Poly (ADP-ribose) polymerase and DNA-dependent protein kinase: differential activation in vivo.
DNA damage-activated homodimer of PARP-1 binds to single-strand breaks and catalyzes the synthesis and transfer of negatively charged ADP-ribose polymers to nuclear protein acceptors, including itself. It also undergoes site-specific proteolysis during apoptosis. On the other hand, DNA-PK is a heterotrimeric enzyme that specifically binds to double-strand breaks and phosphorylates its target proteins. Because both DNA breaks and apoptosis are known to occur following irradiation, whole-body irradiation was administered to find out the temporal pattern and dose-response of PARP expression and the activity pattern of DNA-PK. To assess the temporal response, male Wistar rats were subjected to a radiation dose of 3Gy and killed at various time intervals (1-24 hours). Both the PARP activity and expression were enhanced 4 hours after irradiation. Fragmented PARP was not observed until 24 hours after irradiation. The differential expression at DNA-PK various doses (0.1-5.0 Gy) was examined. The maximum expression of PARP was noted at 1 Gy, whereas the activation of DNA-PK was maximally observed at 3 Gy. We did not observe any increase in the expression of PARP until the dose of 3Gy was reached, which contradicted the findings in previous in vitro reports of PARP activation at high radiation doses. DNA-PK, however, showed a dose-dependent increase. Our results indicate that although both the PARP and the DNA-PK are nuclear enzymes with similar roles, the activation of these enzymes is dependent on the dose, and any extrapolation of data from in vitro observations can lead to misinterpretation.
Radiation Biology and Health Sciences Division, Bhabha Atomic Research Center, Mumbai, India.
Himanshi
H
Narang
Malini
M
Krishna
Naresh Chandra
NC
Verma
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000201:enzymology / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D008099:Liver / Q000201:enzymology / Q000528:radiation effects*; D008297:Male; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014916:Whole-Body Irradiation; D000077191:Wortmannin
D000730:Androstadienes; D004268:DNA-Binding Proteins; D011065:Poly(ADP-ribose) Polymerases; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin