Androgen-regulation of ornithine decarboxylase and S-adenosylmethionine decarboxylase genes

Metabolic adaptations in prostate cancer

Prostate cancer is one of the most commonly diagnosed cancers in men and is a major cause of cancer-related deaths worldwide. Among the molecular processes that contribute to this disease, the weight of metabolism has been placed under the limelight in recent years. Tumours exhibit metabolic adaptations to comply with their biosynthetic needs. However, metabolites also play an important role in supporting cell survival in challenging environments or remodelling the tumour microenvironment, thus being recognized as a hallmark in cancer. Prostate cancer is uniquely driven by androgen receptor signalling, and this knowledge has also influenced the paths of cancer metabolism research. This review provides a comprehensive perspective on the metabolic adaptations that support prostate cancer progression beyond androgen signalling, with a particular focus on tumour cell intrinsic and extrinsic pathways.

Magnesium Supplementation Attenuates Ultraviolet-B-Induced Damage Mediated through Elevation of Polyamine Production in Human HaCaT Keratinocytes

Magnesium ions (Mg²⁺) have favorable effects such as the improvement of barrier function and the reduction of inflammation reaction in inflammatory skin diseases. However, its mechanisms have not been fully understood. Microarray analysis has shown that the gene expressions of polyamine synthases are upregulated by MgCl₂ supplementation in human HaCaT keratinocytes. Here, we investigated the mechanism and function of polyamine production. The mRNA and protein levels of polyamine synthases were dose-dependently increased by MgCl₂ supplementation, which were inhibited by U0126, a MEK inhibitor; CHIR-99021, a glycogen synthase kinase-3 (GSK3) inhibitor; and Naphthol AS-E, a cyclic AMP-response-element-binding protein (CREB) inhibitor. Similarly, reporter activities of polyamine synthases were suppressed by these inhibitors, suggesting that MEK, GSK3, and CREB are involved in the transcriptional regulation of polyamine synthases. Cell viability was reduced by ultraviolet B (UVB) exposure, which was rescued by MgCl₂ supplementation. The UVB-induced elevation of reactive oxygen species was attenuated by MgCl₂ supplementation, which was inhibited by cysteamine, a polyamine synthase inhibitor. Our data indicate that the expression levels of polyamine synthases are upregulated by MgCl₂ supplementation mediated through the activation of the MEK/GSK3/CREB pathway. MgCl₂ supplementation may be useful in reducing the UVB-induced oxidative stress in the skin.

The essential role of methylthioadenosine phosphorylase in prostate cancer

Prostatic epithelial cells secrete high levels of acetylated polyamines into the prostatic lumen. This distinctive characteristic places added strain on the connected pathways, which are forced to increase metabolite production to maintain pools. The methionine salvage pathway recycles the one-carbon unit lost to polyamine biosynthesis back to the methionine cycle, allowing for replenishment of SAM pools providing a mechanism to help mitigate metabolic stress associated with high flux through these pathways. The rate-limiting enzyme involved in this process is methylthioadenosine phosphorylase (MTAP), which, although commonly deleted in many cancers, is protected in prostate cancer. We report near universal retention of MTAP expression in a panel of human prostate cancer cell lines as well as patient samples. Upon metabolic perturbation, prostate cancer cell lines upregulate MTAP and this correlates with recovery of SAM levels. Furthermore, in a mouse model of prostate cancer we find that both normal prostate and diseased prostate maintain higher SAM levels than other tissues, even under increased metabolic stress. Finally, we show that knockdown of MTAP, both genetically and pharmacologically, blocks androgen sensitive prostate cancer growth in vivo. Our findings strongly suggest that the methionine salvage pathway is a major player in homeostatic regulation of metabolite pools in prostate cancer due to their high level of flux through the polyamine biosynthetic pathway. Therefore, this pathway, and specifically the MTAP enzyme, is an attractive therapeutic target for prostate cancer.

