13-acetate (TPA) further increases the relative content of F-actin and the rate and extent to which the cells spread. Conversely, inhibition of PKC by calphostin C blocked both cell spreading and the increase of F-actin content. The increased F-actin content induced by PKC activators also was observed in suspension cells treated with TPA, and the kinetics of F-actin were similar to that for PKC activation. In addition, PKC epsilon, which is the PKC isoform most involved in regulating HeLa cell spreading in response to AA production, is more rapidly translocated to the membrane in response to TPA treatment than is the increase in F-actin. Blocking the activities of either PLA2 or LOX inhibited F-actin formation and cell spreading, both of which were reversed by TPA treatment. This result is consistent with AA and a LOX metabolite of AA as being upstream second messengers of activation of PKC and its regulation of F-actin formation and cell spreading. PKC appears to activate actin polymerization in the entire body of the cell and not just in the region of cell-substrate adhesion because activated PKC was associated not only with the basolateral plasma membrane domain contacting the culture dish but also with the apical plasma membrane domain exposed to the culture medium and with an intracellular membrane fraction. In addition to the facilitation of F-actin formation, activation of PKC induces the exocytotic upregulation of beta 1 integrins from an intracellular domain to the cell surface, possibly in a microtubule-dependent manner because the upregulation is inhibited by Nocodazole. The results support the concept that cell-attachment-induced AA production and its metabolism by LOX results in the activation of PKC, which has a dual role in regulating the cytoskeletal machinery during HeLa cell spreading. One is through the formation of F-actin that induces the structural reorganization of the cells from round to spread, and the other is the exocytotic upregulation of collagen receptors to the cell surface to enhance cell spreading.

Selenocompounds induce a redox modulation of protein kinase C in the cell, compartmentally independent from cytosolic glutathione: its role in inhibition of tumor promotion

Since selenite and other redox-active selenocompounds can modify protein kinase C (PKC) in the test tube, we have determined whether or not this redox regulation occurs inside the cell despite having high concentrations of GSH and the role of this regulation in the inhibition of tumor promotion. By using phorbol ester-promoted JB6 epidermal cell transformation assay, the concentrations of selenite, selenocystine, and selenodiglutathione which are optimal for chemopreventive activity were determined. At such concentrations (0.5 to 2 microM) in the cells treated with these agents, only a slight but transient decrease in PKC activity was observed when measured with a low (5 microM), but not with a high (100 microM) concentration of ATP. However, when the cells were serum starved or pretreated with 2-deoxyglucose, there was a pronounced but transient inactivation of PKC when assayed with both low and high concentrations of ATP. The inactivation was reversed in the cell by an endogenous mechanism or by treatment with thiol agents in the test tube. In spite of a substantial (90%) depletion of GSH in the cells by pretreatment with buthionine sulfoximine, there was no further increase in the redox modification of PKC by selenite as well as no change in the inhibitory effect of selenite on the phorbol ester-stimulated induction of ornithine decarboxylase, which is an intermediate marker related to cell transformation. While GSH is known to influence certain actions of selenium, it may not be required to mediate the effects of selenite tested in this study. The water-soluble cytosolic GSH did not interfere with the redox modification of PKC probably due to the shielding of the cysteine-rich region of the enzyme by a weak hydrophobic association with the membrane. Due to the presence of cofactors in the crude cell extracts, PKC was more sensitive to selenite than in the purified form and was inactivated by low concentrations of selenite (IC50 = 0.05 microM). This modification was reversed by thiol agents as well as by NADPH. A protein disulfide reductase, which can regenerate PKC, was present in the homogenate. Conceivably, selenite and other selenocompounds induce a redox modification of cellular PKC, compartmentally independent from the cytosolic GSH, but intimately connected to a NADPH-dependent reductase system, to mediate, at least in part, some of the cancer-preventive actions.

