Polyamine depletion induces rapid NF-kappa B activation in IEC-6 cells

Insights into diet-associated oxidative pathomechanisms in inflammatory bowel disease and protective effects of functional amino acids

There has been a substantial rise in the incidence and prevalence of clinical patients presenting with inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis. Accumulating evidence has corroborated the view that dietary factors (particularly diets with high levels of saturated fat or sugar) are involved in the development and progression of IBD, which is predominately associated with changes in the composition of the gut microbiota and an increase in the generation of reactive oxygen species. Notably, the ecological imbalance of the gut microbiome exacerbates oxidative stress and inflammatory responses, leading to perturbations of the intestinal redox balance and immunity, as well as mucosal integrity. Recent findings have revealed that functional amino acids, including L-glutamine, glycine, L-arginine, L-histidine, L-tryptophan, and hydroxyproline, are effectively implicated in the maintenance of intestinal redox and immune homeostasis. These amino acids and their metabolites have oxygen free-radical scavenging and inflammation-relieving properties, and they participate in modulation of the microbial community and the metabolites in the gut. The principal focus of this article is a review of recent advances in the oxidative pathomechanisms of IBD development and progression in relation to dietary factors, with a particular emphasis on the redox and signal transduction mechanisms of host cells in response to unbalanced diets and enterobacteria. In addition, an update on current understanding of the protective effects of functional amino acids against IBD, together with the underlying mechanisms for this protection, have been provided.

Polyamines: Functions, Metabolism, and Role in Human Disease Management

Putrescine, spermine, and spermidine are the important polyamines (PAs), found in all living organisms. PAs are formed by the decarboxylation of amino acids, and they facilitate cell growth and development via different cellular responses. PAs are the integrated part of the cellular and genetic metabolism and help in transcription, translation, signaling, and post-translational modifications. At the cellular level, PA concentration may influence the condition of various diseases in the body. For instance, a high PA level is detrimental to patients suffering from aging, cognitive impairment, and cancer. The levels of PAs decline with age in humans, which is associated with different health disorders. On the other hand, PAs reduce the risk of many cardiovascular diseases and increase longevity, when taken in an optimum quantity. Therefore, a controlled diet is an easy way to maintain the level of PAs in the body. Based on the nutritional intake of PAs, healthy cell functioning can be maintained. Moreover, several diseases can also be controlled to a higher extend via maintaining the metabolism of PAs. The present review discusses the types, important functions, and metabolism of PAs in humans. It also highlights the nutritional role of PAs in the prevention of various diseases.

Regulatory role of l-proline in fetal pig growth and intestinal epithelial cell proliferation

l-proline (Pro) is a precursor of ornithine, which is converted into polyamines via ornithine decarboxylase (ODC). Polyamines plays a key role in the proliferation of intestinal epithelial cells. The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro. Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77% alanine (Ala, iso-nitrogenous control), 1% Pro or 1% Pro + 0.0167% α-difluoromethylornithine (DFMO) from d 15 to 70 of gestation. The fetal body weight and number of fetuses per litter were determined, and the small and large intestines were obtained on d 70 ± 1.78 of gestation. The in vitro study was performed in intestinal porcine epithelial (IPEC-J2) cells cultured in Dulbecco's modified Eagle medium-high glucose (DMEM-H) containing 0 μmol/L Pro, 400 μmol/L Pro, or 400 μmol/L Pro + 10 mmol/L DFMO for 4 d. The results showed that maternal dietary supplementation with 1% Pro increased fetal weight; the protein and DNA concentrations of the fetal small intestine; and mRNA levels for potassium voltage-gated channel, shaker-related subfamily, member 1 (Kv1.1) in the fetal small and large intestines (P < 0.05). Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells (P < 0.05). In comparison with the Pro group, the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine, as well as the concentrations of putrescine, spermidine and spermine in IPEC-J2 cells (P < 0.05). Meanwhile, the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation, whereas depletion of cellular polyamines with DFMO increased tumor protein p53 (p53) mRNA levels (P < 0.05). Taken together, dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis.

The old and new biochemistry of polyamines

Polyamines are ubiquitous positively charged amines found in all organisms. These molecules play a crucial role in many biological functions including cell growth, gene regulation and differentiation. The three major polyamines produced in all mammalian cells are putrescine, spermidine and spermine. The intracellular levels of these polyamines depend on the interplay of the biosynthetic and catabolic enzymes of the polyamine and methionine salvage pathway, as well as the involvement of polyamine transporters. Polyamine levels are observed to be high in cancer cells, which contributes to malignant transformation, cell proliferation and poor patient prognosis. Considering the critical roles of polyamines in cancer cell proliferation, numerous anti-polyaminergic compounds have been developed as anti-tumor agents, which seek to suppress polyamine levels by specifically inhibiting polyamine biosynthesis, activating polyamine catabolism, or blocking polyamine transporters. However, in terms of the development of effective anti-cancer therapeutics targeting the polyamine system, these efforts have unfortunately resulted in little success. Recently, several studies using the iron chelators, O-trensox and ICL670A (Deferasirox), have demonstrated a decline in both iron and polyamine levels. Since iron levels are also high in cancer cells, and like polyamines, are required for proliferation, these latter findings suggest a biochemically integrated link between iron and polyamine metabolism.

Polyamines: Bio-Molecules with Diverse Functions in Plant and Human Health and Disease

Biogenic amines-polyamines (PAs), particularly putrescine, spermidine and spermine are ubiquitous in all living cells. Their indispensable roles in many biochemical and physiological processes are becoming commonly known, including promoters of plant life and differential roles in human health and disease. PAs positively impact cellular functions in plants-exemplified by increasing longevity, reviving physiological memory, enhancing carbon and nitrogen resource allocation/signaling, as well as in plant development and responses to extreme environments. Thus, one or more PAs are commonly found in genomic and metabolomics studies using plants, particulary during different abiotic stresses. In humans, a general decline in PA levels with aging occurs parallel with some human health disorders. Also, high PA dose is detrimental to patients suffering from cancer, aging, innate immunity and cognitive impairment during Alzheimer and Parkinson diseases. A dichotomy exists in that while PAs may increase longevity and reduce some age-associated cardiovascular diseases, in disease conditions involving higher cellular proliferation, their intake has negative consequences. Thus, it is essential that PA levels be rigorously quantified in edible plant sources as well as in dietary meats. Such a database can be a guide for medical experts in order to recommend which foods/meats a patient may consume and which ones to avoid. Accordingly, designing both high and low polyamine diets for human consumption are in vogue, particularly in medical conditions where PA intake may be detrimental, for instance, cancer patients. In this review, literature data has been collated for the levels of the three main PAs, putrescine, spermidine and spermine, in different edible sources-vegetables, fruits, cereals, nuts, meat, sea food, cheese, milk, and eggs. Based on our analysis of vast literature, the effects of PAs in human/animal health fall into two broad, Yang and Yin, categories: beneficial for the physiological processes in healthy cells and detrimental under pathological conditions.

Polyamines: therapeutic perspectives in oxidative stress and inflammatory diseases

Polyamines are naturally occurring aliphatic compounds, particularly essential elements for biological functions. These compounds play a central role in regulating molecular pathways which are responsible for cellular proliferation, growth, and differentiation. Importantly, excessive polyamine catabolism can lead to a prominent source of oxidative stress which increases inflammatory response and thought to be involved in several diseases including stroke, renal failure, neurological disease, liver disease, and even cancer. Moreover, polyamine supplementation increases life span in model organisms and may encounter oxidative stress via exerting its potential anti-oxidant and anti-inflammatory properties. The revealed literature indicates that an emerging role of polyamine biosynthetic pathway could be a novel target for drug development against inflammatory diseases. In this review, we expand the knowledge on the metabolism of polyamines, and its anti-oxidant and anti-inflammatory activities which might have future implications against inflammatory diseases in humans and animals.

