Induction of spermidine N¹-acetyltransferase by sodium N-butyrate and phytohemagglutinin in bovine lymphocytes

An increased activity of spermidine N¹-acetyltransferase was induced in bovine lymphocytes by stimulation with either sodium n-butyrate or phytohemagglutinin (PHA). The acetylase activity was elevated by 2- to 3-fold 24 h after the addition of butyrate, whereas a similar increase of the enzyme activity was found 48 h after stimulation with PHA. When butyrate and PHA were added to the lymphocyte suspensions simultaneously, the peak of enzyme induction was observed at 24 h after the addition and the increase (9-fold) was found to be more than additive. Since the increases in acetylase activity by both butyrate and PHA were markedly inhibited by actinomycin D or cycloheximide, they appear to have resulted from the synthesis of new protein rather than the release of the enzyme from a cryptic inactive form. The enzyme induced by the two agents was most active with spermidine as a substrate, but spermine was also acetylated to a smaller extent (25% of spermidine). Virtually no acetylation was observed with putrescine. Also, the product formed from spermidine and acetyl CoA was more than 90% N¹-acetylspermidine. These results indicate that the acetylases induced by the two agents are similar. Although the addition of indomethacin or 8-bromocyclic AMP to PHA-stimulated lymphocytes caused an inhibition of the enzyme induction, no such inhibitory effect was found in the case of enzyme induction by butyrate. These results indicate that both sodium n-butyrate and PHA induce spermidine N¹-acetyltransferase in bovine lymphocytes, but the induction mechanisms are different from each other.