title: Molecular characterization of inter-telomere and intra-telomere mutations in human ALT cells.
abstract: Telomeres in most immortal cells are maintained by the enzyme telomerase, allowing cells to divide indefinitely. Some telomerase-negative tumors and immortal cell lines maintain long heterogeneous telomeres by the ALT (alternative lengthening of telomeres) mechanism; such tumors are expected to be resistant to anti-telomerase drug therapies. Occasionally telomerase-negative Saccharomyces cerevisiae mutants survive, and 10% of them (type II survivors) have unstable telomeres. As in human ALT+ cells, short telomeres in yeast type II survivors lengthen abruptly; in yeast, this is dependent on the recombination proteins Rad52p and Rad50p. In human cells, ALT involves copying of sequence from a donor to a recipient telomere. We have characterized for the first time a class of complex telomere mutations seen only in ALT+ cells. The mutant telomeres are defined by the replacement of the progenitor telomere at a discrete point (fusion point) with a different telomere repeat array. Among 19 characterized fusion points, one occurred within the first six repeats of the telomere, indicating that these recombination-like events can occur anywhere within the telomere. One mutant telomere may have been involved in a secondary recombination-like mutation event, suggesting that these mutations are sporadic but ongoing in ALT+ cells. We also identified simple intra-allelic mutations at high frequency, which evidently contribute to telomere instability in ALT+ cells.
authors.affiliation: Department of Genetics, University of Leicester, University Road, Leicester, LE1 7RH, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Varley
authors.forename: Hilda A
authors.initials: HA
authors.lastname: Pickett
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Foxon
authors.forename: Roger R
authors.initials: RR
authors.lastname: Reddel
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Royle
mesh_terms: D002460:Cell Line; D006801:Humans; D009154:Mutation; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D016615:Telomere