Fecal Microbiota and Metabolome in a Mouse Model of Spontaneous Chronic Colitis: Relevance to Human Inflammatory Bowel Disease

BACKGROUND

Dysbiosis of the gut microbiota may be involved in the pathogenesis of inflammatory bowel disease (IBD). However, the mechanisms underlying the role of the intestinal microbiome and metabolome in IBD onset and its alteration during active treatment and recovery remain unknown. Animal models of chronic intestinal inflammation with similar microbial and metabolomic profiles would enable investigation of these mechanisms and development of more effective treatments. Recently, the Winnie mouse model of colitis closely representing the clinical symptoms and characteristics of human IBD has been developed. In this study, we have analyzed fecal microbial and metabolomic profiles in Winnie mice and discussed their relevance to human IBD.

METHODS

The 16S rRNA gene was sequenced from fecal DNA of Winnie and C57BL/6 mice to define operational taxonomic units at ≥97% similarity threshold. Metabolomic profiling of the same fecal samples was performed by gas chromatography-mass spectrometry.

RESULTS

Composition of the dominant microbiota was disturbed, and prominent differences were evident at all levels of the intestinal microbiome in fecal samples from Winnie mice, similar to observations in patients with IBD. Metabolomic profiling revealed that chronic colitis in Winnie mice upregulated production of metabolites and altered several metabolic pathways, mostly affecting amino acid synthesis and breakdown of monosaccharides to short chain fatty acids.

CONCLUSIONS

Significant dysbiosis in the Winnie mouse gut replicates many changes observed in patients with IBD. These results provide justification for the suitability of this model to investigate mechanisms underlying the role of intestinal microbiota and metabolome in the pathophysiology of IBD.

Copper-induced tight junction mRNA expression changes, apoptosis and antioxidant responses via NF-κB, TOR and Nrf2 signaling molecules in the gills of fish: preventive role of arginine

This study explored the possible preventive effects of dietary arginine on copper (Cu)-induced tight junction mRNA expression changes, apoptosis and antioxidant responses in the gills of young grass carp (Ctenopharyngodon idella). The results indicated that exposure to 0.7 mg/L (11.01 μmol/L) Cu for 96 h induced the production of reactive oxygen species (ROS), thereby increasing protein oxidation, lipid peroxidation and DNA damage in the gills of fish. However, these oxidative effects were prevented by arginine supplementation. Arginine also prevented the toxic effects of Cu on the activities of copper/zinc superoxide dismutase (SOD1), glutathione-S-transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR) and the glutathione (GSH) content (P<0.05). However, Cu induced an adaptive increase in the activity of catalase (CAT), and arginine supplementation further increased CAT activity (P<0.05). Moreover, Cu induced increases in the relative mRNA expressions of SOD1, CAT, GPx, GST, caspase-3, caspase-9, NF-E2-related factor 2 (Nrf2), Kelch-like-ECH-associated protein 1a (Keap1a), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-8 (IL-8), transforming growth factor-β (TGF-β) and nuclear transcription factor-κB p65 (NF-κB p65) in the gills of grass carp (P<0.05). In contrast, the relative mRNA expression levels of occludin, zonula occludens-1 (ZO-1), claudin b, claudin 3, claudin 12, target of rapamycin (TOR) and inhibitor factor κBα (IκBα) in the gills were decreased by Cu (P<0.05). However, pre-treatment of fish with arginine prevented Cu-induced relative mRNA expression decrease. Interestingly, Cu exposure resulted in increases in claudin 15a mRNA expression (P<0.05) but could not induce claudin c, caspase-8 and interleukin-10 (IL-10) mRNA expression changes in the gill of fish (P>0.05). These results indicated that Cu exposure induced apoptosis and antioxidant system and tight junction mRNA changes in the fish gills, which could be completely blocked by dietary arginine pre-supplementation.

Polyamines inhibit the assembly of stress granules in normal intestinal epithelial cells regulating apoptosis

Polyamines regulate multiple signaling pathways and are implicated in many aspects of cellular functions, but the exact molecular processes governed by polyamines remain largely unknown. In response to environmental stress, repression of translation is associated with the assembly of stress granules (SGs) that contain a fraction of arrested mRNAs and are thought to function as mRNA storage. Here we show that polyamines modulate the assembly of SGs in normal intestinal epithelial cells (IECs) and that induced SGs following polyamine depletion are implicated in the protection of IECs against apoptosis. Increasing the levels of cellular polyamines by ectopic overexpression of the ornithine decarboxylase gene decreased cytoplasmic levels of SG-signature constituent proteins eukaryotic initiation factor 3b and T-cell intracellular antigen-1 (TIA-1)-related protein and repressed the assembly of SGs induced by exposure to arsenite-induced oxidative stress. In contrast, depletion of cellular polyamines by inhibiting ornithine decarboxylase with α-difluoromethylornithine increased cytoplasmic eukaryotic initiation factor 3b and TIA-1 related protein abundance and enhanced arsenite-induced SG assembly. Polyamine-deficient cells also exhibited an increase in resistance to tumor necrosis factor-α/cycloheximide-induced apoptosis, which was prevented by inhibiting SG formation with silencing SG resident proteins Sort1 and TIA-1. These results indicate that the elevation of cellular polyamines represses the assembly of SGs in normal IECs and that increased SGs in polyamine-deficient cells are crucial for increased resistance to apoptosis.

Spermine, a molecular switch regulating EGFR, integrin β3, Src, and FAK scaffolding

Intracellular polyamine levels are highly regulated by the activity of ornithine decarboxylase (ODC), which catalyzes the first rate-limiting reaction in polyamine biosynthesis, producing putrescine, which is subsequently converted to spermidine and spermine. We have shown that polyamines regulate proliferation, migration, and apoptosis in intestinal epithelial cells. Polyamines regulate key signaling events at the level of the EGFR and Src. However, the precise mechanism of action of polyamines is unknown. In the present study, we demonstrate that ODC localizes in lamellipodia and in adhesion plaques during cell spreading. Spermine regulates EGF-induced migration by modulating the interaction of the EGFR with Src. The EGFR interacted with integrin β3, Src, and focal adhesion kinase (FAK). Active Src (pY418-Src) localized with FAK during spreading and migration. Spermine prevented EGF-induced binding of the EGFR with integrin β3, Src, and FAK. Activation of Src and FAK was necessary for EGF-induced migration in HEK293 cells. EGFR-mediated Src activation in live HEK293 cells using a FRET based Src reporter showed that polyamine depletion significantly increased Src kinase activity. In vitro binding studies showed that spermine directly binds Src, and preferentially interacts with the SH2 domain of Src. The physical interaction between Src and the EGFR was severely attenuated by spermine. Therefore, spermine acts as a molecular switch in regulating EGFR-Src coupling both physically and functionally. Upon activation of the EGFR, integrin β3, FAK and Src are recruited to EGFR leading to the trans-activation of both the EGFR and Src and to the Src-mediated phosphorylation of FAK. The activation of FAK induced Rho-GTPases and subsequently migration. This is the first study to define mechanistically how polyamines modulate Src function at the molecular level.

Regulation of polyamine metabolism by translational control

Polyamines are low molecular weight, positively charged compounds that are ubiquitous in all living cells. They play a crucial role in many biochemical processes including regulation of transcription and translation, modulation of enzyme activities, regulation of ion channels and apoptosis. A strict balance between synthesis, catabolism and excretion tightly controls the cellular concentration of polyamines. The concentrations of rate-limiting enzymes in the polyamine synthesis and degradation pathways are regulated at different levels, including transcription, translation and degradation. Polyamines can modulate the translation of most of the enzymes required for their synthesis and catabolism through feedback mechanisms that are unique for each enzyme. Translational control is associated with cis-acting and trans-acting factors that can be influenced by the concentration of polyamines through mechanisms that are not completely understood. In this review, we present an overview of the translational control mechanisms of the proteins in the polyamine pathway, including ornithine decarboxylase (ODC), ODC antizyme, S-adenosylmethionine decarboxylase and spermidine/spermine N(1) acetyltransferase, highlighting the areas where more research is needed. A better understanding of the translational control of these enzymes would offer the possibility of a novel pharmacological intervention against cancer and other diseases.

A recombinant catalytic domain of matriptase induces detachment and apoptosis of small-intestinal epithelial IEC-6 cells cultured on laminin-coated surface

Matriptase is a type-II transmembrane serine protease that is expressed strongly in the epithelial elements of various organs. In the small intestine, it is expressed prominently at the villus tip where aged epithelial cells undergo shedding and/or apoptosis. This observation, together with the ability of matriptase to cleave laminin (a basement membrane component critical for epithelial cell attachment), prompted us to hypothesize that it plays an important part in the removal of aged epithelial cells in the small intestine. We tested this hypothesis by determining whether a recombinant catalytic domain of rat matriptase (His(6)t-S-CD) causes detachment and/or apoptosis of small-intestinal epithelial IEC-6 cells. His(6)t-S-CD caused detachment of cells attached to laminin-coated plates but did not detach cells attached to fibronectin- or type-IV collagen-coated plates. Pre-treatment of laminin-coated plates with His(6)t-S-CD decreased the attachment of cells, suggesting that the recombinant matriptase caused detachment through a mechanism involving a direct effect on laminin. His(6)t-S-CD was also found to induce apoptosis in the cells cultured on laminin-coated plates, as assessed by annexin-V staining, DNA fragmentation and caspase-3 activity assays. These findings support our hypothesis regarding the role of matriptase in the small intestine.

Metabolic correlations of glucocorticoids and polyamines in inflammation and apoptosis

Glucocorticoid hormones (GC) are essential in all aspects of human health and disease. Their anti-inflammatory and immunosuppressive properties are reasons for therapeutic application in several diseases. GC suppress immune activation and uncontrolled overproduction and release of cytokines. GC inhibit the release of pro-inflammatory cytokines and stimulate the production of anti-inflammatory cytokines. Investigation of GC's mechanism of action, suggested that polyamines (PA) may act as mediators or messengers of their effects. Beside glucocorticoids, spermine (Spm) is one of endogenous inhibitors of cytokine production. There are many similarities in the metabolic actions of GC and PA. The major mechanism of GC effects involves the regulation of gene expression. PA are essential for maintaining higher order organization of chromatin in vivo. Spermidine and Spm stabilize chromatin and nuclear enzymes, due to their ability to form complexes with negatively charged groups on DNA, RNA and proteins. Also, there is an increasing body of evidence that GC and PA change the chromatin structure especially through acetylation and deacetylation of histones. GC display potent immunomodulatory activities, including the ability to induce T and B lymphocyte apoptosis, mediated via production of reactive oxygen species (ROS) in the mitochondrial pathway. The by-products of PA catabolic pathways (hydrogen peroxide, amino aldehydes, acrolein) produce ROS, well-known cytotoxic agents involved in programmed cell death (PCD) or apoptosis. This review is an attempt in the better understanding of relation between GC and PA, naturally occurring compounds of all eukaryotic cells, anti-inflammatory and apoptotic agents in physiological and pathological conditions connected to oxidative stress or PCD.

Inhibition of arginase activity enhances inflammation in mice with allergic airway disease, in association with increases in protein S-nitrosylation and tyrosine nitration

Pulmonary inflammation in asthma is orchestrated by the activity of NF-kappaB. NO and NO synthase (NOS) activity are important modulators of inflammation. The availability of the NOS substrate, l-arginine, is one of the mechanisms that controls the activity of NOS. Arginase also uses l-arginine as its substrate, and arginase-1 expression is highly induced in a murine model of asthma. Because we have previously described that arginase affects NOx content and interferes with the activation of NF-kappaB in lung epithelial cells, the goal of this study was to investigate the impact of arginase inhibition on the bioavailability of NO and the implications for NF-kappaB activation and inflammation in a mouse model of allergic airway disease. Administration of the arginase inhibitor BEC (S-(2-boronoethyl)-l-cysteine) decreased arginase activity and caused alterations in NO homeostasis, which were reflected by increases in S-nitrosylated and nitrated proteins in the lungs from inflamed mice. In contrast to our expectations, BEC enhanced perivascular and peribronchiolar lung inflammation, mucus metaplasia, NF-kappaB DNA binding, and mRNA expression of the NF-kappaB-driven chemokine genes CCL20 and KC, and lead to further increases in airways hyperresponsiveness. These results suggest that inhibition of arginase activity enhanced a variety of parameters relevant to allergic airways disease, possibly by altering NO homeostasis.

Induced TRPC1 expression increases protein phosphatase 2A sensitizing intestinal epithelial cells to apoptosis through inhibition of NF-kappaB activation

Transient receptor potential canonical-1 (TRPC1) functions as a store-operated Ca2+ channel in intestinal epithelial cells (IECs), and induced TRPC1 expression sensitizes IECs to apoptosis by inhibiting NF-kappaB activation. However, the exact mechanism by which increased TRPC1 results in NF-kappaB inactivation remains elusive. Protein phosphatase 2A (PP2A) is a widely conserved protein serine/threonine phosphatase that is implicated in the regulation of a wide array of cellular functions including apoptosis. The present study tests the hypothesis that induced TRPC1 expression inhibits NF-kappaB activation by increasing PP2A activity through Ca2+ influx in IECs. The expression of TRPC1 induced by stable transfection with the wild-type TRPC1 gene increased PP2A activity as indicated by increases in levels of PP2A proteins and their phosphatase activity. Increased levels of PP2A activity in stable TRPC1-transfected IEC-6 cells (IEC-TRPC1) were associated with decreased nuclear levels of NF-kappaB proteins and a reduction in NF-kappaB-dependent transcriptional activity, although there were no changes in total NF-kappaB protein levels. Inhibition of PP2A activity by treatment with okadaic acid or PP2A silencing with small interfering RNA not only enhanced NF-kappaB transactivation but also prevented the increased susceptibility of IEC-TRPC1 cells to apoptosis induced by treatment with tumor necrosis factor-alpha (TNF-alpha)/cycloheximide (CHX). Decreasing Ca2+ influx by exposure to the Ca2+-free medium reduced PP2A mRNA levels, destabilized PP2A proteins, and induced NF-kappaB activation, thus blocking the increased sensitivity of IEC-TRPC1 cells to TNF-alpha/CHX-induced apoptosis. These results indicate that induced TRPC1 expression increases PP2A activity through Ca2+ influx and that increased PP2A sensitizes IECs to apoptosis as a result of NF-kappaB inactivation.

Polyamines modulate the subcellular localization of RNA-binding protein HuR through AMP-activated protein kinase-regulated phosphorylation and acetylation of importin alpha1

Polyamines are required for maintenance of intestinal epithelial integrity, and a decrease in cellular polyamines increases the cytoplasmic levels of RNA-binding protein HuR stabilizing p53 and nucleophosmin mRNAs, thus inhibiting IEC (intestinal epithelial cell) proliferation. The AMPK (AMP-activated protein kinase), an enzyme involved in responding to metabolic stress, was recently found to be implicated in regulating the nuclear import of HuR. Here, we provide evidence showing that polyamines modulate subcellular localization of HuR through AMPK-regulated phosphorylation and acetylation of Impalpha1 (importin alpha1) in IECs. Decreased levels of cellular polyamines as a result of inhibiting ODC (ornithine decarboxylase) with DFMO (D,L-alpha-difluoromethylornithine) repressed AMPK activity and reduced Impalpha1 levels, whereas increased levels of polyamines as a result of ODC overexpression induced both AMPK and Impalpha1 levels. AMPK activation by overexpression of the AMPK gene increased Impalpha1 but reduced the cytoplasmic levels of HuR in control and polyamine-deficient cells. IECs overexpressing wild-type Impalpha1 exhibited a decrease in cytoplasmic HuR abundance, while cells overexpressing Impalpha1 proteins bearing K22R (lacking acetylation site), S105A (lacking phosphorylation site) or K22R/S105A (lacking both sites) mutations displayed increased levels of cytoplasmic HuR. Ectopic expression of these Impalpha1 mutants also prevented the increased levels of cytoplasmic HuR following polyamine depletion. These results indicate that polyamine-mediated AMPK activation triggers HuR nuclear import through phosphorylation and acetylation of Impalpha1 in IECs and that polyamine depletion increases cytoplasmic levels of HuR as a result of inactivation of the AMPK-driven Impalpha1 pathway.

