The role of polyamines in cell cycle progression

In an attempt to shed light on the role of the polyamines, putrescine, spermidine, and spermine in cell cycle progression, polyamine biosynthesis has been analyzed during the cell cycle of Chinese hamster ovary cells, and cell cycle kinetics have been investigated in cells treated with polyamine biosynthesis inhibitors. Cells were synchronized with the mitotic detachment technique, and at various times after seeding, they were sampled for analysis of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) activities, as well as their mRNA levels and polyamine contents. The results imply that polyamine biosynthesis was regulated at the levels of transcription, translation, and post-translation. The effect of polyamine depletion on cell cycle kinetics was studied with a bromodeoxyuridine - flow cytometry technique. Polyamine depletion was achieved by treating the cells with either 2-difluoromethylornithine (DFMO), an inhibitor of ODC, or 4-amidinoindan-1-one 21-amidinohydrazone (CGP 48664), an inhibitor of AdoMetDC. DFMO treatment resulted in depletion of the putrescine and spermidine pools, while CGP 48664 treatment resulted in depletion of the spermidine and spermine pools. Treatment with either of the inhibitors resulted in a reduction in the rate of progression through S phase within one cell cycle. This was not caused by an affect on the G1/S transition. The results indicate that polyamine depletion reduced the rate of DNA elongation without affecting the initiation of DNA replication. CGP 48664 treatment resulted in a more pronounced inhibition of S phase progression than did DFMO treatment, indicating that spermine may have a more pronounced role in DNA replication than the other polyamines.