c-Jun activation-dependent tumorigenic transformation induced paradoxically by overexpression or block of S-adenosylmethionine decarboxylase

Polyamine depletion limits progression of acute leukaemia

Cancer cells are addicted to polyamines, polycations essential for cellular function. While dual targeting of cellular polyamine biosynthesis and polyamine uptake is under clinical investigation in solid cancers, preclinical and clinical studies into its potential in haematological malignancies are lacking. Here we investigated the preclinical efficacy of polyamine depletion in acute leukaemia. The polyamine biosynthesis inhibitor difluoromethylornithine (DFMO) inhibited growth of a molecularly diverse panel of acute leukaemia cell lines, while non-malignant cells were unaffected. Responsiveness to DFMO was linked to decreased levels of its molecular target, the rate-limiting polyamine biosynthesis enzyme ODC1, and of the polyamine transporters ATP13A2 and ATP13A3. DFMO increased polyamine uptake and upregulated expression of polyamine transporters in acute leukaemia cells, a compensatory effect abolished by treatment with the polyamine transport inhibitor AMXT 1501. This drug, currently in a phase 1 clinical trial in solid tumours in combination with DFMO, potentiated the inhibitory effects of DFMO, and their combination synergistically inhibited the growth of acute leukaemia cell lines by inducing apoptosis. DFMO and AMXT 1501 limited disease progression in highly aggressive xenograft models of infant KMT2A-rearranged leukaemia, even when treatment was initiated at high disease burden. Increased expression of c-MYC was associated with enhanced sensitivity to the combination of DFMO and AMXT 1501, suggesting this oncoprotein as a potential predictive marker of response to the drug combination. In conclusion, targeting polyamine biosynthesis and polyamine uptake limits disease progression in models of acute leukaemia, supporting further preclinical and clinical investigation into this approach for acute leukaemia.

Cancer metabolism and dietary interventions

Metabolic remodeling is a key feature of cancer development. Knowledge of cancer metabolism has greatly expanded since the first observation of abnormal metabolism in cancer cells, the so-called Warburg effect. Malignant cells tend to modify cellular metabolism to favor specialized fermentation over the aerobic respiration usually used by most normal cells. Thus, targeted cancer therapies based on reprogramming nutrient or metabolite metabolism have received substantial attention both conceptually and in clinical practice. In particular, the management of nutrient availability is becoming more attractive in cancer treatment. In this review, we discuss recent findings on tumor metabolism and potential dietary interventions based on the specific characteristics of tumor metabolism. First, we present a comprehensive overview of changes in macronutrient metabolism. Carbohydrates, amino acids, and lipids, are rewired in the cancer microenvironment individually or systematically. Second, we summarize recent progress in cancer interventions applying different types of diets and specific nutrient restrictions in pre-clinical research or clinical trials.

ZnCl2 sustains the adriamycin-induced cell death inhibited by high glucose

Hyperglycemia, the condition of high blood glucose, is typical of diabetes and obesity and represents a significant clinical problem. The relationship between hyperglycemia and cancer risk has been established by several studies. Moreover, hyperglycemia has been shown to reduce cancer cell response to therapies, conferring resistance to drug-induced cell death. Therefore, counteracting the negative effects of hyperglycemia may positively improve the cancer cell death induced by chemotherapies. Recent studies showed that zinc supplementation may have beneficial effects on glycemic control. Here we aimed at evaluating whether ZnCl2 could counteract the high-glucose (HG) effects and consequently restore the drug-induced cancer cell death. At the molecular level we found that the HG-induced expression of genes known to be involved in chemoresistance (such as HIF-1α, GLUT1, and HK2 glycolytic genes, as well as NF-κB activity) was reduced by ZnCl2 treatment. In agreement, the adryamicin (ADR)-induced apoptotic cancer cell death was significantly impaired by HG and efficiently re-established by ZnCl2 cotreatment. Mechanistically, the ADR-induced c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) phosphorylation, inhibited by HG, was efficiently restored by ZnCl2. The JNK involvement in apoptotic cell death was assessed by the use of JNK dominant-negative expression vector that indeed impaired the ZnCl2 ability to restore drug-induced cell death in HG condition. Altogether, these findings indicate that ZnCl2 supplementation efficiently restored the drug-induced cancer cell death, inhibited by HG, by both sustaining JNK activation and counteracting the glycolytic pathway.

S-adenosylmethionine decarboxylase overexpression inhibits mouse skin tumor promotion

Neoplastic growth is associated with increased polyamine biosynthetic activity and content. Tumor promoter treatment induces the rate-limiting enzymes in polyamine biosynthesis, ornithine decarboxylase (ODC), and S-adenosylmethionine decarboxylase (AdoMetDC), and targeted ODC overexpression is sufficient for tumor promotion in initiated mouse skin. We generated a mouse model with doxycycline (Dox)-regulated AdoMetDC expression to determine the impact of this second rate-limiting enzyme on epithelial carcinogenesis. TetO-AdoMetDC (TAMD) transgenic founders were crossed with transgenic mice (K5-tTA) that express the tetracycline-regulated transcriptional activator within basal keratinocytes of the skin. Transgene expression in TAMD/K5-tTA mice was restricted to keratin 5 (K5) target tissues and silenced upon Dox treatment. AdoMetDC activity and its product, decarboxylated AdoMet, both increased approximately 8-fold in the skin. This enabled a redistribution of the polyamines that led to reduced putrescine, increased spermine, and an elevated spermine:spermidine ratio. Given the positive association between polyamine biosynthetic capacity and neoplastic growth, it was somewhat surprising to find that TAMD/K5-tTA mice developed significantly fewer tumors than controls in response to 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate chemical carcinogenesis. Importantly, tumor counts in TAMD/K5-tTA mice rebounded to nearly equal the levels in the control group upon Dox-mediated transgene silencing at a late stage of tumor promotion, which indicates that latent viable initiated cells remain in AdoMetDC-expressing skin. These results underscore the complexity of polyamine modulation of tumor development and emphasize the critical role of putrescine in tumor promotion. AdoMetDC-expressing mice will enable more refined spatial and temporal manipulation of polyamine biosynthesis during tumorigenesis and in other models of human disease.

Polyamines regulate c-Myc translation through Chk2-dependent HuR phosphorylation

All mammalian cells depend on polyamines for normal growth and proliferation, but the exact roles of polyamines at the molecular level remain largely unknown. The RNA-binding protein HuR modulates the stability and translation of many target mRNAs. Here, we show that in rat intestinal epithelial cells (IECs), polyamines enhanced HuR association with the 3'-untranslated region of the c-Myc mRNA by increasing HuR phosphorylation by Chk2, in turn promoting c-Myc translation. Depletion of cellular polyamines inhibited Chk2 and reduced the affinity of HuR for c-Myc mRNA; these effects were completely reversed by addition of the polyamine putrescine or by Chk2 overexpression. In cells with high content of cellular polyamines, HuR silencing or Chk2 silencing reduced c-Myc translation and c-Myc expression levels. Our findings demonstrate that polyamines regulate c-Myc translation in IECs through HuR phosphorylation by Chk2 and provide new insight into the molecular functions of cellular polyamines.

Identification of integrins alpha6 and beta7 as c-Jun- and transformation-relevant genes in highly invasive fibrosarcoma cells

Understanding the mechanisms of tumor cell invasion is essential for our attempts to prevent cancer deaths. We screened by DNAmicroarrays the c-Jun- and transformation-related gene expression changes in S-adenosylmethionine decarboxylase (AdoMetDC)-overexpressing mouse fibroblasts that are highly invasive in vivo, and their derivatives expressing a tetracycline-inducible dominant-negative mutant of c-Jun (TAM67) or c-Jun shRNA. Among the small set of target genes detected were integrins alpha6 and beta7, cathepsin L and thymosin beta4, all upregulated in the AdoMetDC-transformed cells and downregulated upon reversal of transformation by TAM67 or c-Jun shRNA. The upregulation of integrin alpha6 subunit, pairing with integrin beta1, endowed the transformed cells with the capability to attach to basement membrane laminin and to spread. Further, inhibition of integrin alpha6 or beta1 function with neutralizing antibodies blocked the invasiveness of AdoMetDC-transformants and human HT-1080 fibrosarcoma cells in three-dimensional Matrigel. Moreover, immunohistochemical analyses showed strong integrin alpha6 staining in high-grade human fibrosarcomas. Our data show that c-Jun can regulate all three key steps of invasion: cell adhesion (integrin alpha6), basement membrane/extracellular matrix degradation (cathepsin L) and cell migration (thymosin beta4). In addition, this is the first study to associate integrin beta7, known as a leukocyte-specific integrin binding to endothelial/epithelial cell adhesion molecules, with the transformed phenotype in cells of nonleukocyte origin. As tumor cell invasion is a prerequisite for metastasis, the observed critical role of integrin alpha6beta1 in fibrosarcoma cell invasion/spreading allures testing antagonists to integrin alpha6beta1, alone or combined with inhibitors of cathepsin L and thymosin beta4, as chemotherapeutic agents.

Calcineurin activates cytoglobin transcription in hypoxic myocytes

Cardiac hypertrophy develops in response to a variety of cardiovascular stresses and results in activation of numerous signaling cascades and proteins. In the present study, we demonstrate that cytoglobin is a stress-responsive hemoprotein in the hypoxia-induced hypertrophic myocardium and it is transcriptionally regulated by calcineurin-dependent transcription factors. The cytoglobin transcript level is abundantly expressed in the adult heart and in response to hypoxia cytoglobin expression is markedly up-regulated within the hypoxia-induced hypertrophic heart. To define the molecular mechanism resulting in the induction of cytoglobin, we undertook a transcriptional analysis of the 5' upstream regulatory region of the cytoglobin gene. Evolutionarily conserved binding elements for transcription factors HIF-1, AP-1, and NFAT are located within the upstream region of the cytoglobin gene. Transcriptional assays demonstrated that calcineurin activity modulates cytoglobin transcription. Increased calcineurin activity enhances the ability of NFAT and AP-1 to bind to the putative cytoglobin promoter, especially under hypoxic conditions. In addition, inhibition of calcineurin, NFAT, and/or AP-1 activities decreases endogenous cytoglobin transcript and protein levels. Thus, the regulation of cytoglobin transcription by calcineurin-dependent transcription factors suggests that cytoglobin may have a functional role in calcium-dependent events accompanying cardiac remodeling.

Adenovirus-mediated expression of both antisense ornithine decarboxylase and S-adenosylmethionine decarboxylase inhibits lung cancer cell growth

Polyamine biosynthesis is controlled primarily by ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC). Antisense sequences of ODC and AdoMetDC genes were cloned into an adenoviral vector (named Ad-ODC-AdoMetDCas). To evaluate the effects of recombinant adenovirus Ad-ODC-AdoMetDCas that can simultaneously express both antisense ODC and AdoMetDC, the human lung cancer cell line A-549 was infected with Ad-ODC-AdoMetDCas or the control vector. Viable cell counting, determination of polyamine concentrations, cell cycle analysis, and Matrigel invasion assays were carried out to assess the properties of tumor growth and invasiveness. Our study showed that adenovirus-mediated antisense ODC and AdoMetDC expression inhibits tumor cell growth through blocking the polyamine synthesis pathway. Tumor cells were arrested at the G1 phase after gene transfer and the invasiveness was reduced. It suggested that the recombinant adenovirus Ad-ODC-AdoMetDCas might be a new anticancer reagent in the treatment of lung cancers.

Polyamine depletion by ODC-AdoMetDC antisense adenovirus impairs human colorectal cancer growth and invasion in vitro and in vivo

BACKGROUND

Polyamine biosynthesis is controlled primarily by ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC). Polyamine concentrations are elevated in colorectal cancer. Depletion of polyamine content in colorectal cancer by chemotherapy is related to tumor regression and impaired tumorigenicity. The current study evaluates the therapeutic effects of antisense ODC and AdoMetDC sequences on colorectal cancer in vitro and in vivo.

METHODS

Antisense ODC and AdoMetDC sequences were cloned into an adenoviral vector (Ad-ODC-AdoMetDCas). The human colon cancer cell lines, HT-29 and Caco-2, were infected with Ad-ODC-AdoMetDCas as well as with control vector. Viable cell counting, determination of polyamine concentrations, cell cycle analysis, and Matrigel invasion assays were performed in order to assess properties of tumor growth and invasiveness. Furthermore, the antitumor effects of Ad-ODC-AdoMetDCas were also evaluated in vivo in a nude mouse tumor model.

RESULTS

Our study demonstrated that adenovirus-mediated ODC and AdoMetDC antisense expression inhibits tumor cell growth through a blockade of the polyamine synthesis pathway. This inhibitory effect cannot be reversed by the administration of putrescine. Tumor cells were arrested at the G1 phase of the cell cycle after gene transfer and had reduced invasiveness. The adenovirus also induced tumor regression in established tumors in nude mice.

CONCLUSIONS

Our study suggests that Ad-ODC-AdoMetDCas has antitumor activity and therapeutic potential for the treatment of colorectal cancer.