Ornithine decarboxylase interferes with macrophage-like differentiation and matrix metalloproteinase-9 expression by tumor necrosis factor alpha via NF-kappaB

Ornithine decarboxylase (ODC), a tumor promoter, provokes cell proliferation, and inhibits cell death; but the mechanism involved in cell differentiation remains unknown. Herein, we examine whether it functions during macrophage-like differentiation. Previous studies reveal that ODC, a rate-limiting enzyme of polyamine biosynthesis, and polyamines are involved in restraining immune response in activated macrophage. By using 12-O-tetradecanoylphorbol-13-acetate (TPA)-differentiated human promyelocytic HL-60 and promonocytic U-937 cells, we discover that polyamines block the expression, secretion and activation of MMP-9. Meanwhile conventional expression of ODC represses tumor necrosis factor-alpha (TNF-alpha) expression and nuclear factor-kappaB (NF-kappaB) activation as well as MMP-9 enzyme activity. Following stimulation by TNF-alpha, the secretion of MMP-9 is restored in ODC-overexpressed cells. In addition, the NF-kappaB inhibitors (pyrrolidinedithiocarbamate, BAY-11-7082 and lactacystin) suppress the TPA-induced MMP-9 enzyme activity. Concurrently, both the irreversible inhibitor of ODC, alpha-difluoromethylornithine, and TNF-alpha could not recover MMP-9 activation following NF-kappaB inhibitor treatment in parental cells. Furthermore, ODC could directly inhibit and attenuate NF-kappaB DNA binding and transcriptional activation. Therefore, we suggest that ODC inhibits the TNF-alpha-elevated MMP-9 activation via NF-kappaB as TPA-induced macrophage-like differentiation and this interrupting mechanism may provide a new conceivable resolution why leukemia is poorly differentiated besides atypical growth.

Decreased apoptosis in polyamine depleted IEC-6 cells depends on Akt-mediated NF-kappaB activation but not GSK3beta activity

The PI3-kinase/Akt pathway promotes cell survival in many different cell types including intestinal epithelial cells. Increased AKT activation in polyamine depleted intestinal epithelial cells correlated well with the decrease in TNF-alpha-induced apoptosis. Increased Akt activation and GSK3beta (Ser 9) phosphorylation without significant effect on Bad (Ser136) phosphorylation indicate that Akt-mediated protection is independent of Bad phosphorylation but may depend on GSK3beta. Pretreatment of polyamine-depleted cells with LY294002 increased caspase-9 and caspase-3 activation and decreased basal levels of GSK-3beta phosphorylation. Inhibition of GSK3beta activity using AR-A014418 or lithium chloride or siRNA-mediated downregulation of its expression had no effect on apoptosis. Inhibition of PI3-kinase and over-expression of dominant negative Akt (DN-AKT), significantly increased apoptosis in polyamine depleted cells. DN-Akt expression reversed the protective effect of polyamine depletion on apoptosis. DN-Akt, as well as the PI3-kinase inhibitors, prevented Akt activation and subsequent translocation of NF-kappaB to the nucleus. Constitutively active Akt (CA-AKT) expression increased resistance to TNF-alpha-induced apoptosis. Constitutively active-Akt expression increased nuclear staining of NF-kappaB. Moreover, polyamine depletion of DN-Akt cells prevented basal and TNF-alpha-induced IkappaBalpha phosphorylation. Prevention of NF-kappaB activation in DN-IkappaBalpha-transfected cells increased apoptosis in control cells and restored it in polyamine-depleted cells to control levels. These data indicate that Akt regulates the mitochondrial pathway, preventing activation of caspase-9 and thereby caspase-3 via NF-kappaB and these effects are independent of GSK-3beta activity.

Inflammation and polyamine catabolism: the good, the bad and the ugly

The induction of polyamine catabolism by specific anti-tumour polyamine analogues has increased interest in the roles polyamine catabolism play in cell growth, death and response to various anti-tumour agents. The relatively recent finding of an inducible mammalian spermine oxidase (SMO/PAOh1), in addition to the two-step spermidine/spermine N(1)-acetyltransferanse (SSAT)/N(1)-acetylpolyamine oxidase (APAO) catabolic pathway, underscores the complexities of the regulation of polyamine catabolism by various stimuli. Furthermore, recent data indicate that infectious agents and mediators of inflammation can also up-regulate polyamine catabolism. Induction of SSAT by these agents can reduce intracellular polyamine concentrations and cell growth rate, thus providing a beneficial mechanism by which cells may adapt to inflammatory stress. However, increased polyamine catabolism can also result in substantial increases in intracellular reactive oxygen species (ROS) through the production of H(2)O(2) as a by-product of either APAO or SMO/PAOh1 activity. This increased generation of ROS can have different results, depending on the mechanism of induction and cell types involved. Targeted killing of tumour cells by agents that stimulate SSAT/APAO and/or SMO/PAOh1 is obviously a 'good' effect. However, induction of SMO/PAOh1 by inflammation or infectious agents has the potential to produce sufficient ROS in normal, non-tumour cells to lead to DNA damage, mutation and, potentially, carcinogenic transformation ('bad'). The variation in the induction of these polyamine catabolic enzymes, as well as the level and timing of this induction will dictate the cellular outcome in the presence of both desirable and undesirable effects ('ugly'). Here we discuss the relative role of each of the steps in polyamine catabolism in response to inflammatory stress.

Polyamines and the intestinal tract

Owing to their high turnover, the intestinal mucosal cells have a particularly high requirement for polyamines. Therefore, they are an excellent charcol for the study of polyamine function in rapid physiological growth and differentiation. After a cursory introduction to the major aspects of polyamine metabolism, regulation, and mode of action, we discuss the contribution of the polyamines to the maintenance of normal gut function, the maturation of the intestinal mucosa, and its repair after injuries. Repletion of cellular polyamine pools with (D,L)-2-(difluoromethyl)ornithine has considerably improved our understanding of how the polyamines are involved in the regulation of normal and neoplastic growth. Unfortunately, the attempts to exploit polyamine metabolism as a cancer therapeutic target have not yet been successful. However, the selective inactivation of ornithine decarboxylase appears to be a promising chemopreventive method in familial adenomatous polyposis. Presumably, it relies on the fact that ornithine decarboxylase is a critical regulator of the proliferative response of the protooncogene c-myc, but not of its apoptotic response.

p53-Dependent NDRG1 expression induces inhibition of intestinal epithelial cell proliferation but not apoptosis after polyamine depletion

Normal intestinal mucosal growth requires polyamines that regulate expression of various genes involved in cell proliferation, growth arrest, and apoptosis. Our previous studies have shown that polyamine depletion stabilizes p53, resulting in inhibition of intestinal epithelial cell (IEC) proliferation, but the exact downstream targets of induced p53 are still unclear. The NDRG1 (N- myc downregulated gene-1) gene encodes a growth-related protein, and its transcription can be induced in response to stress. The current study tests the hypothesis that induced p53 inhibits IEC proliferation by upregulating NDRG1 expression following polyamine depletion. Depletion of cellular polyamines by inhibiting ornithine decarboxylase (ODC) with α-difluoromethylornithine not only induced p53 but also increased NDRG1 transcription as indicated by induction of the NDRG1 promoter activity and increased levels of NDRG1 mRNA and protein, all of which were prevented by using specific p53 siRNA and in cells with a targeted deletion of p53. In contrast, increased levels of cellular polyamines by ectopic expression of the ODC gene decreased p53 and repressed expression of NDRG1. Consistently, polyamine depletion-induced activation of the NDRG1-promoter was decreased when p53-binding sites within the NDRG1 proximal promoter region were deleted. Ectopic expression of the wild-type NDRG1 gene inhibited DNA synthesis and decreased final cell numbers regardless of the presence or absence of endogenous p53, whereas silencing NDRG1 promoted cell growth. However, overexpression of NDRG1 failed to directly induce cell death and to alter susceptibility to apoptosis induced by tumor necrosis factor-α/cycloheximide. These results indicate that NDRG1 is one of the direct mediators of induced p53 following polyamine depletion and that p53-dependent NDRG1 expression plays a critical role in the negative control of IEC proliferation.

