Interleukin-1-induced growth inhibition of human melanoma cells. Interleukin-1-induced antizyme expression is responsible for ornithine decarboxylase activity down-regulation

Inhibition of the polyamine synthesis enzyme ornithine decarboxylase sensitizes triple-negative breast cancer cells to cytotoxic chemotherapy

Treatment of patients with triple-negative breast cancer (TNBC) is limited by a lack of effective molecular therapies targeting this disease. Recent studies have identified metabolic alterations in cancer cells that can be targeted to improve responses to standard-of-care chemotherapy regimens. Using MDA-MB-468 and SUM-159PT TNBC cells, along with LC-MS/MS and HPLC metabolomics profiling, we found here that exposure of TNBC cells to the cytotoxic chemotherapy drugs cisplatin and doxorubicin alter arginine and polyamine metabolites. This alteration was because of a reduction in the levels and activity of a rate-limiting polyamine biosynthetic enzyme, ornithine decarboxylase (ODC). Using gene silencing and inhibitor treatments, we determined that the reduction in ODC was mediated by its negative regulator antizyme, targeting ODC to the proteasome for degradation. Treatment with the ODC inhibitor difluoromethylornithine (DFMO) sensitized TNBC cells to chemotherapy, but this was not observed in receptor-positive breast cancer cells. Moreover, TNBC cell lines had greater sensitivity to single-agent DFMO, and ODC levels were elevated in TNBC patient samples. The alterations in polyamine metabolism in response to chemotherapy, as well as DFMO-induced preferential sensitization of TNBC cells to chemotherapy, reported here suggest that ODC may be a targetable metabolic vulnerability in TNBC.

IL-1 Signaling in Tumor Microenvironment

Interleukin 1 (IL-1) has long been known for its pleiotropic effects on inflammation that plays a complex, and sometimes contrasting, role in different stages of cancer development. As a major proinflammatory cytokine, IL-1β is mainly expressed by innate immune cells. IL-1α, however, is expressed by various cell types under physiological and pathological conditions. IL-1R1 is the main receptor for both ligands and is expressed by various cell types, including innate and adaptive immune cell types, epithelial cells, endothelial cells, adipocytes, chondrocytes, fibroblasts, etc. IL-1 and IL-1R1 receptor interaction leads to a set of common signaling pathways, mainly the NF-kB and MAP kinase pathways, as a result of complex positive and negative regulations. The variety of cell types with IL-1R1 expression dictates the role of IL-1 signaling at different stages of cancer, which under certain circumstances leads to contrasting roles in tumor development. Recent availability of IL-1R1 conditional knockout mouse model has made it possible to dissect the role of IL-1/IL-1R1 signaling transduction in different cell types within the tumor microenvironment. This chapter will focus on the role of IL-1/IL-1R1 in different cell types within the tumor microenvironment and discuss the potential of targeting this pathway in cancer therapy.

Developing a novel FRET assay, targeting the binding between Antizyme-AZIN

Antizyme inhibitor (AZIN) stimulates cell proliferation by binding to and sequestering the cell cycle suppressor antizyme. Despite the important role of the antizyme-AZIN protein-protein interaction (PPI) in cell cycle regulation, there are no assays for directly measuring the binding of AZIN to antizyme that are amenable to high throughput screening. To address this problem, we developed and validated a novel antizyme-AZIN intramolecular FRET sensor using clover and mRuby2 fluorescent proteins. By introducing alanine mutations in the AZIN protein, we used this sensor to probe the PPI for key residues governing the binding interaction. We found that like many PPIs, the energy of the antizyme-AZIN binding interaction is distributed across many amino acid residues; mutation of individual residues did not have a significant effect on disrupting the PPI. We also examined the interaction between Clover-AZIN and antizyme-mRuby2 in cells. Evidence of a direct interaction between Clover-AZIN and antizyme-mRuby2 was observed within cells, validating the use of this FRET sensor for probing intracellular antizyme-AZIN PPI. In conclusion, we have developed and optimized a FRET sensor which can be adapted for high throughput screening of either in vitro or intracellular activity.

Alarmins and immunity

More than a decade has passed since the conceptualization of the "alarmin" hypothesis. The alarmin family has been expanding in terms of both number and the concept. It has recently become clear that alarmins play important roles as initiators and participants in a diverse range of physiological and pathophysiological processes such as host defense, regulation of gene expression, cellular homeostasis, wound healing, inflammation, allergy, autoimmunity, and oncogenesis. Here, we provide a general view on the participation of alarmins in the induction of innate and adaptive immune responses, as well as their contribution to tumor immunity.

[Interluekin-1: from regulation of cell proliferation to chronic inflammatory diseases]

  Interleukin 1 (IL-1) was initially defined as a factor which is produced by macrophages and exhibits proliferative activity on thymocytes and fibroblasts, B cell activation and endogenous pyrogen activity. Now IL-1 is known to exhibit pleiotropic activities on various cell types and play important roles in the regulation of immune, nervous and endocrine systems, progression of tumor cells, hematopoietic cell proliferation/differentiation and especially in inflammatory diseases. In 1985 I found that IL-1 exhibits cytocidal activity against human melanoma cells. Since then I have been engaged in the research of various aspects of IL-1. This review summarizes current knowledge of IL-1, including our research and beneficial effect of IL-1 blocking on inflammatory diseases.

Contribution of extracellular signal-regulated kinases to the IL-1-induced growth inhibition of human melanoma cells A375

The role of ERK1/2 in the IL-1-induced growth inhibition was investigated using human melanoma A375-6 cells. A selective inhibitor of ERK1/2 pathway, PD98059 and a selective inhibitor of p38MAPK, SB203580 each alone significantly reversed the IL-1-induced growth inhibition of A375-6 cells. Co-treatment with PD98059 and SB203580 completely reversed the IL-1-induced growth inhibition. ERK1/2 was constitutively activated in A375-6 cells, and IL-1 further augmented ERK activation. Antiproliferative effect of IL-1 was attenuated by the expression of dominant negative form of ERK2. IL-1 induced cell cycle arrest in G(0)/G(1) phase, expression of p21 and p27 proteins, and down-regulation of cyclin D/cyclin-dependent kinase (CDK) 2 and CDK4 activities. These effects of IL-1 were reversed by PD98059. PD98059 also reversed the IL-1-induced hypophosphorylation of RB protein (pRB) and down-regulation of E2F activity. These findings demonstrate that ERK1/2 contribute to the IL-1-induced growth inhibition through induction of CDK inhibitors, down-regulation of CDK activity, pRB phosphorylation and E2F activity.

Unusual aspects of the polyamine transport system affect the design of strategies for use of polyamine analogues in chemotherapy

One strategy for inhibiting tumour cell growth is the use of polyamine mimetics to depress endogenous polyamine levels and, ideally, obstruct critical polyamine-requiring reactions. Such polyamine analogues make very unusual drugs, in that extremely high intracellular concentrations are required for growth inhibition or cytotoxicity. Cells exposed to even sub-micromolar concentrations of such analogues can achieve effective intracellular levels because these compounds are incorporated by the very aggressive polyamine uptake system. Once incorporated to these levels, many of these analogues induce the synthesis of a regulatory protein, antizyme, which inhibits both polyamine synthesis and the transporter they used to enter the cell. Thus this feedback system allows steady-state maintenance of effective cellular doses of such analogues. Accordingly, effective cellular levels of polyamine analogues are generally inversely related to their capacity to induce antizyme. Antizyme activity is down-regulated by interaction with several binding partners, most notably antizyme inhibitor, and at least a few tumour tissues exhibit deficiencies in antizyme expression. Our studies explore the role of antizyme induction by several polyamine analogues in their physiological response and the possibility that cell-to-cell differences in antizyme expression may contribute to variable sensitivities to these agents.

IL-1beta acts in synergy with endogenous IL-1beta in A375-S2 human melanoma cell apoptosis through mitochondrial pathway

Interleukin-1beta (IL-1beta) is a pivotal proinflammatory cytokine. To investigate the mechanism of IL-1beta-induced cell death in human malignant melanoma A375-S2 cells, MTT assay, photomicroscopical observation, DNA agarose gel electrophoresis, radioimmunoassay and Western blot analysis were carried out. IL-1beta did not only induce nuclear condensation and DNA fragmentation, but also increased degradation of two substrates of caspase-3, poly ADP-ribose polymerase (PARP) and inhibitor of caspase-activated DNase (ICAD). Simultaneously, release of precursor of IL-1beta (pro-IL-1beta) and endogenous IL-1beta production were involved in the apoptotic process. IL-1beta enhanced the ratio of Bax/Bcl-2 and Bax/Bcl-xL expression and up-regulated apoptosis inducing factor (AIF) expression, which required the activation of downstream caspases. These results suggest that IL-1beta induces endogenous IL-1beta production, enhances cleavage of caspase downstream substrates and promotes mitochondria mediated apoptosis in A375-S2 cells.

Evodiamine Induced Human Melanoma A375-S2 Cell Death Partially through Interleukin 1 Mediated Pathway

We have reported that caspase cascade accompanied by the regulation of Bax/Bcl-2 and MAPK signaling were involved in evodiamine-induced A375-S2 cell death. In this study, pretreatment with interleukin 1 (IL-1) receptor antagonist (IL-1Ra) rescued the cell viability loss and reversed the ratio of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells induced by evodiamine. IL-1Ra was capable of attenuating the expression of Fas-ligand (Fas-L) and the cleavage of procaspas-8 and -3 caused by evodiamine. Subsequently, IL-1Ra reduced evodiamine-induced DNA degradation, p53 activation and up-regulation of Bax/Bcl-2 ratio. However, IL-1Ra attenuated the enhanced phosphorylation level of p38 mitogen-activated protein kinase (p38 MAPK) without affecting extracellular signal-regulated protein kinase (ERK) inactivation induced by evodiamine. In conclusion, IL-1-induced death cascade in melanoma A375-S2 cell might be one of the targets for natural product evodiamine, and increased Fas-L expression via IL-1 mediated pathway stands at the initiation phase, leading to consequent events that culminate in the death of the cells.

Polyamine metabolism and cancer

Polyamines are aliphatic cations present in all cells. In normal cells, polyamine levels are intricately controlled by biosynthetic and catabolic enzymes. The biosynthetic enzymes are ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase, and spermine synthase. The catabolic enzymes include spermidine/spermine acetyltransferase, flavin containing polyamine oxidase, copper containing diamine oxidase, and possibly other amine oxidases. Multiple abnormalities in the control of polyamine metabolism and uptake might be responsible for increased levels of polyamines in cancer cells as compared to that of normal cells. This review is designed to look at the current research in polyamine biosynthesis, catabolism, and transport pathways, enumerate the functions of polyamines, and assess the potential for using polyamine metabolism or function as targets for cancer therapy.

TGFbeta down-regulates IFN-gamma production in IL-18 treated NK cell line LNK5E6

Transforming growth factor beta (TGFbeta) is a critical immunosuppressive cytokine that inhibits the cell-mediated immune responses partly via inhibition of immunostimulatory cytokine production from T cells, NK cells, and macrophages. Here we investigated the effect of TGFbeta on NK cell activation induced by interleukin 18 (IL-18) using a murine NK cell line LNK5E6. IL-18 activated LNK5E6 cells to produce antiviral activity against vesicular stomatitis virus (VSV) and TGFbeta inhibited this activation. TGFbeta inhibited interferon-gamma (IFN-gamma) production in LNK5E6 cells treated with IL-18. TGFbeta also suppressed the IL-18 induced mRNA expression of IFN-gamma. Moreover, TGFbeta did not affect the transcriptional activity of IFN-gamma but decreased the half-life of IFN-gamma mRNA induced by IL-18. These results suggest that the destabilization of IFN-gamma mRNA induced by TGFbeta leads to the inhibition of antiviral activity and IFN-gamma production in IL-18 stimulated LNK5E6 cells.