Pro-apoptotic role of c-Jun in NMDA-induced neurotoxicity in the rat retina

We examined the role of c-Jun on N-methyl-D-aspartate (NMDA)-induced neurotoxicity in the rat retina. An increase in c-Jun mRNA, c-Jun protein and phosphorylated c-Jun (p-c-Jun) levels in the retina was detected 3 hr after intravitreal injection of NMDA (20 nmol). These levels peaked after 12 hr, and then returned to their control levels by 24 hr. c-Jun and p-c-Jun immunoreactivities were observed in the retinal ganglion cell layer (RGCL), especially in retinal ganglion cells (RGCs), and in the inner nuclear layer (INL) 12 hr after NMDA injection, and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL)-positive cells were immunopositive for c-Jun and p-c-Jun. A c-Jun antisense oligodeoxynucleotide (AS ODN), which was simultaneously injected with NMDA, penetrated the cells in the RGCL and the INL, suppressed the NMDA-induced increase in c-Jun and p-c-Jun protein levels and reduced the number of TUNEL-positive cells in the RGCL 12 hr after the injection. The protective effect of c-Jun AS ODN on the NMDA-treated retina was also shown by the RGCL cell count and measurement of the IPL thickness, as well as by quantitative real-time PCR analysis of Thy-1 mRNA 7 days after the injection. These results suggest that c-Jun synthesis and phosphorylation participate in NMDA-induced neuronal cell death.

Overproduction of cardiac S-adenosylmethionine decarboxylase in transgenic mice

The present study was designed to provide a better understanding of the role played by AdoMetDC (S-adenosylmethionine decarboxylase), the key rate-controlling enzyme in the synthesis of spermidine and spermine, in controlling polyamine levels and the importance of polyamines in cardiac physiology. The alphaMHC (alpha-myosin heavy chain) promoter was used to generate transgenic mice with cardiac-specific expression of AdoMetDC. A founder line (alphaMHC/AdoMetDC) was established with a >100-fold increase in AdoMetDC activity in the heart. Transgene expression was maximal by 1 week of age and remained constant into adulthood. However, the changes in polyamine levels were most pronounced during the first week of age, with a 2-fold decrease in putrescine and spermidine and a 2-fold increase in spermine. At later times, spermine returned to near control levels, whereas putrescine and spermidine levels remained lower, suggesting that compensatory mechanisms exist to limit spermine accumulation. The alphaMHC/AdoMetDC mice did not display an overt cardiac phenotype, but there was an increased cardiac hypertrophy after beta-adrenergic stimulation with isoprenaline ('isoproterenol'), as well as a small increase in spermine content. Crosses of the alphaMHC/AdoMetDC with alphaMHC/ornithine decarboxylase mice that have a >1000-fold increase in cardiac ornithine decarboxylase were lethal in utero, presumably due to increase in spermine to toxic levels. These findings suggest that cardiac spermine levels are highly regulated to avoid polyamine-induced toxicity and that homoeostatic mechanisms can maintain non-toxic levels even when one enzyme of the biosynthetic pathway is greatly elevated but are unable to do so when two biosynthetic enzymes are increased.

Thymosin beta4 is a determinant of the transformed phenotype and invasiveness of S-adenosylmethionine decarboxylase-transfected fibroblasts

S-adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the synthesis of polyamines essential for cell growth and proliferation. Its overexpression induces the transformation of murine fibroblasts in both sense and antisense orientations, yielding highly invasive tumors in nude mice. These cell lines hence provide a good model to study cell invasion. Here, the gene expression profiles of these cells were compared with their normal counterpart by microarray analyses (Incyte Genomics, Palo Alto, CA, and Affymetrix, Santa Clara, CA). Up-regulation of the actin sequestering molecule thymosin beta4 was the most prominent change in both cell lines. Tetracycline-inducible expression of thymosin beta4 antisense RNA caused a partial reversal of the transformed phenotype. Further, reversal of transformation by dominant-negative mutant of c-Jun (TAM67) caused reduction in thymosin beta4 mRNA. Interestingly, a sponge toxin, latrunculin A, which inhibits the binding of thymosin beta4 to actin, was found to profoundly affect the morphology and proliferation of the AdoMetDC transformants and to block their invasion in three-dimensional Matrigel. Thus, thymosin beta4 is a determinant of AdoMetDC-induced transformed phenotype and invasiveness. Up-regulation of thymosin beta4 was also found in ras-transformed fibroblasts and metastatic human melanoma cells. These data encourage testing latrunculin A-like and other agents interfering with thymosin beta4 for treatment of thymosin beta4-overexpressing tumors with high invasive and metastatic potential.

