title: Association of BLM and BRCA1 during Telomere Maintenance in ALT Cells.
abstract: 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.
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Samir
authors.initials: S
authors.lastname: Acharya
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Zeenia
authors.initials: Z
authors.lastname: Kaul
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: April Sandy
authors.initials: AS
authors.lastname: Gocha
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Alaina R
authors.initials: AR
authors.lastname: Martinez
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Julia
authors.initials: J
authors.lastname: Harris
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Parvin
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Joanna
authors.initials: J
authors.lastname: Groden
mesh_terms: D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D004260:DNA Repair / Q000235:genetics / Q000502:physiology; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D034741:RNA, Small Interfering; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism*; D059505:Telomere Homeostasis / Q000235:genetics / Q000502:physiology*
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D034741:RNA, Small Interfering; C097151:Bloom syndrome protein; D053484:RecQ Helicases
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