Inhibition of polyamine synthesis reduces the growth rate and delays the expression of differentiated phenotypes in primary cultures of embryonic mesoderm from chick

Exogenous spermidine modulates glycosaminoglycan accumulation and epithelial differentiation in chick embryonic skin

We have previously shown that feather formation in chick embryonic skin depends on accumulation of sulphated glycosaminoglycans in the underlying mesenchyme, and that addition of spermidine to chick embryo fibroblasts increases the extracellular sulphated glycosaminoglycans. In the present work, using histological, histochemical and biochemical procedures, we have investigated the effects on glycosaminoglycan accumulation and on epithelial differentiation of adding spermidine and bis-cyclohexylammonium sulphate, a spermidine inhibitor, to embryonic chick skin cultures. Our results demonstrate that spermidine induces an accumulation of sulphated glycosaminoglycan and an increase in feather formation, suggesting that the morphogenetic effect of spermidine may be dependent on specific glycosaminoglycan accumulation.

Putrescine-stimulated intracellular Ca2+ release for invasiveness of rat ascites hepatoma cells

Our previous study showed that treatment of highly invasive rat ascites hepatoma (LC-AH) cells with alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, decreased both their intracellular level of putrescine and their in vitro invasion of a monolayer of calf pulmonary arterial endothelial (CPAE) cells, and that both these decreases were completely reversed by exogenous putrescine, but not spermidine or spermine. Here we show that all adhering control (DFMO-untreated) cells migrated beneath CPAE monolayer with morphological change from round to cauliflower-shaped cells (migratory cells). DFMO treatment increased the number of cells that remained round without migration (nonmigratory cells). Exogenous putrescine, but not spermidine or spermine, induced transformation of all nonmigratory cells to migratory cells with a concomitant increase in their intracellular Ca2+ level, [Ca2+]i. The putrescine-induced increase in their [Ca2+]i preceded their transformation and these effects of putrescine were not affected by antagonists of the voltage-gated Ca2+ channel, but were completely suppressed by ryanodine, which also suppressed the invasiveness of the control cells. The DFMO-induced decreases in both [Ca2+]i and the invasiveness of the cells were restored by thapsigargin, which elevated [Ca2+]i by inhibiting endoplasmic Ca2+-ATPase, indicating that thapsigargin mimics the effects of putrescine. These results support the idea that putrescine is a cofactor for Ca2+ release through the Ca2+ channel in the endoplasmic reticulum that is inhibited by ryanodine, this release being initiated by cell adhesion and being a prerequisite for tumor cell invasion.

The upstream open reading frame of the mRNA encoding S-adenosylmethionine decarboxylase is a polyamine-responsive translational control element

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the pathway of polyamine biosynthesis. The cellular levels of the polyamines specifically regulate AdoMetDC translation through the 5'-leader of the mRNA, which contains a small upstream open reading frame (uORF) 14 nucleotides from the cap. Mutating the initiation codon of the uORF, which encodes a peptide product with the sequence MAGDIS, abolished regulation. In addition, the uORF is sufficient, by itself, to provide polyamine regulation when inserted into the 5'-leader of the human growth hormone mRNA. Changing the amino acid sequence at the carboxyl terminus of the peptide product of the uORF abolished polyamine regulation. In contrast, altering the nucleotide sequence of the uORF at degenerate positions, without changing the amino acid sequence of the peptide, did not affect regulation. Extending the distance between cap and uORF, thereby changing the rate of initiation at the initiator AUG of the uORF, did not alter polyamine regulation. When the uORF was extended so as to overlap, out of frame, the downstream major cistron, polyamine regulation was abolished. We propose that polyamines do not modulate the rate of recognition of the uORF but rather regulate interaction of the peptide product of the uORF with its target.

Ethanol-induced insulin resistance suppresses the expression of embryonic ornithine decarboxylase activity

In utero exposure to ethanol is associated with significant increases in fetal morbidity and mortality as well as with behavioral and learning problems that appear later in life. Growth suppression of the developing child is the most frequent physical effect of ethanol exposure and is correlated with specific molecular changes within the developing organism. The present report suggests that embryonic ethanol exposure suppresses the normal developmental increase in ornithine decarboxylase (ODC) activity. The loss of ODC activity during the early stages of development is dose-dependent and is correlated with the degree of growth suppression. Because ODC is the rate-limiting step for the synthesis of the polyamines and thus appears to be a focal enzyme for the regulation of growth, we have investigated the biochemical consequences of an ethanol-induced inhibition of ODC activity. Using intact chick embryos as well as cultured embryonic tissue, these studies indicate that ethanol-induced changes in tissue putrescine content result in growth suppression because a single dose of exogenous putrescine blocked the growth suppression. In cultured tissue, ethanol exposure inhibited the ability of a known trophic factor (insulin) to induce ODC activity. The loss of insulin-inducible decarboxylase activity as a result of ethanol exposure was specific to ODC, but ethanol per se had no effect on ODC activity in vitro. The data suggest that exposure to ethanol results in a resistance of the embryonic tissue to the action of insulin and thereby disrupts the molecular path by which this mitogenic compound induces the expression of ODC enzymatic activity.

Effect of cocaine, ethanol or nicotine on ornithine decarboxylase activity in early chick embryo brain

Fetal drug exposure causes multiple deficits in the developing child. For both humans and animal models, the single most common drug-related problem is fetal growth suppression. This defect is associated with significant perinatal morbidity and mortality and may also be related to significant behavioral problems appearing later in life. Studies focussed on the molecular mechanism of fetal drug effects in placental models are complicated by multiple interactions of the drug with mother, placenta and fetus. Using early (76-168 h) chick embryos as a non-placental model, and three common drugs of abuse (nicotine, ethanol and cocaine) it was found that each drug suppressed the peak in fetal brain ornithine decarboxylase (ODC) activity that normally occurs at 120 h of development. For each drug, the decrease in ODC activity at 120 h was followed by a small but significant increase in ODC. Thus, although the drug-treated embryos were smaller in size, they appeared to be undergoing compensatory growth and, in fact, became equal in weight to the vehicle-treated animals, if allowed to hatch.