Role of polyamines at the G1/S boundary and G2/M phase of the cell cycle

The role of polyamines at the G(1)/S boundary and in the G(2)/M phase of the cell cycle was studied using synchronized HeLa cells treated with thymidine or with thymidine and aphidicolin. Synchronized cells were cultured in the absence or presence of alpha-difluoromethylornithine (DEMO), an inhibitor of ornithine decarboxylase, plus ethylglyoxal bis(guanylhydrazone) (EGBG), an inhibitor of S-adenosylmethionine decarboxylase. When polyamine content was reduced by treatment with DEMO and EGBG, the transition from G(1) to S phase was delayed. In parallel, the level of p27(Kip1) was greatly increased, so its mechanism was studied in detail. Synthesis of p27(Kip1) was stimulated at the level of translation by a decrease in polyamine levels, because of the existence of long 5'-untranslated region (5'-UTR) in p27(Kip1) mRNA. Similarly, the transition from the G(2)/M to the G(1) phase was delayed by a reduction in polyamine levels. In parallel, the number of multinucleate cells increased by 3-fold. This was parallel with the inhibition of cytokinesis due to an unusual distribution of actin and alpha-tubulin at the M phase. Since an association of polyamines with chromosomes was not observed by immunofluorescence microscopy at the M phase, polyamines may have only a minor role in structural changes of chromosomes at the M phase. In general, the involvement of polyamines at the G(2)/M phase was smaller than that at the G(1)/S boundary. (C) 2013 Elsevier Ltd. All rights reserved.