CORRELATION OF POLYAMINE AND GROWTH-RESPONSES TO N-1,N-11-DIETHYLNORSPERMINE IN PRIMARY FETAL FIBROBLASTS DERIVED FROM TRANSGENIC MICE OVEREXPRESSING SPERMIDINE SPERMINE N-1-ACETYLTRANSFERASE/

A recently generated transgenic mouse line having activated polyamine catabolism due to systemic overexpression of spermidine/spermine N-1-a cetyltransferase (SSAT) was used to isolate primary fetal fibroblasts as a means to further elucidate the cellular consequences of activated polyamine catabolism, Basal levels of SSAT activity and steady-state mRNA in the transgenic fibroblasts were about similar to 20- and simil ar to 40-fold higher than in nontransgenic fibroblasts, Consistent wit h activated polyamine catabolism, there was an overaccumulation of put rescine and N-1-acetylspermidine and a decrease in spermidine and sper mine pools. Treatment with the polyamine analogue N-1,N-11-diethylnors permine (DENSPM) increased SSAT activity in the transgenic fibroblasts similar to 380-fold, whereas mRNA increased only similar to 3-fold, i ndicating post-mRNA regulation, SSAT activity in the nontransgenic fib roblasts increased similar to 200-fold, By Western blot, enzyme protei n was found to increase similar to 46 times higher in the treated tran sgenic fibroblasts than non-transgenic fibroblasts: a value comparable to 36-fold differential in enzyme activity, With DENSPM treatment, sp ermidine pools were more rapidly depleted in the transgenic fibroblast s than in nontransgenic fibroblasts, Similarly, transgenic fibroblasts were much more sensitive to DENSPM-induced growth inhibition, This wa s not diminished by co-treatment with an inhibitor of polyamine oxidas e, suggesting that growth inhibition was due to polyamine depletion pe r se as opposed to oxidative stress, Since the two fibroblasts were ge netically identical except for the transgene, the various metabolic an d growth response differences are directly attributable to overexpress ion of SSAT.