Polyamines are involved in the regulation of S phase and DNA synthesis

Sammanfattning: Our research group has previously shown that treatment with the polyamine biosynthesis inhibitors a-difluoromethylornithine (DFMO) or amidinoindan-1-one 2´-amidinohydrazone (CGP 48664) inhibited S phase progression before any other cell cycle phase was affected. This study was undertaken to further investigate the role of polyamines in the regulation of S phase progression and DNA synthesis. I have found that treatment with the polyamine analog N¹,N¹¹-diethylnorspermine (DENSPM) also caused a prolongation of the S phase. The common denominator for DFMO, CGP 48664, or DENSPM treatment is a depletion of the cellular spermidine pool. CGP 48664 and DENSPM in addition deplete the spermine pool. CGP 48664 or DENSPM treatment prolonged the S phase more than did DFMO treatment. Thus, mainly spermine but also spermidine may have a function in S phase progression. Using the single cell gel electrophoresis assay, I have shown that polyamine deficiency resulted in DNA strand breaks. I have also shown that the topoisomerase II that is present in polyamine deficient cells is not functional. The results imply that there might be a change in chromatin structure rendering topoisomerase II non-functional in polyamine deficient cells. The number and organization of replicon clusters was not affected by polyamine deficiency. However, replicon clusters were less fluorescent in polyamine deficient cells compared to control cells, pointing to a lower rate of DNA elongation in the former cells. Polyamine deficiency resulted in an aberrant regulation of cell cycle progression in Chinese hamster ovary cells (CHO). The results may be related to the fact that CHO cells have a mutated p53 gene. MCF-7 cells, which have a wild type p53 gene, reacted somewhat differently to polyamine deficiency than did CHO cells. As a general conclusion of my results I suggest that normal levels of spermidine and spermine are required for an optimal rate of S phase progression and that the first cell cycle phase affected by polyamine biosynthesis inhibition is the S phase. I do believe that many of the effects observed after more than 1-2 days of polyamine biosynthesis inhibitor treatment are secondary to the initial perturbances that have taken place.