title: Depletion of Ku70/80 reduces the levels of extrachromosomal telomeric circles and inhibits proliferation of ALT cells.
abstract: In normal cells, telomeres shorten each time a cell divides ultimately resulting in cell senescence. In contrast, cancer cells counteract the loss of telomeric DNA either by inducing the expression of telomerase or by activating the alternative lengthening of telomeres (ALT) pathway. ALT cells are characterized by heterogeneous telomeres and the presence of extrachromosomal circular double-stranded DNA molecules containing telomeric repeat sequences. These telomeric circles (t-circles) are though to be generated through a recombination process and utilized as templates for telomere elongation by rolling-circle-replication, although their precise mechanism of formation and role in telomere maintenance and cell proliferation is largely unknown. Here we show that shRNA-mediated knockdown of the Ku70/80 heterodimer, a factor with functions at both pathological and natural DNA ends, inhibits ALT cell growth and results in a significant decrease in the levels of t-circles without affecting overall telomere length. These findings demonstrate that non homology-based processes contribute to the maintenance of t-circles and proliferation of ALT cells.
authors.affiliation: Department of Molecular Microbiology and Immunology, Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Baomin
authors.initials: B
authors.lastname: Li
authors.forename: Sita
authors.initials: S
authors.lastname: Reddy
authors.forename: Lucio
authors.initials: L
authors.lastname: Comai
mesh_terms: D034961:Antigens, Nuclear / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation; D016922:Cellular Senescence / Q000235:genetics; D004270:DNA, Circular / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D000072200:Ku Autoantigen; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D000071657:Werner Syndrome Helicase
chemical_list: D034961:Antigens, Nuclear; D004270:DNA, Circular; D004268:DNA-Binding Proteins; D021122:Protein Subunits; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D049452:Green Fluorescent Proteins; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen