This study analyzes the effects of polyamine starvation on cell cycle traverse of an arginase-deficient CHO cell variant (CHO-A7). These cells grow well in serum-free medium, provided that it contains ornithine or polyamines or both. In the absence of ornithine or polyamines or both, the CHO-A7 cells develop severe polyamine deficiency and, as a consequence, grow more slowly. When grown to a stationary phase in the presence of ornithine or putrescine or both, the CHO-A7 cells became arrested in GO/early G1. However, when starved for ornithine and polyamines, they accumulated in the S and G2 phases. Ornithine and polyamine starvation of CHO-A7 cells causes an increase in ornithine decarboxylase activity. When this increase was prevented by treatment with DL-a-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, growth was further suppressed, and a greater fraction of cells were found in the S and G2 phases of the cell cycle.A high rate of synthesis of the polyamines putrescine, spermidine, and spermine is associated with cell growth and division (6,18,27). In eucaryotes, putrescine is formed solely by decarboxylation of ornithine in a reaction catalyzed by ornithine decarboxylase (ODC) (18). Ornithine is either taken up from the plasma or synthesized intracellularly by the action of arginase (18). In fact, arginase may be considered the initial enzyme ih the polyamine biosynthetic pathway, at least in cells that do not have a complete set of urea cycle enzymes (11,18).An obvious means of determining the physiological function of the polyamines is to use mutants with specific defects in the various steps of polyamine biosynthesis. The first successful isolation of polyamine-dependent mammalian cells was recently reported. Thus, arginase-deficient (8,21) and ODC-deficient (25) Chinese hamster ovary (CHO) cell lines are presently being characterized. In the absence of polyamines in the medium, these cells develop severe polyamine deficiency, and their proliferation gradually decreases and eventually ceases (21,25). These findings clearly demonstrate the requirement of polyamines for growth.Our present conception of cell cycle kinetics of polyamine-deficient cells is entirely based on experiments with inhibitors of polyamine biosynthetic enzymes (6). It is irrefutably important to compare these results with results of experiments in which polyamine deficiency has been achieved by other means. Therefore, we have studied the effects of polyamine starvation on the cell cycle kinetics of the arginase-deficient CHO cell variant CHO-A7. Because these cells cannot make their own ornithine and are maintained in the absence of serum (a normal source of arginase) (8, 24), they are dependent on the addition of ornithine for polyamine synthesis.Flow cytometric analysis revealed a progressive lengthening of the S and G2 phases, relative to G1, during the course of starvation for ornithine and polyamines. Since the polyamine-starved cells exhibited a compensatory increase in * Correspondi...

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The activities of ornithine decarboxylase (ODC) and ODC inhibitory protein (ODC-antizyme) were studied in Ehrlich ascites tumor cells, separated according to their position in the cell cycle by centrifugal elutriation. Release and/or synthesis of ODC-antizyme was induced by putrescine treatment. Each mouse received an intraperitoneal injection of 25 mumoles of putrescine at 0, 1, 2, and 3 hr after tumor transplantation. Tumor cells obtained from putrescine-treated and control mice at 4 hr after transplantation were separated into fractions representing all phases of the cell cycle. The cell cycle distribution of the tumor cells in each fraction was determined by flow cytometry. In control tumor cells the ODC activity exhibited two maxima; in late-G1/early-S and in late-S/G2. A marked decrease in ODC activity was observed in mid-S phase. This decrease coincided with maximum ODC-antizyme activity (revealed by putrescine treatment), suggesting that ODC-antizyme is involved in the regulation of ODC activity during the cell cycle.