Antizyme induction by polyamine analogues as a factor of cell growth inhibition

The polyamines spermidine and spermine and their diamine precursor putrescine are essential for mammalian cell growth and viability, and strategies are sought for reducing polyamine levels in order to inhibit cancer growth. Several structural analogues of the polyamines have been found to decrease natural polyamine levels and inhibit cell growth, probably by stimulating normal feedback mechanisms. In the present study, a large selection of spermine analogues has been tested for their effectiveness in inducing the production of antizyme, a key protein in feedback inhibition of putrescine synthesis and cellular polyamine uptake. Bisethylnorspermine, bisethylhomospermine, 1,19-bis-(ethylamino)-5,10,15-triazanonadecane, longer oligoamine constructs and many conformationally constrained analogues of these compounds were found to stimulate antizyme synthesis to different levels in rat liver HTC cells, with some producing far more antizyme than the natural polyamine spermine. Uptake of the tested compounds was found to be dependent on, and limited by, the polyamine transport system, for which all these have approximately equal affinity. These analogues differed in their ability to inhibit HTC cell growth during 3 days of exposure, and this ability correlated with their antizyme-inducing potential. This is the first direct evidence that antizyme is induced by several polyamine analogues. Selection of analogues with this potential may be an effective strategy for maximizing polyamine deprivation and growth inhibition.

Regulation of ornithine decarboxylase in B16 mouse melanoma cells: synergistic activation of melanogenesis by alphaMSH and ornithine decarboxylase inhibition

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in the biosynthesis of polyamines, a family of cationic compounds required for optimal cell proliferation and differentiation. Within mammalian melanocytes, the expression of genes regulating cell growth and/or differentiation can be controlled by alpha-melanocyte-stimulating hormone (alphaMSH) and other melanogenesis modulating agents. In the B16 mouse melanoma model, alphaMSH stimulates melanogenesis by upmodulation of tyrosinase (tyr) activity, whereas the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) inhibits melanin synthesis. Therefore, we analyzed the regulation of ODC by these agents, as related to changes in the melanogenic pathway. Treatment of B16 cells with TPA or alphaMSH rapidly stimulated ODC activity. The effect was stronger for TPA and appeared mainly posttranslational. Irreversible inhibition of ODC with the active site-directed inhibitor alpha-difluoromethylornithine (DFMO) did not block TPA-mediated inhibition of tyr. Conversely, prolonged treatment of B16 cells with DFMO stimulated tyr activity by a posttranslational mechanism, probably requiring polyamine depletion. Combination treatment with alphaMSH and DFMO synergistically activated tyr. Therefore, ODC induction is not involved in the melanogenic response of B16 cells to alphaMSH. Rather, increased intracellular concentrations of polyamines following ODC induction might constitute a feedback mechanism to limit melanogenesis activation by alphaMSH.

CHOP, a basic leucine zipper transcriptional factor, contributes to the antiproliferative effect of IL-1 on A375 human melanoma cells through augmenting transcription of IL-6

Interleukin-1 (IL-1) inhibits the proliferation of A375 human melanoma cells. We have demonstrated previously that p38 mitrogen-activated protein kinase (MAPK) mediated the antiproliferative effect of IL-1 partially through the downregulation of activity and protein level of ornithine decarboxylase (ODC). In this study, we investigated the role of CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), one of the p38 MAPK target transcriptional factors. The mRNA level of CHOP was not affected by IL-1 treatment in A375-6 cells. Unexpectedly, CHOP was constitutively phosphorylated, and IL-1 or p38 MAPK inhibitor, SB203580, did not affect the phosphorylation level. However, A375-6 cells exhibited enhanced sensitivity to IL-1 by transfecting CHOP expression plasmid and reduced sensitivity to IL-1 by antisense CHOP mRNA expression plasmid. Furthermore, CHOP appeared to regulate positively IL-6 production at the transcriptional level. The experiments using CHOP muteins revealed that dimerization ability - but not p38 MAPK-dependent phosphorylation or DNA binding activity - is important for the IL-6 inducing activity of CHOP. These results indicate that CHOP contributes to the IL-1 growth-inhibitory signal through augmenting IL-6 production.

