Ornithine decarboxylase gene expression is aberrantly regulated via the cAMP signal transduction pathway in malignant H-ras transformed cell lines

Polyamines and related signaling pathways in cancer

Polyamines are aliphatic compounds with more than two amino groups that play various important roles in human cells. In cancer, polyamine metabolism dysfunction often occurs, and regulatory mechanisms of polyamine. This review summarizes the existing research on the metabolism and transport of polyamines to study the association of oncogenes and related signaling pathways with polyamines in tumor cells. Drugs that regulate enzymes have been developed for cancer treatment, and in the future, more attention should be paid to treatment strategies that simultaneously modulate polyamine metabolism and carcinogenic signaling pathways. In addition, the polyamine pathway is a potential target for cancer chemoprevention. As an irreversible suicide inhibitor of the ornithine decarboxylase (a vital enzyme of polyamine synthesis), Difluoro-methylornithine had been shown to have the chemoprevention effect on cancer. Therefore, we summarized and analyzed the chemoprophylaxis effect of the difluoromethylornithine in this systematic review.

A perspective of polyamine metabolism

Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation. In addition, novel features such as the +1 frameshift required for antizyme production and the rapid turnover of several of the enzymes involved in the pathway make the regulation of polyamine metabolism a fascinating subject. The link between polyamine content and human disease is unequivocal, and significant success has been obtained in the treatment of a number of parasitic infections. Targeting the polyamine pathway as a means of treating cancer has met with limited success, although the development of drugs such as DFMO (alpha-difluoromethylornithine), a rationally designed anticancer agent, has revolutionized our understanding of polyamine function in cell growth and provided 'proof of concept' that influencing polyamine metabolism and content within tumour cells will prevent tumour growth. The more recent development of the polyamine analogues has been pivotal in advancing our understanding of the necessity to deplete all three polyamines to induce apoptosis in tumour cells. The current thinking is that the polyamine inhibitors/analogues may also be useful agents in the chemoprevention of cancer and, in this area, we may yet see a revival of DFMO. The future will be in adopting a functional genomics approach to identifying polyamine-regulated genes linked to either carcinogenesis or apoptosis.

K-FGF mediated transformation and induction of metastatic potential involves altered ornithine decarboxylase and S-adenosylmethionine decarboxylase expression--role in cellular invasion

Omithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) expression was investigated in NIH-3T3 fibroblasts that secrete K-FGF. Correlations between altered ODC and SAMDC expression and malignant potential were determined. Increased ODC and SAMDC expression was associated with increased expression of both ODC and SAMDC mRNA and enzyme activity levels. Transcriptional and post-transcriptional regulatory mechanisms were found to account for the increased expression of both ODC and SAMDC. Amplification of the ODC gene also played a role. Correlations between the expression of ODC and the invasion ability of the K-FGF overexpressing cells were also found. Additionally, putrescine, which is a cellular polyamine, was found to play a role in determining the nature of the invasive capacity of the K-FGF overexpressing cells. The results of this study which established correlations between alterations in the expression of ODC and SAMDC, the key rate limiting and regulatory activities in the synthesis of cellular polyamines, and malignant potential as a consequence of K-FGF overexpression supports a model which suggests that growth factor modulation of ODC and SAMDC expression is part of the altered growth regulatory program associated with cellular transformation and malignant progression.

Growth factor-mediated altered expression and regulation of S-adenosylmethionine decarboxylase in a H-ras transformed cell line capable of malignant progression

Mammalian S-adenosylmethionine decarboxylase (SAMDC) is a regulatory activity, which is involved in the biosynthesis of polyamines. The polyamines, namely putrescine, spermidine, and spermine, are essential for mammalian cell proliferation. SAMDC expression was examined in a H-ras transformed cell capable of metastasis formation. Serum stimulation of these cells resulted in increased SAMDC mRNA and enzyme activity expression. The effect of several physiologically relevant growth factors on SAMDC expression was also determined. SAMDC mRNA expression was increased in response to epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) stimulation but was unaffected by transforming growth factor beta(1) (TGF-beta(1)) and platelet derived growth factor (PDGF). Increased SAMDC enzyme activity occurred in response to exposure to EGF, bFGF, TGF-beta(1), and PDGF. The EGF and bFGF mediated alterations in SAMDC mRNA expression were apparently not due to alterations in the transcriptional apparatus but occurred partly through post-transcriptional mechanisms involving increased SAMDC message stability. EGF and bFGF were able both to cooperate with cycloheximide, an inhibitor of protein synthesis, to augment the expression of SAMDC mRNA. Furthermore, studies with NIH-3T3 fibroblasts transfected with either the normal basic fibroblast growth factor coding sequence that lacks a known secretory signal sequence or a chimeric bFGF sequence that targets the growth factor to the secretory pathway revealed that increased SAMDC expression occurred only in those cells which contained the chimeric bFGF sequence that targets the growth factor to the secretory pathway suggesting that the increase in expression of SAMDC occurs through an autocrine mechanism. Increased ornithine decarboxylase (ODC) expression was found to occur in both types of bFGF transfected cells suggesting that altered ODC expression in response to bFGF stimulation may occur through both autocrine and intracrine mechanisms. In addition, a correlation was found to exist between SAMDC expression and regulation in response to growth factor stimulation and malignant potential. This correlation supports the view that growth factor induced alterations in SAMDC expression, although not sufficient on their own to induce metastasis, are important in the promotion and establishment of events important to the phenotype expressed by H-ras transformed cells capable of malignant progression.

