Androgen-regulated ornithine decarboxylase mRNAs of mouse kidney

Polyamines in Microalgae: Something Borrowed, Something New

Microalgae of different evolutionary origins are typically found in rivers, lakes, and oceans, providing more than 45% of global primary production. They provide not only a food source for animals, but also affect microbial ecosystems through symbioses with microorganisms or secretion of some metabolites. Derived from amino acids, polyamines are present in almost all types of organisms, where they play important roles in maintaining physiological functions or against stress. Microalgae can produce a variety of distinct polyamines, and the polyamine content is important to meet the physiological needs of microalgae and may also affect other species in the environment. In addition, some polyamines produced by microalgae have medical or nanotechnological applications. Previous studies on several types of microalgae have indicated that the putative polyamine metabolic pathways may be as complicated as the genomes of these organisms, which contain genes originating from plants, animals, and even bacteria. There are also several novel polyamine synthetic routes in microalgae. Understanding the nature of polyamines in microalgae will not only improve our knowledge of microalgal physiology and ecological function, but also provide valuable information for biotechnological applications.

Involvement of polyamine binding protein D (PotD) of Synechocystis sp. PCC 6803 in spermidine uptake and excretion

The in vivo function of polyamine binding protein D (PotD) in Synechocystis sp. PCC 6803 for the transport of spermidine was investigated using Synechocystis mutant disrupted in potD gene. The growth rate of potD mutant was similar to that of wild-type when grown in BG11 medium. However, the mutant exhibited severely reduced growth compared to the wild-type when BG11 medium was supplemented with 0.5 mM spermidine. The mutant accumulated a higher spermidine level than the wild-type when grown in the medium with or without spermidine. Transport experiments revealed that the mutant had a reduction in both the uptake and the excretion of spermidine. Moreover, [(14)C]spermidine-loaded wild-type and mutant cells showed a decrease of [(14)C]spermidine excretion when the assay medium contained exogenous spermidine. These data suggest that PotD is involved in both the uptake and the excretion of spermidine in Synechocystis cells.

Site-specific impacts on gene expression and behavior in fathead minnows (Pimephales promelas) exposed in situ to streams adjacent to sewage treatment plants

BACKGROUND

Environmental monitoring for pharmaceuticals and endocrine disruptors in the aquatic environment traditionally employs a variety of methods including analytical chemistry, as well as a variety of histological and biochemical endpoints that correlate with the fish fitness. It is now clear that analytical chemistry alone is insufficient to identify aquatic environments that are compromised because these measurements do not identify the biologically available dose. The biological endpoints that are measured are important because they relate to known impairments; however, they are not specific to the contaminants and often focus on only a few known endpoints. These studies can be enhanced by looking more broadly at changes in gene expression, especially if the analysis focuses on biochemical pathways. The present study was designed to obtain additional information for well-characterized sites adjacent to sewage treatment plants in MN that are thought to be impacted by endocrine disruptors.

RESULTS

Here we examine five sites that have been previously characterized and examine changes in gene expression in fathead minnows (Pimephales promelas) that have been caged for 48 h in each of the aquatic environments. We find that the gene expression changes are characteristic and unique at each of the five sites. Also, fish exposed to two of the sites, 7 and 12, present a more aggressive behavior compared to control fish.

CONCLUSION

Our results show that a short-term exposure to sewage treatment plant effluents was able to induce a site-specific gene expression pattern in the fathead minnow gonad and liver. The short-term exposure was also enough to affect fish sexual behavior. Our results also show that microarray analysis can be very useful at determining potential exposure to chemicals, and could be used routinely as a tool for environmental monitoring.

Background gene expression in rat kidney: influence of strain, gender, and diet

In order to gain better insight into factors (strain, gender, and diet) influencing background variability in kidney gene expression, we examined the transcriptomes of male and female Crl:CD(SD)IGSBR (Sprague-Dawley [SD]) and CDF(Fischer 344)/CrlBR rats maintained for 19 days on three different diets (ad libitum [AL], diet restriction-75% of AL, and casein-based phytoestrogen-free diet). Kidney RNA was analyzed using Agilent Rat oligo microarrays (approximately 20,000 genes). Principal component analysis demonstrated that strain and gender have the most impact on the variability in gene expression, while diet had a lesser effect. The majority of the affected genes differed by a magnitude of four-fold or less between strains/gender, with some previously known to be sex-hormone regulated (SLC22A7 and SLC21A1). One gene of particular interest was ornithine decarboxylase, a significant marker of cell proliferation and tumor promotion, which was expressed at an 18-fold greater level in SD rats. Further analysis revealed that the difference in expression was due to the use of an alternate polyadenylation signal resulting in the production of two different sizes of transcripts. These results demonstrate that gender and strain have significant influence on gene expression which could be a confounder when comparing results, especially when it involves predictive fingerprint/patterns.

A stable, inducible, dose-responsive ODC overexpression system in human cell lines

ODC is a labile protein subject to rapid turnover, and a conditional expression system providing long-term overexpression may be helpful in further understanding the biochemical properties of this enzyme and elucidating aspects of the polyamine biosynthetic pathway that have otherwise been difficult to study. HEK293 and LNCaP cell lines were engineered to stably and inducibly overexpress ODC using a Tet-on inducible construct. Clones from both cell lines were characterized by evaluating ODC mRNA expression, ODC activity, intracellular and extracellular polyamine levels, SSAT activity and growth kinetics. The ODC-inducible cell lines were time- and dose-responsive providing a mechanism to increase ODC and putrescine accumulation to a desired level in a flexible and controllable manner. The findings demonstrate that LNCaP ODC overexpressing cells maintained over a 100-fold increase in ODC activity and over a 10-fold increase in intracellular putrescine after 6 h. ODC induction at the highest levels was accompanied by a slight decline in intracellular spermidine and spermine levels and this observation was supported by the finding that SSAT activity was induced over 40-fold under these conditions. Growth rate remained unaffected following at least 12 h of ODC overexpression. Similar results were observed in the HEK293 ODC overexpressing cells.

Stable siRNA-mediated silencing of antizyme inhibitor: regulation of ornithine decarboxylase activity

Ornithine decarboxylase (ODC) is the rate-limiting enzyme involved in the biosynthesis of polyamines essential for cell growth and differentiation. Aberrant upregulation of ODC, however, is widely believed to be a contributing factor in tumorigenesis. Antizyme is a major regulator of ODC, inhibiting ODC activity through the formation of complexes and facilitating degradation of ODC by the 26S proteasome. Moreover, the antizyme inhibitor (AZI) serves as another factor in regulating ODC, by binding to antizyme and releasing ODC from ODC-antizyme complexes. In our previous report, we observed elevated AZI expression in tumor specimens. Therefore, to evaluate the role of AZI in regulating ODC activity in tumors, we successfully down-regulated AZI expression using RNA interference technology in A549 lung cancer cells expressing high levels of AZI. Two AZI siRNAs, which were capable to generate a hairpin dsRNA loop targeting AZI, could successively decrease the expression of AZI. Using biological assays, antizyme activity increased in AZI-siRNA-transfected cells, and ODC levels and activity were reduced as well. Moreover, silencing AZI expression decreased intracellular polyamine levels, reduced cell proliferation, and prolonged population doubling time. Our results directly demonstrate that downregulation of AZI regulates ODC activity, intracellular polyamine levels, and cell growth through regulating antizyme activity. This study also suggests that highly expressed AZI may be partly responsible for increased ODC activity and cellular transformation.

