Transforming growth factor beta 1 selectively regulates ornithine decarboxylase gene expression in malignant H-ras transformed fibrosarcoma cell lines

Salinity- and population-dependent genome regulatory response during osmotic acclimation in the killifish (Fundulus heteroclitus) gill

The killifish Fundulus heteroclitus is abundant in osmotically dynamic estuaries and it can quickly adjust to extremes in environmental salinity. We performed a comparative osmotic challenge experiment to track the transcriptomic and physiological responses to two salinities throughout a time course of acclimation, and to explore the genome regulatory mechanisms that enable extreme osmotic acclimation. One southern and one northern coastal population, known to differ in their tolerance to hypo-osmotic exposure, were used as our comparative model. Both populations could maintain osmotic homeostasis when transferred from 32 to 0.4 p.p.t., but diverged in their compensatory abilities when challenged down to 0.1 p.p.t., in parallel with divergent transformation of gill morphology. Genes involved in cell volume regulation, nucleosome maintenance, ion transport, energetics, mitochondrion function, transcriptional regulation and apoptosis showed population- and salinity-dependent patterns of expression during acclimation. Network analysis confirmed the role of cytokine and kinase signaling pathways in coordinating the genome regulatory response to osmotic challenge, and also posited the importance of signaling coordinated through the transcription factor HNF-4α. These genome responses support hypotheses of which regulatory mechanisms are particularly relevant for enabling extreme physiological flexibility.

Isothiocyanate sulforaphane inhibits protooncogenic ornithine decarboxylase activity in colorectal cancer cells via induction of the TGF-β/Smad signaling pathway

SCOPE

The objective of this study was to elucidate molecular mechanisms behind the antitumor activities of the isothiocyanate sulforaphane (SFN) in colorectal cancer cells.

METHODS AND RESULTS

Cell growth was determined by BrdU incorporation and crystal violet staining. Protein levels were examined by Western blot analysis. Ornithine decarboxylase (ODC) activity was assayed radiometrically. Reverse transcriptase-PCR was used for measuring mRNA expression. For reporter gene assays plasmids were transfected into cells via lipofection and luciferase activity was measured luminometrically. Acetyl-histone H3 and H4 chromatin immunoprecipitation (ChIP) assays were performed followed by PCR with TGF-β-receptor II promoter specific primers. We could show that SFN-mediated cell growth inhibition closely correlates with a dose-dependent reduction of protein expression and enzymatic activity of ODC. This effect seems to be due to reduced protein levels and transactivation activity of transcription factor c-myc, a direct regulator of ODC expression, as a consequence of SFN-induced TGF-β/Smad signaling. The coherency of these results was further confirmed by using TGF-β receptor kinase inhibitor SB431542, which largely abolishes inhibitory effects of SFN on both, ODC activity and cell growth.

CONCLUSION

Since elevated ODC enzyme activity is associated with enhanced tumor development, SFN may be a dietary phytochemical with potential to prevent carcinogenesis.

HSG cells differentiated by culture on extracellular matrix involves induction of S-adenosylmethione decarboxylase and ornithine decarboxylase

The human salivary gland (HSG) epithelial cell line can differentiate when cultured on extracellular matrix preparations. We previously identified >30 genes upregulated by adhesion of HSG cells to extracellular matrix. In the current studies, we examined the role of one of these genes, the polyamine pathway biosynthetic enzyme S-adenosylmethionine decarboxylase (SAM-DC) and the related enzyme, ornithine decarboxylase (ODC), on HSG cell differentiation during culture on extracellular matrix. HSG cells cultured on fibronectin-, collagen I gel-, and Matrigel-coated substrates for 12-24 h upregulated SAM-DC and ODC mRNA expression and enzyme activity compared to cells cultured on non-precoated substrates. After 3-5 days, HSG cells grown on Matrigel- or collagen I gel-coated substrates acquired a differentiated phenotype: the cells showed changes in culture morphology and increased expression of salivary gland differentiation markers (vimentin, SN-cystatin, and alpha-amylase). Further, culturing the cells on substrates precoated with an anti-beta1-integrin-antibody promoted differentiation-like changes. HSG cells cultured on collagen I- or Matrigel-coated substrates rapidly entered the cell cycle but showed decreased cell proliferation at longer times. In contrast, cell proliferation was enhanced on fibronectin-coated substrates compared to cells on non-precoated substrates. Treatment with the polyamine synthesis inhibitors, difluoromethylornithine (DFMO), and methylglyoxal bis-(guanylhydrazone) (MGBG), inhibited cell proliferation and delayed (3)H-thymidine incorporation in HSG cells cultured on all of the substrates. Further, inclusion of DFMO and MGBG inhibited or delayed acquisition of the differentiated phenotype in HSG cells cultured on Matrigel- or collagen I gel-coated substrates. This suggests that the adhesion-dependent expression of SAM-DC and ODC contributes to extracellular matrix-dependent HSG cell differentiation.

