Simultaneous analysis of cell cycle kinetics at two different DNA ploidy levels based on DNA content and cyclin B...

The methods of cell cycle analysis that rely on DNA content measurements cannot discriminate between cells at different phases of the cycle if these cells have similar DNA content. This limitation can be circumvented by measurement of another cell cycle phase-specific cell constituent in addition to DNA content, followed by bivariate analysis of the correlated data. The aim of the present study was to explore the utility of a monoclonal antibody against the G2- and M phase-specific regulatory protein cyclin B for discrimination of cell populations with overlapping DNA content. This analysis, which was based on correlated DNA/cyclin B content measurements by flow cytometry, was applied to human lymphocytic leukemic MOLT-4 cells. The onset of cyclin B synthesis was observed in the last one third of S phase with its maximum accumulation in G2 and M phases; cells in G1 and early- and mid-S phases were negative. Cells arrested in metaphase by vinblastine expressed high levels of this protein, although not as high as in cells arrested in G2 by the DNA topoisomerase II inhibitor m-AMSA. Disruption of cytokinesis by the protein kinase inhibitor staurosporine led to DNA rereplication, cell progression through the chromatin cycle at higher DNA ploidy, and induction of polyploidy. It was possible, utilizing the cyclin B antibody, to discriminate between G2 + M cells with a 2C level of DNA and G1 cells with 4C DNA, as well as to distinguish doublets of G1 cells with a 2C DNA level. Thus, the rate of cell entrance to G1 at the 4C DNA level and the rates of progression through the cycle at both the 2C and 4C DNA levels could be simultaneously estimated. The data indicate that, in the presence of 0.1 microM staurosporine, cytokinesis of all MOLT-4 cells is impaired and the cells enter to and progress through the chromosome cycle at 4C DNA at the same rates as at 2C DNA. This approach can be helpful in the analysis of DNA ploidy and the cell cycle of human tumors when there is an overlap in DNA content values between normal stromal or infiltrating cells and aneuploid tumor cell population and may be the method of choice to investigate the activity of antitumor drugs which impair cytokinesis but do not interfere with progression of cells through the chromatin cycle.