Testosterone down-regulates ornithine aminotransferase gene and up-regulates arginase II and ornithine decarboxylase genes for polyamines synthesis in the murine kidney

The enzymes ornithine aminotransferase (OAT) and ornithine decarboxylase (ODC) share L-ornithine as a common substrate and arginase II produces this amino acid. In the murine kidney, testosterone induced ODC gene expression and polyamine production, but it is unknown how OAT gene is expressed under androgen treatment. These experiments were designed to study the influence of testosterone on the renal expression of OAT gene. Pharmacological and physiological doses of testosterone were injected into female and castrated male mice. Total RNA and soluble proteins extracted from whole kidneys were analyzed by Northern and Western blots, respectively. The results clearly indicate that pharmacological doses of testosterone simultaneously down-regulated the level of OAT protein and up-regulated the expression of arginase II and ODC genes. Variations of the levels of OAT protein and arginase II mRNA and protein were strongly correlated with testosteronemia. Orchidectomy increased the renal level of OAT protein and decreased that of ODC and arginase II. These effects were reversed by injecting a physiological dose of testosterone into castrated male mice. In conclusion, OAT and ODC genes are inversely regulated by testosterone in the mouse kidney. Consequently, in kidneys of testosterone-treated mice, L-arginine-derived ornithine produced by arginase II might be preferentially used by ODC for putrescine production rather than by OAT. This metabolic fate of L-ornithine was facilitated by decreasing OAT gene expression. In contrast, in female and castrated male mice devoided of testosterone, OAT gene is highly expressed and L-ornithine is converted into L-glutamate.

Influence of testosterone on regulation of ODC, antizyme, and N1-SSAT gene expression in mouse kidney

Polyamines are involved in the control of the cell cycle and cell growth. In murine kidney, testosterone enhances gene expression of ornithine decarboxylase (ODC), the first enzyme in polyamine biosynthesis. In this study, we document the time course effect of testosterone on 1) gene expression of ODC, antizyme 1 (AZ1), and spermidine/spermine-N1-acetyltransferase (N1-SSAT); 2) ODC activity in proximal convoluted tubules (PCT) and cortical proximal straight tubules (CPST); and 3) renal polyamine levels. Female mice were treated with testosterone for a period of 1, 2, 3, and 5 consecutive days. ODC gene expression was extremely low in kidneys of untreated female mice compared with that of males. Consequently, the renal putrescine level was sevenfold lower in females than in males, whereas spermidine and spermine levels did not differ between sexes. In female kidneys, testosterone treatment sharply increased ODC mRNA and protein levels as well as ODC activity. Testosterone increased the expression of ODC in PCT and CPST over different time courses, which suggests that ODC activity is differentially regulated in distinct tubules. The expression of AZ1 and N1-SSAT mRNA was similar in male and female mouse kidneys. Testosterone treatment enhanced AZ1 and N1-SSAT mRNA levels in a time-dependent manner by unknown molecular mechanisms. Putrescine and spermidine levels increased after testosterone treatment in female kidneys. Surprisingly, although ODC protein and activity were undetectable in female kidneys, the levels of AZ1 mRNA and protein were similar to those in males. Therefore, one may propose that ODC protein could be continuously degraded by AZ1 in female kidneys.

Increases in ornithine decarboxylase activity in the positive inotropism induced by androgens in isolated left atrium of the rat

It is well established that the intracellular receptors of androgens act as transcription factors upon their activation by androgen binding. However, a growing number of studies have associated androgens with rapid biological responses independent of their classical action mechanism. In this sense, 5alpha- and 5beta-dihydrotestosterone elicited a rapid positive inotropism in the isolated left atrium of the rat via cAMP-dependent mechanisms that may involve genomic effects. In addition, polyamines are mediators of several biological actions including those acute and long-term effects induced by androgens in the heart. The present study analyzed the role of polyamine synthesis in the cardiotonic effect of androgens in the left atrium of male Wistar rats, electrically stimulated (0.5 Hz, 5 ms and supramaximal voltage) and placed in an organ bath in 10 ml of Tyrode's solution. Incubation in the organ bath with an inhibitor of ornithine decarboxylase activity, alpha-difluoromethylornithine 10 mM, significantly decreased the positive inotropism induced by 5alpha- and 5beta-dihydrotestosterone (0.1-100 microM). This suggests that ornithine decarboxylase seems to be involved in androgen-induced positive inotropism. Furthermore, 6-min exposure to 5alpha- or 5beta-dihydrotestosterone significantly increased the activity of ornithine decarboxylase from 61.81+/-7.53 (control) to 93.28+/-9.45 and 80.28+/-12 pmol/h/mg of protein, respectively. Northern blot analysis showed that 5alpha- and 5beta-dihydrotestosterone did not modify the level of expression of the ornithine decarboxylase gene. Therefore, our results suggest that polyamine synthesis might be involved in the positive inotropism elicited by androgens through the stimulation of ornithine decarboxylase activity without changes in the expression of the ornithine decarboxylase gene.

Abnormal ornithine decarboxylase activity in transgenic mice increases tumor formation and infertility

A transgenic mouse line carrying ornithine decarboxylase cDNA as the transgene under the control of a mouse mammary tumor virus long terminal repeat (MMTV LTR) promoter was generated in order to study whether ornithine decarboxylase transgene expression will have any physiological or pathological effect during the entire life of a transgenic mouse. The high frequency of infertile animals and the loss of pups made the breeding of homozygous mice unsuccessful. However, a colony of heterozygous transgenic mice was followed for 2 years. In adult heterozygous transgenic mice, ornithine decarboxylase activity was significantly increased in the testis, seminal vesicle and preputial gland when compared to non-transgenic controls. In contrast, ornithine decarboxylase activity was decreased in the kidney and prostate of transgenic mice. No significant changes in ornithine decarboxylase activity were found in the ovary and mammary gland and only moderate changes in ornithine decarboxylase activity were detected in the heart, brain, pancreas and lung. The most common abnormalities found in adult animals (12 males and 20 females) of the transgenic line were inflammatory processes, including pancreatitis, hepatitis, sialoadenitis and pyelonephritis. Spontaneous tumors were observed in eight animals, including two benign tumors (one dermatofibroma, one liver hemangioma) and six malignant tumors (one lymphoma, one intestinal and three mammary adenocarcinomas and one adenocarcinoma in the lung). No significant pathological changes were found in 17 nontransgenic controls.

Dietary induction of ornithine decarboxylase in male mouse kidney

In male mouse kidney, ornithine decarboxylase (ODC) is induced after feeding, and the induction depends on dietary protein content. 24 h after feeding with 50% casein-containing meal, ODC activity and amount of immunoreactive ODC protein increased more than 10-fold, ODC mRNA level increased 2-fold, and the ODC half-life extended 7-fold. The renal ODC induction after feeding is, therefore, due mainly to stabilization of ODC protein. Urinary excretion of putrescine increased in response to the ODC induction, but the renal polyamine contents scarcely changed. Consistently, the level of antizyme, a polyamine-inducible protein, determined as the ODC-antizyme complex level, scarcely changed after feeding, and the antizyme/ODC ratio in the kidney largely decreased, resulting in the stabilization of ODC protein. The present results suggest that the strong excretion system of the kidney for newly synthesized polyamines enables renal ODC escape from antizyme-mediated feedback regulation.

Glucocorticoid regulation of ornithine decarboxylase in the postnatal rat lung

Ornithine decarboxylase (ODC) is thought to play a critical role in pulmonary development. The purpose of this study was to characterize the effects of dexamethasone on ODC gene expression and enzyme activity in the lung of rat pups. Subcutaneous administration of dexamethasone (10 mg/kg) was shown to suppress ODC activity in 2-, 6- and 10-day-old rats for as long as 24 h after injection. In contrast, dexamethasone treatment stimulated liver ODC activity indicating that the inhibition of lung ODC is tissue specific. Contrary to expectation, the glucocorticoid enhanced lung ODC expression as indicated by an increased accumulation of ODC mRNA transcripts. The latter effect was associated with an heightened expression of c-myc and max mRNAs, the encoded proteins of which act as transactivators of the ODC gene. Dexamethasone did not alter lung levels of"antizyme" (AZ), an inducible protein that specifically promotes the degradation of the ODC protein enzyme. However, the lack of AZ induction does not necessarily mean that ODC degradation is not the mechanism for the decrease in lung ODC activity of dexamethasone-treated animals. The results obtained indicate that glucocorticoids can downregulate lung ODC activity, and that the effect is mediated by post-transcriptional rather than transcriptional mechanisms. These findings are consistent with the idea that endogenous glucocorticoids play an important role in the modulation of ODC activity and early pulmonary development.

