12-O-tetradecanoylphorbol-13-acetate induces an immediate, but transient increase in mitotic activity uncoupled from DNA synthesis in the monolayer cultures of rat keratinocyte.

A single wave of mitotic activity was observed in a monolayer culture of rat keratinocytes immediately after exposure to 12-O-tetradecanoylphorbol-13-acetate. A peak for cells in prophase, observed at 10 min after the exposure, was followed by a peak for metaphase at 20 min, for anaphase at 25 min and telophase at 30 min after the exposure. Thereafter, the mitotic activity began to subside. This transient stimulation of mitotic activity resulted in an increase of population density in the monolayer culture. There was neither a stimulation of DNA synthesis during this period nor a change of the DNA content after the mitotic activity was completed. This single burst of synchronous mitotic activity which did not require a substantial stimulation of DNA synthesis suggests that the effect was on the initiation process of mitosis among a subpopulation of cells, presumably cells delayed in the G2 phase of the cell cycle.