Effect of poly(adenosine diphosphate-ribose) polymerase inhibitors on neocarzinostatin-induced G2 delay in HeLa-S3 cells
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Abstract:
The antitumor antibiotic neocarzinostatin (NCS), which produces single-strand breaks in mammalian cell DNA in vivo, stimulated the activity of chromatin bound enzyme, poly(ADP-ribose) polymerase in HeLa-S3 cells. Because of the possible causal relationship between the poly ADP-ribosylation of chromatin protein and NCS-induced temporary G2 arrest in the cell cycle, several classes of inhibitors of poly(ADP-ribose) polymerase were examined to evaluate the effect on NCS-induced polymerase activity as well as on progression in the cell cycle of synchronized HeLa cells which had been treated with NCS in G2. Compared at the same concentration of 2 mM, the polymerase-inhibiting activity was larger in the order of thymidine, 3-aminobenzamide, nicotinamide, theophylline, and caffeine. Among these agents, caffeine, theophylline, and thymidine caused a reduction in the G2 delay in this order by stimulating the cells to undergo mitosis after NCS treatment. However, 3-aminobenzamide and nicotinamide were poor reducers, if any, of NCS-induced G2 delay. These results suggest that there is not a direct involvement of poly ADP-ribosylation of chromatin protein in the mechanism of NCS-induced G2 delay. The effect of caffeine on G2 delay will probably be independent of its activity as a poly(ADP-ribose) polymerase inhibitor.
Insights
Neocarzinostatin (NCS) stimulates poly(ADP-ribose) polymerase, but inhibiting this enzyme does not prevent NCS-induced G2 cell cycle delay. This suggests poly ADP-ribosylation is not directly involved in NCS-induced G2 arrest.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Neocarzinostatin (NCS) is an antitumor antibiotic that induces DNA strand breaks.
- NCS stimulates poly(ADP-ribose) polymerase (PARP) activity in mammalian cells.
- NCS causes temporary G2 cell cycle arrest, potentially linked to PARP activity.
Purpose of the Study:
- To investigate the role of poly ADP-ribosylation in NCS-induced G2 cell cycle arrest.
- To evaluate the effect of PARP inhibitors on NCS-induced polymerase activity and cell cycle progression.
Main Methods:
- Synchronized HeLa cells were treated with NCS in the G2 phase.
- Various poly(ADP-ribose) polymerase inhibitors (thymidine, 3-aminobenzamide, nicotinamide, theophylline, caffeine) were used.
- Effects on NCS-induced polymerase activity and G2 delay were measured.
Main Results:
- All tested inhibitors reduced NCS-induced polymerase activity.
- Caffeine, theophylline, and thymidine reduced G2 delay, while 3-aminobenzamide and nicotinamide had minimal effect.
- The order of G2 delay reduction was caffeine > theophylline > thymidine.
Conclusions:
- Poly ADP-ribosylation of chromatin protein is not directly involved in the mechanism of NCS-induced G2 delay.
- Caffeine's effect on G2 delay is likely independent of its PARP inhibitory activity.