EXCESS PUTRESCINE ACCUMULATION INHIBITS THE FORMATION OF MODIFIED EUKARYOTIC INITIATION-FACTOR 5A (EIF-5A) AND INDUCES APOPTOSIS

DH23A cells, an alpha-difluoromethylornithine-resistant variant of the parental hepatoma tissue culture cells, express high levels of stable ornithine decarboxylase. Aberrantly high expression of ornithine deca rboxylase results in a large accumulation of endogenous putrescine and increased apoptosis in DH23A cells when alpha-difluoromethylornithine is removed from the culture. Treatment of DH23A cells with exogenous putrescine in the presence of alpha-difluoromethylornithine mimics the effect of drug removal, suggesting that putrescine is a causative age nt or trigger of apoptosis. Accumulation of excess intracellular putre scine inhibits the formation of hypusine in vivo, a reaction that proc eeds by the transfer of the butylamine moiety of spermidine to a lysin e residue in eukaryotic initiation factor 5A (eIF-5A). Treatment of DH 23A cells with diaminoheptane, a competitive inhibitor of the post-tra nslational modification of eIF-5A, causes both the suppression of eIF- 5A modification in vivo and induction of apoptosis. These data support the hypothesis that rapid degradation of ornithine decarboxylase is a protective mechanism to avoid cell toxicity from putrescine accumulat ion. Further, these data suggest that suppression of modified eIF-5A f ormation is one mechanism by which cells may be induced to undergo apo ptosis.