S-Adenosylmethionine decarboxylase gene expression is regulated by the cAMP signal transduction pathway in H-ras transformed fibrosarcoma cells capable of malignant progression

The hypothesis that H-ras transformed cells contain alterations in signalling pathways important in controlling the expression of S-adenosylmethionine decarboxylase, (SAMDC) a highly regulated activity in the biosynthesis of polyamines was tested. Mouse 10 T1/2 fibroblasts and H-ras transformed cell lines of varying degrees of malignant potential were treated with agents which affect cAMP levels within cells. Elevations in SAMDC expression were noted in H-ras transformed metastatic C3 cells, which were not observed in either parental, non-transformed 10 T1/2 fibroblast cells, or in ras transformed NR3 cells, which are only capable of benign tumour formation. Forskolin, a stimulator of cAMP synthesis, was able to increase SAMDC enzyme activity but the response which occurred was dependent upon the cellular phenotype expressed. Actinomycin D pre-treatment of C3 cells prior to exposure to forskolin did not abrogate the elevation observed in SAMDC gene expression suggesting that this was not a transcriptional process mediated event. Forskolin pre-treatment of C3 cells did result in a marked increase in the half-life of SAMDC mRNA transcripts suggesting a role for post-transcriptional stabilization. Furthermore, cycloheximide treatment of malignant C3 cells resulted in elevated SAMDC mRNA levels. Treatment of malignant C3 cells with both cycloheximide and forskolin together resulted in a further additive elevation in SAMDC message levels. Cycloheximide treatment alone was found to affect the half-life of SAMDC mRNA through a mechanism of post-transcriptional stabilization. Additionally, altered SAMDC gene expression in C3 cells which occurred in response to cAMP alterations, was enhanced by stimulation of a protein kinase C pathway suggesting possible interactions between protein kinase C-and cAMP-mediated pathways which affect the regulation of SAMDC expression in highly malignant C3 cells. These results demonstrate aberrant regulation of signalling pathways involved in controlling SAMDC gene expression in H-ras transformed cells capable of malignant progression and provide further insight into the altered growth regulatory program associated with H-ras mediated cellular transformation and malignant progression. J. Cell. Biochem. Suppl. 36: 209-221, 2001.

Platelet-derived growth factor mediated altered expression and regulation of ornithine decarboxylase in H-ras-transformed cell lines

This study demonstrates a novel link between alterations in platelet-derived growth factor (PDGF) regulation of ornithine decarboxylase (ODC) expression during malignant conversion. H-ras-transformed cell lines exhibited PDGF-mediated alterations in ODC gene expression. These alterations involved transcriptional, posttranscriptional, and cycloheximide-mediated events. PDGF-mediated alterations in ODC gene expression in NR3 cells (capable of only benign tumour formation) were ras-dependent, involved a tyrosine kinase activity and mitogen-activated protein (MAP) kinase-mediated signalling events, and were independent of both protein kinase C (PKC) events and pertussis toxin-sensitive (PTS) G-protein-mediated signalling. PDGF-mediated alterations in ODC gene expression in C2 cells [capable of malignant progression (metastasis formation)] were ras-dependent, required a tyrosine kinase activity, involved both MAP kinase-mediated events and phosphatidylinositol-3-kinase (PI-3-kinase)-mediated events, and were dependent upon PTS G-protein-mediated signalling but independent of PKC-mediated events. PDGF-mediated regulation of ODC gene expression changes in response to H-ras-mediated cellular transformation and malignant progression.