Response of primary rabbit kidney proximal tubule cells to estrogens

The effects of estrogens on the growth and function of primary rabbit kidney proximal tubule (RPT) cells have been examined in hormonally defined phenol red-free medium. 17beta-estradiol was observed to stimulate growth at dosages as low as 10(-10) M. The growth stimulatory effects of 17beta-estradiol were mitigated in the presence of hydrocortisone, suggesting that these two steroid hormones acted at least in part by common mechanisms. The effects of other steroids known to interact with the estrogen receptor were examined. Alpha estradiol was found to be growth stimulatory over a concentration range of 10(-9) to 10(-8) M, albeit to a lower extent than beta estradiol. In addition, the anti-estrogen tamoxifen was also growth stimulatory (unlike the case with the human mammary tumor cell line MCF-7). The effects of several metabolic precursors of 17beta-estradiol were examined, including testosterone, which was growth stimulatory, and progesterone, which was growth inhibitory. The growth stimulatory effects of 17beta-estradiol, alpha estradiol, and tamoxifen could possibly be explained by their interaction with an estrogen receptor. Indeed, metabolic labelling and immunoprecipitation studies indicated the presence of such an estrogen receptor in the primary cultures. The rate of biosynthesis of the estrogen receptor was found to be affected by the presence of exogenously added 17beta-estradiol. 17beta-estradiol was also observed to increase the activity of two brush border enzymes, alkaline phosphatase and gamma glutamyl transpeptidase, during the growth phase of the primary cultures.

Bovine ornithine decarboxylase gene: cloning, structure and polymorphisms

Bovine ornithine decarboxylase (ODC) genomic clones were isolated from a bacteriophage lambda DASH genomic library. A total of 9452 bp sequence was determined which covers the entire sequence of the bovine ODC gene. Sequence analysis showed that the bovine ODC gene consisted of 12 exons which encode a protein identical to that inferred from a bovine ODC cDNA. Comparison of the structure and nucleotide sequence of the bovine, human and mouse ODC genes revealed that the gene was highly conserved. Primer extension analysis demonstrated that the transcription start point of bovine ODC mRNA was located 378 bp upstream from the A residue in the translation initiation codon. The 5'-untranslated region (UTR) of ODC mRNA was highly G + C rich, particularly in its 5'-most portion, and computer predictions suggested a very stable secondary structure for this region, with an overall free energy of formation of -134.4 kcal/mol. Conserved sequences and potential promoter elements including a TATA box, a possible CCAAT element, SP1 ranscription factor binding sites (GC boxes) and cAMP response elements (CRE) were identified in the 5'-flanking region of the gene. Two polymorphic restriction sites, a TaqI and a MspI, were mapped to the ODC gene and PCR-based methods for detection of the 2 polymorphisms were developed.

Lysophosphatidylcholine regulates cationic amino acid transport and metabolism in vascular smooth muscle cells. Role in polyamine biosynthesis

Lysophosphatidylcholine (lyso-PC) is a major component of atherogenic lipids that stimulate vascular smooth muscle cell (SMC) proliferation. Because cationic amino acids are metabolized to growth-stimulatory polyamines, we examined whether lyso-PC regulates the transcellular transport and metabolism of cationic amino acids by vascular SMC. Treatment of SMC with lyso-PC initially (0-2 h) decreased cationic amino acid uptake, whereas longer exposures (6-24 h) progressively increased transport. Kinetic studies indicated that lyso-PC-induced inhibition was associated with a decrease in affinity for cationic amino acids, but the stimulation was mediated by an increase in transport capacity. Lyso-PC strongly induced the expression of cationic amino acid transporter-2 mRNA while modestly elevating the level of cationic amino acid transporter-1 mRNA. In addition, lyso-PC stimulated intracellular cationic amino acid metabolism by inducing ornithine decarboxylase activity and mRNA expression and also by inducing arginase activity in vascular SMC. In contrast, lyso-PC inhibited the catabolism of L-arginine to nitric oxide by blocking inducible nitric oxide synthase expression. Lyso-PC increased markedly the capacity of SMC to generate putrescine, a polyamine, from extracellular L-ornithine and L-arginine. The lyso-PC-mediated increase in the production of putrescine was reversed by NG-methyl-L-arginine, a competitive inhibitor of cationic amino acid transport, or by alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor. The formation of putrescine from L-arginine was also prevented by arginase inhibitor NG-hydroxy-L-arginine. These results demonstrate that lyso-PC stimulates polyamine synthesis in vascular SMC by inducing the expression of the genes that regulate both the transport and metabolism of cationic amino acids. The actions of lyso-PC in stimulating cationic amino acid uptake and directing their metabolism to growth-stimulatory polyamines while simultaneously inhibiting the synthesis of antiproliferative NO, may contribute to lyso-PC-induced SMC proliferation and atherosclerotic lesion formation.

Central administration of morphine inhibits brain and liver ornithine decarboxylase activity in neonatal rats: involvement of transcription- and non-transcription-dependent mechanisms

This study examined whether the developmental deficits usually observed in infants born to opiate addicted mothers could involve effects on ornithine decarboxylase, a growth-controlling enzyme. Intracerebroventricular (i.c.v.) injection of a single dose of morphine (2 microg) to 6-day-old rats markedly decreased basal brain and liver ornithine decarboxylase activity as well as the increases in hepatic ornithine decarboxylase activity produced by subcutaneously (s.c.) administered insulin, an important trophic hormone. Centrally applied morphine acts supraspinally to downregulate peripheral ornithine decarboxylase activity, since s.c. administration of the same dose as used i.c.v. decreased neither basal liver ornithine decarboxylase levels nor tissue responsiveness to insulin. This does not imply that the opiate is unable to affect ornithine decarboxylase when applied systemically. In fact, a robust inhibition of both basal and induced liver ornithine decarboxylase activity was obtained in rat pups given 20 microg of morphine s.c. This larger dose is able to trigger the hepatic ornithine decarboxylase effects presumably by stimulating opiate receptors located at central sites after crossing the blood-brain barrier and penetrating into the brain. Concomitant administration of naloxone plus morphine i.c.v. prevented morphine from downregulating ornithine decarboxylase activity, confirming the participation of supraspinal opioid receptors in morphine ornithine decarboxylase actions. Finally, as was the case for insulin induced stimulation of ornithine decarboxylase activity, i.c.v. injection of morphine markedly diminished insulin induced stimulation of hepatic ornithine decarboxylase mRNA accumulation. In turn, contrary to the inhibition of basal ornithine decarboxylase activity, morphine did not lower basal hepatic ornithine decarboxylase mRNA levels when given alone. Thus, CNS morphine can apparently suppress tissue ornithine decarboxylase expression through both transcriptional and posttranscriptional mechanisms. The evidence obtained suggest that postnatal exposure to opiate drugs might detrimentally affect development by altering normal tissue ornithine decarboxylase ontogeny.

Transcription-dependent and -independent regulation of hepatic ornithine decarboxylase activity by CNS beta-endorphin in rat pups

We have previously shown that intracerebroventricular administration of relatively low doses of beta-endorphin suppresses basal levels of hepatic ODC activity as well as tissue ODC responsiveness to administered insulin in developing rats. Using Northern blotting analysis, the current studies examine whether these effects of CNS beta-endorphin may be mediated by changes in ODC gene expression. Subcutaneous administration of insulin (20 IU/kg body weight) rapidly and profoundly increased liver ODC activity. The time course of the response was characterized by proportionally increased levels of ODC mRNA, suggesting that insulin-induced stimulation of ODC activity is due to an increased transcription of ODC mRNA. Pretreatment with actinomycin D (2 mg/kg body weight, intraperitoneally) completely prevented the insulin-induced increase in ODC activity, confirming the requirement for the de novo synthesis of ODC mRNA for the effect. More importantly, intracerebroventricular but not subcutaneous injection of beta-endorphin (1 microgram) markedly diminished the stimulatory effect of insulin on hepatic ODC mRNA accumulation. The time course and magnitude of the inhibition of mRNA accumulation essentially mirrored that of the peptide on ODC activity. On the other hand, contrary to the inhibitory effect of beta-endorphin on basal ODC activity, the peptide did not lower basal ODC mRNA levels when given alone. Taken together, the results from these studies provide evidence for the existence of at least two separate mechanisms through which CNS beta-endorphin might downregulate ODC activity in peripheral organs of rat pups. The peptide can suppress insulin-induced ODC activity in the liver tissue by decreasing the rate of transcription of the ODC gene, whereas the inhibition of basal ODC activity appears to involve posttranscriptional mechanisms.