One-Carbon Metabolism in Prostate Cancer: The Role of Androgen Signaling

Cancer cell metabolism differs significantly from the metabolism of non-transformed cells. This altered metabolic reprogramming mediates changes in the uptake and use of nutrients that permit high rates of proliferation, growth, and survival. The androgen receptor (AR) plays an essential role in the establishment and progression of prostate cancer (PCa), and in the metabolic adaptation that takes place during this progression. In its role as a transcription factor, the AR directly affects the expression of several effectors and regulators of essential catabolic and biosynthetic pathways. Indirectly, as a modulator of the one-carbon metabolism, the AR can affect epigenetic processes, DNA metabolism, and redox balance, all of which are important factors in tumorigenesis. In this review, we focus on the role of AR-signaling on one-carbon metabolism in tumorigenesis. Clinical implications of one-carbon metabolism and AR-targeted therapies for PCa are discussed in this context.

Ornithine Decarboxylase Activity Is Required for Prostatic Budding in the Developing Mouse Prostate

The prostate is a male accessory sex gland that produces secretions in seminal fluid to facilitate fertilization. Prostate secretory function is dependent on androgens, although the mechanism by which androgens exert their effects is still unclear. Polyamines are small cationic molecules that play pivotal roles in DNA transcription, translation and gene regulation. The rate-limiting enzyme in polyamine biosynthesis is ornithine decarboxylase, which is encoded by the gene Odc1. Ornithine decarboxylase mRNA decreases in the prostate upon castration and increases upon administration of androgens. Furthermore, testosterone administered to castrated male mice restores prostate secretory activity, whereas administering testosterone and the ornithine decarboxylase inhibitor D,L-α-difluromethylornithine (DFMO) to castrated males does not restore prostate secretory activity, suggesting that polyamines are required for androgens to exert their effects. To date, no one has examined polyamines in prostate development, which is also androgen dependent. In this study, we showed that ornithine decarboxylase protein was expressed in the epithelium of the ventral, dorsolateral and anterior lobes of the adult mouse prostate. Ornithine decarboxylase protein was also expressed in the urogenital sinus (UGS) epithelium of the male and female embryo prior to prostate development, and expression continued in prostatic epithelial buds as they emerged from the UGS. Inhibiting ornithine decarboxylase using DFMO in UGS organ culture blocked the induction of prostatic buds by androgens, and significantly decreased expression of key prostate transcription factor, Nkx3.1, by androgens. DFMO also significantly decreased the expression of developmental regulatory gene Notch1. Other genes implicated in prostatic development including Sox9, Wif1 and Srd5a2 were unaffected by DFMO. Together these results indicate that Odc1 and polyamines are required for androgens to exert their effect in mediating prostatic bud induction, and are required for the expression of a subset of prostatic developmental regulatory genes including Notch1 and Nkx3.1.

Combined administration of testosterone plus an ornithine decarboxylase inhibitor as a selective prostate-sparing anabolic therapy

Because of its anabolic effects on muscle, testosterone is being explored as a function-promoting anabolic therapy for functional limitations associated with aging; however, concerns about testosterone's adverse effects on prostate have inspired efforts to develop strategies that selectively increase muscle mass while sparing the prostate. Testosterone's promyogenic effects are mediated through upregulation of follistatin. We show here that the administration of recombinant follistatin (rFst) increased muscle mass in mice, but had no effect on prostate mass. Consistent with the results of rFst administration, follistatin transgenic mice with constitutively elevated follistatin levels displayed greater muscle mass than controls, but had similar prostate weights. To elucidate signaling pathways regulated differentially by testosterone and rFst in prostate and muscle, we performed microarray analysis of mRNAs from prostate and levator ani of castrated male mice treated with vehicle, testosterone, or rFst. Testosterone and rFst shared the regulation of many transcripts in levator ani; however, in prostate, 593 transcripts in several growth-promoting pathways were differentially expressed after testosterone treatment, while rFst showed a negligible effect with only 9 transcripts differentially expressed. Among pathways that were differentially responsive to testosterone in prostate, we identified ornithine decarboxylase (Odc1), an enzyme in polyamine biosynthesis, as a testosterone-responsive gene that is unresponsive to rFst. Accordingly, we administered testosterone with and without α-difluoromethylornithine (DFMO), an Odc1 inhibitor, to castrated mice. DFMO selectively blocked testosterone's effects on prostate, but did not affect testosterone's anabolic effects on muscle. Co-administration of testosterone and Odc1 inhibitor presents a novel therapeutic strategy for prostate-sparing anabolic therapy.

