Relationship between Ca2+ and L-asparagine in the induction of ornithine decarboxylase in H-35 rat hepatoma cells

: The activity of ornithine decarboxylase (ODC) in H-35 hepatoma cells depleted of Ca2+ by washing with 2 mM EGTA increased 35-fold after incubating for 4 h in a simple salt-glucose solution containing 10 mM L-asparagine and only if Ca2+ was replenished. Actinomycin D (5 micrograms/ml) and cycloheximide (20 microM) reduced the stimulatory effect by 84 and 100% respectively. Increase of active enzyme protein was also demonstrated by a 3-fold increase in alpha-difluoromethylornithine binding. Asparagine prolonged the half-life of induced ODC by 20% whereas Ca2+ reduced it by 32%. The observed inductive effects are not accounted for entirely by a direct influence of Ca2+ and asparagine on the turnover of ODC protein. These factors are likely to be parts of a signalling pathway leading to amplification of cellular ODC.