Regulation of thyroid ornithine decarboxylase by the polyamines. Induction of a protein inhibitor of ornithine decarboxylase by the end-products of the reaction

Non-competitive inhibition of ornithine decarboxylase by a phosphopeptide and phosphoamino acids

In Tetrahymena pyriformis the cytosolic ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity is considerably inhibited by the presence of polyamines in the growth medium, while the nuclear ornithine decarboxylase is only slightly affected. Experimental evidence suggests that the presence of putrescine and/or spermidine elicits the appearance of non-competitive inhibitors of ornithine decarboxylase. One of the inhibitors has a molecular weight of 25,000 and properties of antizyme. In addition, two other low molecular weight inhibitors are extracted, one which is a phosphoserine oligopeptide, and the other which is phosphotyrosine. All inhibit non-competitively the homologous and heterologous (Escherichia coli and rat liver) ornithine decarboxylases. Similarly, non-competitive inhibition was obtained when the commercially available phosphoamino acids were tested against the already mentioned ornithine decarboxylases.

Regulation of polyamine biosynthesis by antizyme and some recent developments relating the induction of polyamine biosynthesis to cell growth. Review

This review considers the role of antizyme, of amino acids and of protein synthesis in the regulation of polyamine biosynthesis. The ornithine decarboxylase of eukaryotic cells and of Escherichia coli can be non-competitively inhibited by proteins, termed antizymes, which are induced by di- and poly- amines. Some antizymes have been purified to homogeneity and have been shown to be structurally unique to the cell of origin. Yet, the E. coli antizyme and the rat liver antizyme cross react and inhibit each other's biosynthetic decarboxylases. These results indicate that aspects of the control of polyamine biosynthesis have been highly conserved throughout evolution. Evidence for the physiological role of the antizyme in mammalian cells rests upon its identification in normal uninduced cells, upon the inverse relationship that exists between antizyme and ornithine decarboxylase as well as upon the existence of the complex of ornithine decarboxylase and antizyme in vivo. Furthermore, the antizyme has been shown to be highly specific; its Keq for ornithine decarboxylase is 1.4 X 10(11) M-1. In addition, mammalian cells contain an anti-antizyme, a protein that specifically binds to the antizyme of an ornithine decarboxylase-antizyme complex and liberates free ornithine decarboxylase from the complex. In E. coli, in which polyamine biosynthesis is mediated both by ornithine decarboxylase and by arginine decarboxylase, three proteins (one acidic and two basic) have been purified, each of which inhibits both these enzymes. They do not inhibit the biodegradative ornithine and arginine decarboxylases nor lysine decarboxylase. The two basic inhibitors have been shown to correspond to the ribosomal proteins S20/L26 and L34, respectively. The relationship of the acidic antizyme to other known E. coli proteins remains to be determined. In mammalian cells, ornithine decarboxylase can be induced by a broad spectrum of compounds. These range from hormones and growth factors to natural amino acids such as asparagine and to non-metabolizable amino acid analogues such as alpha-amino-isobutyric acid. The amino acids that induce ornithine decarboxylase as well as those that promote polyamine uptake utilize the sodium dependent A and N transport systems. Consequently, they act in concert and increase intracellular polyamine levels by both mechanisms. The induction of ornithine decarboxylase by growth factors, such as NGF, EGF, and PDGF as well as by insulin requires the presence of these same amino acids and does not occur in their absence. However, the inducing amino acid need not be incorporated into protein nor covalently modified.(ABSTRACT TRUNCATED AT 400 WORDS)

An inhibitor of ornithine decarboxylase in the thymus and spleen of dexamethasone-treated rats