Polyamines transduce the nongenomic, androgen-induced calcium sensitization in intestinal smooth muscle

Androgens regulate body development and differentiation through a variety of genotropic mechanisms, mostly in reproductive organs. In recent years a different scenario for sex hormone actions has emerged: the intestinal muscle. Thus, although estrogens relax intestinal muscle, androgens are powerful inducers of mechanical potentiation. This effect of androgens was intriguing because it is observed at physiological concentrations, is mediated by nongenomic mechanisms, and involves a phenomenon of calcium sensitization of contractile machinery by stimulating phosphorylation of 20 kDa myosin light chain by Rho-associated kinase. Here we have deciphered the molecular mechanisms underlying calcium sensitization and mechanical potentiation by androgens in male intestinal muscle as well as its tight relationship to polyamine metabolism. Thus, androgens stimulate polyamine synthesis, and the inhibition of polyamine synthesis abolishes androgen-induced calcium sensitization and 20 kDa myosin light chain phosphorylation. We demonstrate that the first molecular step in the induction of calcium sensitization is a nonconventional activation of the adaptor protein RhoA, triggered by a transglutaminase-catalyzed polyamination of RhoA, which is then targeted to the membrane to activate Rho-associated kinase. Altogether, these results demonstrate that the physiological levels of androgens, through the modulation of polyamine metabolism and posttanslational modification of RhoA, activate a new signal transduction pathway in the intestinal smooth muscle to induce calcium sensitization. Furthermore, apart from being one of the few physiologically relevant nongenomic effects of androgens, these results might underlie the well-known gender differences in intestinal transits, thus expanding the nature's inventory of sex hormones effects.

Expression and distribution of genes encoding for polyamine-metabolizing enzymes in the different zones of male and female mouse kidneys

The role of polyamines in renal physiology is only partially understood. Moreover, most of the data on the enzymes of polyamine metabolism come from studies using whole kidneys. The aim of the present study was to analyze the mRNA abundance of the genes implicated in both the polyamine biosynthetic and catabolic pathways in different renal zones of male and female mice, by means of the quantitative reverse transcription-polymerase chain reaction. Our results indicate that there is an uneven distribution of the different mRNAs studied in the five renal zones: superficial cortex, deep cortex, outer stripe of the outer medulla (OS), inner stripe of the outer medulla (IS), and the inner medulla + papilla (IM). The biosynthetic genes, ornithine decarboxylase (ODC) and spermine synthase, were more expressed in the cortex, whereas the mRNAs of the catabolic genes spermine oxidase (SMO) and diamine oxidase were more abundant in IS and IM. The genes involved in the regulation of polyamine synthesis (AZ1, AZ2 and AZIN1) were expressed in all the renal zones, predominantly in the cortex, while AZIN2 gene was more abundant in the OS. ODC, SMO, spermidine synthase and spermidine/spermine acetyl transferase expression was higher in males than in females. In conclusion, the genes encoding for the polyamine metabolism were specifically and quantitatively distributed along the corticopapillary axis of male and female mouse kidneys, suggesting that their physiological role is essential in defined renal zones and/or nephron segments.

