Differential induction of spermidine/spermine N-1-acetyltransferase activity in cisplatin-sensitive and -resistant ovarian cancer cells in response to N-1,N-12-bis(ethyl)spermine involves transcriptional and post-transcriptional regulation

The growth inhibition that occurs in cisplatin-sensitive 2008 human ovarian cancer cells in response to the spermine analogue, N-1,N-12-bis(ethyl)sper mine (BESpm), is associated with a potent induction of spermidine/spermine N'-acetyltransferase (SSAT), the rate-limiting enzyme in polyamine cataboli sm. Conversely, in cisplatin-resistant C13* cells, which are less responsiv e to BESpm, enzyme induction does not occur at comparable levels after expo sure to the bis(ethyl)-derivative. In this study, we investigated the molec ular mechanisms underlying the differential induction of SSAT activity in c isplatin-sensitive and -resistant cells. Northern blot analysis revealed a difference in the level of SSAT mRNA expression in the two cell lines. in p articular, 2008 cells treated with 10 muM BESpm for progressively increasin g periods of time accumulated more heteronuclear (3.5 kb) and mature (1.3/1 .5 kb) SSAT mRNAs than its resistant variant. SSAT mRNA accumulation parall eled enzyme activity and both were almost completely prevented in the two l ines by co-treatment with 5 mug/ml actinomycin-D (Act-D), suggesting that t ranscription plays a major role in the analogue-mediated induction of SSAT. Moreover, when Act-D was added 48 h after BESpm exposure, SSAT mRNA and en zyme activity were stabilised in both cell lines. Therefore, the marked dif ference in the induction of SSAT activity seems to be related to increased enzyme synthesis, particularly in sensitive cells, whose SSAT protein turno ver was also greatly reduced (half-life > 12 h in 2008 cells versus 5 h in C13* cells) in the presence of BESpm. These findings suggest that cisplatin -resistance modulates the SSAT response to BESpm at transcriptional and pos t-transcriptional levels. (C) 2001 Elsevier Science Ltd. All rights reserve d.