A marked decrease in activity of ornithine decarboxylase in thymus and spleen occurs soon after treatment of rats with a glucocorticoid. In the present study, evidence was obtained that extracts of these tissues prepared 5 h after administration of dexamethasone, when the enzyme activity is very low, contain an inhibitor of ornithine decarboxylase. The inhibitor is also present at 12 h after treatment and, in lesser amount, at 2.5 h, but was not evident at 24 h. The inhibitory activity was destroyed by treatment with heat or with trypsin, and was not lost on dialysis of the extract. Preliminary experiments indicate that the Mr of the inhibitor is greater than 50 000, which differentiates it from antizyme, an inhibitor of ornithine decarboxylase found in several other cell types. The inhibitor seems to act by a non-catalytic and non-competitive mechanism. The inhibition is dependent on the amount of inhibitor and does not change with time. Since inhibition is not changed by dialysis of the inhibitory extract, its activity apparently does not require small-Mr substances. This differentiates it from inhibitors which inactivate ornithine decarboxylase by covalent modification, such as the polyamine-dependent protein kinase or transglutaminase. The formation of this inhibitor is an early event in lymphoid tissues in response to dexamethasone and may be important in causing the inhibition of cell division which precedes the destruction of lymphocytes.

Detection of ornithine decarboxylase antizyme in mouse brain

Ornithine decarboxylase, the rate-limiting enzyme in polyamine synthesis, is known to be regulated by a macromolecular inhibitor, termed antizyme, in a number of cellular systems. The present results show that the antizyme is also a functional component of polyamine metabolism in the brain. It could be demonstrated both in normal randomly selected mice and in animals which had been subjected either to intracerebroventricular injection of saline, which is known to cause a transient activation of ornithine decarboxylase, or to 1,3-diamino-2-propanol, an antizyme-inducing agent. When compared to tissues or cell systems studied so far, the cytosol fraction from mouse brain homogenate appeared to contain an exceptionally high amount of antizyme, that was bound to some material other than active ornithine decarboxylase. This feature was seen in all the animal groups studied, being most prominent after saline injection, when the amount of dissociable antizyme exceeded 14-fold the corresponding released ornithine decarboxylase activity. In untreated animals the excess was about eightfold and after 1,3-diamino-2-propanol about fivefold.

Induction by 3, 5, 3' L-triiodothyronine of L-ornithine decarboxylase in rat heart muscle

Injection of 3,5,3' L-triiodothyronine (15 micrograms/100 g) induces a biphasic enhancement of rat heart ornithine decarboxylase (EC. 4.1.17) activity after 4 and 21 hours. This induction is observed after each daily injection, but to a lesser extent. The properties of partially purified basal enzyme and induced enzyme, at 21h, after single injections have been compared. 1) Affinity for ornithine is the same for both enzymes, but affinity for pyridoxal-phosphate is 40-fold higher for the induced one. 2) Thermostability studies suggest that basal and induced enzymes have different conformations. 3) The two enzymes have similar immuno-reactivity. 4) The comparisons of the time-dependent activity curve after injection and of the antigen/activity ratio suggests that triiodothyronine induces the synthesis of new molecules of enzymes and that an inhibition of the enzyme activity also occurs which explains the biphasic induction.

Cellular control of ornithine decarboxylase activity by its antizyme

Conditions have been established under which the antizyme of ornithine decarboxylase (E.C. 4.1.1.17, L-ornithine carboxy-lyase, ODC) a non-competitive protein inhibitor of ODC, can be detected in cells in response to as little as 10(-7) M putrescine. The maintenance of intracellular antizyme activity depends upon the continued presence of putrescine in the medium. Removal of putrescine results in a rapid decline of antizyme activity. These phenomena are unaffected by the presence of cycloheximide and are comparable to the requirement of L-asparagine for the maintenance of ODC activity. The extent to which the antizyme level is increased is inversely related to the preexisting level of intracellular ODC at the time of addition of putrescine. The time of appearance of free antizyme is delayed in cells that have high levels of ODC; the amount of free antizyme that can be assayed for in these cells, at any particular time is correspondingly less. The converse is also true. In cells that have high levels of antizyme, the delay in appearance of ODC is greater and the amount of ODC that can be assayed for is correspondingly less than in cells with low levels of antizyme. These experiments, as well as others, indicate that the ODC antizyme and ODC interact in vivo with each other to modify their respective activities.

