Association of BLM and BRCA1 during Telomere Maintenance in ALT Cells

• Published in: PloS one Vol. 9; no. 8; p. e103819
• Main Authors: Acharya, Samir, Kaul, Zeenia, Gocha, April Sandy, Martinez, Alaina R, Harris, Julia, Parvin, Jeffrey D, Groden, Joanna
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.08.2014; Public Library of Science (PLoS)
• Subjects: Biology and Life Sciences; Bloom's syndrome; Blotting, Western; BRCA1 protein; BRCA1 Protein - genetics; BRCA1 Protein - metabolism; Breast cancer; Cell cycle; Cell Cycle - genetics; Cell Cycle - physiology; Cell Line, Tumor; Cells (Biology); Chromosomes; Deoxyribonucleic acid; DNA; DNA damage; DNA helicase; DNA repair; DNA Repair - genetics; DNA Repair - physiology; Fluorescent Antibody Technique; Genetic recombination; Genomes; HeLa Cells; Homologous recombination; Homology; Humans; Immunology; Immunoprecipitation; Maintenance; Mammals; Medicine; Metabolism; Physiological aspects; Proteins; RecQ Helicases - genetics; RecQ Helicases - metabolism; Repair; Research and Analysis Methods; RNA polymerase; RNA, Small Interfering; Substrates; Surveillance; Telomerase; Telomere Homeostasis - genetics; Telomere Homeostasis - physiology; Telomeres; Tumor suppressor genes; Tumors; Unwinding; Virology; Yeast; United States > US; Ohio
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0103819

Fifteen percent of tumors utilize recombination-based alternative lengthening of telomeres (ALT) to maintain telomeres. The mechanisms underlying ALT are unclear but involve several proteins involved in homologous recombination including the BLM helicase, mutated in Bloom's syndrome, and the BRCA1 tumor suppressor. Cells deficient in either BLM or BRCA1 have phenotypes consistent with telomere dysfunction. Although BLM associates with numerous DNA damage repair proteins including BRCA1 during DNA repair, the functional consequences of BLM-BRCA1 association in telomere maintenance are not completely understood. Our earlier work showed the involvement of BRCA1 in different mechanisms of ALT, and telomere shortening upon loss of BLM in ALT cells. In order to delineate their roles in telomere maintenance, we studied their association in telomere metabolism in cells using ALT. This work shows that BLM and BRCA1 co-localize with RAD50 at telomeres during S- and G2-phases of the cell cycle in immortalized human cells using ALT but not in cells using telomerase to maintain telomeres. Co-immunoprecipitation of BRCA1 and BLM is enhanced in ALT cells at G2. Furthermore, BRCA1 and BLM interact with RAD50 predominantly in S- and G2-phases, respectively. Biochemical assays demonstrate that full-length BRCA1 increases the unwinding rate of BLM three-fold in assays using a DNA substrate that models a forked structure composed of telomeric repeats. Our results suggest that BRCA1 participates in ALT through its interactions with RAD50 and BLM.