Regulation of ornithine decarboxylase activity by amino acids, cyclic AMP and luteinizing hormone in cultured mammalian cells

Sodium-dependent co-transported analogues of glucose stimulate ornithine decarboxylase mRNA expression in LLC-PK1 cells

Non-metabolizable analogues of glucose, including 1-O-methyl alpha-D-glucopyranoside (alpha MDG), that are co-transported with Na+ increase the specific activity of ornithine decarboxylase (ODC) in LLC-PK1 cells [Lundgren and Vacca (1990) Am. J. Physiol. 259, C647-C653]. The present study examines the effect of alpha MDG on LLC-PK1-cell ODC mRNA expression. The relative concentration of ODC mRNA in cells incubated in Earle's balanced salts solution minus glucose (EBSS--G) plus 3 mM alpha MDG was 5-6-fold higher than the concentration of ODC mRNA in cells incubated in either EBSS--G alone or in EBSS--G plus 3 mM 3-O-methyl-D-glucopyranose, a non-metabolizable analogue of glucose that is taken up by a passive carrier-mediated glucose transporter. Actinomycin D and cycloheximide completely blocked the increase in ODC activity induced by alpha MDG. Actinomycin D was also a potent inhibitor of ODC mRNA expression by alpha MDG. Cycloheximide had very little effect on the ability of this sugar to increase ODC mRNA. The relative concentration of ODC mRNA increased as a function of the incubation time in EBSS--G plus alpha MDG. The amount of ODC mRNA also increased as a function of the concentration of alpha MDG in EBSS--G. The addition of phlorizin (100 microM) to EBSS--G prevented alpha MDG from increasing ODC mRNA in LLC-PK1 cells. Phlorizin did not prevent phorbol 12-myristate 13-acetate (PMA) from enhancing LLC-PK1-cell ODC mRNA expression. The positive effect of both alpha MDG and TPA on ODC mRNA expression was suppressed when cells were incubated in hypertonic EBSS--G. From these results it is suggested that the uptake of Na(+)-dependent cotransported sugars increase ODC activity by enhancing ODC gene transcription and that this process may be dependent on cell volume expansion.

Nonmetabolizable glucose analogues and ornithine decarboxylase expression in LLC-PK1 cells

This report examines the effect of nonmetabolizable glucose analogues on ornithine decarboxylase (ODC) activity in LLC-PK1 cells. The addition of Na(+)-dependent cotransported glucose analogues, 1-O-methyl-alpha-D-glucopyranoside (alpha-MDG) and 1-O-methyl-beta-D-glucopyranoside, to Earle's balanced salt solution minus glucose (EBSS-G) increased ODC activity five- to sevenfold above basal levels. The passive carrier-mediated transported glucose analogue 3-O-methyl-D-glucopyranose had very little effect on enzyme activity. alpha-MDG increased ODC activity in quiescent but not growing cells. ODC activity increased as a function of both the incubation time in EBSS-G + alpha-MDG and the concentration of alpha-MDG in EBSS-G. Phlorizin significantly reduced the level of enzyme activity induced by alpha-MDG. ODC expression by alpha-MDG was reduced in cells incubated in hypertonic EBSS-G + alpha-MDG. Enzyme activity, in the absence of extracellular organic substrates, was markedly elevated in cells incubated in hypotonic media. It is suggested that an influx of Na+ and/or an increase in cell volume elevates one or more signal transducers that regulate ODC expression.

Glucose elevates ornithine decarboxylase expression in Vero cells

The addition of Earle's balanced salt solution (EBSS) of amino acids that are transported by a Na+-dependent cotransport system was not required by Vero cells for ornithine decarboxylase (ODC:EC 4.1.1.17) amplification. Vero cell ODC activity was elevated tenfold above basal levels when confluent cells were incubated for 5 hr in EBSS alone. ODC activity increased as a function of the incubation time in EBSS and was not elevated above basal enzyme levels when cells were incubated in EBSS minus glucose. ODC expression increased as a function of the glucose concentration in EBSS, with 20 mM glucose producing a 90-fold increase in ODC activity. ODC expression is more responsive to glucose in high-density quiescent cultures than in low-density growing cultures. Enhanced ODC expression by glucose depended on Na+ and K+ concentrations. The specific activity of ODC was also elevated above basal levels when mannose or fructose replaced glucose in EBSS. The addition of alanine or asparagine to EBSS enhanced ODC activity above levels obtained with EBSS containing standard (5.5 mM) glucose concentrations. In the absence of glucose, alanine was more effective than asparagine in enhancing ODC expression. These results suggest that the transport of amino acids is not an absolute requirement for Vero cell ODC expression and that ODC expression is linked to changes in cellular energetics and/or ion fluxes.

