Effect of inhibitors of S-adenosylmethionine decarboxylase on the contents of ornithine decarboxylase and S-adenosylmethionine decarboxylase in L1210 cells

Abstract

Treatment of L1210 cells with either of two inhibitors of S-adenosylmethionine decarboxylase (AdoMetDC), namely 5'-deoxy-5'-[N-methyl-N-[2-(amino-oxy)ethyl])aminoadenosine or 5'-deoxy-5'-[N-methyl-N-(3-hydrazinopropyl)]aminoadenosine, produced a large increase in the amount of ornithine decarboxylase (ODC) protein. The increased enzyme content was due to a decreased rate of degradation of the protein and to an increased rate of synthesis, but there was no change in its mRNA content. The inhibitors led to a substantial decline in the amounts of intracellular spermidine and spermine, but to a big increase in the amount of putrescine. These results indicate that the content of ODC is negatively regulated by spermidine and spermine at the levels of protein translation and turnover, but that putrescine is much less effective in bringing about this repression. Addition of either spermidine or spermine to the cells treated with the AdoMetDC inhibitors led to a decrease in ODC activity, indicating that either polyamine can bring about this effect, but spermidine produced effects at concentrations similar to those found in the control cells and appears to be the physiologically important regulator. The content of AdoMetDC protein (measured by radioimmunoassay) was also increased by these inhibitors, and a small increase in its mRNA content was observed, but this was insufficient to account for the increase in protein. A substantial stabilization of AdoMetDC occurred in these cells, contributing to the increased enzyme content, but an increase in the rate of translation cannot be ruled out.

Polyamine Acetylation Modulates Polyamine Metabolic Flux, a Prelude to Broader Metabolic Consequences

“…Treatment of cells with SAMDC inhibitors typically increases Put significantly due to a compensatory increase in ODC (45,46) and the inability of the enzyme product Put to be processed forward to Spd due to SAMDC inhibition. Thus, MDL-78311 treatment gave rise to intraand extracellular accumulation of both Put and Fl-Put.…”

Feedback regulation of mammalian ornithine decarboxylase

“…This is most likely due to the cellular depletion of polyamines, since the addition of either spermidine or spermine counteracts this effect [14,191. COS cells transfected with the control vector responded in a similar way to F,MeOrn treatment (Fig.…”

“…Another feature of the feedback control of ODC is that inhibition of polyamine synthesis, using for example the ODC inhibitor F,MeOrn, causes a marked increase in the cellular content of ODC protein [13,14,191. This is most likely due to the cellular depletion of polyamines, since the addition of either spermidine or spermine counteracts this effect [14,191.…”

“…However, to obtain this effect large quantities of polyamines, often at millimolar concentrations, have to be used. Nevertheless, ODC is downregulated by the addition of micromolar concentrations of polyamines to cells [14,16,17, 191. Furthermore, treatment with polyamine synthesis inhibitors causes a marked increase in cellular ODC content which cannot be explained by a change in the apparent turnover of the enzyme [13,14, 191.…”

“…Nevertheless, ODC is downregulated by the addition of micromolar concentrations of polyamines to cells [14,16,17, 191. Furthermore, treatment with polyamine synthesis inhibitors causes a marked increase in cellular ODC content which cannot be explained by a change in the apparent turnover of the enzyme [13,14, 191. Using pulse radiolabeling with [35S]methionine, it has been shown that the incorporation of radioactivity into ODC is increased when the cellular levels of polyamines are low, and decreased when the cells are supplied with polyamines at micromolar concentrations in their growth medium [17,[19][20][21].…”