Bowman-Birk protease inhibitor activates DNA-dependent protein kinase and reduces formation of radiation-induced dicentric chromosomes.
OBJECTIVE
To test a stimulatory effect of the radioprotector Bowman Birk protease inhibitor (BBI) upon DNA repair processes.


METHODS
An effect of BBI upon DNA repair was investigated by quantification of radiation-induced dicentric chromosomes. Sensitivity to ionizing radiation was determined by clonogenic survival assay. Quantification of activity of the DNA-dependent kinase was performed by immunoprecipitation and phosphorylation of a TP53-derived peptide.


RESULTS
The formation of radiation-induced dicentric chromosomes was reduced significantly after pretreatment of cells with BBI. By using a cell line with an inducible expression of a mutated TP53, it was shown that the BBI-mediated reduction of dicentric chromosome formation depended on the presence of wild-type TP53. To get further insights into the molecular mode of action of BBI, activity of the DNA-dependent protein kinase (DNA-PK) was quantified. BBI treatment resulted in a stimulation of basal (DNA-PK) activity. In SCID mouse fibroblasts deficient in DNA-PK activity, BBI failed to reduce the amount of radiation-induced dicentric chromosomes and the radioprotective effect was absent. Likewise, cells expressing mt.TP53 did not show radioprotection by BBI.


CONCLUSIONS
It was observed that BBI exerts its radioprotective effect by a reduction of incorrect DNA repair, resulting in a reduced amount of dicentric chromosomes. This effect on the fidelity of DNA repair is TP53 dependent and correlated with induction of DNA-PK activity.
Dittmann
K
K
Section of Radiobiology and Environmental Research, Department of Radiation Oncology University of Tübingen Röntgenweg 11 D-72076 Tübingen Germany.
Virsik-Köpp
P
P
Mayer
C
C
Rave-Fränk
M
M
Rodemann
H P
HP
D002283:Carcinoma, Bronchogenic / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002869:Chromosome Aberrations / Q000187:drug effects*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D020536:Enzyme Activators / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000378:metabolism*; D011829:Radiation Dosage; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D016511:Severe Combined Immunodeficiency / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000378:metabolism*
D004268:DNA-Binding Proteins; D020536:Enzyme Activators; D011837:Radiation-Protective Agents; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D016159:Tumor Suppressor Protein p53; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases