Abstract
We have previously reported that cyclical phases of accumulation and depletion of polyamines occur during cell-cycle progression. Regulatory ornithine decarboxylase (ODC) catalyses the first step of polyamine biosynthesis. Ornithine decarboxylase antizyme (OAZ), induced by high polyamine levels, inhibits ODC activity and prevents extracellular polyamine uptake. Spermidine/spermine N1-acetyltransferase (SSAT) regulates the polyamine degradation/excretion pathway. Here we show that 24 h transient transfection of immortalized human prostatic epithelial cells (PNT1A and PNT2) with antisense ODC RNA or OAZ cDNA, or both, while effectively causing marked decreases of ODC activity and polyamine (especially putrescine) concentrations, resulted in accumulation of cells in the S phase of the cell cycle. Transfection with SSAT cDNA led to more pronounced decreases in spermidine and spermine levels and resulted in accumulation of cells in the G2/M phases. Transfection with all three constructs together produced maximal depletion of all polyamines, accompanied by accumulation of PNT1A cells in the S phase and PNT2 cells in the G0/G1 and G2/M phases. Accumulation of PNT1A cells in the S phase progressively increased at 15, 18 and 24 h of transfection with antisense ODC and/or OAZ cDNA. At 24 h, the DNA content was always reduced, as a possible outcome of altered chromosome condensation. A direct link between polyamine metabolism, cell proliferation and chromatin structure is thus proposed.