Morphogenesis of giant telomeric nuclear bodies in cancer cells with alternative lengthening of telomeres

Abstract

Some cancer cells lengthen their telomeres by alternative lengthening of telomeres (ALT); these are referred to as ALT cancer cells and do not express telomerase. The ALT mechanism involves the elongation of telomeric DNA repeats by homologous recombination. In interphase nuclei of ALT cancer cells, giant telomeres can be specifically observed by fluorescence in situ hybridization (FISH) to detect telomeric repeats, and they are co-localized with promyelocytic-leukemia nuclear-bodies (PML-NBs). However, it how large telomeres specific to ALT and how they form a structural relation with PML-NBs. We refer to giant telomeres specific to interphase ALT cancer cells giant-telomeric nuclear-bodies (GT-NBs). To quantitatively define GT-NBs, we performed telomeric FISH of both interphase nuclei and metaphase chromosomes and analyzed telomere sizes by integrated FISH signals. The distributions of telomere sizes in telomerase-positive cells were similar in interphase nuclei and chromosomes. However, the distribution of telomere sizes in ALT cancer cells differed between interphase nuclei and chromosomes. Giant telomeres that were larger than those at chromosomal ends were only observed in interphase nuclei of ALT cancer cells. Accordingly, GT-NBs could be quantitatively defined as larger than the maximum size of telomeres at chromosomal ends. Furthermore, ALT cancer cells demonstrated fewer telomeric signals in interphase nuclei than in chromosomes. These findings indicate that GT-NBs could be formed by the aggregation of two or more telomeres at chromosomal ends. Furthermore, super-resolution microscopy showed that GT-NBs contain one or two PML-NBs. GT-NBs are considered aggregates of telomeres and could contain multiple sites of homologous recombination accompanied by PML-NBs. These findings may contribute to the development of therapeutic approaches for ALT cancer. (251 words)