PKC regulation of microfilament network organization in keratinocytes defined by a pharmacological study with PKC activators and inhibitors

The modulation by PKC activators and inhibitors of adhesion, spreading, migration, actin cytoskeleton organization, and focal complex formation in keratinocytes attaching to type I collagen was studied. Two actin microfilament networks, stress fibers and cortical actin, could be distinguished on the basis of cellular distribution and opposite regulation by growth factors, tyrosine kinase inhibitors, and PKC activators. Stress fiber formation was stimulated by growth factors and by PMA (100 ng/ml) and these stimulations were blocked by tyrosine kinase inhibitors (0.3 mM genistein and 1 microM herbimycin A). By contrast, the cortical network occurred in quiescent cells, was unaffected by tyrosine kinase inhibitors, and was broken down after PKC activation by PMA. Spreading, migration, and actin polymerization were completely blocked while adhesion efficacy was significantly decreased by three specific PKC inhibitors. Half-inhibition of migration was obtained with 0.025, 1, and 3 microM concentrations of calphostin C, chelerytrine chloride, and D-erythrosphingosine, respectively, which are concentrations close to those known to inhibit the PKC kinase function in vitro. Paxillin clustering, which was observed even in the presence of tyrosine kinase inhibitors, disappeared only when actin polymerization was completely impaired, i.e., in cells treated with PKC inhibitors or with both tyrosine kinase inhibitors and PMA, which indicated that focal complex formation was highly dependent on microfilament reorganization. The analysis of these data underscores a major regulation function of PKC in the molecular events involved in growth factor and adhesion-dependent regulation of microfilament dynamics.

Increased 12-lipoxygenase expression in breast cancer tissues and cells. Regulation by epidermal growth factor

The interaction of growth factors, such as epidermal growth factor (EGF) with their receptors, on breast cancer cells can lead to the hydrolysis of phospholipids and release of fatty acids, such as arachidonic acid, which can be further metabolized by the lipoxygenase (LO) pathway. Several LO products have been shown to stimulate oncogenes and have mitogenic and chemotactic effects. In this study, we have evaluated the regulation of 12-LO activity and expression in breast cancer cells and tissues. Leukocyte-type 12-LO messenger RNA (mRNA) expression was studied by a specific RT-PCR method in matched, normal, uninvolved and cancer-involved breast tissue RNA samples from six patients. In each of these six patients, the cancer-involved section showed a much higher level of 12-LO mRNA than the corresponding normal section. 12-LO mRNA levels also were greater in two breast cancer cell lines, MCF-7 and COH-BR1, compared with the nontumorigenic breast epithelial cell line, MCF-10F. The growth of the MCF-7 cells was significantly inhibited by two specific LO blockers but not by a cyclooxygenase blocker. Treatment of serum-starved MCF-7 cells with EGF for 4 h led to a dose-dependent increase in the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid. EGF treatment also increased the levels of the leukocyte-type 12-LO protein expression at 24 h. These results suggest that activation of the 12-LO pathway may play a key role in basal and EGF-induced breast cancer cell growth.

Requirement for epidermal growth factor receptor tyrosine kinase and for 12-lipoxygenase activity in the expression of 12-lipoxygenase in human epidermoid carcinoma cells

We studied the dependency of basal 12-lipoxygenase (12-LOX; arachidonate:oxygen 12-oxidoreductase, EC 1.13.11.31) expression and activity on functional protein tyrosine kinase of the epidermal growth factor receptor (EGF-R) and on 12-LOX activity in human A431 epidermoid carcinoma cells. Treatment of cells with inhibitors of high specificity for EGF-R tyrosine kinase, namely PD 153035 and 4,5-dianilinophthalimide (DAPH1), decreased cellular 12-LOX at mRNA, protein, and activity levels in a time- and dose-dependent manner, with PD 153035 being effective at concentrations below 1 microM. After 24-hr incubation with 10 microM PD 153035 or DAPH1, 12-LOX activity dropped to 14% (39%), and 12-LOX protein to 25% (24%) of control level. Inhibition of 12-LOX activity by the compound N-benzyl-N-hydroxy-5-phenylpentanamide (BHPP) also resulted in a substantial decrease in 12-LOX protein expression. 12-LOX mRNA levels were diminished or undetectable by reverse transcription-polymerase chain reaction after cell treatment with these inhibitors. Our results suggest that basal 12-LOX expression in A431 tumor cells largely depends on functional EGF-R tyrosine kinase, and that 12-LOX activity is required in the EGF-elicited intracellular signaling maintaining the expression of 12-LOX.