Chronic difluoromethylornithine treatment impairs spatial learning and memory in rats

Recent evidence suggests that polyamines putrescine, spermidine and spermine are essential in maintaining normal cellular function. The present study investigated the effects of chronic treatment of difluoromethylornithine (DFMO, 3% in drinking water), a potent inhibitor of putrescine synthesis, for 54 consecutive days on animals'behavior and neurochemical levels in the CA1, CA2/3 and dentate gyrus sub-regions of the hippocampus and the prefrontal cortex. The DFMO group showed performance impairments in the place navigation and the probe test conducted 24 h after the training in the reference memory version of the water maze task, but not in the elevated plus maze, open field, object recognition, cued navigation and the working memory version of the water maze task when compared to the control group (drinking water only). DFMO treatment resulted in approximately 80-90% and 20% of reductions in the putrescine and spermidine levels, respectively, in the four brain regions examined, and a small reduction in agmatine level in the CA2/3, with no effects on spermine, glutamate and γ-aminobutyrate. The DFMO group showed decreased body weight relative to the control one. However, there were no significant differences between groups in the normalized brain, kidney and liver weights. The present study demonstrates that chronic treatment of DFMO depletes putrescine and decreases spermidine levels in the brain, inhibits growth, and impairs spatial learning and memory in the reference memory version of the water maze specifically. These findings merit further investigation to fully understand the functional role of endogenous polyamines in learning and memory.

Androgens are powerful non-genomic inducers of calcium sensitization in visceral smooth muscle

Androgens are recognized as genotropic inducers of a number of physiological functions mainly associated with the development of sexual characteristics. However, as in the case of estrogens, the number of studies evidencing androgen actions in non-reproductive tissues has steadily grown over the past years. Here, we show that androgens acutely ( approximately 30min) alter the frequency spectrum of peristaltic activity of intestinal smooth muscle and augment the amplitude agonist-induced contractile activity. Maximal stimulation occurred at physiological concentrations of androgens with EC(50) values in the picomolar range. Androgen-induced potentiation was prevented by preincubation with androgen receptor (AR) antagonists but unaffected by cycloheximide plus actinomycin D, indicating that potentiation was mediated by ARs via a non-genomic mechanism. The effects of androgens were mimicked by polyamines and were completely blocked by inhibitors of polyamine synthesis. Using ionomycin-permeabilized intestinal smooth muscle preparations, we demonstrate that androgens exert their effects by inducing a mechanism of sensitization to calcium and not by altering intracellular calcium homeostasis. Correspondingly, the potentiation of mechanical activity induced by androgens was accompanied by an increase in the phosphorylation of the regulatory myosin light chain (LC(20)) within the same time-course than calcium sensitization and mechanical potentiation. The pursuit of potential signalling pathways linking androgen receptor activation with calcium sensitization revealed that mechanical potentiation of intestinal muscle by androgens involve activation of the Rho pathway, whose downstream effector, Rho-associated kinase (ROCK), is eventually responsible for displacement of the phosphorylation/dephosphorylation state of LC(20) towards its phosphorylated form.

Polyamine biosynthesis impacts cellular folate requirements necessary to maintain S-adenosylmethionine and nucleotide pools

Folate (vitamin B9) is utilized for synthesis of both S-adenosylmethionine (AdoMet) and deoxythymidine monophosphate (dTMP), which are required for methylation reactions and DNA synthesis, respectively. Folate depletion leads to an imbalance in both AdoMet and nucleotide pools, causing epigenetic and genetic damage capable of initiating tumorigenesis. Polyamine biosynthesis also utilizes AdoMet, but polyamine pools are not reduced under a regimen of folate depletion. We hypothesized that high polyamine biosynthesis, due to the high demand on AdoMet pools, might be a factor in determining sensitivity to folate depletion. We found a significant correlation (P<0.001) between polyamine biosynthesis and the amount of folate required to sustain cell line proliferation. We manipulated polyamine biosynthesis by genetic and pharmacological intervention and mechanistically demonstrated that we could thereby alter AdoMet pools and increase or decrease demand on folate availability needed to sustain cellular proliferation. Furthermore, growing a panel of cell lines with 100 nM folate led to imbalanced nucleotide and AdoMet pools only in cells with endogenously high polyamine biosynthesis. These data demonstrate that polyamine biosynthesis is a critical factor in determining sensitivity to folate depletion and may be particularly important in the prostate, where biosynthesis of polyamines is characteristically high due to its secretory function.