Regulation of rat ornithine decarboxylase promoter activity by binding of transcription factor Sp1

Ornithine decarboxylase (ODC) is the rate-limiting enzyme of polyamine biosynthesis. We investigated the transcriptional regulation of the rat ODC gene using transient expression assays. The 5'-flanking region (-1156 to +13) of the ODC gene was sufficient to mediate strong basal expression of a luciferase reporter. Sequences between -345 and -93 contributed to basal promoter activity. This region, containing five potential Sp1 binding sites, was analyzed by electrophoretic mobility shift assays. Three specific DNA-protein complexes were identified using H35 nuclear extracts and the -345/-93 ODC probe. Binding to all three was eliminated by competition with an oligonucleotide containing an Sp1 binding site, but not by a mutant Sp1 oligonucleotide. Preincubation with an antibody against Sp1 supershifted complexes associated with one or more of Sp1 binding sites 1-4 as well as with site 5. DNase I footprinting revealed two protected regions: PR-I (-92 to -130) and PR-II (-304 to -332). PR-I contains a putative binding site for Sp1 that was protected by recombinant Sp1 protein. Transfection studies in Schneider SL2 cells demonstrated that the ODC promoter is transactivated up to 350-fold by Sp1 and that this transactivation is dependent on the presence of Sp1 binding sites 1-4. Thus, although the ODC promoter binds multiple nuclear proteins, Sp1 or a related protein appears to be a critical determinant of ODC transcription, possibly through cooperative interactions between Sp1 and additional transcription factors.

Methylation status and chromatin structure of an early response gene (ornithine decarboxylase) in resting and stimulated NIH-3T3 fibroblasts

The early response gene ornithine decarboxylase (odc) is indispensable for normal and malignant cell growth. Although DNA methylation is generally associated with chromatin condensation and gene inactivation, the odc gene is heavily methylated at CCGG-sequences in animal cell lines. In this work we analyzed the chromatin structure and the DNA methylation status at the CpG-rich promoter sequences at the odc locus in mouse 3T3 fibroblasts. We show that the proximal promoter region of the odc locus is not hypermethylated, while the distal promoter sequences appear to have a few methylated CCGG-sites and display methylation polymorphism. Furthermore, it was found that the 5' promoter region of odc is constitutively more sensitive to micrococcal nuclease than the coding and 3' regions of the odc gene. Stimulation of the cells with serum resulted in an appearance of a DNase I sensitive site at the promoter region. The chromatin structure of the mid-coding and 3' regions of the odc gene also underwent structural changes that were accompanied by the rapid accumulation of odc mRNA. Such changes were not detected in the chromatin structure of glyceraldehyde-3-phosphate dehydrogenase (gadph) gene, whose expression remains invariant upon serum stimulation. These data suggest that the chromatin structure may play an important role in the rapid transcriptional activation of odc and other immediate early genes during serum stimulation.

Expression of a growth arrest specific gene (gas-6) during liver regeneration: molecular mechanisms and signalling pathways

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. To define the role of gas genes in a model of cell proliferation in vivo we analyzed the expression of one of these genes (gas-6) during liver regeneration after partial hepatectomy (PH). We found that gas-6 mRNA was down-regulated 4 hours after PH, within the G0 to G1 transition. Later on, gas-6 mRNA increased over the level found in normal liver with a peak at 16 hours, before the onset of DNA synthesis. This surge was probably triggered by an inflammatory response caused by the surgical trauma, because an increase of similar extent occurring with the same time course was present in livers of sham-operated and turpentine-treated rats. Comparison of mRNA steady state levels with nuclear transcription rates indicated that gas-6 expression is post-transcriptionally regulated. As we found that down-regulation of gas-6 expression was prevented by treatment with Actinomycin D, a labile protein might be involved in the determination of gas-6 mRNA stability. To investigate the mitogenic signals controlling gas-6 expression during liver regeneration we treated hepatectomized rats with a specific alpha-1-adrenoceptor blocker (prazosin) as well as with drugs which modify intracellular calcium levels. The decrease of gas-6 mRNA 4 hours after PH was prevented by prazosin and by neomycin, an inhibitor of calcium release from endogenous stores. These findings suggest that down-regulation of gas-6 expression during hepatic regeneration is triggered by catecholamines interaction with alpha-1-adrenergic receptors and by subsequent calcium release. In addition we found that the rise of gas-6 gene expression occurring at 16 hours after PH was not affected by prazosin but was inhibited by trifluoperazine. Therefore, we suggest that up-regulation of gas-6 gene expression is mediated by the interaction of calcium with calmodulin, independently of catecholamines.

Regulation of ornithine decarboxylase in the kidney of autoimmune mice with the lpr gene

The lymphoproliferative lpr gene confers a lupus-like disease with lymphadenopathy, antinuclear antibody production, and glomerulonephritis in MRL-lpr/lpr mice. Upregulation of ornithine decarboxylase (ODC) activity and polyamine levels have been observed in the kidney and lymphoid organs of this strain. Inhibition of ODC with 0.5-1.5% (w/v) difluoromethylornithine (DFMO) in drinking water prolonged life-span and ameliorated renal disease. Glomerulonephritis is a major cause of morbidity and mortality in human and murine lupus. In order to elucidate the mechanism(s) of ODC regulation in lupus nephritis, we characterized ODC at the protein and mRNA levels in 3 strains of autoimmune mice with the lpr genetic background (MRL-lpr/lpr, C3H-lpr/lpr and C57BL/6J-lpr/lpr) using Western blotting, enzyme kinetics, turnover rate measurements, Northern blot hybridization, and reverse transcription-polymerase chain reaction (RT-PCR). Normal BALB/c mice were used as a control. We found that ODC activity in the kidney of lpr strains was 4- to 6-fold higher than that of BALB/c mice. The intensity of the major ODC protein band at 54 kD in Western blot was 4-fold higher in MRL-lpr/lpr and C3H-lpr/lpr kidney compared to that of BALB/c kidney. Putrescine levels were 2- to 4-fold higher in kidney of lpr strains than that of BALB/c and DFMO-treated MRL-lpr/lpr mice. DFMO treatment significantly reduced ODC activity and polyamine levels. The half-life of ODC enzyme in MRL-lpr/lpr, C3H-lpr/lpr, B6-lpr/lpr and BALB/c mouse kidneys was 15, 5, 8 and 23 min, respectively. There was no significant difference in the Km values of different strains, whereas Vmax values differed significantly. There was no difference in the level of SAMDC, another enzyme involved in the polyamine biosynthetic pathway, in various strain. Steady-state levels of ODC mRNA were lower in lpr strains compared to that of BALB/c mouse. Our results suggest that the basis for up-regulation of ODC is not at the transcriptional level, but may involve post-transcriptional modification(s) in lpr strains. The link between aberrant regulation of ODC and the immunopathogenesis of murine lupus nephritis indicates novel targets for lupus therapy.