Role of polyamines in myocardial ischemia/reperfusion injury and their interactions with nitric oxide

Polyamines (putrescine, spermidine, and spermine) are present in all higher eukaryotic cells and are essential for cell growth, differentiation and apoptosis. Sharing common precursor with polyamines, nitric oxide (NO) is associated with myocardial ischemia/reperfusion injury by the generation of peroxynitrite. Although polyamines have been implicated in tissue ischemia injury, their metabolism and interactions with NO in myocardial ischemia/reperfusion injury have not been fully understood. In our experiment, when Langendorff perfused rat hearts were subjected to 40 min ischemia without reperfusion, both ornithine decarboxylase (ODC) and Spermidine/spermine N(1)-acetyltransferase (SSAT) activities were up-regulated and putrescine accumulated. While after reperfusion, ODC activity decreased and SSAT activity increased, resulting in putrescine accumulation and decreased spermidine and spermine. Meanwhile NO content was increased. In addition, sodium nitroprusside (SNP, a NO donor) decreased ODC activity in cardiac tissue homogenate but increased SSAT activity in a dose-dependent manner. Pre-treatment of isolated heart with N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, an inhibitor of NO synthase) increased ODC activity. Exogenous spermine (1 mM) administration prior to ischemia prevented spermine decrease, reduced cardiac myocyte necrosis and apoptosis, and promoted the recovery of cardiac function after ischemia/reperfusion. These results suggest that acute heart ischemia activates myocardial polyamine stress response characterized by increased ODC and SSAT activities and accumulation of putrescine. Ischemia/reperfusion disturbs polyamine metabolism, and the loss of spermine might be associated with NO increase and thereby influences myocardial cell viability. Exogenous spermine may protect the hearts from myocardial ischemia/reperfusion injury.

Integrin beta3-mediated Src activation regulates apoptosis in IEC-6 cells via Akt and STAT3

Intestinal epithelial (IEC-6) cells are resistant to apoptosis following the inhibition of ODC (ornithine decarboxylase) and subsequent polyamine depletion. The depletion of polyamines rapidly activates NF-kappaB (nuclear factor kappaB) and STAT3 (signal transducer and activator of transcription 3), which is responsible for the observed decrease in apoptosis. Since both NF-kappaB and STAT3 signalling pathways can be activated by Src kinase, we examined its role in the antiapoptotic response. Inhibition of ODC by DFMO (alpha-difluoromethylornithine) increased the activity of Src and ERK1/2 (extracellular-signal-regulated kinase 1/2) within 30 min, which was prevented by exogenous polyamines added to the DFMO-containing medium. Conversely, epidermal growth factor-mediated Src and ERK1/2 activation was not prevented by the addition of polyamines. Inhibition of Src with PP2 {4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine} and a DN-Src (dominant-negative Src) construct prevented the activation of Akt, JAK (Janus kinase) and STAT3. Spontaneous apoptosis was increased in DN-Src-expressing cells and the protective effect of polyamine depletion was lost. Polyamine depletion by DFMO increased integrin beta3 Tyr785 phosphorylation. Cells plated on fibronectin had significantly higher beta3 phosphorylation and Src activation compared with plastic. Exogenous polyamines added to the fibronectin matrix prevented Src activation. Arg-Gly-Asp-Ser inhibited beta3, Src and Akt phosphorylation and sensitized polyamine-depleted cells to tumour necrosis factor alpha/cycloheximide-mediated apoptosis. Fibronectin activated Src and subsequently protected cells from apoptosis. Together, these results suggest that the inhibition of ODC rapidly removes a small pool of available polyamines triggering the activation of beta3 integrin, which in turn activates Src. The subsequent Akt and JAK activation is accompanied by translocation of NF-kappaB and STAT3 to the nucleus and the synthesis of antiapoptotic proteins.

Tumor Necrosis Factor α Induces Spermidine/Spermine N1-Acetyltransferase through Nuclear Factor κBin Non-small Cell Lung Cancer Cells

Tumor necrosis factor alpha (TNFalpha) is a potent pleiotropic cytokine produced by many cells in response to inflammatory stress. The molecular mechanisms responsible for the multiple biological activities of TNFalpha are due to its ability to activate multiple signal transduction pathways, including nuclear factor kappaB (NFkappaB), which plays critical roles in cell proliferation and survival. TNFalpha displays both apoptotic and antiapoptotic properties, depending on the nature of the stimulus and the activation status of certain signaling pathways. Here we show that TNFalpha can lead to the induction of NFkappaB signaling with a concomitant increase in spermidine/spermine N(1)-acetyltransferase (SSAT) expression in A549 and H157 non-small cell lung cancer cells. Induction of SSAT, a stress-inducible gene that encodes a rate-limiting polyamine catabolic enzyme, leads to lower intracellular polyamine contents and has been associated with decreased cell growth and increased apoptosis. Stable overexpression of a mutant, dominant negative IkappaBalpha protein led to the suppression of SSAT induction by TNFalpha in these cells, thereby substantiating a role of NFkappaB in the induction of SSAT by TNFalpha. SSAT promoter deletion constructs led to the identification of three potential NFkappaB response elements in the SSAT gene. Electromobility shift assays, chromatin immunoprecipitation experiments and mutational studies confirmed that two of the three NFkappaB response elements play an important role in the regulation of SSAT in response to TNFalpha. The results of these studies indicate that a common mediator of inflammation can lead to the induction of SSAT expression by activating the NFkappaB signaling pathway in non-small cell lung cancer cells.

Induced TRPC1 expression sensitizes intestinal epithelial cells to apoptosis by inhibiting NF-kappaB activation through Ca2+ influx

Apoptosis occurs within crypts and at the intestinal luminal surface and plays a critical role in mucosal homoeostasis. NF-kappaB (nuclear factor-kappaB) is the central regulator of the transcription of genes involved in apoptosis, and its activity is highly regulated in the intestinal mucosa. We have recently demonstrated that TRPC1 (transient receptor potential canonical-1) is expressed in IECs (intestinal epithelial cells) and functions as a Ca2+ permeable channel activated by Ca2+ store depletion. The present study tests the hypothesis that TRPC1 channels are implicated in the regulation of apoptosis by inhibiting NF-kappaB through the induction of TRPC1-mediated Ca2+ influx in the IEC-6 line. The expression of TRPC1 induced by stable transfection of IEC-6 cells with the wild-type TRPC1 gene (IEC-TRPC1 cells) increased Ca2+ influx after Ca2+ store depletion and repressed NF-kappaB transactivation, which was associated with an increase in susceptibility to apoptosis induced by exposure to TNFalpha (tumour necrosis factor-alpha) plus CHX (cycloheximide) (TNF-alpha/CHX), or STS (staurosporine). By contrast, the induction of endogenous NF-kappaB activity, by the depletion of cellular polyamines, promoted resistance to apoptosis, which was prevented by the ectopic expression of the IkappaBalpha super-repressor. Furthermore, inhibition of TRPC1 expression by transfection with siRNA (small interfering RNA) targeting TRPC1 (siTRPC1) decreased Ca2+ influx, increased NF-kappaB transactivation, and prevented the increased susceptibility of IEC-TRPC1 cells to apoptosis. Decreasing Ca2+ influx by exposure to a Ca2+-free medium also induced NF-kappaB activity and blocked the increased susceptibility to apoptosis of stable IEC-TRPC1 cells. These results indicate that induced TRPC1 expression sensitizes IECs to apoptosis by inhibiting NF-kappaB activity as a result of the stimulation of Ca2+ influx.