Modulation of breast cancer cell adhesion by unsaturated fatty acids

Triglycerides, which are major constituents of dietary fat, contain a mixture of saturated and unsaturated fatty acids. One newly recognized function of unsaturated fatty acids is modulation of cell adhesion to components of the extracellular matrix. Alterations in cell adhesiveness or cell adhesion molecule expression accompany the onset of a number of diseases including arthritis, atherosclerosis, and cancer. Cell adhesion is necessary for the metastatic spread of cancer cells to new organs. Circulating cancer cells adhere to endothelial cells and the underlying subendothelial basement membrane as an initial step in the process of invading target organs during metastasis. Several recent studies have provided convincing evidence that unsaturated fatty acids and their metabolites influence adhesion of cultured human cancer cells to individual components of the basement membrane. These unsaturated fatty acid effects appear to be dependent in some instances on the expression of specific cell surface adhesion molecules. Unsaturated fatty acids influence the development of metastases in animal tumor models by largely unexplored mechanisms; the possibility that cell adhesion is involved in this process has not been thoroughly investigated. Future studies of unsaturated fatty acid effects on cell adhesion molecule expression in breast cancer patients should reveal the clinical relevance of the studies reviewed here.

Cloning, sequencing and expression of a 5-lipoxygenase from Syrian hamster embryo fibroblasts

The hamster ortholog of human and rat 5-lipoxygenase (5-LO) was cloned from a Syrian hamster embryo (SHE) cell line. A combination of polymerase chain reaction (PCR) and 5' and 3' RACE (rapid amplification of cDNA ends) was used to isolate the complete cDNA for this gene. The cDNA sequence demonstrates the extreme sequence conservation found in this gene family, with a deduced amino acid sequence 95% identical to the rat 5-LO, and 90% identical to the human enzyme. The hamster 5-LO was expressed in E. coli. The expressed protein was detected by an antibody to human 5-LO, and had an apparent molecular weight of 75-80 kD. The products of the action of this enzyme on arachidonic acid are 5-HETE and the diHETEs resulting from the breakdown of LTA4, in a pattern similar to that produced by the recombinant human 5-LO. No oxidation of linoleic acid by this enzyme was detected.

Arachidonate lipoxygenases as essential regulators of cell survival and apoptosis

Arachidonic acid (AA) metabolites derived from both cyclooxygenase (COX) and lipoxygenase (LOX) pathways transduce a variety of signals related to cell growth. Here, we report that the AA LOX pathway also functions as a critical regulator of cell survival and apoptosis. Rat Walker 256 (W256) carcinosarcoma cells express 12-LOX and synthesize 12(S)- and 15(S)-hydroxyeicosatetraenoic acids as their major LOX metabolites. W256 cells transfected with 12-LOX-specific antisense oligonucleotide or antisense oligonucleotides directed to conserved regions of LOXs underwent time- and dose-dependent apoptosis. Likewise, treatment of W256 cells with various LOX but not COX inhibitors induced apoptotic cell death, which could be partially inhibited by exogenous 12(S)- or 15(S)-hydroxyeicosatetraenoic acids. The W256 cell apoptosis induced by antisense oligos and LOX inhibitors was followed by a rapid downregulation of bcl-2 protein, a dramatic decrease in the bcl-2/bax ratio, and could be suppressed by bcl-2 overexpression. In contrast, p53, which is wild type in W256 cells, did not undergo alterations during apoptosis induction. The results suggest that the LOX pathway plays an important physiological role in regulating apoptosis.