Cisplatin-resistance modulates the effect of protein synthesis inhibitors on spermidine/spermine N(1)-acetyltransferase expression

Cisplatin (DDP)-resistance confers a deficient expression of spermidine/spermine N(1)-acetyltransferase (SSAT) gene in response to the spermine analog N(1),N(12)-bis(ethyl)spermine (BESpm) in the DDP-resistant human ovarian carcinoma cell line (C13*), compared with their parental DDP-sensitive 2008 cells. This SSAT gene deficiency is correlated with a reduced growth sensitivity to spermine analogs. This study was performed to determine whether SSAT gene expression of resistant cells was kept suppressed by labile repressor proteins developed during resistance selection. We show here that inhibitory concentrations of cycloheximide (CHX) and anisomycin (ANISO) differentially affect BESpm-induced SSAT activity in 2008 and in C13* cells in a concentration-dependent manner and allow resistant cells to reach activation levels comparable to those of the sensitive cells. Northern blot analysis revealed that both CHX and ANISO in combination with BESpm caused a synergistic BESpm-mediated accumulation of SSAT mRNA in C13* cells, with respect to each drug alone, while in 2008 cells only a slight increase was observed. The more pronounced effect of inhibitors on the SSAT activity induced by BESpm in the resistant cells was also the result of a more prolonged stabilization of SSAT mRNA and enzyme protein. By contrast, sub-inhibitory concentrations of CHX and ANISO did not significantly stimulate BESpm-induced SSAT transcription and activity. These results suggest that labile repressor proteins, related to DDP-resistance phenotype, play a regulatory role in SSAT gene expression, and further indicate that by overcoming this inhibitory control it is possible to recover BESpm response.

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.

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.

Transforming growth factor β1 selectively regulates ferritin gene expression in malignant H-ras-transformed fibrosarcoma cell lines

Transforming growth factor β1 is an important growth regulator in many cell types, usually exerting a negative effect on cellular growth. Inhibition of DNA synthesis and cell proliferation is frequently lost during malignant transformation, and in some cases, tumor cell proliferation is actually stimulated by TGF-β1. The present study demonstrates a novel link between alterations in TGF-β1 regulation during malignant conversion, and the expression of ferritin, an important activity involved in a number of biological functions including iron homeostasis and cell-growth control. A series of H-ras-transformed mouse 10 T 1/2 cell lines, exhibiting increasing malignant potential, was investigated for possible TGF-β1-mediated changes in ferritin gene expression. Selective induction of gene expression was observed, since only H-ras-transformed cells with malignant potential exhibited marked elevations in ferritin gene expression, in particular, alterations in H-ferritin gene expression. The regulation of H-ferritin gene expression in response to TGF-β 1 did not involve alterations in transcription, but occurred through mechanisms of post-transcriptional stabilization of the H-ferritin mRNA. Additionally, evidence was obtained for a cycloheximide-sensitive regulator of H-ferritin gene expression, since the presence of this protein synthesis inhibitor increased H-ferritin message levels, and in combination with TGF-β1, cooperated in an additive manner to augment H-ferritin gene expression. These results show for the first time that TGF-β1 can regulate ferritin gene expression in malignant H-ras transformed cells, and suggest a mechanism for growth factor stimulation of malignant cells, in which early alterations in the control of H-ferritin gene expression are important.Key words: TGF-β1, ferritin gene expression, malignant transformation.

Expression and localization of ornithine decarboxylase in reversible papillomatosis induced by uracil in rat bladder

Direct mechanical irritation by uracil calculi formed following feeding of 3% uracil in the diet to male rats produces severe papillary hyperplasia (papillomatosis, which is reversible) of bladder epithelium. To evaluate the mechanism of the appearance of uracil-induced papillomatosis, we examined the changes of the enzyme activity and the localization of ornithine decarboxylase (ODC), as well as polyamine biosynthesis, and epithelial proliferation, that accompany the sequential bladder epithelial changes following administration and withdrawal of uracil. Moreover, expression of ODC mRNA was investigated using northern blotting and localization of ODC mRNA was demonstrated using in situ hybridization. ODC activity during uracil administration was maintained at a high level compared to that in normal epithelium, but sharply decreased after cessation of uracil treatment. The accumulation of ODC protein was observed in the proliferating bladder epithelium by immunohistochemical examination and western blotting analysis, and even after cessation of treatment, the protein binding to anti-ODC antibody remained mildly elevated. Sequential changes of proliferating cell nuclear antigen (PCNA)-positive cells in the epithelium during the development and disappearance of papillomatosis correlated with ODC activity. ODC mRNA was expressed strongly in the proliferating epithelium in rats treated with uracil and weakly in normal epithelium, in accordance with the location of ODC protein. Consequently, our data demonstrate that cell proliferation in the development of papillomatosis is closely associated with polyamine metabolism, and moreover suggest that ODC activity is up-regulated at a post-translational step.

