BRCA1 localization to the telomere and its loss from the telomere in response to DNA damage.
BRCA1, a tumor suppressor, participates in DNA damage signaling and repair. Previously, we showed that BRCA1 overexpression caused inhibition of telomerase activity and telomere shortening in breast and prostate cancer cells. We now report that BRCA1 knockdown causes increased telomerase reverse transcriptase expression, telomerase activity, and telomere length; but studies utilizing a combination of BRCA1 and telomerase reverse transcriptase small interfering RNAs suggest that BRCA1 also regulates telomere length independently of telomerase. Using telomeric chromatin immunoprecipitation assays, we detected BRCA1 at the telomere and demonstrated time-dependent loss of BRCA1 from the telomere following DNA damage. Further studies suggest that BRCA1 interacts with TRF1 and TRF2 in a DNA-dependent manner and that some of the nuclear BRCA1 colocalizes with TRF1/2. Our findings further suggest that Rad50 is required to localize BRCA1 at the telomere and that the association of BRCA1 with Rad50 does not require DNA. Finally, we found that BRCA1 regulates the length of the 3' G-rich overhang in a manner that is dependent upon Rad50. Our findings suggest that BRCA1 is recruited to the telomere in a Rad50-dependent manner and that BRCA1 may regulate telomere length and stability, in part through its presence at the telomere.
Department of Biochemistry and Molecular and Cellular Biology, Washington, D. C. 20057.
Rahul D
RD
Ballal
Department of Oncology, Georgetown University School of Medicine, Washington, D. C. 20057.
Tapas
T
Saha
Department of Oncology, Georgetown University School of Medicine, Washington, D. C. 20057.
Saijun
S
Fan
Department of Oncology, Georgetown University School of Medicine, Washington, D. C. 20057.
Bassam R
BR
Haddad
Department of Biochemistry and Molecular and Cellular Biology, Washington, D. C. 20057; Department of Oncology, Georgetown University School of Medicine, Washington, D. C. 20057. Electronic address: emr36@georgetown.edu.
Eliot M
EM
Rosen
D017766:Acid Anhydride Hydrolases; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004249:DNA Damage; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D055785:Gene Knockdown Techniques; D006801:Humans; D034741:RNA, Small Interfering; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000235:genetics; D035321:Telomeric Repeat Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D035341:Telomeric Repeat Binding Protein 2 / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; C504753:TERF2 protein, human; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; C509186:TERT protein, human; D019098:Telomerase; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes