Effect of tumour promoters on poly ADP-ribosylation in human epidermoid carcinoma HeP2 cells.

The present work was undertaken with the basic objective to compare the effect of related tumour promoters phorbol-12-myristate-13-acetate (PMA), benzoyl peroxide (BP) and mezerein (M) on poly ADP-ribosylation in HeP2 cells. PMA, BP and mezerein showed an increase in the enzyme activity to the extent of 66, 89 and 35% respectively. This was accompanied by a drop in NAD levels of 22% with PMA, 24% with BP and 49% with mezerein, PMA-treated cells showed a decrease in the enzyme activity of 42% with superoxide dismutase (SOD) and catalase (CAT), 18% with butylated hydroxy toluene (BHT), 52% with indomethacin and 32% with 3-aminobenzamine (3AB). However, for BP the inhibition was 16% with CAT, 41% with SOD, 18% with BHT, 34% with 3AB and there was no inhibition with indomethacin. The involvement of active oxygen species was supported by a 2.5-fold increase in superoxide anion levels with PMA and BP and no change with mezerein. There was a twofold and a 2.5-fold increase in Ca2+ influx after PMA and BP treatment respectively. It is concluded that PMA and BP mediate their effect on poly ADP-ribosylation through active oxygen species which in turn stimulates the influx of Ca2+ into cells and this may play an important role in signal transduction.