Polyamine-mediated reduction in human airway epithelial migration in response to wounding is PGE2 dependent through decreases in COX-2 and cPLA2 protein levels

Both ornithine decarboxylase inhibition to deplete polyamines and cyclooxygenase inhibition diminish the migration response to injury of human airway epithelial cells in tissue culture monolayers by approximately 75%. Restoration of normal migration responses is achieved in the polyamine depleted system either by exogenous reconstitution of polyamines or the addition of prostaglandin E(2) (PGE(2)). However, only PGE(2) was able to restore migration in the cyclooxygenase-inhibited systems. Western blot for cyclooxygenase-2 and cytosolic phospholipase A(2) protein levels and ELISAs for PGE(2) secretion demonstrate dramatic increases over 24-48 h after monolayer wounding. These increases are completely abolished by polyamine depletion or cyclooxygenase inhibition. We conclude that polyamine inhibition decreases cellular migration in response to injury in airway epithelial cells at least in part through inhibiting normal PGE(2) production in response to injury. This may be brought about by decreases in cytosolic phospholipase A(2) and cyclooxygenase-2 protein levels.

Polyamine depletion increases cytoplasmic levels of RNA-binding protein HuR leading to stabilization of nucleophosmin and p53 mRNAs

Polyamines are essential for maintaining normal intestinal epithelial integrity, an effect that relies, at least in part, on their ability to keep low levels of nucleophosmin (NPM) and p53 mRNAs. The RNA-binding protein HuR associates with the p53 mRNA, as reported previously, and with the NPM mRNA, computationally predicted to be a target of HuR. Here, we show that HuR binds the NPM and p53 3'-untranslated regions and stabilizes these mRNAs in polyamine-depleted intestinal epithelial cells. Depletion of cellular polyamines by inhibiting ornithine decarboxylase with alpha-difluoromethylornithine dramatically enhanced the cytoplasmic abundance of HuR, whereas ectopic ornithine decarboxylase overexpression decreased cytoplasmic HuR; neither intervention changed whole-cell HuR levels. HuR was found to specifically bind the 3'-untranslated regions of NPN and p53 mRNAs. HuR silencing rendered the NPM and p53 mRNAs unstable and prevented increases in NPM and p53 mRNA and protein in polyamine-deficient cells. These results indicate that polyamines modulate cytoplasmic HuR levels in intestinal epithelial cells, in turn controlling the stability of the NPM and p53 mRNAs and influencing NPM and p53 protein levels.

Revisiting the immunomodulators tacrolimus, methotrexate, and mycophenolate mofetil: their mechanisms of action and role in the treatment of IBD

Inflammatory bowel diseases (IBDs) are thought to result from unopposed immune responses to normal gut flora in a genetically susceptible host. A variety of immunomodulating therapies are applied for the treatment of patients with IBDs. The first-line treatment for IBDs consists of 5-aminosalicylate and/or budesonide. However, these first-line therapies are often not suitable for continuous treatment or do not suffice for the treatment of severe IBD. Recently, efforts have been made to generate novel selective drugs that are more effective and have fewer side effects. Despite promising results, most of these novel drugs are still in a developmental stage and unavailable for clinical application. Yet, another class of established immunomodulators exists that is successful in the treatment of inflammatory bowel diseases. While waiting for emerging novel therapies, the use of these more established drugs should be considered. Furthermore, one of the advantages of using established immunomodulators is the well-documented knowledge on the long-term side effects and on the mechanisms of action. In this review, the authors discuss 3 well-known immunomodulators that are being applied with increased frequency for the treatment of IBD: tacrolimus, methotrexate, and mycophenolate mofetil. These agents have been used for many years as treatment modalities for immunosuppression after organ transplantation, for the treatment of cancer, and for immunomodulation in several other immune-mediated diseases. First, this review discusses the potential targets for immunomodulating therapies in IBDs. Second, the immunomodulating mechanisms and effects of the 3 immunomodulators are discussed in relationship to these treatment targets.

STAT3-mediated transcription of Bcl-2, Mcl-1 and c-IAP2 prevents apoptosis in polyamine-depleted cells

Activation of STAT3 (signal transducer and activator of transcription 3) plays a crucial role in cell survival and proliferation. The aim of the present study was to clarify the role of STAT3 signalling in the protection of polyamine-depleted intestinal epithelial cells against TNF-alpha (tumour necrosis factor-alpha)-induced apoptosis. Polyamine depletion by DFMO (alpha-difluoromethylornithine) caused phosphorylation of STAT3 at Tyr-705 and Ser-727. Phospho-Tyr-705 STAT3 was immunolocalized at the cell periphery and nucleus, whereas phospho-Ser-727 STAT3 was predominantly detected in the nucleus of polyamine-depleted cells. Sustained phosphorylation of STAT3 at tyrosine residues was observed in polyamine-depleted cells after exposure to TNF-alpha. Inhibition of STAT3 activation by AG490 or cell-membrane-permeant inhibitory peptide (PpYLKTK; where pY represents phospho-Tyr) increased the sensitivity of polyamine-depleted cells to apoptosis. Expression of DN-STAT3 (dominant negative-STAT3) completely eliminated the protective effect of DFMO against TNF-alpha-induced apoptosis. Polyamine depletion increased mRNA and protein levels for Bcl-2, Mcl-1 (myeloid cell leukaemia-1) and c-IAP2 (inhibitor of apoptosis protein-2). Significantly higher levels of Bcl-2 and c-IAP2 proteins were observed in polyamine-depleted cells before and after 9 h of TNF-alpha treatment. Inhibition of STAT3 by AG490 and DN-STAT3 decreased Bcl-2 promoter activity. DN-STAT3 decreased mRNA and protein levels for Bcl-2, Mcl-1 and c-IAP2 in polyamine-depleted cells. siRNA (small interfering RNA)-mediated inhibition of Bcl-2, Mcl-1 and c-IAP2 protein levels increased TNF-alpha-induced apoptosis. DN-STAT3 induced the activation of caspase-3 and PARP [poly(ADP-ribose) polymerase] cleavage in polyamine-depleted cells. These results suggest that activation of STAT3 in response to polyamine depletion increases the transcription and subsequent expression of anti-apoptotic Bcl-2 and IAP family proteins and thereby promotes survival of cells against TNF-alpha-induced apoptosis.

Induced focal adhesion kinase expression suppresses apoptosis by activating NF-kappaB signaling in intestinal epithelial cells

Focal adhesion kinase (FAK) integrates various extracellular and intracellular signals and is implicated in a variety of biological functions, but its exact role and downstream targeting signals in the regulation of apoptosis in intestinal epithelial cells (IECs) remains unclear. The current study tested the hypothesis that FAK has an antiapoptotic role in the IEC-6 cell line by altering NF-kappaB signaling. Induced FAK expression by stable transfection with the wild-type (WT)-FAK gene increased FAK phosphorylation, which was associated with an increase in NF-kappaB activity. These stable WT-FAK-transfected IECs also exhibited increased resistance to apoptosis when they were exposed to TNF-alpha plus cycloheximide (TNF-alpha/CHX). Specific inhibition of NF-kappaB by the recombinant adenoviral vector containing the IkappaBalpha superrepressor prevented increased resistance to apoptosis in WT-FAK-transfected cells. In contrast, inactivation of FAK by ectopic expression of dominant-negative mutant of FAK (DNM-FAK) inhibited NF-kappaB activity and increased the sensitivity to TNF-alpha/CHX-induced apoptosis. Furthermore, induced expression of endogenous FAK by depletion of cellular polyamines increased NF-kappaB activity and resulted in increased resistance to TNF-alpha/CHX-induced apoptosis, both of which were prevented by overexpression of DNM-FAK. These results indicate that increased expression of FAK suppresses TNF-alpha/CHX-induced apoptosis, at least partially, through the activation of NF-kappaB signaling in IECs.

