Abstract
Abstract The promyelocytic leukemia protein (PML) is tightly associated with a defining feature of the cancer specific, telomerase-independent telomere-maintenance pathway known as alternative lengthening of telomeres (ALT); therefore, PML is an important potential target for chemotherapeutics. Cells running ALT contain large accumulations of telomeric DNA and RNA in the nucleoplasm that are frequently coated in a polymer shell of PML protein. These structures are known as ALT-associated PML bodies (APBs). APBs have been postulated to be major sites of the telomeric sequence homologous recombination believed to be the basis of telomere maintenance in ALT. A CRISPR based strategy was used to knock out the PML gene in two widely used ALT positive osteosarcoma-derived human cell lines; U2OS, and SAOS2. Knockout clones from both cell lines continued to proliferate past passage 90 without crisis, and knockouts were validated at the genetic and protein levels by Sanger sequencing and western blotting, respectively. Chromosome orientation fluorescent in situ hybridization (COFISH) was carried out to determine the number of telomere sequence exchanges occurring in a single cell cycle in these knockouts. A twofold increase in telomere-specific exchanges, presumably telomere sister chromatid exchanges (T-SCE), over the parental line was detected. Intrachromosomal exchanges not specific to telomeres were also analyzed by the harlequin chromosome staining method. A significant increase in these types of exchanges was also observed. In conclusion, the presence of PML is not required for ALT to continue to function, and may be acting to modulate homologous recombination frequency and location in ALT positive cells. Citation Format: Walter Barry, Christopher Heaphy, Alan Meeker. The promyelocytic leukemia (PML) protein modulates rate and localization of homologous recombination in human cell lines with the alternative lengthening of telomeres (ALT) pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3470. doi:10.1158/1538-7445.AM2017-3470
Published Version
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