Differences in the mode of regulation of ornithine decarboxylase activity in undifferentiated versus differentiated mouse N-18 neuroblastoma cells

Asparagine markedly induces the expression of ornithine decarboxylase gene in transformed mammalian cells but not in their untransformed counterparts

We have previously shown that asparagine alone induces a 10-15-fold increase in ornithine decarboxylase (ODC) mRNA level in DF-40 mouse neuroblastoma cells. The induction is due to an accumulation of ODC mRNA through a post-transcriptional stabilization mechanism (Chen, Z.P. and Chen, K.Y. (1992) J. Biol. Chem., 267, 6946-6951). In the present study we showed that asparagine induced ODC gene expression in v-Ha-ras-transformed 3T3 (ras-3T3) cells but not in 3T3 cells. Other growth related genes including c-src, c-ras, and c-fos were not affected by asparagine in ras-3T3 cells. Southern blot analysis indicated that the pronounced asparagine effect was not due to ODC gene amplification in ras-3T3 cells. The effect of asparagine on the induction of ODC mRNA could account for the significant increases in the ODC activity in ras-3T3 cells. We also examined the effect of asparagine on ODC gene expression in human KD cells and their transformed counterparts. Our findings strongly suggest that the induction of ODC mRNA by asparagine may represent a component of an altered growth regulatory program associated most prominently with cell transformation.

Changes in inducibility of ornithine decarboxylase activity in differentiating human neuroblastoma cells

Human SH-SY5Y neuroblastoma cells could be induced to differentiate morphologically and biochemically in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA), retinoic acid (RA), or a combination of these two substances. The phenotypical changes induced by these substances differed, but one effect of both was an inhibition of the cell growth. Addition of TPA or RA to non-treated cells had no effect on the activation of ornithine decarboxylase (ODC, EC 4.1.1.17.), while a change to fresh medium stimulated the ODC to maximum activity after 4-6 h. The activity was not altered by the presence of RA in the fresh medium, but TPA partially inhibited the medium-stimulated ODC activity. Cells treated for 4 or 8 days with TPA or a combination of TPA and RA had a low ODC activity which could not be induced by fresh medium. However, RA-treated (and thus growth-inhibited) cells still responded to a change of medium by exhibiting an ODC activity of the same magnitude and duration as in medium-stimulated control cells. The results seem to suggest that the growth inhibition induced by TPA and RA, respectively, is mediated by different mechanisms.

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.

Studies on the role of protein synthesis and of sodium on the regulation of ornithine decarboxylase activity

The minimum requirements for eliciting or enhancing ornithine decarboxylase activity (EC. 4.1.1.17); L-ornithine carboxylase) in neuroblastoma cells incubated in salts-glucose solutions have been investigated. These incubation conditions permit the study of changes in ornithine decarboxylase activity independently of the growth-associated reactions that occur in cell culture media (Chen, K.Y. and Canellakis, E.S. (1977) Proc. Natl, Acad. Sci. U.S.A. 74, 3791-3795). Ornithine decarboxylase activity can be elicited by a variety of asparagine and other amino acid analogs, including alpha-aminoisobutyric acid, that cannot participate in protein synthesis. Of the eleven asparagine analogs tested, alpha-N-CH3-DL-asparagine is the most potent in eliciting ornithine decarboxylase activity and is equivalent to asparagine in this regard. Inclusion of polar groups into the asparagine molecule results in the loss of its ability to elicit ornithine decarboxylase activity. With the use of these analogs and of analogs of other amino acids it is shown that the rapid fall in ornithine decarboxylase activity that is noted following cycloheximide treatment may not be a consequence of the inhibition of protein synthesis. The rapid fall in ornithine decarboxylase activity is primarily due to the removal of the agent that elicits and stabilizes its activity. These results, the finding that alpha-aminoisobutyric acid stimulates ornithine decarboxylase activity and that sodium is required for the stimulation of ornithine decarboxylase activity are discussed in relation to the "A" amino acid transport system.

Changes of ornithine decarboxylase activity and polyamine content upon differentiation of mouse NB-15 neuroblastoma cells

The possible functions of ornithine decarboxylase (ODC) and polyamines in the differentiation of mouse NB-15 neuroblastoma cells were investigated by examining the changes of these parameters in the differentiating and nondifferentiating NB-15 cells over a 5-day culture period. Differentiation of NB-15 cells was induced by the addition of dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine (1BMX) to the growth medium and was monitored by neurite outgrowth, increases of acetylcholinesterase (AChE), and RI cAMP-binding protein. Plating of NB-15 cells in fresh serum-containing growth medium was accompanied by rapid growth and a marked increase of ODC activity; this early increase of ODC activity was attenuated, both in duration and in magnitude, in the differentiating cells. The spermidine content of the differentiating neuroblastoma cells was significantly lower than that of the nondifferentiating cells. In the fully differentiated neuroblastoma cells, the ODC activity and spermidine content were lower than that of the undifferentiated cells by approximately 15-fold and five-fold, respectively. Based on these results it is proposed that changes of polyamine metabolism may be of significance in the differentiation of mouse neuroblastoma cells.