Opposite effects of TPA on G1/S transition and on cell size in the low metastatic B16F1 with respect to high metastatic BL6 murine melanoma cells

Phorbol esters, known activators of c- and n-protein kinase C (PKC) isoforms, play a pivotal role in tumor promotion. In order to better understand the relationships between PKC activation, the metastatic potential and the proliferative capacity, we have analyzed the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment on the proliferative as well as on the cell cycle distribution and on the cell size of low and high metastatic murine B16F1 and B16-BL6 (BL6) melanoma cells, respectively. TPA-treated B16F1 cells showed an increased proliferative capacity up to 72 h, the cytofluorimetric analysis revealing an increased number of cells in the S+G2-M phase of the cell cycle. In contrast, TPA-treated BL6 cells reached a plateau at 48 h and showed an increased cell volume in the G1 and S phases of the cell cycle, with a reduction in the percentage of cells in the S+G2-M phase. Taken together, our results indicate opposite effects of TPA treatment in murine melanoma cells of different metastatic potential. TPA could cause a block in the G1 phase of the cell cycle with enhanced cell volume in high metastatic BL6 cells. The same treatment, on the contrary, induced an increased entry into the cell cycle of low metastatic B16F1 cells, suggesting a relationship between cell proliferation and the metastatic potential of B16 murine melanoma cells. Moreover, under the present conditions, classical PKC isoforms were inactivated, suggesting the involvement of the TPA-dependent novel PKCs.