Hepatocyte growth factor induces pro-apoptotic genes in HepG2 hepatoma but not in B16-F1 melanoma cells

Hepatocyte growth factor (HGF) exerts a cytostatic effect on HepG2 and B16-F1 cell lines. To evaluate the possible involvement of the apoptotic process in this effect, we performed studies at cellular and molecular levels. HGF induced apoptosis only in HepG2 hepatoma cells at day 3 in about 20% of the cells undergoing growth inhibition, while hallmarks of apoptosis did not occur in B16-F1 melanoma cells. During the first 24 h after HGF treatment, enhanced expression of the pro-apoptotic genes bax and c-Myc was observed at level of mRNA and protein. Concomitant induction of antizyme (AZ) might lower ornithine decarboxylase (ODC) protein level though a huge increase in ODC mRNA level took place. This was suggested as a signal for apoptosis decisional phase. The levels of the proteins examined except that of AZ fell down thereafter when HepG2 cells underwent apoptosis. In B16-F1 cells, only ODC and AZ protein levels were elevated probably in relation to the initial elevated growth rate and the absence of apoptosis involvement in the following cytostatic effect of HGF in melanoma cells. Consistent with this hypothesis, bax mRNA and protein levels were unchanged or even lower relative to control values.

Polyamine regulation of ornithine decarboxylase and its antizyme in intestinal epithelial cells

Ornithine decarboxylase (ODC) is feedback regulated by polyamines. ODC antizyme mediates this process by forming a complex with ODC and enhancing its degradation. It has been reported that polyamines induce ODC antizyme and inhibit ODC activity. Since exogenous polyamines can be converted to each other after they are taken up into cells, we used an inhibitor of S-adenosylmethionine decarboxylase, diethylglyoxal bis(guanylhydrazone) (DEGBG), to block the synthesis of spermidine and spermine from putrescine and investigated the specific roles of individual polyamines in the regulation of ODC in intestinal epithelial crypt (IEC-6) cells. We found that putrescine, spermidine, and spermine inhibited ODC activity stimulated by serum to 85, 46, and 0% of control, respectively, in the presence of DEGBG. ODC activity increased in DEGBG-treated cells, despite high intracellular putrescine levels. Although exogenous spermidine and spermine reduced ODC activity of DEGBG-treated cells close to control levels, spermine was more effective than spermidine. Exogenous putrescine was much less effective in inducing antizyme than spermidine or spermine. High putrescine levels in DEGBG-treated cells did not induce ODC antizyme when intracellular spermidine and spermine levels were low. The decay of ODC activity and reduction of ODC protein levels were not accompanied by induction of antizyme in the presence of DEGBG. Our results indicate that spermine is the most, and putrescine the least, effective polyamine in regulating ODC activity, and upregulation of antizyme is not required for the degradation of ODC protein.

Expression of ODC and its regulatory protein antizyme in the adult rat brain

Ornithine decarboxylase and its inhibitor protein, antizyme are key regulators of polyamine biosynthesis. We examined their expression in the adult rat brain using in situ hybridization and immunocytochemistry. Both genes were widely expressed and their expression patterns were mostly overlapping and relatively similar. The levels of antizyme mRNA were always higher than those of ornithine decarboxylase mRNA. The highest expression for both genes was detected in the cerebellar cortex, hippocampus, hypothalamic paraventricular and supraoptic nuclei, locus coeruleus, olfactory bulb, piriform cortex and pontine nuclei. Ornithine decarboxylase and antizyme mRNAs appeared to be localized in the nerve cells. ODC antibody displayed mainly cytoplasmic staining in all brain areas. Antizyme antibody staining was mainly cytoplasmic in the most brain areas, although predominantly nuclear staining was detected in some areas, most notably in the cerebellar cortex, anterior olfactory nucleus and frontal cortex. Our study is the first detailed and comparative analysis of ornithine decarboxylase and antizyme expression in the adult mammalian brain.

