CSIG-32. RECURRENT ACROCENTRIC TRANSLOCATIONS AND ANAPHASE BRIDGES ARE AN EARLY PHENOTYPE OF PRE-CANCEROUS ASTROCYTES WITH DYSFUNCTIONAL TELOMERES

Abstract Genomic stability in human cells relies on intact p53 and pRb cell cycle checkpoints. Their suppression can lead to telomere dysfunction (TD) and genomic instability, which is a characteristic feature of many cancers, including diffuse glioma. To investigate the genomic evolution of otherwise normal astrocytes undergoing TD, we transduced normal human astrocyte (NHA) cells with retroviruses containing the viral HPV-18 E6/E7 oncoproteins and cultured them over extended periods of time. Immunofluorescence microscopy was used to detect mitotic abnormalities and demonstrated anaphase bridges in a sizable proportion of NHA-E6E7 cells (n = 47/99, 47.5%) when compared to un-transduced NHA cells (n = 0/25, 0%), confirming ongoing TD. Using multiplexed fluorescence in situ hybridization (M-FISH) to characterize large-scale chromosomal abnormalities, we observed t(2;13)(q32.2;q21.1) in n = 20/30 (66.7%) of transduced cells from a bulk NHA-E6E7 clone. Furthermore, one copy of chromosome 13 was either truncated or deleted in all cells (n = 30/30, 100%). Surprisingly, the acrocentric chromosomes 13, 14, 15, 21 and 22 appeared to be especially prone to cytogenetic abnormalities, with the per chromosome average aberration counts being 2.83 folds higher in acrocentric chromosomes when comparing to other chromosomes. This observation potentially explains the central nuclear clustering of the short arms of the acrocentric chromosomes into the nucleolus. Unexpectedly, the frequency of t(2;13)(q32.2;q21.1) translocations decreased in later passages, suggesting that this event was detrimental to cell survival. Consistent with that observation, the FISH-confirmed t(2;13)(q32.2;q21.1) abnormality was not strongly supported by long-read DNA sequencing, indicating that it is a large-scale transient event occurring sporadically in individual cells. These findings underscore the critical role of p53 and pRb-mediated pathways in maintaining genomic integrity and suggest that recurrent acrocentric translocations and mitotic abnormalities are key phenotypic manifestations of telomere dysfunction and genomic instability in early glioma genesis.