Polyamines and apoptosis

The natural polyamines putrescine, spermidine and spermine are in multiple ways involved in cell growth and the maintenance of cell viability. In the course of the last 15 years more and more evidence hinted also at roles in gene regulation. It is therefore not surprising that the polyamines are involved in events inherent to genetically programmed cell death. Following inhibition of ornithine decarboxylase, a key step in polyamine biosynthesis, numerous links have been identified between the polyamines and apoptotic pathways. Examples of activation and prevention of apoptosis due to polyamine depletion are known for several cell lines. Elevation of polyamine concentrations may lead to apoptosis or to malignant transformation. These observations are discussed in the present review, together with possible mechanisms of action of the polyamines. Contradictory results and incomplete information blur the picture and complicate interpretation. Since, however, much interest is focussed at present on all aspects of programmed cell death, a considerable progress in the elucidation of polyamine functions in apoptotic signalling pathways is expected, even though enormous difficulties oppose pinpointing specific interactions of the polyamines with pro- and anti-apoptotic factors. Such situation is quite common in polyamine research.

Polyamine depletion inhibits NF-kappaB binding to DNA and interleukin-8 production in human chondrocytes stimulated by tumor necrosis factor-alpha

The activation of the NF-kappaB pathway by pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNFalpha), can be an important contributor for the re-programming of chondrocyte gene expression, thereby making it a therapeutic target in articular diseases. To search for new approaches to limit cartilage damage, we investigated the requirement of polyamines for NF-kappaB activation by TNFalpha in human C-28/I2 chondrocytes, using alpha-difluoromethylornithine (DFMO), a specific polyamine biosynthesis inhibitor. The NF-kappaB pathway was dissected by using pharmacological inhibitors or by expressing a transdominant IkappaBalpha super repressor. Treatment of C-28/I2 chondrocytes with TNFalpha resulted in a rapid enhancement of nuclear localization and DNA binding activity of the p65 NF-kappaB subunit. TNFalpha also increased the level and extracellular release of interleukin-8 (IL-8), a CXC chemokine that can have a role in arthritis, in an NF-kappaB-dependent manner. Pre-treatment of chondrocytes with DFMO, while causing polyamine depletion, significantly reduced NF-kappaB DNA binding activity. Moreover, DFMO also decreased IL-8 production without affecting cellular viability. Restoration of polyamine levels by the co-addition of putrescine circumvented the inhibitory effects of DFMO. Our results show that the intracellular depletion of polyamines inhibits the response of chondrocytes to TNFalpha by interfering with the DNA binding activity of NF-kappaB. This suggests that a pharmacological and/or genetic approach to deplete the polyamine pool in chondrocytes may represent a useful way to reduce NF-kappaB activation by inflammatory cytokines in arthritis without provoking chondrocyte apoptosis.

Polyamine depletion reduces TNFalpha/MG132-induced apoptosis in bone marrow stromal cells

Polyamines are powerful modulators of both growth and survival in mammalian cells. In this study, we investigated the possibility of attenuating the process of apoptosis in bone marrow stromal cells (BMSCs), which comprise mesenchymal stem cells, by reducing the intracellular levels of polyamines. BMSCs were isolated from rat femurs and expanded for 12 days. At this time, BMSCs were CD34neg, CD45neg, and mostly CD90pos. BMSCs were grown for an additional 2 days in the presence of 1 mM alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, which reduced the content of both putrescine and spermidine by nearly 90%. DFMO treatment progressively slowed down BMSC proliferation, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay, without arresting their growth completely. The effect of polyamine depletion on caspase-3 activity was evaluated in BMSCs after treatment with 500 U/ml tumor necrosis factor-alpha (TNFalpha) and 5 microM MG132, an inhibitor of proteasome. Caspase-3 activity increased linearly over a period of 24-hour stimulation (p<.01), but this augmentation was blunted by 50% after DFMO administration (p<.05). The effect of DFMO on TNFalpha/MG132-induced upregulation of caspase-3 activity was reversed by the addition of 100 microM putrescine, confirming that polyamines were really involved in the apoptotic process. Also, the number of apoptotic BMSCs after TNFalpha/MG132 treatment, as determined by terminal transferase-mediated dUTP nick end-labeling (TUNEL) assay, were threefold reduced after polyamine depletion (p<.05). On the contrary, DFMO did not affect the MG132-mediated increase in p53 abundance, nor its translocation to the nucleus. Thus, polyamine depletion can be considered a useful tool for counteracting programmed cell death in BMSCs without involving the p53 proapoptotic protein.

Akt kinase activation blocks apoptosis in intestinal epithelial cells by inhibiting caspase-3 after polyamine depletion

Apoptosis plays a critical role in the maintenance of gut mucosal homeostasis and is regulated by numerous factors including polyamines. Although the exact roles of polyamines in apoptotic pathway are still unclear, inhibition of polyamine synthesis promotes the resistance of intestinal epithelial cells to apoptosis. Akt is a serine-threonine kinase that has been established as an important intracellular signaling in regulating cell survival. The current studies test the hypothesis that polyamines are involved in the control of Akt activity in normal intestinal epithelial cells (IEC-6 line) and that activated Akt mediates suppression of apoptosis following polyamine depletion. Depletion of cellular polyamines by alpha-difluoromethylornithine induced levels of phosphorylated Akt and increased Akt kinase activity, although it had no effect on expression of total Akt, pERK, p38, and Bcl-2 proteins. This activated Akt was associated with both decreased levels of active caspase-3 and increased resistance to tumor necrosis factor-alpha/cycloheximide-induced apoptosis. Inactivation of Akt by either treatment with LY294002 or ectopic expression of a dominant negative Akt mutant (DNMAkt) not only enhanced the caspase-3 activation in polyamine-deficient cells but also prevented the increased resistance to tumor necrosis factor-alpha/cycloheximide-induced apoptosis. Phosphorylation of glycogen synthase kinase-3, a downstream target of Akt, was also increased in alpha-difluoromethylornithine-treated cells, which was prevented by inactivation of Akt by LY294002 or DNMAkt overexpression. These results indicate that polyamine depletion induces the Akt activation mediating suppression of apoptosis via inhibition of caspase-3 in normal intestinal epithelial cells.

NF-kappaB-mediated IAP expression induces resistance of intestinal epithelial cells to apoptosis after polyamine depletion

Apoptosis plays a crucial role in maintenance of intestinal epithelial integrity and is highly regulated by numerous factors, including cellular polyamines. We recently showed that polyamines regulate nuclear factor (NF)-kappaB activity in normal intestinal epithelial (IEC-6) cells and that polyamine depletion activates NF-kappaB and promotes resistance to apoptosis. The current study went further to determine whether the inhibitors of apoptosis (IAP) family of proteins, c-IAP2 and XIAP, are downstream targets of activated NF-kappaB and play a role in antiapoptotic activity of polyamine depletion in IEC-6 cells. Depletion of cellular polyamines by alpha-difluoromethylornithine not only activated NF-kappaB activity but also increased expression of c-IAP2 and XIAP. Specific inhibition of NF-kappaB by the recombinant adenoviral vector containing IkappaBalpha superrepressor (AdIkappaBSR) prevented the induction of c-IAP2 and XIAP in polyamine-deficient cells. Decreased levels of c-IAP2 and XIAP proteins by inactivation of NF-kappaB through AdIkappaBSR infection or treatment with the specific inhibitor Smac also overcame the resistance of polyamine-depleted cells to apoptosis induced by the combination of tumor necrosis factor (TNF)-alpha and cycloheximide (CHX). Although polyamine depletion did not alter levels of procaspase-3 protein, it inhibited formation of the active caspase-3. Decreased levels of c-IAP2 and XIAP by Smac prevented the inhibitory effect of polyamine depletion on the cleavage of procaspase-3 to the active caspase-3. These results indicate that polyamine depletion increases expression of c-IAP2 and XIAP by activating NF-kappaB in intestinal epithelial cells. Increased c-IAP2 and XIAP after polyamine depletion induce the resistance to TNF-alpha/CHX-induced apoptosis, at least partially, through inhibition of the caspase-3 activity.