Inhibition of spermidine synthase gene expression by transforming growth factor-beta 1 in hepatoma cells

We screened genes responsive to transforming growth factor-beta (TGF-beta 1) protein in a human hepatoma cell line (Hep3B) using a PCR-mediated differential display technique, in order to investigate the mechanisms involved in TGF-beta-induced growth suppression. We found a gene that was down-regulated by TGF-beta 1 to be completely identical in an approx. 620 bp segment to the gene for the enzyme spermidine synthase, which mediates the conversion of putrescine into spermidine. Both spermidine synthase mRNA expression and its enzyme activity were decreased after TGF-beta 1 treatment of Hep3B cells. The inhibition of spermidine synthase gene expression by TGF-beta 1 protein was also observed in other hepatoma cell lines. The expression of genes for other biosynthetic enzymes in polyamine metabolism (ornithine decarboxylase and S-adenosylmethionine decarboxylase) was also inhibited to the same extent as for spermidine synthase, while the gene expression of spermidine/spermine N1-acetyltransferase, a catabolic enzyme, was relatively resistant to TGF-beta 1. Spermine levels in Hep3B cells were decreased by TGF-beta 1 treatment, although the levels of spermidine and putrescine were unchanged, probably due to compensation by remaining spermidine/spermine N1-acetyltransferase activity. Exogenously added spermidine or spermine, but not putrescine, partially antagonized the growth-inhibitor effects of TGF-beta 1 on Hep3B cells. Our data suggest that down-regulation of gene expression of the enzymes involved in polyamine metabolism, including spermidine synthase, may be associated with the mechanism of TGF-beta-induced growth suppression.

Regulation of eukaryotic messenger RNA turnover

We have demonstrated the existence of multiple mRNA binding proteins that interact specifically with defined regions in posttranscriptionally regulated mRNAs. These domains appear to be destabilizers whose function can be attenuated by the interaction with the specific binding proteins. Thus, the ability to alter mRNA decay rates on demand, given different environmental or intracellular conditions, appears to be mediated by controlling the localization, activity, and overall function of the cognate binding protein. Based on our limited experience, we predict that most, if not all, of similarly regulated mRNAs will ultimately be found to interact with regulatory mRNA binding proteins. Under conditions whereby the mRNA binding proteins are constitutively active (e.g., tumor cell lines), abnormal mRNA decay will result, with accumulation and overtranslation. Such appears to be the case for cytokines and possibly amyloid protein precursor mRNAs in cancer and Alzheimer's disease, respectively. Conversely, mutagenesis of these critical 3' untranslated region elements will likely have comparable deleterious effects on the regulation of gene expression. To the extent that such derangements exist in human disease, attention to understanding the mechanistic detail at this level may provide insights into the development of appropriate therapeutics or treatment strategies.

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.

Basic fibroblast growth factor selectively regulates ornithine decarboxylase gene expression in malignant H-ras transformed cells

Cell growth regulation by fibroblast growth factors (FGFs) is highly complex. The present study demonstrates a novel link between alterations in bFGF regulation during malignant conversion and the expression of ornithine decarboxylase, a key rate-limiting and regulatory activity in the biosynthesis of polyamines. H-ras transformed mouse 10T 1/2 cell lines exhibiting increasing malignant potential were investigated for possible bFGF-mediated changes in ornithine decarboxylase gene expression. Selective induction of ornithine decarboxylase gene expression was observed, since, in contrast to nontransformed 10T 1/2 cells and cells capable of only benign tumor formation, H-ras transformed metastatic cells exhibited marked elevations in ornithine decarboxylase message levels. Evidence for regulation of ornithine decarboxylase gene expression by bFGF at both transcription and posttranscription was found. Actinomycin D pretreatment of malignant cells prior to bFGF exposure inhibited the increase in ornithine decarboxylase message. Furthermore, striking differences in the rates of ornithine decarboxylase message decay were observed when cells treated with bFGF were compared to untreated control cells, with the half-life of ornithine decarboxylase mRNA increasing from 2.4 h in untreated cells to 12.5 h in cells exposed to bFGF. Evidence was also obtained for a cycloheximide-sensitive regulator of ornithine decarboxylase gene expression whose effect, in combination with bFGF, resulted in a further augmentation of ornithine decarboxylase gene expression. Furthermore, evidence is presented to suggest a possible role for G-protein-coupled events in the bFGF-mediated regulation of ornithine decarboxylase gene expression. The bFGF regulation of ornithine decarboxylase expression in H-ras transformed malignant cells appeared to occur independent of protein kinase C-mediated events. These results show that bFGF can modulate ornithine decarboxylase gene expression in malignant H-ras transformed cells and further suggests a mechanism of growth factor stimulation of malignant cells wherein early alterations in the regulatory control of ornithine decarboxylase gene expression are critical.

