Skewed somatic X inactivation (XCI), X-linked gene overexpression and abnormal X
content have been associated with breast and ovarian cancer. Partial or complete
reactivation of the inactive X in females may be a step in breast and ovarian cancer
progression, leading to overexpression of some tumour enhancing gene. Markers of an X
reactivation event were examined: X gene dosage, expression, and methylation in 8
ovarian cancer cell lines. Another marker of an X reactivation event, skewed XCI, was
assayed in peripheral blood DNA from 106 breast and/or ovarian cancer patients (52
BRCA1 mutation carriers, 24 BRCA2 mutation carriers, 30 non-mutation carriers), 147
age-matched population controls. Combined RNA/DNA FISH was used to quantify the
number of inactive Xs compared to total number of Xs. Five cell lines had increased X
content. Three cell lines localized XIST to the presumptive inactive X; however the
numbers of inactive Xs were variable. Expression levels of 8 X-linked genes were
assessed by real-time PCR. Expression was inconsistent between different genes and
among cell lines, ranging from a 2 to 300-fold increase compared to a control. Overall,
expression was greatly increased for genes subject to inactivation but not increased in
genes that escape inactivation for most ovarian cancer cell lines. Methylation at AR and FMR1 was quantified by a real-time PCR based assay and SNuPE respectively.
Methylation was lower than expected for 7 of 8 ovarian cancer cell lines at AR or FMR1,
while three cell lines had low or no methylation for both genes. Skewed XCI was
evaluated using a methylation-based PCR assay at AR. There was no significant increase in skewing above 90% for any cancer group assayed. In addition, two markers of X reactivation were assayed in two low passage cultures of normal ovarian surface epithelium from BRCA1 mutation positive breast cancer patients. One sample did not
localize XIST to the inactive X and three of five genes subject to inactivation were
overexpressed. In summary, there is evidence for loss of X silencing or gain of active X
content in ovarian cancer cell lines and normal ovarian surface epithelium from BRCA1
mutation carriers.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/212 |
| Date | 05 1900 |
| Creators | Harbord, Sara Helen Alison |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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