Nuclear and membrane receptor-mediated signalling pathways modulate polyamine biosynthesis and interconversion

Polyamines play an important role in cell growth and differentiation, while their overproduction has potentially oncogenic consequences. Polyamine homoeostasis, a critical determinant of cell fate, is precisely tuned at the level of biosynthesis, degradation and transport. The enzymes ODC (ornithine decarboxylase), AdoMetDC (S-adenosylmethionine decarboxylase) and SSAT (spermidine/spermine N(1)-acetyltransferase) are critical for polyamine pool maintenance. Our experiments were designed to examine the expression of these enzymes in testosterone-induced hypertrophic and antifolate-induced hyperplastic mouse kidney, characterized by activation of AR (androgen receptor) and HGF (hepatocyte growth factor) membrane receptor c-Met respectively. The expression of these key enzymes was up-regulated by antifolate CB 3717 injury-evoked activation of HGF/c-Met signalling. In contrast, activation of the testosterone/AR pathway remarkably induced a selective increase in ODC expression without affecting other enzymes. Studies in catecholamine-depleted kidneys point to a synergistic interaction between the signalling pathways activated via cell membrane catecholamine receptors and AR, as well as c-Met. We found that this cross-talk modulated the expression of ODC and AdoMetDC, enzymes limiting polyamine biosynthesis, but not SSAT. This is in contrast with the antagonistic cross-talk between AR- and c-Met-mediated signalling which negatively regulated the expression of ODC, but affected neither AdoMetDC nor SSAT.

Androgens differentially potentiate mouse intestinal smooth muscle by nongenomic activation of polyamine synthesis and Rho kinase activation

We demonstrate that testosterone and its active metabolite 5alpha-dihydrotestosterone acutely (approximately 30 min) potentiate mouse ileal, but not duodenal, muscle activity. Androgens augment the amplitude of spontaneous peak-to-peak oscillations, alter the spontaneous activity frequency spectrum, and increase the amplitude of calcium-induced and carbachol-induced contractions. Concentration-dependence analyses revealed that maximal potentiation (449-910%) occurred at physiological concentrations of androgens (100 pM to 10 nM) with EC50 values in the picomolar range (8-20 pM). Western blot analyses using an antiandrogen receptor (anti-AR) antibody revealed the presence of two different AR proteins migrating at 87 and 110 kDa in ileal, but not duodenal, extracts. Androgen-induced potentiation was prevented by preincubation with AR antagonists flutamide or cyproterone acetate but was unaffected by pretreatment with cycloheximide plus actinomycin D, indicating that potentiation was mediated by ARs via a novel nongenomic mechanism. Androgen effects were mimicked by polyamines putrescine and spermine and were blocked by the ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase inhibitors alpha-difluoromethylornithine and berenil, respectively. Accordingly, androgens increase alpha-difluoromethylornithine-sensitive ornithine-decarboxylase- mediated L-ornithine decarboxylation in ileal tissues within the same time course as isometric potentiation. Both putrescine and dihydrotestosterone induced Ca2+ sensitization of ionomycin-permeabilized ileal smooth muscle. Finally, inhibition of the Rho kinase (ROK) pathway with the specific inhibitor Y27632 completely prevented androgen-induced potentiation. In agreement, androgens elicited ROK-induced Ser19 phosphorylation of myosin light chain 2 in ileal muscle. These data indicate that androgens potentiate ileal contractile activity by an AR-dependent nongenomic mechanism involving intracellular polyamine signaling and Ca2+ sensitization via ROK activation.

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.

