Early effects of the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate on the cell cycle traverse of asynchronous HeLa cells.

Within 24 hr after incubation of synchronous HeLa cell cultures with small nontoxic doses of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-7) or 10(-8) M), a variety of transient alterations in the cell cycle traverse was detected by different techniques. The measurement of thymidine incorporation rates into DNA, of labeling and mitotic indices, and of flow cytometry revealed (a) an inhibition of cells in G1 shortly prior to their entering S phase, (b) a reduced rate of DNA synthesis and a delayed passage of cells through S phase which were in this phase on addition of TPA, (c) a delayed passage through G2 of a portion of cells which were somewhere in the first half of the S phase on addition of TPA, and (d) an instant but short-lasting blockage in G2 immediately before mitosis. The effects of TPA are reminiscent of published results on X-irradiated cell cultures. None of these effects was noticed with the hyperplasiogenic but nonpromoting phorbol ester 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate (10(-6) M). The data were confirmed by experiments with synchronized HeLa cells as described in an accompanying paper.