Cloning and sequence analysis of the gene and cDNA encoding mouse spermidine/spermine N1-acetyltransferase--a gene uniquely regulated by polyamines and their analogs

The polyamine catabolizing enzyme, spermidine/spermine N1-acetyltransferase (SSAT), has been implicated as a critical determinant of polyamine pool maintenance. SSAT has recently been shown to be positively regulated in human cell lines by polyamines and their analogs at the level of mRNA accumulation. Mouse LA-4 lung adenoma cells treated with either spermine or the spermine analog, N1,N12-bis(ethyl)spermine, produced a 2.3 and 6.5-fold increase, respectively, in SSAT mRNA. Prior evidence for transcriptional control of the enzyme prompted investigation of SSAT gene structure and its regulatory elements. The mouse SSAT gene was isolated as a 3650 bp EcoRI fragment from a lambda-J1 Mus saxicola genomic library by hybridization with human SSAT cDNA. An additional 431 bp downstream from the 3' EcoRI site were sequenced from a BamHI fragment (total gene sequence, 4066 bp). The gene contains six exons and five introns. Sequence analysis of the 774 bp of the 5' non-coding region revealed the absence of TATAA or CCAAT sequence motifs and the presence of a number of binding motifs in the 5' region of the gene with consensus binding sequences for transcription factors SP1, AP1, E2F, AP2, PEA-3 and others. The deduced amino acid sequence of the coding region differs from that of the human SSAT cDNA by five amino acids. The 527 bp of the 3' non-coding region contains four possible polyadenylation signal sites of which only one displays a typical consensus sequence. A 940 bp SSAT cDNA was isolated from Mus domesticus (BALB-C) liver lambda gt11 cDNA library. It contains a 5' untranslated region 89 bp in length and a 3' untranslated region 376 bp in length. The amino acid sequence deduced from Mus domesticus differs from that of Mus saxicola by one amino acid, from the hamster cDNA, by four amino acids and from the human cDNA by six amino acids. Further elucidation of the structural features of the SSAT gene may reveal how it is positively regulated by polyamines and their analogs.

Gly387 of murine ornithine decarboxylase is essential for the formation of stable homodimers

In its active form mammalian ornithine decarboxylase (ODC) is a homodimer composed of two 53-kDa subunits while the monomer retains no enzymic activity. In the present study we demonstrate that Gly387 of mouse ODC plays an important role in enabling dimer formation. Gly387 of mouse ODC, an evolutionary conserved residue, was converted to all possible 19 amino acids using site-directed mutagenesis. With the exception of alanine, all other substitutions of Gly387 completely abolished enzymic activity. Cross-linking analysis and fractionation through a Superose-12 sizing column have demonstrated that mutant subunits are detected only in their monomeric form. These results strongly suggest that the primary lesion of substitution at position 387 of mouse ODC is the inability of mutant subunits to associate with each other to form the active homodimers. In agreement with this conclusion, G387A, the only mutant that retained partial activity, displayed reduced dimerization. The degradation rate of ODC mutants in which Gly387 was substituted by aspartic acid or alanine was enhanced compared to the wild-type enzyme, suggesting that monomers may be more susceptible to degradation.

Heterogeneous expression of ornithine decarboxylase gene in the proximal tubule of the mouse kidney following testosterone treatment

The expression of the ornithine decarboxylase (ODC) gene in the mouse kidney following testosterone treatment was examined using in situ hybridization histochemistry. Testosterone (n = 5) or vehicle (n = 5) was subcutaneously injected (1 mg/animal) into male BALB/c mice (8 weeks in age) 14 h before sacrifice. Animals were sacrificed under ether anesthesia, their kidneys were removed and immediately frozen in liquid nitrogen. Frozen sections (10-microns-thick) were cut on a cryostat. Sections were hybridized with 35S-labeled sense or antisense RNA probe. The hybridization continued for 24 h at 50 degrees C and emulsion autoradiography was subsequently performed. A marked increase in ODC mRNA was exclusively detected in the proximal tubule of the renal cortex in the testosterone-treated animals. The hybridization signal was greater in the outer portion of the proximal tubule than in the inner portion. No significant hybridization signal was detected either in the distal tubule, renal corpuscle or peritubular tissues. These results indicate that testosterone induces the expression of the ODC gene in the proximal tubule of the renal cortex, leading to the increase in ODC activity in the same region.

Domains within the mammalian ornithine decarboxylase messenger RNA have evolved independently and episodically

Ornithine decarboxylase (ODC) is the first enzyme in the polyamine biosynthetic pathway. We have studied the evolutionary history of the mammalian ODC mRNA, focusing on the rate of accumulation of sequence divergence within specific subregions of the molecule. The phylogenetic relationships among the mRNAs from several mammalian species, including two mouse species, rat, hamster, and human, were determined based upon the numbers of synonymous substitutions in pairwise comparisons of mRNA coding regions. The separation times for the mRNAs were very similar to those for the corresponding species, suggesting that ODC is encoded by orthologous genes in the different species. Analysis of divergence patterns in four subregions, or domains, of the mRNA (the 5'-untranslated region, the coding region, and two domains of the 3'-untranslated region) showed that the domains have evolved in a noncoordinate fashion. Furthermore, evolution of each subregion has been episodic, with periods of both rapid and slow sequence divergence. We suggest that the episodic pattern of ODC mRNA evolution may indicate the existence of selection pressures that were exerted in a time- and domain-specific manner during mammalian speciation.

Regulation of ovarian ornithine decarboxylase activity and its mRNA by gonadotropins in the immature rat

Previous studies have demonstrated that gonadotropin increases ornithine decarboxylase (ODC) activity in the rat ovary. The increase of ODC activity following gonadotropin stimulation is localized primarily to proliferating granulosa cells. The present studies were undertaken to characterize the mechanism of this hormone-induced increase of ODC. A single intraperitoneal injection of PMSG resulted in a 15-fold increase in ODC activity (p < 0.0001). Activity was maximal 1 day following PMSG administration, and thereafter declined with time. PMSG also induced an increase in ODC mRNA levels (p < 0.0001). However, ODC mRNA increased only 2-fold, as compared with a 15-fold increase in ODC activity. Actin mRNA levels were unaffected by PMSG. These results demonstrate that PMSG-induced increase in ODC activity cannot be fully explained by an increase in ODC mRNA, thus indicating that part of the regulation of ODC by PMSG is occurring at the translational and/or posttranslational level. Such regulation is likely a necessary dimension of the fine control of the levels/activity of this important enzyme which has a very short half-life.

The induction of ornithine decarboxylase by ornithine takes place at post-transcriptional level in perifused Ehrlich carcinoma cells

The increase in ODC activity during perifusion of Ehrlich carcinoma cells with 0.5 mM ornithine correlates with an increase in 'de novo' synthetized ODC protein. ODC synthesis was followed by immunoprecipitation of equal quantities of 35S-labelled proteins after 10, 20 and 30 min of labelling. In addition, the rate of 'de novo' protein synthesis is very much elevated in cells perifused with saline buffer supplemented with 0.5 mM ornithine than in cells perifused with the saline buffer only. In spite of the higher specific ODC activity observed in cells perifused with saline buffer plus 0.5 mM ornithine respect to cells perifused with only saline buffer for 3.5 h, no elevation in ODC mRNA was observed when the cells were perifused in the presence of 0.5 mM ornithine.

Estradiol is trophic for colon cancer in mice: effect on ornithine decarboxylase and c-myc messenger RNA

The mitogenic role of estradiol on the growth of colon cancer was examined in mice. Sham-operated or ovariectomized mice were injected with cancer cells and received estradiol treatment. Tumor growth was noted: tumor weights were higher in female than male mice. The growth of the tumors was least in ovariectomized mice and highest in estradiol-treated ovariectomized mice. Tumor messenger RNA (mRNA) levels for ornithine decarboxylase (ODC) and proto-oncogenes c-myc, c-fos, and H-ras were examined. Two transcripts (2.2 and 2.7 kilobase pairs) of ODC were observed. The steady-state mRNA levels for ODC paralleled the changes observed in the weight of the tumors in all groups of animals. Less dramatic changes were observed in c-myc mRNA levels. No significant differences were observed in the mRNA levels for H-ras and c-fos. It thus appears likely that an increase in the ODC mRNA levels and, to a lesser extent, an increase in c-myc mRNA levels may be some of the important mechanisms by which estradiol mediates its growth effects on colon cancer cells in vivo.