Phorbol ester tumour promoter mediated altered expression and regulation of matrix metalloproteinase-2 in a H-ras transformed cell line capable of benign tumour formation

The matrix metalloproteinases (MMPs) are thought to play key roles in tumour formation and malignant progression. The present study demonstrates alterations in the regulation of matrix metalloproteinase-2 (MMP-2) expression in response to the phorbol ester tumour promoter, PMA, in a H-ras transformed cell line, NR3, which is capable of benign tumour formation. PMA treatment of NR3 cells resulted in decreased expression of MMP-2 mRNA levels. Following a lag period, an accompanying change in gelatinolytic activity was also found. These PMA-mediated alterations in MMP-2 mRNA levels were independent of de novo protein synthesis and involved both transcriptional and post-transcriptional events. Most notably, PMA regulates MMP-2 mRNA expression through a mechanism involving message de-stabilization. Additionally, protein kinase C mediated events were found to play a role(s) in the regulation of MMP-2 message expression in NR3 cells. This study demonstrates several novel aspects regarding the regulation of MMP-2 expression in a H-ras transformed cell line and thereby provides further insight into the altered growth regulatory programs associated with H-ras mediated cellular transformation.

Tumour promoter mediated altered expression and regulation of ornithine decarboxylase and S-adenosylmethionine decarboxylase in H-ras-transformed fibrosarcoma cell lines

Alterations in cellular growth are important in the progression of malignant disease. Cell growth regulation by tumour promoters can be complex. The present study demonstrates a novel link between alterations in phorbol ester tumour promoter mediated regulation during malignant conversion and the expression of ornithine decarboxylase and S-adenosylmethionine decarboxylase, key rate-limiting and regulatory activities in the biosynthesis of polyamines. H-ras-transformed mouse 10 T 1/2 cell lines exhibiting increasing malignant potential were investigated for possible phorbol ester tumour promoter mediated changes in ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) gene expression. Selective induction of ODC and SAMDC gene expression was observed, since in contrast to nontransformed parental 10 T1/2 cells, ras-transformed cells capable of benign tumour formation (NR3 cells) and ras-transformed cells capable of metastasis formation (C2 cells) exhibited marked alterations in the levels of ODC and SAMDC gene expression. Increased ODC gene and SAMDC gene expression in response to phorbol-12-myristate-13-acetate (PMA) treatment was found to involve transcriptional events in both NR3 cells and in C2 cells. Post-transcriptional events also played a role in the regulation of ODC gene expression in NR3 cells and in C2 cells, and in the regulation of SAMDC gene expression in C2 cells but not in NR3 cells. In NR3 cells, alterations in ODC and in SAMDC gene expression was an event requiring de novo protein synthesis, whereas in highly malignant C2 cells, protein synthesis inhibition following cycloheximide treatment in cooperation with PMA resulted in an augmentation of both ODC and SAMDC gene expression. Evidence is presented to suggest that the PMA-mediated alterations in ODC and in SAMDC gene expression in NR3 cells and in C2 cells involved protein kinase C - mediated events. The status of the cellular polyamine levels was also an important determinant of the PMA-mediated alterations that occurred in ODC and in SAMDC expression in these H-ras transformed cells. Collectively, these results suggest that PMA can modulate ODC and SAMDC expression in H-ras transformed cells and that the mechanisms involved in the PMA- mediated regulation of ODC and SAMDC gene expression changes as a function of H-ras mediated cellular transformation and malignant progression. This study further suggests a mechanism of PMA stimulation of transformed cells wherein early alterations in the regulatory control of ODC and SAMDC gene expression are important and critical.Key words: PMA, ornithine decarboxylase, S-adenosylmethionine decarboxylase, malignant progression.

Insulin-mediated alterations in S-adenosylmethionine decarboxylase expression in H-ras transformed cells of varying degrees of malignancy