Polyamines are required for activation of c-Jun NH2-terminal kinase and apoptosis in response to TNF-alpha in IEC-6 cells

Intracellular polyamine homeostasis is important for the regulation of cell proliferation and apoptosis and is necessary for the balanced growth of cells and tissues. Polyamines have been shown to play a role in the regulation of apoptosis in many cell types, including IEC-6 cells, but the mechanism is not clear. In this study, we analyzed the mechanism by which polyamines regulate the process of apoptosis in response to tumor necrosis factor-alpha (TNF-alpha). TNF-alpha or cycloheximide (CHX) alone did not induce apoptosis in IEC-6 cells. Significant apoptosis was observed when CHX was given along with TNF-alpha, as indicated by a significant increase in the detachment of cells, caspase-3 activity, and DNA fragmentation. Polyamine depletion by treatment with alpha-difluoromethylornithine significantly reduced the level of apoptosis, as judged by DNA fragmentation and the caspase-3 activity of attached cells. Apoptosis in IEC-6 cells was accompanied by the activation of upstream caspases-6, -8, and -9 and NH2-terminal c-Jun kinase (JNK). Inhibition of JNK activation prevented caspase-9 activation. Polyamine depletion prevented the activation of JNK and of caspases-6, -8, -9, and -3. SP-600125, a specific inhibitor of JNK activation, prevented cytochrome c release from mitochondria, JNK activation, DNA fragmentation, and caspase-9 activation in response to TNF-alpha/CHX. In conclusion, we have shown that polyamine depletion delays and decreases TNF-alpha-induced apoptosis in IEC-6 cells and that apoptosis is accompanied by the release of cytochrome c, the activation of JNK, and of upstream caspases as well as caspase-3. Polyamine depletion prevented JNK activation, which may confer protection against apoptosis by modulation of upstream caspase-9 activation.

The requirement for polyamines for intestinal epithelial cell migration is mediated through Rac1

The rapid migration of intestinal epithelial cells is important to the healing of mucosal ulcers and wounds. This cell migration requires the presence of polyamines and the activation of RhoA. RhoA activity, however, is not sufficient for migration because polyamine depletion inhibited the migration of IEC-6 cells expressing constitutively active RhoA. The current study examines the role of Rac1 and Cdc42 in cell migration and whether their activities are polyamine-dependent. Polyamine depletion with alpha-difluoromethylornithine inhibited the activities of RhoA, Rac1, and Cdc42. This inhibition was prevented by supplying exogenous putrescine in the presence of alpha-difluoromethylornithine. IEC-6 cells transfected with constitutively active Rac1 and Cdc42 migrated more rapidly than vector-transfected cells, whereas cells expressing dominant negative Rac1 and Cdc42 migrated more slowly. Polyamine depletion had no effect on the migration of cells expressing Rac1 and only partially inhibited the migration of those expressing Cdc42. Although polyamine depletion caused the disappearance of actin stress fibers in cells transfected with empty vector, it had no effect on cells expressing Rac1. Constitutively active Rac1 increased RhoA and Cdc42 activity in both normal and polyamine-depleted cells. These results demonstrate that Rac1, RhoA, and Cdc42 are required for optimal epithelial cell migration and that Rac1 activity is sufficient for cell migration in the absence of polyamines due to its ability to activate RhoA and Cdc42 as well as its own effects on the process of cell migration. These data imply that the involvement of polyamines in cell migration occurs either at Rac1 itself or upstream from Rac1.

Inhibitory effects of the ginsenoside Rg3 on phorbol ester-induced cyclooxygenase-2 expression, NF-kappaB activation and tumor promotion

Our previous studies demonstrated the anti-oxidant and anti-tumor promotional properties of the methanol extract of heat-processed Panax ginseng C.A. Meyer [Cancer Lett. 150 (2000) 41]. In the present work, we have evaluated anti-inflammatory as well as anti-tumor promoting effects of Rg(3), a major ginsenoside derived from heat-processed ginseng. Pretreatment of dorsal skins of female ICR mice with Rg(3) significantly inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase activity and 7,12-dimethylbenz[a]anthracene-initiated papilloma formation. In another experiment, Rg(3) pretreatment abrogated the expression of cyclooxygenase-2 in TPA-stimulated mouse skin. Rg(3) also inhibited the TPA-induced activation of the eukaryotic transcription factor, NF-kappaB in both mouse skin and cultured human pro-myelocytic leukemia (HL-60) cells. Moreover, Rg(3) exerted potent inhibitory effects on the activation of another transcription factor, activator protein-1 (AP-1) that is responsible for c-jun and c-fos oncogenic transactivation. Based on these findings, it is likely that the anti-tumor promoting activity of Rg(3) is mediated possibly through down-regulation of NF-kappaB and AP-1 transcription factors.

Antizyme is a target of sex-lethal in the Drosophila germline and appears to act downstream of hedgehog to regulate sex-lethal and cyclin B

The sex determination master switch, Sex-lethal, has been shown to regulate the mitosis of early germ cells in Drosophila melanogaster. Sex-lethal is an RNA binding protein that regulates splicing and translation of specific targets in the soma, but the germline targets are unknown. In an experiment aimed at identifying targets of Sex-lethal in early germ cells, the RNA encoded by gutfeeling, the Drosophila homolog of Ornithine Decarboxylase Antizyme, was isolated. gutfeeling interacts genetically with Sex-lethal. It is not only a target of Sex-lethal, but also appears to regulate the nuclear entry and overall levels of Sex-lethal in early germ cells. This regulation of Sex-lethal by gutfeeling appears to occur downstream of the Hedgehog signal. We also show that Hedgehog, Gutfeeling, and Sex-lethal function to regulate Cyclin B, providing a link between Sex-lethal and mitosis.

Caspase activation in etoposide-treated fibroblasts is correlated to ERK phosphorylation and both events are blocked by polyamine depletion

Activation of the extracellular signal-regulated kinases (ERKs) 1 and 2 is correlated to cell survival, but in some cases ERKs can act in signal transduction pathways leading to apoptosis. Treatment of mouse fibroblasts with 20 microM etoposide elicited a sustained phosphorylation of ERK 1/2, that increased until 24 h from the treatment in parallel with caspase activity. The inhibitor of ERK activation PD98059 abolished caspase activation, but caspase inhibition did not reduce ERK 1/2 phosphorylation, suggesting that ERK activation is placed upstream of caspases. Both ERK and caspase activation were blocked in cells depleted of polyamines by the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO). In etoposide-treated cells, DFMO also abolished phosphorylation of c-Jun NH(2)-terminal kinases triggered by the drug. Polyamine replenishment with exogenous putrescine restored the ability of the cells to undergo caspase activation and ERK 1/2 phosphorylation in response to etoposide. Ornithine decarboxylase activity decreased after etoposide, indicating that DFMO exerts its effect by depleting cellular polyamines before induction of apoptosis. These results reveal a role for polyamines in the transduction of the death signal triggered by etoposide.