Inhibition of ornithine decarboxylase of HeLa cells by diamines and polyamines. Effect on cell proliferation

1. Ornithine decarboxylase activity is stimulated in high-density HeLa-cell cultures by dilution of or replacement of spent culture medium with fresh medium containing 10% (v/v) horse serum. 2. After stimulation, ornithine decarboxylase activity reaches a peak at 4-6h, then rapidly declines to the low enzyme activity characteristic of quiescent cultures, where it remains during the remainder of the cell cycle. 3. The stimulation of ornithine decarboxylase is eliminated by the addition of 0.5mum-spermine or -spermidine or 10mum-putrescine to the HeLa-cell cultures at the time of re-feeding with fresh medium. Much higher concentrations (1mm) of the non-physiological diamines, 1,3-diamino-propane or 1,3-diamino-2-hydroxypropane, are required to eliminate the stimulation of ornithine decarboxylase in re-fed HeLa-cell cultures. 4. A heat-labile, non-diffusible inhibitor, comparable with the inhibitory protein ornithine decarboxylase antizyme, is induced in HeLa cells by the addition of exogenous diamines or polyamines. 5. Intracellular putrescine is eliminated, intracellular spermidine and spermine are severely decreased and proliferation of HeLa cells is inhibited when cultures are maintained for 48h in the presence of the non-physiological inducer of ornithine decarboxylase antizyme, 1,3-diamino-2-hydroxypropane. Exogenous putrescine, a physiological inducer of the antizyme, does not decrease intracellular polyamines or interfere with proliferation of HeLa cells.

Effects of 1,3-diaminopropane on testosterone induced hypertrophy and polyamine synthesis in mouse kidney

The effects of prolonged treatment with 1,3-diaminopropane, a structural analogue of putrescine, on polyamine metabolism and growth in kidney tissue, were studied in mice in which renal hypertrophy was induced by testosterone treatment. Injections of 1,3-diaminopropane resulted in an almost total suppression of the testosterone induced stimulation of ornithine decarboxylase activity and prevented the accumulation of putrescine and spermidine in the kidneys. Renal spermine concentration was even lowered. Administration of 1,3-diaminopropane effectively prevented the testosterone induced increase in renal weight and RNA. In mice receiving 1,3-diaminopropane proteinuria was observed and histological examination revealed renal damage. Due to the nephrotoxic action of 1,3-diaminopropane caution is essential in relating the prevention of renal hypertrophy and the inhibition of polyamine synthesis.

Two distinct mechanisms for ornithine decarboxylase regulation by polyamines in rat hepatoma cells

Exogenous diamines and polyamines added to rat hepatoma (HTC) cells in culture rapidly decrease ornithine decarboxylase (ODC) activity. Previous evidence has suggested that these amines set either at the level of blocking new enzyme synthesis or by the induction of a non-competitive protein inhibitor, termed antizyme, which complexes with ODC to form an inactive complex. Wth the use of HMOA cells, a recently cloned rat hepatoma cell line that has a greatly stabilized ODC, it has been possible to demonstrate that 10(-5) M of exogenous putrescine blocks the increase in ODC activity, but unlike in the parent HTC cell line, without induction of the antizyme or formation of any inactive ODC-antizyme complex. However, complete blockade of ODC at 10(-2) M putrescine is effected by induction of antizyme and formation of the ODC-antizyme complex, as now evidenced by the isolation of the active enzyme and antizyme components after Sephadex column chromatography in the presence of 250 mM NaCl. These findings indicate clearly that two polyamine-regulatory mechanisms for ODC exist and are separable in this cell line.

Control of ornithine decarboxylase activity in Physarum by polyamines

The addition of putrescine, spermidine, or spermine, to cultures of Physarum polycephalum rapidly reduced the activity of ornithine decarboxylase, with maximal inhibition, 80-90%, occurring after 90 min. This response was not due to a decrease in enzyme molecules, but rather to the rapid conversion of the active enzyme to a stable, catalytically less active form. This response to exogenous polyamines was not accompanied by the appearance of a macromolecular inhibitor (antizyme) either free, or bound to the enzyme. Physiological levels of the polyamines were also found to inhibit this enzyme in vitro both competitively and non-competitively, and to promote complete yet reversible inactivation of this enzyme in the absence of reducing agents. The data suggest that the control of this enzyme by endogenous polyamine levels may be distinct from its response to exogenous polyamines.