Cisplatin (DDP)-resistance confers a deficient expression of
spermidine/spermine N(1)-acetyltransferase (SSAT) gene in response to the
spermine analog
N(1),N(12)-bis(ethyl)spermine (
BESpm) in the DDP-resistant human ovarian
carcinoma cell line (C13*), compared with their parental DDP-sensitive 2008 cells. This SSAT gene deficiency is correlated with a reduced growth sensitivity to
spermine analogs. This study was performed to determine whether SSAT gene expression of resistant cells was kept suppressed by labile
repressor proteins developed during resistance selection. We show here that inhibitory concentrations of
cycloheximide (CHX) and
anisomycin (ANISO) differentially affect
BESpm-induced SSAT activity in 2008 and in C13* cells in a concentration-dependent manner and allow resistant cells to reach activation levels comparable to those of the sensitive cells. Northern blot analysis revealed that both CHX and ANISO in combination with
BESpm caused a synergistic
BESpm-mediated accumulation of SSAT
mRNA in C13* cells, with respect to each
drug alone, while in 2008 cells only a slight increase was observed. The more pronounced effect of inhibitors on the SSAT activity induced by
BESpm in the resistant cells was also the result of a more prolonged stabilization of SSAT
mRNA and
enzyme protein. By contrast, sub-inhibitory concentrations of CHX and ANISO did not significantly stimulate
BESpm-induced SSAT transcription and activity. These results suggest that labile
repressor proteins, related to DDP-resistance phenotype, play a regulatory role in SSAT gene expression, and further indicate that by overcoming this inhibitory control it is possible to recover
BESpm response.