Differential regulation of responsiveness to fMLP and C5a upon dendritic cell maturation: correlation with receptor expression

The trafficking of immature and mature dendritic cells (DCs) to different anatomical sites in vivo is critical for fulfilling their roles in the induction of Ag-specific immune responses. Although this process is complex and regulated by many mediators, the capacity of DCs to migrate is predominantly dependent on the expression of particular chemotactic receptors on the surface of DCs that enable them to move along chemotactic gradients formed by the corresponding chemokines and/or classical chemoattractants. Here we show that immature DCs (iDCs) respond to both fMLP and C5a as determined by chemotaxis and Ca2+ mobilization, whereas mature DCs (mDCs) respond to C5a, but not fMLP. Additionally, iDCs express the receptors for both fMLP and C5a at mRNA and protein levels. Upon maturation of DCs, fMLP receptor expression is almost completely absent, whereas C5a receptor mRNA and protein expression is maintained. Concomitantly, mDCs migrate chemotactically and mobilize intracellular Ca2+ in response to C5a, but not fMLP. Thus the interaction between C5a and its receptor is likely involved in the regulation of trafficking of both iDCs and mDCs, whereas fMLP mobilizes only iDCs. The differential responsiveness to fMLP and C5a of iDCs and mDCs suggests that they play different roles in the initiation of immune responses.

Discovery of a spermatogenesis stage-specific ornithine decarboxylase antizyme: antizyme 3

Previous studies with mice overproducing ornithine decarboxylase have demonstrated the importance of polyamine homeostasis for normal mammalian spermatogenesis. The present study introduces a likely key player in the maintenance of proper polyamine homeostasis during spermatogenesis. Antizyme 3 is a paralog of mammalian ornithine decarboxylase antizymes. Like its previously described counterparts, antizymes 1 and 2, it inhibits ornithine decarboxylase, which catalyzes the synthesis of putrescine. Earlier work has shown that the coding sequences for antizymes 1 and 2 are in two different, partially overlapping reading frames. Ribosomes translate the first reading frame, and just before the stop codon for that frame, they shift to the second reading frame to synthesize a trans-frame product. The efficiency of this frameshifting depends on polyamine concentration, creating an autoregulatory circuit. Antizyme 3 cDNA has the same arrangement of reading frames and a potential shift site with definite, although limited, homology to its evolutionarily distant antizyme 1 and 2 counterparts. In contrast to antizymes 1 and 2, which are widely expressed throughout the body, antizyme 3 transcription is restricted to testis germ cells. Expression starts early in spermiogenesis and finishes in the late spermatid phase. The potential significance of antizyme 3 expression during spermatogenesis is discussed in this paper.

Two zebrafish (Danio rerio) antizymes with different expression and activities

Cellular polyamines are regulated by a unique feedback mechanism involving ornithine decarboxylase (ODC) antizyme. The synthesis of mammalian antizyme requires a programmed translational frameshift event induced by polyamines. Antizyme represses ODC, a key enzyme for polyamine synthesis, through accelerating enzyme degradation by the 26 S proteasome. Antizyme also inhibits the cellular uptake of polyamines. In the present study we isolated two distinct zebrafish (Danio rerio) antizyme cDNA clones (AZS and AZL) from an embryonic library. Their sequences revealed that both clones required translational frameshifting for expression. Taking account of +1 frameshifting, AZS and AZL products were 214 and 218 residues long respectively and shared 51.8% amino acid identity. In rabbit reticulocyte lysates, both mRNA species were translated through spermidine-induced frameshifting. The presence of the two antizyme mRNA species in embryos, adult fish and a cultured cell line was confirmed by Northern blot analysis. The ratio of AZS mRNA to AZL mRNA in the adult fish was 1.8-fold higher than in the embryos. Whole-mount hybridization in situ demonstrated that both mRNA species are expressed in every tissue in embryo, but predominantly in the central nervous system and the eyes. Bacterial expression products of both cDNA species inhibited ODC activity, but only the AZS product accelerated ODC degradation in vitro. These results show that both zebrafish antizymes are induced by polyamines but their mRNA species are expressed differently during development. The difference in activities on ODC degradation suggests their functional divergence.

