FLOW CYTOMETRIC ANALYSIS OF THE CELL-CYCLE IN POLYAMINE-DEPLETED CELLS

Polyamines are found in all cells but their function is not fully unde rstood. We have studied the effect of polyamines on the passage of cel ls through the cell cycle using a polyamine auxotrophic mutant, CHO-P2 2, which has no detectable ornithine decarboxylase activity. The abili ty of these cells to grow without serum allows efficient polyamine dep letion. A flow cytometric analysis of DNA content and bromodeoxyuridin e labeling showed that without added polyamines the cells accumulated in S-phase, the rate of DNA synthesis was retarded, and the entry into mitosis was blocked. Addition of polyamines to cultures deprived of p olyamines induced cells in all phases of the cell cycle to reinitiate cycling. Earlier studies have shown that cells with damaged DNA are bl ocked from entering into mitosis but caffeine can partly overcome this block and induce premature chromosome condensation. Polyamine-deplete d CHO-P22 cells responded to caffeine in the same way as cells with da maged DNA. These results show that polyamine depletion in CHO-P22 cell s primarily affects DNA synthesis. The finding that polyamine-starved cells continuously take up bromodeoxyuridine without a corresponding i ncrease in the amount of DNA is compatible with extensive repair of er roneous and/or damaged DNA. Polyamine auxotrophic Chinese hamster ovar y (CHO) cells might be useful in studies on the regulation of mitosis in mammalian cells. (C) 1994 Wiley-Liss, Inc.