Suppression of the radiation-sensitive phenotype of hamster irs1 and irs2 strains selected for resistance to 3-aminobenzamide.
OBJECTIVE
The radiosensitive hamster cell lines irs1 and irs2 have phenotypic similarities to cells defective in the early response to DNA-damaging agents as a result of mutations of the genes encoding poly(ADP-ribose)polymerase (PARP) or ataxia-telangiectasia mutated (ATM). Whether modification of PARP activity through selection of strains resistant to 3-aminobenzamide (3-AB) would affect the radiosensitive phenotype of irs1 and irs2 was examined.


METHODS
3-AB-resistant strains of irs1, irs2 and their parent line V79 were established and their sensitivity to DNA-damaging agents was measured. In some 3-AB-resistant strains, the radiation resistance of DNA synthesis and the induction of apoptosis were also assayed. Additionally, a number of aspects of PARP function were measured.


RESULTS
Independently selected 3-AB-resistant strains of irs2 showed nearly complete suppression of radiation sensitivity, sensitivity to topoisomerase inhibitors, and radioresistant DNA synthesis. 3-AB-resistant strains of irs1 showed partial suppression of phenotype while 3-AB-resistant strains of V79 had no sensitivity changes. The induction of apoptosis in 3-AB-resistant strains of irs2 required substantially higher radiation doses than for irs2 itself. 3-AB-resistant strains had no detectable alteration of PARP level or cleavage following ionizing irradiation and there were no mutations in the PARP gene.


CONCLUSIONS
Suppression of radiosensitivity associated with 3-AB resistance has important implications for mechanisms of tolerance to damage because it is able to override responses associated with specific genetic defects.
Ganesh
A
A
Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah, USA.
Phillips
E
E
Thacker
J
J
Meuth
M
M
D000818:Animals; D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects; D001549:Benzamides / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000096:biosynthesis / Q000528:radiation effects; D004249:DNA Damage; D004261:DNA Replication / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D010641:Phenotype; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000502:physiology; D011836:Radiation Tolerance / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D001549:Benzamides; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011838:Radiation-Sensitizing Agents; D005047:Etoposide; C025160:3-aminobenzamide; D004247:DNA; D011065:Poly(ADP-ribose) Polymerases; D002166:Camptothecin