Antiproliferative Effect of IL-1 Is Mediated by p38 Mitogen-Activated Protein Kinase in Human Melanoma Cell A375

The role of p38 mitogen-activated protein kinase (MAPK) in IL-1-induced growth inhibition was investigated using IL-1-sensitive human melanoma A375-C2-1 cells and IL-1-resistant A375-R8 cells. In both cells, p38 MAPK was activated by IL-1. A selective inhibitor for p38 MAPK, SB203580, almost completely recovered the IL-1-induced growth inhibition in A375-C2-1 cells. IL-1-induced IL-6 production was also suppressed by SB203580. However, the reversal effect of SB203580 was not due to the suppression of IL-6 production because the SB203580 effect was still observed in the presence of exogenous IL-6. Down-regulation of ornithine decarboxylase (ODC) activity as well as its protein level has been shown to be essential for IL-1-induced growth inhibition. SB203580 also reversed the IL-1-induced down-regulation of ODC activity and intracellular polyamine levels without affecting ODC mRNA levels in A375-C2-1 cells. In IL-1-resistant R8 cells, however, IL-1 only slightly suppressed ODC activity. In A375-C2-1 cells, the mRNA expression level of antizyme (AZ), a regulatory factor of ODC activity, has been shown to be up-regulated by IL-1. IL-1-induced up-regulation of AZ mRNA level was not affected by SB203580. These findings demonstrate that p38 MAPK plays an important role in IL-1-induced growth inhibition in A375 cells through down-regulating ODC activity without affecting the level of ODC mRNA and AZ mRNA. In IL-1-resistant A375-R8 cells, IL-1 signaling pathway is deficient between p38 MAPK activation and down-regulation of ODC activity.

Structure of human ornithine decarboxylase antizyme 2 gene

Ornithine decarboxylase antizyme 1, a negative regulator of polyamine levels, acts by destabilizing the first enzyme in the polyamine biosynthetic pathway (ODC) and by inhibiting uptake of polyamines. Recently, a second mammalian antizyme was discovered. Here, we report the genomic organization and chromosomal position of the new human gene, HuAZ2, and make a comparison with its antizyme 1 homologue. Fluorescence in-situ hybridization (FISH) localized the sequences from a bacterial artificial chromosomal (BAC) clone containing HuAZ2 at band 22 of the long arm of chromosome 15. This gene spans at least 15kb and contains five exons. No CAAT or TATA sequences could be identified within 800bp upstream of the translation initiation codon, but the 5'-flanking region contains several putative binding sites for other transcription factors. Transcription initiation of this gene appears to be heterogeneous.

Direct and indirect modulation of ornithine decarboxylase and cyclooxygenase by UVB radiation in human skin cells

Exposure to solar ultraviolet (UV) B radiation is responsible for skin inflammation and tumour progression. Cyclooxygenase and ornithine decarboxylase are believed to be involved in such processes since they participate in the synthesis of mediators of inflammation and cell differentiation, respectively. We have investigated the in vitro modulation of expression of such genes by UVB radiation in different skin cell lines. We have observed that accumulation of ornithine decarboxylase mRNA is unaffected by even high UVB doses in both human epidermal keratinocytes and dermal fibroblasts, whereas cyclooxygenase-2 levels were significantly up-regulated by low UVB doses in KB human epidermoid keratinocytes. Depletion of total intracellular glutathione levels in KB cells amplified the activation, revealing a role for an oxidative component of UVB in modulating cyclooxygenase gene expression. Transfer of medium from UVB irradiated keratinocytes to fibroblasts resulted in a significant activation of cyclooxygenase expression and activity, while ornithine decarboxylase levels were unaffected. We conclude that UVB radiation can activate cyclooxygenase gene expression in human skin cells both by direct activation pathways or indirectly by inducing a paracrine mechanism.

Anti-tumor activity of antizyme which targets the ornithine decarboxylase (ODC) required for cell growth and transformation

Anti-tumor activity of antizyme which targets the ornithine decarboxylase (ODC) required for cell growth and transformation Cell proliferation and transformation induced by growth factor stimulation or by carcinogens, viruses, or oncogenes are characterized by an associated increase in polyamine levels, which is mediated by increased polyamine biosynthesis and enhanced uptake of polyamines. Polyamine biosynthesis is catalyzed particularly, in the level of ornithine decarboxylase (ODC). The elevation of cellular polyamine levels on the other hand accelerates the induction of ornithine decarboxylase antizyme (antizyme), which is involved not only in ODC-degradation, but in the negative regulation of polyamine transport. Taking advantage of these characteristics of antizyme, the potential of antizyme as a factor having anti-cell growth and anti-tumor activity was investigated. We show that antizyme can induce cell death associated with a rapid decline of intracellular polyamine contents. The possible anti-tumor activities of ectopically expressed antizyme were tested in p21H-ras (Val 12)-transformed NIH3T3 cells and several human malignant cell lines including a line with loss of p53 expression, and they were shown to be as sensitive as nontransformed NIH3T3 cells in vitro. The in vivo anti-tumor activity was also tested using nude mice inoculated with H-ras transformed NIH3T3 cells that had been transfected with inducible antizyme expression vector and the results showed that antizyme expression in vivo blocks tumor formation in these mice. These results suggest that ectopic antizyme expression is of possible therapeutic benefit in the treatment of cancer, which is mediated by ODC inactivation and intracellular polyamine depletion.