Identification of an X-linked locus modifying mouse skin tumor susceptibility

The enhancing effect of overexpression of an ornithine decarboxylase (Odc) transgene on skin tumor susceptibility can be modified by genetic loci present in several inbred mouse strains. The BALB/cJ strain is among the most resistant strains so far examined; tumor multiplicity following 7,12-dimethylbenz(a)anthracene (DMBA) treatment is reduced by 90% when the K6/ODC transgene is expressed on a BALB/cJ background versus the susceptible C57BL/6J background. Further, transgenic BALB/cJ males developed more tumors than females, indicating the presence of sex-dependent modifier pathway. Analysis of 263 F2 intercross mice revealed significant linkage of markers on the X chromosome to tumor multiplicity. This analyses as well as a similar genome-wide scan of 136 backcross mice found evidence for other modifier loci on chromosomes 4, 6, and 17. Identification of these modifier genes should reveal the effector pathways responsive to Odc overexpression that mediate susceptibility to skin tumorigenesis.

Differences in ornithine decarboxylase and androgen receptor allele frequencies among ethnic groups

Recent evidence suggests that the A allele of the ornithine decarboxylase (ODC) gene is a genetic risk factor for prostate cancer. ODC is a target gene of the highly polymorphic androgen receptor (AR) gene, short alleles of which have been associated in some studies with increased prostate cancer risk. We determined ODC allele frequencies and distribution of AR alleles in American Caucasians, African-Americans, Hispanics, Europeans, and Africans. The frequency of the ODC A allele varied from 0.183 (Hispanics, Europeans) to 0.415 (Africans) with American Caucasian and African-Americans having intermediate values. The mean number of CAG repeats in the AR gene varied from 19.8 (African-Americans) to 25.1 (Hispanics). It is possible that ethnic differences in risk alleles for ODC and AR may account for some of the ethnic variation in prostate cancer risk.

Association Among an Ornithine Decarboxylase Polymorphism, Androgen Receptor Gene (CAG) Repeat Length and Prostate Cancer Risk

PURPOSE

A single nucleotide substitution of guanine to adenine (A) at base +316 in the ornithine decarboxylase (ODC) gene may be associated with greater ODC expression and increased tumor growth. ODC is induced by androgens in human prostatic epithelial cells, presumably via transcriptional activation of androgen receptor (AR) and also by nicotine. A nested case-control study was done to examine the association between this ODC genotype and prostate cancer risk, and whether it varies by AR gene CAG repeat length and smoking.

MATERIALS AND METHODS

A total of 164 cases were matched to 2 controls each from a community based cohort. ODC and AR genotyping was performed using a TaqMan (PE Applied Biosystems, Foster City, California) based assay and automated fragment analysis, respectively. Conditional logistic regression was used to estimate the OR and 95% CI.

RESULTS

The presence of the ODC A allele was not significantly associated with an increased risk of prostate cancer (OR 1.33, 95% CI 0.90 to 1.96). However, men who inherited at least 1 ODC A alleles and less than 22 AR CAG repeats were at twice the risk of prostate cancer compared with those with 2 guanine alleles and 22 or greater AR CAG repeats (OR 2.09, 95% CI 1.23 to 3.57). Smoking was associated with prostate cancer only in men carrying a least 1 ODC A allele (p interaction = 0.02).

CONCLUSIONS

The ODC A allele was not associated with a statistically significant increased risk of prostate cancer. However, this association may vary according to the number of CAG repeats in the AR receptor and smoking status.

Distribution patterns of ornithine decarboxylase in cells and tissues: facts, problems, and postulates

Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis. Increased polyamine levels are required for growth, differentiation, and transformation of cells. In situ detection of ODC in cells and tissues has been performed with biochemical, enzyme cytochemical, immunocytochemical, and in situ hybridization techniques. Different localization patterns at the cellular level have been described, depending on the type of cells or tissues studied. These patterns varied from exclusively cytoplasmic to both cytoplasmic and nuclear. These discrepancies can be partially explained by the (lack of) sensitivity and/or specificity of the methods used, but it is more likely that (sub)cellular localization of ODC is cell type-specific and/or depends on the physiological status (growth, differentiation, malignant transformation, apoptosis) of cells. Intracellular translocation of ODC may be a prerequisite for its regulation and function.

