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(PP369) Background expression of phosphorylated histone H2AX in tumor cells in relation to DNA double strand breaks and karyotypic complexity.
Yu, Ying*,1, Banath, Judit1, MacPhail, Susan1, Olive, Peggy 1, 1 Medical Biophysics Dept., Vancouver, BC, Canada
ABSTRACT- Introduction: Microscopically visible H2AX foci signify individual DNA double strand breaks in X-irradiated cells. However, background or cryptogenic foci are also observed in untreated tumor cells which reduces sensitivity for detecting radiation damage. The goal was to determine the biological relevance of these background foci. Results: To determine if background foci signify double-strand breaks, SW756 and C33A cervical cancer cell lines expressing high (50) or low (5) foci/cell were compared for the differences in DNA breaks. No significant differences were observed using the neutral comet assay. Moreover, 10 cloned lines generated from the SW756 cell line also expressed a high H2AX background indicating that this pattern was inherited. As untreated tumor cell lines typically show higher expression of H2AX than normal cells, the possibility was examined that a high background level of H2AX might be associated with genome instability. Using a series of isogenic SKOV3 cell lines that varied in TP53 status, the H2AX background was significantly higher in TP53 mutant cells compared to wild type cells consistent with the importance of TP53 in maintaining genome stability. Furthermore, for 17 cell lines selected from the NCI drug screening panel that were previously characterized for karyotypic alterations, there was a trend for cells with greater numbers of chromosomal alterations (including increases in chromosome numbers and translocations) to show a higher background H2AX level. Conclusions: Taken together, these results suggest that background H2AX foci do not always signify DNA breaks, and for some tumor cell lines, chromosomal alterations associated with genomic instability may contribute to this background.
Key words: H2AX, genomic instability, DNA double-strand breaks
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