Abstract 4888: The effect of chromatin structure in regulation of telomere length in telomerase negative ALT cells

Telomeres are DNA-protein complexes at the ends of linear eukaryotic chromosomes and composed of tandem repeats of a TTAGGG sequence ending in a 3′ single-stranded overhang, or the G-strand overhang. And telomeres confer chromosomal stability protecting chromosome ends. Most immortalized human cell lines maintain and extend their telomere by activating telomerase. A small number of cells maintain and extend their telomere lengths without telomerase by homologous recombination of telomeres and this mechanism is called as alternative lengthening of telomere (ALT). There are many factors involved in telomere regulation. Recently, it has been known that chromatin structure is closely related to regulation of telomere length. Maintaining telomere length is important process in tumorigenesis and it has been suggested that telomeres are important target for cancer therapy. However, in ALT cells the effect of chromatin structure on regulation of telomere length is not understood. In this study, we induced change of chromatin structure by treating Trichostatin A (TSA), Histone deacetylase inhibitor, in ALT cells. Then, we measured APBs (ALT associated PML bodies) patterns, T-SCE (Telomere Sister Chromatid Exchange) frequency and telomere lengths. APBs patterns were analyzed by FISH (Fluorescence in situ hybridization) combined IF (Immunofluorescence staining). We compared the number of APBs in ALT cells with or without TSA. In GM 847 (ALT cell), APBs positive cells were found to be more frequent in GM 847 with TSA (63/100) compared to GM 847 without TSA (30/100) (p