PC12 cell neuronal differentiation is associated with prolonged p21ras activity and consequent prolonged ERK activity

Expression of oncogenic ras in PC12 cells causes neuronal differentiation and sustained protein tyrosine phosphorylation and activity of extracellular signal-regulated kinases (ERKs), p42erk2 and p44erk1. Oncogenic N-ras-induced neuronal differentiation is inhibited by compounds that block ERK protein tyrosine phosphorylation or ERK activity, indicating that ERKs are not only activated by p21ras but serve as the primary downstream effectors of p21ras. Treatment of PC12 cells with nerve growth factor or fibroblast growth factor results in neuronal differentiation and in a sustained elevation of p21ras activity, of ERK activity, and of ERK tyrosine phosphorylation. Epidermal growth factor, which does not cause neuronal differentiation, stimulates only transient (< 1 hr) activation of p21ras and ERKs. These data indicate that transient activation of p21ras and, consequently, ERKs is not sufficient for induction of neuronal differentiation. Prolonged ERK activity is required: a consequence of sustained activation of p21ras by the growth factor receptor protein tyrosine kinase.

Estradiol regulates class I alcohol dehydrogenase gene expression in renal medulla of male rats by a post-transcriptional mechanism

Rat kidney contains alcohol dehydrogenase (ADH) activity which appears to be identical to the class I ADH expressed in liver. Treatment of male rats with estradiol for 10 days induced ADH activity and protein in the kidney approximately 3-fold. This was not the result of suppression of testosterone levels by estrogen, as castration did not increase ADH activity. In situ hybridization of kidney sections showed that ADH transcripts were localized to the medulla, that the basal level of mRNA is very low in the male, and that the induction of ADH mRNA by estradiol was approximately 10-fold. As estimated from Northern blot analysis, the induction of the mRNA was approximately 7-fold. Thus, induction of ADH mRNA substantially exceeded the increase of ADH activity and protein. Since the estradiol-treated rats lost weight relative to the oil-injected controls, the effect of starvation on ADH mRNA in kidney was examined. Starvation decreased kidney ADH activity by about 30% but increased mRNA about 2-fold. Time course experiments demonstrated induction of ADH mRNA by estradiol within 1 h with the maximum level achieved by 24 h. The transcription rate of the ADH gene as assessed by nuclear run-on assays performed at 1 and 24 h after treatment with estradiol was unchanged. We conclude that estradiol induces ADH mRNA in kidney by a post-transcriptional mechanism.

TGF beta inhibits rat thyroid cell proliferation without alterations in the expression of TSH-induced cell cycle-related genes

Transforming growth factor beta (TGF beta) is a secreted polypeptide factor that is thought to play a major role in the regulation of proliferation of many cell types and various differentiation processes. TGF beta acts on thyroid cells by inhibiting cell proliferation and expression of differentiation markers, such as thyroglobulin production and iodide uptake. Exponentially growing thyroid cells cultures accumulate mostly in G0/G1 after exposure to TGF beta for 48 hours. TGF beta inhibits the TSH induced transition of quiescent thyroid cell from the G0 to the S phase. These effects on the thyroid cell growth, however, are not mediated by changes in the TSH-induced cell cycle-related genes expression; both immediate early and progression genes expression is unaffected by the TGF beta treatment.

Expression of murine cyclin B1 mRNAs and genetic mapping of related genomic sequences

Two cDNAs that encode a protein with 87% identity to human cyclin B1 and that differ only in the length of their 3'-untranslated regions have been isolated from a 70Z/3B murine pre-B leukemia cell library. Three sizes of RNA transcripts were detected in Northern hybridization analyses of a variety of normal tissues and transformed cell lines using the cDNA inserts as probes. The expression of these RNAs can be modulated in tissue culture cell lines by physiologically relevant stimuli, increasing when cells are stimulated to proliferate and decreasing when cells are induced to differentiate. Moreover, RNAs from tissues that contain few proliferating cells have no detectable hybridizing transcripts. The coordinate regulation of these RNAs with other genes that are activated during the cell division cycle and the profound similarity of the predicted amino acid sequence to those of published cyclin B homologues indicate that these genes encode a murine cyclin B1. In Southern hybridization analysis of BALB/cAnPt genomic DNA digested with EcoRI, 12 fragments hybridized with the cDNA probes. Through Southern blot analyses of DNA from backcross and cogenic mice, recombinant inbred strains, and somatic cell hybrids, the genetic loci that produce the cyclin B1-related sequences (designated loci Cycb1-rs1 to Cycb1-rs9) were mapped on mouse chromosomes 5, 1, 17, 4, 14, 13, 7, X, and 8, respectively. Cycb1-rs6 (on chromosome 13) is discussed as the most likely candidate for an expressed structural gene locus.

Chlorpheniramine inhibits the ornithine decarboxylase induction of Ehrlich carcinoma growing in vivo

The antihistaminic (+/-)-chlorpheniramine significantly reduced the progression of Ehrlich carcinoma when it was administered at 0.5 mg/mouse/day from the third day on, after tumour inoculation. The ODC activity of tumour cells was diminished by 70% on day 7 after tumour transplantation, when maximum ODC activity is detected in non-treated tumour growing 'in vivo'. Northern blot analyses indicated that the inhibitory effect of this 1,4-diamine takes place at a post-transcriptional level. Results obtained from serum-free cultured cells indicated that chlorpheniramine inhibits the ODC synthesis rate.

Mapping of the mouse ornithine decarboxylase-related sequence family

A family of DNA sequences homologous to the mRNA encoding ornithine decarboxylase (ODC) and comprising approximately 12 members in the mouse genome has been analyzed genetically. The inheritance of variant DNA restriction fragments detected by ODC cDNA probes on Southern blots of DNA from inbred strain mice was determined in six sets of recombinant inbred (RI) mouse strains. The distributions of these variations among the RI strains were then compared with the RI strain distribution patterns (SDPs) of previously mapped loci. This allowed the identification of nine independent ODC-related loci, of which eight could be localized to specific regions of the mouse genome: Odc-rs1 near Lamb2 on Chromosome (Chr) 1; Odc-rs2 near Psp on Chr 2; Odc-rs5, a complex locus comprising at least 5-7 copies of the ODC sequence, associated with Igk on Chr 6; Odc-rs6 between Abpa and Tam-1 on proximal Chr 7; Odc-rs7 near Hbb on distal Chr 7; Odc-rs12 near Agt and Emv-2 on distal Chr 8; Odc-rs8 associated with the Igh complex on Chr 12; and Odc-rs9 near Otf-3f on Chr 14. The ODC-related sequence family thus comprises a set of genomically dispersed "marker" loci, and alleles for several of these loci can be analyzed simultaneously in DNA from mice or cell lines. DNA from mice of 70 inbred strains has been characterized for alleles at all nine Odc-rs loci.

TSH is able to induce cell cycle-related gene expression in rat thyroid cell

Rat thyroid cells in culture (FRTL-5 strain) require thyrotropic hormone (TSH) for growth. TSH alone in serum free medium is able to induce DNA synthesis of FRTL-5 cells. DNA synthesis occurs 18-20 hours following TSH stimulation of quiescent cells. Here we demonstrate that two sets of genes, related to the entry of cells in the S phase, are induced by TSH: 1) immediate early genes, such as c-jun and a gene coding for a zinc-finger protein Xrox 20/Egr2, both having a pattern of expression similar to the c-fos oncogene; 2) early delayed genes such as ornithine decarboxylase (ODC), 2F-1, a gene that shows a strong similarity in aminoacid sequence to a mitochondrial ADP/ATP carrier, and the asparagine synthetase gene (TS11). Furthermore, an increased expression of the histone H3 gene, a typical marker of S phase, has been observed in TSH-treated FRTL-5 cells.