Cysteine cathepsins are central contributors of invasion by cultured adenosylmethionine decarboxylase-transformed rodent fibroblasts

Adenosylmethionine decarboxylase (AdoMetDC), a key enzyme in the biosynthesis of polyamines, is often up-regulated in cancers. We have demonstrated previously that overexpression of AdoMetDC alone is sufficient to transform NIH 3T3 cells and induce highly invasive tumors in nude mice. Here, we studied the transformation-specific alterations in gene expression induced by AdoMetDC by using cDNA microarray and two-dimensional electrophoresis technologies. We specifically tried to identify the secreted proteins contributing to the high invasive activity of the AdoMetDC-transformed cells. We found a significant increase in the expression and secretion of procathepsin L, which was cleaved and activated in the presence of glycosaminoglycans (heparin), and a smaller increase in cathepsin B. Inhibition of the cathepsin L and B activity by specific peptide inhibitors abrogated the invasive capacity of the AdoMetDC transformants in Matrigel. The transformed cells also showed a small increase in the activity of gelatin-degrading matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator activities, neither of which was sensitive to the inhibitors of cathepsin L and B. Furthermore, the invasive potency of the transformed cells remained unaffected by specific inhibitors of MMPs. The results suggest that cysteine cathepsins are the main proteases contributing to the high invasiveness of the AdoMetDC-transformed cells and that the invasion potential is largely independent of activation of the MMPs.

Reversible Regulation of the Transformed Phenotype of Ornithine Decarboxylase- and Ras-Overexpressing Cells by Dominant-Negative Mutants of c-Jun

c-Jun is an oncogenic transcription factor involved in the regulation of cell proliferation, apoptosis and transformation. We have previously reported that cell transformations induced by ornithine decarboxylase (ODC) and c-Ha-ras oncogene, commonly activated in various cancer cells, are associated with constitutively increased phosphorylation of c-Jun on Ser residues 63 and 73. In the present study, we examined the significance of c-Jun phosphorylation and activation on the phenotype of the ODC- and ras-transformants, by using specific inhibitors and dominant-negative (DN) mutants to c-Jun NH(2)-terminal kinase (JNK) and its upstream kinase, SEK1/MKK4 (mitogen-activated protein kinase kinase 4), and to c-Jun. The transformed morphology of both the ODC- and ras-expressing cells was reversed partially by JNK inhibitors and DN JNK1, more effectively by DN SEK1/MKK4 and phosphorylation-deficient c-Jun mutants (c-Jun(S63,73A), c-Jun(S63,73A,T91,93A)) and most potently by a transactivation domain deletion mutant of c-Jun (TAM67). Moreover, tetracycline-inducible TAM67 expression in ODC- and ras-transformed cells showed that the transformed phenotype of the cells is reversibly regulatable. TAM67 also inhibited the tumorigenicity of the cells in nude mice. These inducible cell lines, together with their parental cell lines, provide good models to identify the genes and proteins relevant to cellular transformation.

TATA-binding protein-associated factor 7 regulates polyamine transport activity and polyamine analog-induced apoptosis

Identification of the polyamine transporter gene will be useful for modulating polyamine accumulation in cells and should be a good target for controlling cell proliferation. Polyamine transport activity in mammalian cells is critical for accumulation of the polyamine analog methylglyoxal bis(guanylhydrazone) (MGBG) that induces apoptosis, although a gene responsible for transport activity has not been identified. Using a retroviral gene trap screen, we generated MGBG-resistant Chinese hamster ovary (CHO) cells to identify genes involved in polyamine transport activity. One gene identified by the method encodes TATA-binding protein-associated factor 7 (TAF7), which functions not only as one of the TAFs, but also a coactivator for c-Jun. TAF7-deficient cells had decreased capacity for polyamine uptake (20% of CHO cells), decreased AP-1 activation, as well as resistance to MGBG-induced apoptosis. Stable expression of TAF7 in TAF7-deficient cells restored transport activity (55% of CHO cells), AP-1 gene transactivation (100% of CHO cells), and sensitivity to MGBG-induced apoptosis. Overexpression of TAF7 in CHO cells did not increase transport activity, suggesting that TAF7 may be involved in the maintenance of basal activity. c-Jun NH2-terminal kinase inhibitors blocked MGBG-induced apoptosis without alteration of polyamine transport. Decreased TAF7 expression, by RNA interference, in androgen-independent human prostate cancer LN-CaP104-R1 cells resulted in lower polyamine transport activity (25% of control) and resistance to MGBG-induced growth arrest. Taken together, these results reveal a physiological function of TAF7 as a basal regulator for mammalian polyamine transport activity and MGBG-induced apoptosis.

