DISSOCIATION OF NUCLEAR AND CYTOPLASMIC CELL-CYCLE PROGRESSION BY DRUGS EMPLOYED IN CELL SYNCHRONIZATION

We have studied the effect of the cell synchronization agents compacti n, ciclopirox olamine, mimosine, aphidicolin, ALLN, and colcemid on se veral parameters of cell cycle progression in mitotically synchronized HeLa S3 cells. Using cell size and cyclin A and B levels as markers o f cytoplasmic progression and DNA content as a measure of nuclear cell cycle position, we have examined coordination of cytoplasmic and nucl ear events during induction synchrony. Each synchronizing agent was un ique in its effect on the coordination of the cytoplasmic and nuclear cycle. Mimosine, aphidicolin, ALLN, and colcemid disrupted cell cycle integration while compactin and ciclopirox olamine did not, Continued net cell growth during cell cycle arrest was the most dramatic in aphi dicolin-treated cells, which averaged a 60% increase in size. Mimosine , ALLN, and colcemid produced an increase in cell size of approximatel y 25%, and ciclopyrox olamine and compactin exerted a negligible effec t. Cyclin A and B were found at mitotic (high) or G1 (low) levels, or in combination of high and low concentrations not correlated with DNA content in drug-treated cells. For example, treatment with mimosine, w hich arrests cells in G1 with 2C DNA, resulted in cyclin A accumulatin g to mitotic levels, whereas cyclin B remained at a low concentration, the first time this phenomenon has been observed. These results demon strate that populations of synchronized cells obtained by different dr ug treatments are blocked at biochemically distinct cell cycle points not apparent by cytometric measurement of DNA content. Our results pro vide conclusive evidence that induced synchrony methods differ with re spect to their impact on cell cycle organization and from the pattern seen with nonperturbing cell selection methods. (C) 1995 Academic Pres s, Inc.