Assembly of functional ALT-associated promyelocytic leukemia bodies requires Nijmegen Breakage Syndrome 1.
Immortalized cells maintain telomere length through either a telomerase-dependent process or a telomerase-independent pathway termed alternative lengthening of telomeres (ALT). Homologous recombination is implicated in the ALT pathway in both yeast and human ALT cells. In ALT cells, two types of DNA double-strand break repair and homologous recombination factors, the Rad50/Mre11/NBS1 complex and Rad51/Rad52 along with replication factors (RPA) and telomere binding proteins (TRF1 and TRF2), are associated with the ALT-associated PML body (APB). DNA synthesis in late S-G(2) is associated with APBs, which contain telomeric DNA and, are therefore, potential sites for telomere length maintenance. Here, we show that the breast cancer susceptibility gene product, breast cancer susceptibility gene 1, and the human homologue of yeast Rap1, hRap1, are also associated with APBs specifically during late S-G(2) phase of the cell cycle. We additionally show that the localization of the double-strand break repair factors with APBs is distinct from their association with ionizing radiation-induced nuclear foci. To systematically explore the mechanism involved in the assembly of APBs, we examine the role of Nijmegen breakage syndrome 1 (NBS1) and TRF1 in this process, respectively. We demonstrated that NBS1 plays a key role in the assembly and/or recruitment of Rad50, Mre11, and breast cancer susceptibility gene 1, but not Rad51 or TRF1, to APBs. The NH(2) terminus of NBS1, specifically the BRCA1 COOH-terminal domain, is required for this activity. Although TRF1 interacts with NBS1 directly, it is dispensable for the association of either Rad50/Mre11/NBS1 or Rad51 with APBs. Perturbation of the interactions between NBS1/Mre11 and APBs correlates with reduced BrdUrd incorporation associated with APBs, consistent with decreased DNA synthesis at these sites. Taken together, these results support a model in which NBS1 has a vital role in the assembly of APBs, which function to maintain telomeres in human ALT cells.
Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245, USA.
Guikai
G
Wu
Xianzhi
X
Jiang
Wen-Hwa
WH
Lee
Phang-Lang
PL
Chen
D017766:Acid Anhydride Hydrolases; D019313:BRCA1 Protein / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D000076228:MRE11 Homologue Protein; D009687:Nuclear Proteins / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism / Q000648:ultrastructure; D016615:Telomere / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000378:metabolism; D014407:Tumor Cells, Cultured; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D035321:Telomeric Repeat Binding Protein 1; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D020827:rap1 GTP-Binding Proteins; D045643:DNA Repair Enzymes