New role for nuclear hormone receptors and coactivators in regulation of BRCA1-mediated DNA repair in breast cancer cell lines.
BACKGROUND
The breast cancer susceptibility gene BRCA1 is involved in the repair of double-strand breaks induced by ionizing radiation and chemotherapy drugs. BRCA1 interacts with coactivators such as p300 and CREB-binding protein (CBP) to activate target gene transcription. Estrogen and retinoic acid receptors (ER and RAR) also require coactivator proteins for their ligand-dependent functions. Few studies have suggested a role for nuclear hormone receptors in DNA repair.


METHODS
DNA damage and repair activity were quantified with the use of single-cell gel electrophoresis and plasmid end-joining assays. Cell cycle progression and apoptosis were determined by bromodeoxyuridine and TdT-mediated dUTP nick end labelling assays. Stable transfection was accomplished with the lipofection procedure. Protein interaction and expression were determined by immunoprecipitation and western blotting.


RESULTS
17beta-estradiol (E2) and all-trans retinoic acid (RA) had opposing effects on DNA damage and breast cancer cell survival after double-strand break damage. Treatment with E2, but not with RA, resulted in complex formation between ERalpha, CBP, and BRCA1 in ER-positive cell lines. Mutant BRCA1 reduced the expression and activity of DNA damage repair proteins but did not block nuclear hormone-dependent effects. Mutant BRCA1 failed to form complexes with ERalpha and CBP, which correlated with its ability to exert E2-independent effects on DNA repair. Mutant BRCA1 inhibited cell cycle progression and produced increased survival in cells with double-strand breaks. Ectopic ERalpha expression reproduced the E2-mediated effects on DNA damage, repair, and survival.


CONCLUSIONS
The present study proposes a new mechanism by which ER and RAR regulate BRCA1-mediated DNA repair by means of CBP.
Crowe
David L
DL
Center for Craniofacial Molecular Biology, University of Southern California, 2250 Alcazar Street, Los Angeles, CA 90033, USA. dcrowe@usc.edu
Lee
Matt K
MK
D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D050882:CREB-Binding Protein / Q000502:physiology*; D002470:Cell Survival; D004249:DNA Damage; D004260:DNA Repair; D004958:Estradiol / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000502:physiology*; D005260:Female; D019398:Genes, BRCA1; D006801:Humans; D047468:Immunoprecipitation; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D047628:Estrogen Receptor alpha; D004958:Estradiol; D014212:Tretinoin; D050882:CREB-Binding Protein; C494363:CREBBP protein, human