6-Methylmercaptopurine riboside is a potent and selective inhibitor of nerve growth factor-activated protein kinase N

Protein kinase N (PKN) is a soluble, apparently novel serine protein kinase that is activated by nerve growth factor (NGF) and other agents in PC12 pheochromocytoma cells as well as in several nonneuronal cell lines. Purine analogs, such as 6-thioguanine and 2-aminopurine, have been found to inhibit PKN in vitro. When applied to intact cells, these compounds suppress certain biological responses to NGF, but not others, a findings suggesting the presence of multiple pathways in the NGF mechanism. We report here that 6-methylmercaptopurine riboside (6-MMPR) inhibits NGF-stimulated PKN activity in vitro with an apparent Ki of approximately 5 nM. This is approximately 1,000-fold lower than the Ki of the most potent purine inhibitor of PKN. Compounds similar to 6-MMPR, but lacking the methyl or riboside groups, were much less potent as PKN inhibitors. A survey of six additional purified protein kinases shows no inhibitory effect of 6-MMPR, thus indicating a good degree of specificity of this compound for PKN. In contrast to NGF-stimulated PKN, a PKN-like activity stimulated in PC12 cells in response to activation of cyclic AMP-dependent protein kinase was nearly insensitive to 6-MMPR. Application of 6-MMPR to intact PC12 cells resulted in blockade of several responses to NGF (neurite regeneration and ornithine decarboxylase induction) but not of several others (rapid enhancement of tyrosine hydroxylase phosphorylation and PKN activation). These findings suggest that 6-MMPR is a potent and selective agent for characterizing PKN in vitro and for assessing its potential role in the multiple pathways of the NGF mechanism of action.

Differential mechanisms of induction of ornithine decarboxylase in rat intestine by L- and D-amino acids

A single intragastric administration of glycine, L- and D-alanine, and L-and D-serine into rats resulted in a more than 20-fold stimulation of intestinal mucosal ornithine decarboxylase (ODC) within 4 h. The stimulation of ODC activity was accompanied by an increase in the amount of immunoreactive ODC protein. The induction of ODC by D-amino acids was in all likelihood attributable to an enhanced accumulation of ODC-specific mRNA species as revealed by Northern blot and dot-blot hybridization analyses. However, the induction by glycine and L-amino acids was not explainable by changes of mRNA since the changes in mRNA contents were only marginal. Since the turnover rates of L-serine-induced and D-serine-induced intestinal ODC protein were the same as the non-induced control, we concluded that the induction by glycine and L-amino acids was brought about by an increased efficiency of translation of the ODC message.

Reversal of the abnormal development of T cell subpopulations in the thymus of autoimmune MRL-lpr/lpr mice by a polyamine biosynthesis inhibitor

Polyamines--putrescine, spermidine, and spermine--are a group of positively charged organic molecules that are present in all living cells. They are important regulators of cell growth and differentiation, but the precise mechanism of their action is not known. Ornithine decarboxylase (ODC) is a key enzyme in the biosynthesis of polyamines. Recent studies demonstrated that down-regulation of polyamine biosynthesis by irreversible inhibition of ODC with difluoromethylornithine (DFMO0 is a novel therapeutic approach for the treatment of murine lupus in autoimmune MRL-lpr/lpr mice. Since murine lupus in this strain is associated with a major alteration in thymic T cell subopulations, we questioned whether abnormal polyamine biosynthesis contributes to aberrant T cell maturation in the thymus of MRL-lpr/lpr mice. Thymocytes were analyzed for cell surface markers, CD4 and CD8 by 2-color flow cytometry using their respective monoclonal antibodies. The proportion of thymocyte subsets in disease-free mice (8-10 week of age) was approximately 72% double positive (DP; CD4+CD8+) cells, 5-7% double negative (DN; CD4-CD8-) cells, 11-16% CD4+ cells and 7-8% CD8+ cells. At 14 weeks of age, a stage of clinical disease expression, thymocytes were marked by the presence of approximately 40% DN cells and approximately 25% DP cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Fine-structure mapping of the complex locus Odc-rs5 relative to Igk and distal loci

Odc-rs5 was previously identified as a complex locus closely linked to the Igk complex on mouse Chromosome (Chr) 6 and comprising at least five copies of a sequence related to the mRNA encoding ornithine decarboxylase (ODC) in the genomes of mice of some inbred strains and at least seven copies in others (Richards-Smith and Elliott, Mammalian Genome 2: 215, 1992). In the present study, Odc-rs5 was shown to be composed of at least seven copies of the ODC sequence in both the Odc-rs5a and Odc-rs5b haplotypes. Based upon the distribution of DNA restriction fragments (RFs) that had previously been associated with Odc-rs5a or Odc-rs5b among 42 mice of inbred laboratory strains having various haplotypes at Igk and in mice of two congenic strains [B6.PL-Ly-2a, Ly-3a(75NS)/Cy and B6.PL-Ly-2a,Ly-3a(85NS)/Cy] and a backcross-derived stock (NAK) known to be recombinant within Igk, a fine structure map of Odc-rs5 was deduced relative to Igk and more distal loci. Odc-rs5-derived RFs were located to three distinct regions within and/or distal to Igk and to a fourth site between (Ly-3, Ly-2) and Raf-1. Additionally, DNAs from 19 mice of inbred strains and random-bred stocks derived from wild progenitors trapped at various locations were analyzed and found to exhibit an unexpected variety of combinations of RFs associated with the two Odc-rs5 haplotypes most frequently observed among inbred laboratory strains of mice.

Translational control mechanism of ornithine decarboxylase by asparagine and putrescine in primary cultured hepatocytes

Asparagine stimulated the translation of ornithine decarboxylase (ODC) mRNA more than 10-fold in cultured hepatocytes which had been pretreated with glucagon in simple salt/glucose medium. Putrescine suppressed the increase in the rate of ODC synthesis caused by asparagine without significant change in the amount of ODC mRNA, suggesting that putrescine inhibited the effect of asparagine at least in part at the level of translation. Polysomal distribution of ODC mRNA was analyzed to examine the site of translational regulation by these effectors. In uninduced hepatocytes, most of the ODC mRNA was sedimented slightly after the 40 S ribosomal subunit. This ODC mRNA was sequestered from translational machinery since it was not shifted to the polysome fraction when peptide elongation was specifically inhibited by a low concentration of cycloheximide. In asparagine-treated cells, 40% of total ODC mRNA was in the polysomal fraction and formed heavier polysomes, indicating that asparagine stimulated both recruitment of ODC mRNA from the untranslatable pool and the initiation steps of translation. Putrescine did not change the distribution pattern of ODC mRNA on polysomes significantly. Thus, 30% of ODC mRNA remained on polysomes even when ODC synthesis was completely inhibited by putrescine. Paradoxically more than 70% of ODC mRNA was shifted into polysomes by putrescine in the presence of low concentrations of cycloheximide. These results, together with changes in the polysome profile, suggested that putrescine nonspecifically stimulated the recruitment of ODC mRNA from the untranslatable pool, whereas it specifically inhibited its translation at both the initiation and the elongation steps.

Role of ornithine decarboxylase for proliferation of mesangial cells in culture

To elucidate the role of polyamine metabolism in the regulation of mesangial cell growth, we examined the involvement of ornithine decarboxylase (ODC), the rate limiting enzyme for polyamine synthesis, in the mitogenesis of cultured rat mesangial cells (MCs). Resting MCs, stimulated with fetal calf serum (FCS 10%), showed an induction of ODC activity from undetectable values in resting cells to mean = 5035 nmol CO2/10(10) cells.hr (range 3157 to 7154, N = 5), which is 25-fold above the detection limit. We found a single peak of ODC activity eight to ten hours after stimulation, declining to 22 to 34% of peak levels after 24 hours. 3H-thymidine (TdR) uptake, an S-phase marker of MC replication, peaked at 24 hours, reaching 10.7-fold values of resting MCs. ODC mRNA levels were low in resting cells. After serum stimulation there was a two- to 10-fold increase in ODC mRNA with a maximum after six hours. ODC activity with similar kinetics but lower peak levels was also induced by incubating MCs with mitogens, such as platelet-derived growth factor (PDGF-AB 20 ng/ml), arginine vasopressin (AVP 10(-7) M), phorbol myristate acetate (PMA 10(-7) M), interleukin 1 alpha and beta (IL-1 alpha 10 U/ml, IL-1 beta 10 U/ml). In the presence of alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ODC, the growth rate of MCs, assessed by cell counts and by 3H-TdR uptake, was markedly reduced by 62 to 100%. This antiproliferative effect of DFMO could be reversed by addition of putrescine, the reaction product of ODC.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoids stimulate ornithine decarboxylase gene expression in pancreatic AR42J cells

