Cell cycle phase-dependent induction of ornithine decarboxylase-antizyme

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.