Is polyamine decrease a common feature of apoptosis? Evidence from γ rays- and heat shock-induced cell death

Here we report that in rat thymocytes undergoing apoptosis upon two different stimuli, such as heat shock treatment and γ irradiation, an early mRNA accumulation of ornithine decarboxylase (ODC) - the rate-limiting enzyme of polyamine biosynthesis was followed by a very marked increase in ODC activity (28-40 and 6-8-fold, respectively). However, polyamine levels started to decrease before the appearance of DNA laddering, being putrescine and spermidine strongly diminished (8-12 hs), and spermine even depleted (12 hs). Taken together with our previous data on another model of apoptosis, i.e., glucocorticoid-induced cell death, these results suggest that an imbalance of polyamine metabolism. i.e. a strong activation of ODC and a paradoxical decrease of the intracellular polyamine content, might be a general feature of the apoptotic process.