Ornithine decarboxylase as a target for chemoprevention

l-Ornithine decarboxylase (ODC) is essential for polyamine synthesis and growth in mammalian cells; it provides putrescine that is usually converted into the higher polyamines, spermidine and spermine. Many highly specific and potent inhibitors of ODC are based on the lead compound alpha-difluoromethylornithine (DFMO), which is an enzyme-activated irreversible inhibitor. DFMO is accepted as a substrate by ODC and is decarboxylated, leading to the formation of a highly reactive species that forms a covalent adduct with either cysteine-360 (90%) or lysine-69 (10%). Both modifications inactivate the enzyme. ODC activity is normally very highly regulated at both transcriptional and post-transcriptional levels according to the growth state of the cell and the intracellular polyamine content. Experimental over-production of ODC can be caused by either transfection with plasmids containing the ODC cDNA with part of the 5'-untranslated region (5'UTR) deleted under the control of a very strong viral promoter, or transfection of plasmids that cause the overproduction of eIF-4E, reported to be a limiting factor in the translation of mRNAs with extensive secondary structures in the 5'UTR. In both cases, unregulated overexpression of ODC transforms NIH 3T3 cells to a neoplastic state. Along with studies showing that many tumor promoters increase ODC activity and that a number of preneoplastic conditions and tumor samples show high levels of ODC, these results suggest that ODC may act as an oncogene in an appropriate background. This provides a rationale for the possible use of ODC inhibitors as chemopreventive agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Antisense oligodeoxyribonucleotide inhibition of TGF-beta 1 gene expression and alterations in the growth and malignant properties of mouse fibrosarcoma cells

Transforming growth factor (TGF-beta) is a family of multifunctional signalling molecules that play a fundamental role in both normal and malignant cell behavior. Procedures that alter mouse TGF-beta 1 gene expression provide an important approach for analyzing the complex regulatory processes associated with this member of the growth factor family. Therefore, we have designed oligodeoxyribonucleotides (oligos) in an antisense orientation, which are complementary to regions of the TGF-beta 1 message, in an attempt to obtain an oligo sequence that specifically reduces TGF-beta 1 synthesis. We observed that oligos containing a mixture of phosphorothioate and phosphodiester linkages were less toxic and more specific when compared to those only containing phosphorothioate. A non-toxic sequence was identified that markedly reduced the levels of TGF-beta 1 in oligo-treated malignant mouse fibrosarcoma cells. The invasive and metastatic properties of these fibrosarcoma cells were also significantly decreased following treatment with the antisense oligo. The results indicate an important role for altered TGF-beta 1 expression in the regulation of malignant cell proliferation, invasion and metastasis. These results also indicate that this oligo sequence is a useful tool for studies directed towards understanding the complex relationships between TGF-beta 1 and cellular regulation.

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

We have tested the hypothesis that H-ras transformed cells contain alterations in signal pathways important in controlling the expression of ornithine decarboxylase (ODC), the highly regulated rate-limiting activity in the biosynthesis of polyamines. Mouse 10T1/2 fibroblasts and a series of 10T1/2 H-ras transformed cell lines were treated with stimulators of cAMP synthesis (forskolin and cholera toxin), a biologically stable analogue of cAMP (8-bromo-cAMP), and an inhibitor of cAMP degradation (3-isobutyl-1-methylxanthine). Elevations in ODC gene expression were noted in H-ras transformed cells that were not observed in parental 10T1/2 fibroblasts. The forskolin-mediated effects were not detected with 1,9-dideoxyforskolin, a compound structurally related to forskolin, which does not activate adenyl cyclase. The effects observed with cholera toxin were not detected when cells were treated with the purified subunits of this compound, indicating that the toxin-induced effects were cAMP-specific. Actinomycin D treatment prior to forskolin exposure reduced the elevation observed in ODC gene expression indicating the involvement of the transcriptional process. Furthermore, we observed that cycloheximide treatment of malignant but not benign H-ras transformed cells significantly elevated ODC message level. Treatment of malignant cells with both cycloheximide and forskolin together resulted in a further additive elevation in ODC message, but a similar treatment of benign tumor cells reduced the forskolin-mediated increase in ODC message. In addition, treatment of H-ras transformed cells with the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) led to an elevation in ODC mRNA levels not observed in parental 10T1/2 fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)