Regulation of spermidine/spermine N¹-acetyltransferase in L6 cells by polyamines and related compounds

Exposure of rat L6 cells in culture to exogenous polyamines led to a very large increase in the activity of spermidine/spermine N¹-acetyltransferase. Spermine was more potent than spermidine in bringing about this increase, but in both cases the elevated acetyltransferase activity increased the cellular conversion of spermidine into putrescine. The N¹-acetyltransferase turned over very rapidly in the L6 cells, with a half-life of 9 min after spermidine and 18 min after spermine. A wide variety of synthetic polyamine analogues also brought about a substantial induction of spermidine/spermine N¹-acetyltransferase activity. These included sym-norspermidine, sym-norspermine, sym-homospermidine, N⁴-substituted spermidine derivatives, 1,3,6-triaminohexane, 1,4,7-triaminoheptane and deoxyspergualin, which were comparable with spermidine in their potency, and N¹N⁸-bis(ethyl)spermidine, N¹N⁹-bis(ethyl)homospermidine, methylglyoxal bis(guanylhydrazone), ethylglyoxal bis(guanylhydrazone) and 1,1'-[(methylethanediylidene)dinitrilo]bis(3-aminoguanidine), which were even more active than spermidine. It is suggested that these polyamine analogues may bring about a decrease in cellular polyamines not only by inhibiting biosynthesis but by stimulating the degradation of spermidine into putrescine.