Jun oncoproteins do not function as primary transcription factors for the mouse major histocompatibility complex class I H-2 genes in fibroblasts

There are several reports in the literature focusing on regulation of major histocompatibility complex (MHC) class I genes by transcription factors of the jun family. The methods employed in these reports differed in various respects, and their results are inconsistent. In mouse Lewis lung carcinoma, B16-melanoma and F9-teratocarcinoma cell lines, c-jun was characterized as a transcriptional activator of the murine MHC class I H2-Kb gene, while c-jun was identified as a direct transcriptional repressor of the swine class I PD1 gene, and c-jun stably transfected clones of mouse L-fibroblasts markedly reduced their H-2 class I gene expression. In this study, we attempted to reproduce this last effect by means of transient transfection coupled to Northern hybridization, upon transfecting L-fibroblasts with expression vectors for all jun family members as well as with an array of c-jun-derived dominant negative mutants. No change in H-2 class I expression could be identified. Next, we derived two additional fibroblastic cell lines from the fibrosarcoma of the H2-Kk/v-jun transgenic mouse and transfected them with the two most potent c-jun dominant negative mutants, again without eliciting any change in H-2 class I mRNA level. We conclude that the negative regulation of H-2 class I genes by c-jun in cells of the fibroblastic lineage is not a primary effect.

Effect of spermine synthase on the sensitivity of cells to anti-tumour agents

The role of spermine in the sensitivity of cells to various established and experimental anti-tumour agents was examined, using paired cell lines that possess or lack spermine synthase. All spermine-synthase-deficient cells had no detectable spermine, and elevated spermidine, content. Spermine content did not alter the cell growth rate. There was little or no difference in sensitivity of immortalized mouse embryonic fibroblasts to doxorubicin, etoposide, cisplatin, methylglyoxal bis(guanylhydrazone) or H(2)O(2) and only a slight increase in sensitivity to vinblastine and nocodazole. However, the absence of spermine clearly increased the sensitivity to 1,3-bis(2-chloroethyl)- N -nitrosourea, suggesting that depletion of spermine may be a useful way to increase the anti-neoplastic effects of anti-tumour agents that form chloroethyl-mediated interstrand DNA cross-links. The effects of spermine on the response to polyamine analogues (which have been proposed to be useful anti-neoplastic agents) were complex, and depended on the compound examined and on the cells tested. Sensitivity to CHENSpm ( N (1)-ethyl- N (11)-[(cycloheptyl)methyl]-4,8-diazaundecane) was substantially greater in immortalized fibroblasts that lack spermine. In contrast, BE-3-4-3 [ N (1), N (12)-bis(ethyl)spermine] and BE-3-3-3 [ N (1), N (11)-bis(ethyl)norspermine] were more active against cells that contained spermine. The presence of spermine correlated with a greater induction of spermidine/spermine- N (1)-acetyltransferase by BE-3-3-3, which is consistent with suggestions that this induction is important for the response to this drug. These findings support the concepts that different polyamine analogues have different sites of action and that CHENSpm has a different site of action from BE-3-3-3.

The cytoprotective aminothiol WR1065 activates p53 through a non-genotoxic signaling pathway involving c-Jun N-terminal kinase

WR1065 is an aminothiol with selective cytoprotective effects in normal cells compared with cancer cells. In a previous study (North, S., El-Ghissassi, F., Pluquet, O., Verhaegh, G., and Hainaut, P. (2000) Oncogene 19, 1206-1214), we have shown that WR1065 activates wild-type p53 in cultured cells. Here we show that WR1065 induces p53 to accumulate through escape from proteasome-dependent degradation. This accumulation is not prevented by inhibitors of phosphatidylinositol 3-kinases and is not accompanied by phosphorylation of Ser-15, -20, or -37, which are common targets of the kinases activated in response to DNA damage. Furthermore, WR1065 activates the JNK (c-Jun N-terminal kinase), decreases complex formation between p53 and inactive JNK, and phosphorylates p53 at Thr-81, a known site of phosphorylation by JNK. A dominant negative form of JNK (JNK-APF) reduces by 50% the activation of p53 by WR1065. Thus, WR1065 activates p53 through a JNK-dependent signaling pathway. This pathway may prove useful for pharmacological modulation of p53 activity through non-genotoxic mechanisms.

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.