The effect of transport system A and N amino acids and of nerve and epidermal growth factors on the induction of ornithine decarboxylase activity

The induction of ornithine decarboxylase (EC 4.1.1.17) (ODC) by amino acids and by the peptide hormones nerve growth factor (NGF) and epidermal growth factor (EGF) in salts-glucose media has been studied. Only those neutral amino acids taken into the cell via one of the Na+ dependent transport systems stimulate ODC activity. Asparagine and the nonmetabolizable alpha-amino-isobutyric acid (AIB) were used as representatives of this class of inducing amino acids, and their intracellular concentrations were related to the levels of ODC induced. A threshold intracellular concentration of asparagine or AIB has to be attained before ODC can be induced. Further slight increases in intracellular concentrations of asparagine or AIB produce disproportionately large increases of ODC, resulting in a sigmoidal curve of ODC induction. These results, and the fact that the decrease in ODC levels caused by valine is associated with a concurrent decrease in the intracellular level of the inducing amino acid, suggest that the intracellular amino acid level is causally related to the induction of ornithine decarboxylase. Glutamic acid, EGF, and NGF do not induce ODC except in the presence of an inducing amino acid. They act synergistically with the inducing amino acid and produce higher ODC levels at the same intracellular concentration of the inducing amino acid.

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)

Permissive effect of glutamine on the differentiation of fetal mouse small intestine in organ culture

The proximal third of the small intestine of 15-day-old mouse embryo can be cultured for 72 h at 37 degrees C. When Trowell-T8 medium is used, the integrity of the explants is maintained, but villi do not form and absorptive cells are poorly differentiated. However, when Leibovitz L-15 or RPMI-1640 medium is used, one can observe the formation of medium-sized villi, and absorptive cells in the explants are more differentiated. Since the chemical composition of T8 medium is quite different from that of the other two media, we decided to test the importance of two major differences, i.e., three amino acids and five vitamins, in order to find out which element(s) is necessary to permit the formation of intestinal villi. Subsequent testing demonstrated that the three amino acids are responsible for the effect on differentiation, and that glutamine is the only critical difference between T8 and the two other media. The results show that the addition of L-glutamine to T8 medium permits the formation of villi, the initiation of absorptive cell differentiation, an increase in DNA synthesis, and finally, an increase in the number of epithelial cells. These findings indicate that undifferentiated fetal mouse small intestine is able to express its phenotype in organ culture, even without any extrinsic regulatory influences, provided that L-glutamine is present at a sufficient level in the culture medium. The use of inhibitors indicated that L-glutamine may be essential as an energetic substrate and/or a precursor for glucosamine.

Cultured hepatoma cells for the study of enzyme regulation: induction of ornithine decarboxylase by insulin and asparagine

The induction and decay of ornithine decarboxylase (ODC) by insulin and asparagine in cultures of H4-II-EC3 (H35) hepatoma cells was studied in a modified Waymouth medium in the presence of fetal bovine serum (FBS) and in serum-free media. The insulin response was enhanced by the presence of asparagine although the effect of asparagine was not so much on the initial increase as it was on a slowing of the decline after the maximum was reached at 6 to 8 h after the supplements were added together with fresh medium. In all cases the initial ODC activity was zero at zero time for addition of media and supplements, and, after reaching the maximum, activity declined to near zero by 24 h. Fetal bovine serum gave induction that followed a similar time course but was inferior to the combination of insulin plus asparagine and, in fact, FBS inhibited the latter response. Putrescine (the product formed from ornithine by ODC), at 10(-5) M, markedly inhibited the induction of ODC by insulin or FBS, but the inhibition was less when asparagine was present.

Effects of amino acid treatments on 12-O-tetradecanoylphorbol-13-acetate-induced ornithine decarboxylase activity in mouse epidermis in vivo and in vitro

We have compared the effects of several amino acid treatments on the induction of ornithine decarboxylase activity and the accumulation of putrescine, spermidine, and spermine by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse epidermis in vivo and in vitro. Incubation of isolated epidermal cells with mM concentrations of glycine, asparagine, glutamic acid, canavanine, arginine, and/or lysine inhibited dramatically the induction of ornithine decarboxylase activity by the tumor promoter. These remarkable inhibitory effects were concentration-dependent and additive. Arginine and its analog, canavanine, inhibited to the same degree TPA-induced ornithine decarboxylase activity, and potentiated to the same extent the inhibitory effects of glutamic acid, asparagine, and glycine on this enzyme. However, the inhibitory effects of arginine and canavanine were not additive. Similar alterations of tumor promoter-induced epidermal ornithine decarboxylase activity were observed in vivo when 62.5 mumol of the amino acids were injected i.p. 2 h before the topical application of 8.5 nmol of TPA to mouse skin. The results suggest the possibility that treatments with glycine, asparagine, glutamic acid, and arginine, the amino acids that were the most effective in inhibiting the tumor promoter-induced accumulation of polyamines in vivo, may reduce the tumor-promoting ability of TPA.

Characterization of ornithine decarboxylase activity in human uterine decidua vera

Ornithine decarboxylase (ODC) catalyzes the rate-limiting step in the biosynthesis of the polyamines putrescine, spermidine, and spermine. In the present study, we characterized the activity of ODC in human uterine decidua vera tissue. We evaluated the activity of the enzyme in decidua vera tissue that was obtained from pregnancies at term before or after the spontaneous onset of labor and in decidua vera tissue that was obtained between 8 and 18 weeks' postconceptional gestational age at the time of elective abortion. Among these tissues, no significant differences in ODC activity were demonstrable.