Benzamide and 4-amino 1,8 naphthalimide treatment inhibit telomerase activity by down-regulating the expression of telomerase associated protein and inhibiting the poly(ADP-ribosyl)ation of telomerase reverse transcriptase in cultured cells.

To test the role of poly(ADP-ribose) polymerase on the telomerase activity, we determined the telomerase activity in leukemic cells K562 treated with benzamide and 4-amino 1,8 naphthalimide (NAP), the inhibitors of PARP. We observed that both the agents inhibited telomerase activity in a dose-dependent manner. The doses of benzamide and NAP that inhibited telomerase activity to 50% of untreated control cells were 10.7 +/- 0.6 mm and 200 +/- 7 microm, respectively. Benzamide treatment (10 mm) inhibited telomerase activity in a time-dependent manner. We also tested the ability of benzamide to inhibit the telomerase activity in Chinese hamster V79 cells and observed similar inhibition of the telomerase activity. Expression of telomerase reverse transcriptase (TERT) and telomerase RNA component, detected by RT-PCR, remained unaltered by treatment with benzamide or NAP. On the contrary, the expression of telomerase associated protein (TEP1/TP1), as detected by RT-PCR and western blot analysis, was reduced by both the agents. Further, in K562 cells, immunoprecipitation with the anti-TERT IgG and probed anti-poly (ADP-ribose) IgG revealed that TERT was poly(ADP-ribosyl)ated in the physiological condition of cell growth and such poly(ADP-ribosyl)ation was inhibited by benzamide treatment. Decrease in TEP1/TP1 expression and poly(ADP-ribosyl)ation of TERT were correlated with the inhibition of PARP activity by benzamide, indicating that PARP had a role in telomerase activity through poly(ADP-ribosyl)ation of TERT and down-regulation of TEP1/TP1.