Regulation of ornithine decarboxylase in 3T3 cells by putrescine and spermidine. Indirect evidence for translational control

Abstract

Addition of putrescine of spermidine prevents the increase in ornithine decarboxylase activity in cultures of 3T3 cells brought about by pituitary growth factors and results in a rapid, specific, and reversible reduction of enzyme activity in cultures previously stimulated by the growth factors. These effects are not due to polyamine toxicity and do not require other organic medium components. The amines apparently share a single carrier-mediated transport system in 3T3 cells. Methylglyoxal bis(guanylhydrazone), an inhibitor of spermidine synthesis from putrescine was found to also inhibit uptake of each amine. Studies with this drug indicate that each amine is effective without further metabolism. Since ornithine decarboxylase activity decays more rapidly in the presence of each polyamine after addition of camptothecin, the major locus of amine action appears to be in the cytoplasm. However, direct inhibition of the enzyme in vivo by assimilated amines appears to account for at most a small part of the reduction in activity, a conclusion supported by the inability to recover activity in vitro. Also, neither amine seems to act by accelerating enzyme inactivation. When amines are removed from the medium, the subsequent recovery of enzyme activity is totally prevented by trichodermin, an inhibitor of protein synthesis, but is only slightly reduced by camptothecin. It is suggested that both putrescine and spermidine reduce ornithine decarboxylase activity by selectively inhibiting translation.

Differential post‐transcriptional control of ornithine decarboxylase and spermidine‐spermine N1‐acetyltransferase by polyamines

“…In contrast to effects on SSAT activity, SPD and SPM sharply reduced ODC activity in CHX-pretreated cells by 6-7-fold. Down-regulation of ODC is not unexpected since it is one of the first recognized cellular events to be unequivocally attributed to exogenous polyamines [30,31]. Basically, two post-transcriptional mechanisms have been implicated: suppression of translation [5] and induction of a specific protein termed antizyme which binds to, inhibits, and contributes to the degradation of ODC (reviewed by Hayashi et al [6]).…”

Cyclic AMP-dependent protein kinase mediates a cyclic AMP-stimulated decrease in ornithine and S-adenosylmethionine decarboxylase activities.

“…The standard incubation mixture contained, in a final volume of 0.25 ml: 0.1 ml of cell extract; 25 tubes. After a 60-min incubation at 370, the reactions were halted by injecting 1 ml of 40% trichloroacetic acid through the rubber stopper.…”

“…The mechanism whereby Bt2cAMP decreases the enzymatic activities in S49 cells is unknown. In other systems addition of putrescine blocks induction of ornithine decarboxylase (25)(26)(27)(28). In some, (26,28) but not all (27) cases, this inhibition is associated with the appearance of an intracellular inhibitor of the enzyme that has been termed an antizyme (28).…”

Polyamines and cellular adenosine 3′ :5′-cyclic monophosphate

“…It has been shown that exogenous polyamines are taken up and metabolized by cultured cells (Siimes & Janne, 1967;Clark & Fuller, 1975;Kremzner et al, 1975). A substantial increase in the intracellular polyamines is observed when extracellular concentrations rise to the endogenous concentrations (Clark & Fuller, 1975;Heller et al, 1978) and furthermore exogenous polyamines appear not to enter the same pool as amines synthesized within the cell (Russell et al, 1970).…”

“…A substantial increase in the intracellular polyamines is observed when extracellular concentrations rise to the endogenous concentrations (Clark & Fuller, 1975;Heller et al, 1978) and furthermore exogenous polyamines appear not to enter the same pool as amines synthesized within the cell (Russell et al, 1970). These findings, together with the observed sensitivity of most cells to exogenous polyamine in the presence of much higher endogenous concentrations (Mitchell et al, 1978;Heller et al, 1978), make it difficult at present to assess the reason for different effects on cyclic AMP of increasing concentrations ofexogenous polyamines.…”