[Effect of the tumor promoter TPA on the distribution of PHA-stimulated human lymphocytes by cell cycle phases].

Patterns of the cell cycle distribution in human peripheral blood lymphocytes, stimulated by PHA alone and PHA plus 12-o-tetradecanoylphorbol-13-acetate (TPA), were studied using DNA cytometry in different times after PHA stimulation. In the first period (nearly 3 days after PHA stimulation) TPA induces no significant differences in the characters under consideration, but in the later period, when the proliferation of the cultures stimulated by PHA alone is reducing, in other cultures stimulated by PHA plus TPA the percentage of cells in S-phase does not reduce, whereas the percentage of cells in G2-phase is rising, which may suggest that this phase is blocked. Concurrently the tetraploid cells are appearing. Accumulation of cells in G2-phase can be overcome by the application of chlorpromazine, which is known to inhibit the membrane-associated protein kinase C.