Cell growth regulation is a highly complex process. The present study demonstrates a novel link between alterations in insulin-mediated regulation during malignant conversion and the expression of S-adenosylmethionine decarboxylase, a key regulatory activity in the biosynthesis of polyamines. H-ras transformed mouse 10 T 1/2 cell lines exhibiting increasing malignant potential were investigated for possible insulin-mediated changes in S-adenosylmethionine decarboxylase gene expression. Selective induction of S-adenosylmethionine decarboxylase gene expression was observed, because, in contrast to nontransformed 10T 1/2 cells, only H-ras transformed cells capable of only benign tumour formation or H-ras transformed metastatic cells exhibited marked elevations in S-adenosylmethionine decarboxylase mRNA levels. Evidence for regulation of S-adenosylmethionine decarboxylase gene expression at both transcriptional and post-transcriptional levels was found. Evidence was also found for a cycloheximide sensitive regulator of S-adenosylmethionine decarboxylase gene expression in H-ras transformed metastatic cells, whose effect, in combination with insulin, resulted in a further augmentation of S-adenosylmethionine decarboxylase gene expression. This regulation was not present in H-ras transformed cells capable of only benign tumour formation. These results suggest that insulin can modulate S-adenosylmethionine decarboxylase gene expression in H-ras transformed cells and further suggests a mechanism of insulin stimulation of transformed cells wherein alterations in the regulatory activity of S-adenosylmethionine decarboxylase gene expression are critical and constitutes a part of an altered growth regulatory program associated with cellular transformation.

Phorbol 12-myristate 13-acetate inhibits epidermal growth factor signalling in human keratinocytes, leading to decreased ornithine decarboxylase activity

Several studies have suggested that murine and human keratinocytes respond differently to phorbol 12-myristate 13-acetate (PMA). Using an in vitro assay, we found that in contrast to its effect on murine skin, PMA did not induce ornithine decarboxylase (ODC) activity in human skin biopsies. To explore the signalling induced by PMA and to determine whether an in vitro culture system could be used to predict biological activity of retinoids in human keratinocytes, we studied a simian virus 40 (SV40)-transformed human keratinocyte cell line. Epidermal growth factor (EGF) stimulates ODC activity and increases the steady-state level of ODC mRNA in a dose- and time-dependent manner in these cells [Prystowsky, Clevenger and Zheng (1993) Exp. Dermatol. 2, 125-132]. In this report, 10(-10) M-10(-7) M PMA induced ODC mRNA and enzyme synthesis at 7 h, but did not significantly induce ODC activity and inhibited the EGF induction of ODC activity. To explore the mechanism whereby PMA interfered with EGF signalling, the effect of PMA on EGF binding to its cell-surface receptor was studied; acute treatment with PMA (within 7 h) decreased EGF binding to 41-57% of the baseline level. In contrast, chronic treatment with PMA (24 h) increased EGF binding to 156% of the baseline level and was associated with an increase in quantity of EGF receptor protein. Protein kinase C (PKC) activation correlated with the acute decrease in EGF binding following PMA treatment. In summary, PMA induced ODC mRNA and ODC enzyme synthesis, while steady-state levels of immunoprecipitable ODC enzyme protein and ODC activity were not increased, demonstrating possible increased turnover of ODC enzyme protein. Additionally, PMA inhibited the induction of ODC by EGF through decreased EGF binding, possibly mediated by PKC activation. Finally treatment of the keratinocytes with retinoids including etretinate, Ro13-7410, etarotene, Ro40-8757, 13-cisretinoic acid, and acitretin blocked the PMA induction of ODC mRNA, suggesting this in vitro model could be a valuable screening assay for predicting biological activity in humans.

Differential post-transcriptional control of ornithine decarboxylase and spermidine-spermine N1-acetyltransferase by polyamines

Ornithine decarboxylase (ODC) and spermidine/ spermine N1-acetyltransferase (SSAT) are short-lived polyamine enzymes with rate-limiting roles in controlling polyamine biosynthesis and catabolism, respectively. We have found that treatment of MALME-3M human melanoma cells for 6 h with 10 micrograms/ml cycloheximide (CHX) increases ODC and SSAT mRNA 6-9-fold. When cells containing CHX-induced SSAT mRNA were washed and post-incubated for an additional 6 h in drug free media, enzyme activity increased only 2-fold above that in untreated cells despite the > 6-fold increase in accumulated mRNA. Inclusion of 10 microM spermine or spermidine in the post-incubation medium increased SSAT activity approximately 7-fold without further elevating SSAT mRNA levels. This indicates post-transcriptional regulation which, due to the similarity between polyamine-mediated increases in SSAT activity and available mRNA, probably occurs at the level of mRNA translation. In contrast to the SSAT response, polyamines markedly reduced ODC activity (but not mRNA) to one sixth that in cells not exposed to polyamines. The findings illustrate how via post-transcriptional mechanisms, shifts in intracellular polyamine pools can simultaneously and differentially regulate polyamine biosynthesis and catabolism. It is hypothesized that these post-transcriptional responses enable cells to rapidly and sensitively control intracellular spermidine and spermine pools.