The effects of dexamethasone on ornithine decarboxylase gene expression were examined in rat pancreatic AR42J cells. Dexamethasone increased ornithine decarboxylase activity and messenger RNA (mRNA) concentrations in a time-dependent manner, with a maximal effect at 12 hours (207% +/- 63% and 327% +/- 34% of control, respectively; n = 5). Ornithine decarboxylase mRNA levels returned to control values at 48 hours, whereas ornithine decarboxylase activity was decreased to 41% +/- 8% of control (n = 3). Dexamethasone induction of ornithine decarboxylase mRNA was dose dependent, with half-maximal effects at 10(-8) mol/L (210% +/- 20% of control; n = 4) and maximal effects at 10(-7) mol/L (327% +/- 26% of control; n = 4). The glucocorticoid antagonist RU 38486 blocked the dexamethasone effects in a dose-dependent manner, with maximal effects occurring at 10(-7) mol/L (120% +/- 18% of control; n = 3). When protein synthesis was blocked by addition of cycloheximide, ornithine decarboxylase mRNA levels remained unchanged in response to glucocorticoids, indicating a primary effect of dexamethasone. Furthermore, cycloheximide by itself had no significant effect on ornithine decarboxylase mRNA levels. Inhibition of transcription with actinomycin D showed a half-life for ornithine decarboxylase mRNA of approximately 240 minutes. Ornithine decarboxylase mRNA stability was not affected by dexamethasone pretreatment for 12 hours. Therefore, these data suggest that dexamethasone regulates ODC gene expression via glucocorticoid receptor-mediated gene transcription. Furthermore, translational mechanisms seem to be involved in glucocorticoid-regulated ornithine decarboxylase induction.

Ornithine decarboxylase activity during development of the mouse inner ear in vivo and in vitro

Ornithine decarboxylase activity was determined during the development of the peripheral auditory system in the murine otocyst with the goal of understanding the role of this enzyme in the morphological and functional maturation of the inner ear. At gestational days 11 and 12 enzyme activity was more than 10-fold higher than adult levels. A sharp decline occurred between day 12 and 13 after which activity rose to a peak around day 15. Activity then dropped continuously until near-adult levels were reached at birth. A lower specific activity of ODC but a similar time-course was seen in otocysts explanted at gestational day 13 and subsequently cultured for 6 days. For two stages of development, enzyme activity and binding of 3H-alpha-difluoromethylornithine were compared. The four-fold difference in enzymatic activity on gestational days 15 and 17 was paralleled by a similar difference in binding. Ornithine decarboxylase activity during inner ear development therefore seems primarily regulated at the level of protein synthesis. Ornithine decarboxylase activity correlates with major inductive events in the morphogenesis of the cartilagenous otic capsule that serves as a template for the formation of the bony labyrinth. The pattern of activity may reflect the changes in the head mesenchyme that is recruited by the otocyst to aggregate and form its protective otic capsule.

Molecular genetic linkage maps of mouse chromosomes 4 and 6

We have generated a moderate resolution genetic map of mouse chromosomes 4 and 6 utilizing a (C57BL/6J x Mus spretus) F1 x Mus spretus backcross with RFLPs for 31 probes. The map for chromosome 4 covers 77 cM and details a large region of homology to human chromosome 1p. The map establishes the breakpoints in the mouse 4-human 1p region of homology to a 2-cM interval between Ifa and Jun in mouse and to the interval between JUN and ACADM in human. The map for mouse chromosome 6 spans a 65-cM region and contains a large region of homology to human 7q. These maps also provide chromosomal assignment and order for a number of previously unmapped probes. The maps should allow the rapid regional assignment of new markers to mouse chromosomes 4 and 6. In addition, knowledge of the gene order in mouse may prove useful in determining the gene order of the homologous regions in human.

Estradiol induces class I alcohol dehydrogenase activity and mRNA in kidney of female rats

Rat kidney contains alcohol dehydrogenase (ADH) activity which appears to be similar or identical to the class I ADH expressed in liver. Both tissues contain a 1.6-kb transcript which hybridizes with an ADH cDNA under stringent conditions. Kidney ADH activity is responsive to estradiol. The enzyme activity in the kidneys of sham-operated and ovariectomized animals was the same. Treatment of either group of animals by intramuscular injection of estradiol (1 mg/kg body wt/day) for 10 days induced ADH activity in kidney two- to threefold, whether the activity was expressed as U/g tissue, U/g protein, or U/mg DNA. Estradiol induced kidney ADH mRNA in both ovariectomized and sham-operated rats approximately twofold. Thus, induction of ADH mRNA accounts for the increase in ADH activity. In situ hybridization indicated that the ADH mRNA was present in the inner cortex and medulla of the kidney. Methylation patterns of the ADH gene were examined. The gene resides in a methylated region of chromatin without any of the typical features of a HpaII tiny fragment (HTF) island. Two MspI sites flanking the transcription start site are undermethylated in liver compared with kidney and spleen. This suggests that methylation of this gene may play a role in the tissue-specific expression of ADH.

Mouse ornithine decarboxylase is phosphorylated by casein kinase-II at a predominant single location (serine 303)

Ornithine decarboxylase (ODC), a key enzyme in the biosynthetic pathway of polyamines in mammalian cells is characterized by an extremely short half-life and by a rapid induction following stimulation with growth-promoting agents. Inspection of its deduced amino acid sequence revealed the presence of sequences that may serve as targets for phosphorylation by casein kinase II (CK-II). In the present study we demonstrate that ODC serves as a substrate for phosphorylation by CK-II in vitro and that it is phosphorylated in intact mammalian cells. One-dimensional phosphopeptide analysis demonstrated that all the phosphopeptides generated by V8 protease digestion of in vivo phosphorylated ODC correspond to the major phosphopeptides of ODC phosphorylated in vitro by CK-II. Phosphopeptide analysis of wild-type ODC and of a mutant in which serine 303 was converted to alanine demonstrated that the latter lacks the phosphopeptides that correspond to those detected in ODC phosphorylated in vivo. In addition, no incorporation of phosphate into the alanine 303 mutant was observed when it was expressed in transfected cos cells. Based on these observations, we conclude that in mammalian cells serine 303 is the major (if not the only) phosphorylated residue of ODC and that CK-II or another cellular kinase with very similar sequence specificity is responsible for manifestation of this modification. The unphosphorylated alanine 303 mutant retained enzymatic activity, which decayed at a similar rate to that of the wild-type enzyme. We therefore conclude that phosphorylation is not essential for maintaining enzymatic activity or regulating ODC turnover.

Genetic mapping of meander tail, a mouse mutation affecting cerebellar development

The meander tail mouse harbors a recessive mutation on chromosome 4 that affects the anterior lobes of the cerebellum and the caudal vertebrae. Examination of the mea/mea cerebellum reveals that the complete disorganization of all cell types seen in the anterior lobes is separated by a sharp and consistent boundary from the normal cytoarchitecture of the posterior lobes. In the absence of any biochemical information regarding the affected gene product, attempts to clone the gene must rely on the strategy of reverse genetics. As an initial step in this process we have constructed a genetic linkage map spanning 68 cM of chromosome 4 using an intersubspecific phenotypic backcross. The loci included in this analysis are Calb, Ggtb, Lv, b, Ifa, mea, D4Rp1, Glut-1, Lck, Lmyc-1, and Eno-1. This analysis positions the mea phenotypic locus in the interval between Ifa and Glut1. These results also further define regions of homology between mouse chromosome 4 and human chromosomes 8, 1, and 9. This linkage map provides the means to evaluate candidate genes, and to identify tightly linked markers useful for cloning the meander tail locus.