Androgen regulation of spermidine synthase expression in the rat prostate

BACKGROUND

Spermidine synthase, an essential enzyme in the polyamine synthesis pathway, was identified as one of the androgen-response genes in the rat ventral prostate. Characterization of androgen regulation of spermidine synthase is important to the understanding of androgenic regulation of polyamine synthesis.

METHODS

Full-length cDNA encoding rat spermidine synthase was isolated from a lambdaZAP cDNA phage library. Young male adult Sprague-Dawley rats were used for castration and androgen replacement. Northern blot and in situ hybridization were used to characterize gene expression.

RESULTS

The amino acid sequence of rat spermidine synthase shares 99% and 94% identity with that of mouse and human spermidine synthase, respectively. Spermidine synthase gene is abundantly expressed and regulated by androgens in the ventral, dorsal, and lateral lobes of the rat prostate, and its expression is localized to the epithelial cells. Spermidine synthase also is regulated by androgens in the seminal vesicles but not in the muscle, brain, kidney, thymus, heart, or liver, suggesting that this enzyme is responsive to androgen in the male sex accessory organs only. The expression of spermidine synthase and two other enzymes involved in polyamine synthesis, S-adenosylmethionine decarboxylase and ornithine decarboxylase, are regulated by androgens coordinately.

CONCLUSIONS

Spermidine synthase is most abundantly expressed and regulated by androgens in the prostatic epithelial cells, suggesting that regulation of spermidine synthase is likely a key step in coordinated androgen regulation of polyamine synthesis in the prostate.

Differential androgen sensitivity is associated with clonal heterogeneity in steroid metabolism, ornithine decarboxylase regulation and IL-1alpha action in mouse mammary tumor cells

Upon androgen deprivation, Shionogi (SC-115) mouse mammary tumors undergo phenotypic changes enabling their escape from growth dependence on androgens. Even within androgen-responsive cell populations, marked clonal heterogeneity is observed in the trophic effects of androgens. The present study compares several parameters of androgen action between three SC-115 cell clonal subpopulations exhibiting high (clone 107), low (clone S1A2) and no trophic response (clone 415) to androgens. These parameters pertain to (1) kinetics of androgen binding, (2) metabolism of 5alpha-dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-diol) and 5alpha-androstane-3beta,17beta-diol (3beta-diol), (3) ornithine decarboxylase (ODC) activity and (4) interleukin-1alpha (IL-1alpha) action on cell proliferation. Only marginal differences in the affinity and abundance of androgen-specific binding sites were detected between the three clones. While clone S1A2 degraded DHT to 3alpha-diol at a much faster rate than the highly androgen-sensitive 107 cells and androgen-insensitive 415 cells, differences in the rates of intracrine conversion of 3alpha-diol and 3beta-diol to DHT did not correlate with the ability of these steroids to stimulate cell proliferation. Induction of ODC activity at the onset of exponential growth was strongly DHT-dependent in 107 cells, whereas this dependence was markedly attenuated in androgen-hyposensitive cells. Unexpectedly, DHT strongly repressed the marked ODC induction resulting from fresh medium addition in 415 cells which show no growth response to androgens. Low IL-1alpha concentrations were mitogenic in all three SC-115 clones. Whereas the mitogenic action of IL-1alpha was completely androgen-dependent in 107 cells, this dependence was relieved in S1A2 cells, which responded to DHT and IL-1alpha in an additive fashion. Thus, clonal heterogeneity in the pattern of steroid metabolism within Shionogi tumors cannot solely account for loss of androgen dependence, which may rather correlate with the constitutive activation of transduction pathways controlling the expression of growth-associated genes (e.g. ODC) by serum growth factors, including IL-1alpha.