A second mammalian antizyme: conservation of programmed ribosomal frameshifting

A second mammalian ornithine decarboxylase antizyme was discovered. The deduced protein sequence of the human antizyme2 is 54% identical and 67% similar to human antizyme1 but 99.5% identical to mouse antizyme2. Polyamine-regulated programmed ribosomal frameshifting is used in decoding antizyme2 mRNA as it is for antizyme1 mRNA. The mRNA signals for the programmed frameshifting are similar in the mRNAs for the two antizymes. However, in the stimulatory pseudoknot 3' of the shift site, while the sequences of the stems are highly conserved, the sequences of the loops are divergent. Functional distinctions between antizymes seem likely, but no distinction in the tissue distribution of human antizyme1 and 2 mRNAs was distinguished, though antizyme2 mRNA is 16-fold less abundant than its antizyme1 counterpart. In addition to the previously characterized human antizyme1 mRNA, a second antizyme1 mRNA with an additional 160 nucleotides at its 3' end was identified, and it has a tissue distribution different from that of the shorter antizyme1 mRNA.

Osmotic stress induces variation in cellular levels of ornithine decarboxylase-antizyme

The polyamines, and especially putrescine, play an integral role in the physiological response of cells to varying extracellular osmotic conditions. Ornithine decarboxylase (ODC) synthesis and stability, as well as the activity of the polyamine transporter, had all been reported to be very sensitive to media osmolarity in different cells and tissues, yet the mechanism of this complex, co-ordinated response was not known. In this study we have determined that all these aspects of osmotic-shock response may be mediated by the common regulatory protein, ODC-antizyme. HTC cells were induced for antizyme and then exposed to media of reduced osmotic strength. Both antizyme activity and protein decreased rapidly, under these conditions, to new steady-state levels that depended upon the degree of reduction in media tonicity. This antizyme reduction was found to be due to a rapid increase in antizyme degradation, with a half-life decrease from 75 min down to 45 min occurring immediately upon exchanging media. In complementary experiments, increased media tonicity induced elevated antizyme levels and stability. The sensitivity of antizyme turnover to osmotic conditions was also observed in DH23b cells, which contain elevated levels of more stable antizyme. Interestingly, the two main antizyme proteins, AZ-1 and AZ-2 (presumably products from the first and second translational start sites), differed in their responses to these changing osmotic conditions. Just as feedback regulation of antizyme synthesis provides an effective mechanism for maintaining stable polyamine levels, these studies suggest that alteration in the rate of antizyme degradation may be the mechanism whereby cells adjust steady-state polyamine levels in response to stimulation or stress.

Characterization of the human antizyme gene

Antizyme is a polyamine-inducible protein involved in feedback regulation of cellular polyamine levels. Recently, we isolated genomic clones for the human antizyme gene and determined its chromosomal location (Matsufuji et al., Genomics 38 (1996) 112-114). In the present study, we report complete nucleotide sequence and organization of the human antizyme gene. The organizations of human and rat genes are very similar, but their introns show divergency in terms of the length and nucleotide sequence. Luciferase reporter assay revealed that the 5'-flanking region of the human gene had a strong transcriptional activity in NIH-3T3 with and without addition of spermidine. The promoter was also effective in transfected COS7 and HeLa cells. A 223-bp region at the proximity of the transcriptional start points carries several regulatory sequence motifs including a TATA box, CAAT boxes and GC boxes, and was shown to be important for the strong transcriptional activity.