Effects of polyamine pool manipulation on genes expressed during the cell cycle
Abstract: The polyamines - putrescine, spermidine and spermine - are polycations found within cells. They have been shown to be essential for optimal cell proliferation and cell survival. Cells maintain their polyamine levels in a well-regulated system involving biosynthesis, catabolism and uptake/excretion. The biosynthetic enzymes - ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) - showed a variation in their half-life activities during the cell cycle in Chinese hamster ovary (CHO) cells. ODC showed a biphasic pattern with prolonged half-life activities at the G1/S and S/G2 transitions, while the AdoMetDC half-life was only prolonged at the G1/S transition. Treatment with the spermine analogue N1, N11-diethylnorspermine (DENSPM) lowered the polyamine content and prolonged the S phase within one cell cycle in semisynchronously proliferating CHO cells. These effects were also observed in semisynchronously proliferating breast adenocarcinoma MCF-7 cells. The levels of several proteins involved in G1 and S phase progression were investigated by Western blots in DENSPM-treated MCF-7 cells. Cyclin A, which is required for proper S phase progression, was decreased by DENSPM treatment on both the mRNA and protein levels. cDNA microarray and 2D protein gel electrophoresis analyses showed altered expression of genes on both mRNA and protein levels after DENSPM treatment. A number of other genes related to cell proliferation, DNA synthesis/repair, protein metabolism, mitochondrial function and stress response were either upregulated or downregulated. DENSPM-induced decrease in polyamine pools caused inhibited cell cycle progression within one cell cycle of drug treatment and this was due to changed gene expression.
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