Early alterations of polyamine metabolism induced after acute administration of clenbuterol in mouse heart

An acute treatment of mice with clenbuterol, a beta-adrenergic agonist, produced a marked increase of polyamines levels in heart, particularly during the early phase of administration of the drug. A single dose of 1.5 mg/kg caused as much as a 10 fold induction in activity of ornithine decarboxylase (ODC) and 3 to 4 fold increase in levels of putrescine, spermidine and spermine in mouse heart. Maximum changes were observed 3 to 4 hours post-administration of clenbuterol. This treatment did not produce any change in S-adenosylmethionine decarboxylase activity. The induction of cardiac ODC by clenbuterol was also dose dependent with a peak at about 5 micromol/kg. Co-administration of difluoromethylornithine, an irreversible inhibitor of ODC, or propranolol, a nonspecific beta-antagonist, with clenbuterol completely prevented the induction of ODC activity as well as the increase in polyamine levels in heart. However, pretreatment with alprenolol or metoprolol, the specific beta1 and beta2-antagonists, respectively, produced only partial prevention. The cardiac ODC from controls as well as clenbuterol treated mice exhibited similar affinity (Km) for its substrate, ornithine, while maximum enzyme activity (Vmax) was about 14 fold higher in clenbuterol treated mouse heart than in the control. Clenbuterol produced no change in the level of specific ODC mRNA or the protein, but the enzyme from the drug-treated mouse heart was considerably more stable than the control. Pretreatment of mice with either cycloheximide or actinomycin D followed by administration of clenbuterol could not prevent the induction in ODC activity suggesting that de novo biosynthesis of the enzyme protein or ODC mRNA was not responsible for induction of ODC activity. Post-translational changes in ODC may be responsible for an early increase of ODC activity due to clenbuterol treatment.

Sequence analysis and characterization of FAR-17c, an androgen-dependent gene in the flank organs of hamsters

This study reports on the isolation and characterization of a cDNA clone, regulated by androgen transcriptionally, in male Golden hamsters' flank organs. Previous studies have reported on the cloning of an androgen-dependent gene, FAR-17a, from the same hamster organ. After castration, the FAR-17c transcription rate decreases faster than FAR-17a but is not suppressed completely. The recovery of transcription by androgen injection is also faster than FAR-17a. In male hamsters, it is expressed strongly in the sebaceous glands and liver, and weakly in the lungs and brain. It has never been expressed in the testes. In the female, it is strongly expressed in the liver and brain and weakly in the lungs and flank organs. Sequence analysis shows that FAR-17c has a long 1062 bp open reading frame and its deduced amino acid sequence (354 residues) is highly homologous to the stearyl-CoA desaturases of the rat liver and mouse adipocytes. Stearyl-CoA desaturase, either in the liver or adipocytes appears to be independent of androgen regulation. Since stearyl-CoA desaturase plays a key role in fatty acid metabolism, further studies on its regulation by androgen are warranted in relation to acne vulgaris.

Ornithine decarboxylase-like immunoreactivity in rat spinal motoneurons and motoric nerves

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in the formation of the polyamines putrescine, spermidine and spermine. In the present study ornithine decarboxylase-like immunoreactivity (ODC-LI) was localized immunocytochemically in rat spinal motoneurons, motoric nerves and myoneural junctions in several muscles. In the spinal cord ODC-LI was expressed in most of the large multipolar neurons located in the ventral horn at cervical and lumbar levels. ODC-LI was localized in the cytoplasm, dendrites and axons of the labelled neurons. The nuclei of motoneurons were unlabelled; however, the nuclear membranes and the surrounding cytoplasm were strongly stained. ODC-immunoreactive (IR) axons could be traced through the white matter entering the ventral roots. The myelinated axons in the ventral roots and in the nerve bundles among the muscles were intensely stained with ODC antiserum. The myoneural junctions apposing individual muscle fibers showed ODC-LI with slightly less intensity. Some ODC-IR nerve fibers were seen in the muscle spindles. The present results show that motoneurons in adult rat spinal cored express ODC-LI and that OCD-LI is transported to motoric nerves and myoneural junctions. This suggests that polyamines can be synthesized both in the motoneuron somata and in their peripheral projections. Polyamines may thus regulate cellular functions in all parts of motoneurons. In addition, polyamines may be secreted from their distal projections and have tropic effects on Schwann cells and/or muscular tissue.