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MOLECULAR AND PHENOTYPIC CHARACTERIZATION OF DISTINCT BREAST CANCER CELL SUBPOPULATIONS PURIFIED USING A SOX2 REGULATORY REGION 2 TRANSCRIPTION ACTIVITY REPORTER
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- Author / Creator
- Jung, Karen KT
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Sex-determining Region Y-box 2 (Sox2) is a transcription factor integral to the maintenance of pluripotency in embryonic stem cells. In recent years, Sox2 expression has been detected and implicated in the pathogenesis of breast and other cancers. Clinically, Sox2 expression has been associated with higher tumour grade, tumour size, lymph node metastases, tamoxifen resistance, disease recurrence, and poor overall survival in breast cancer (BC) patients. Many studies have focused on Sox2 as a marker of enhanced tumourigenic capacity and stem cell-like features in heterogeneous tumour cell subpopulations but little is known about its functional role or transcription activity in tumour cells. Our group has recently identified in estrogen receptor-positive (ER+) BC cells, two phenotypically distinct BC cell subsets separated based on their differential activation of Sox2 regulatory region 2 (SRR2) enhancer transcription activity reporter, the reporter-unresponsive (RU) and the more tumorigenic reporter-responsive (RR) cells. We hypothesize that the cell subsets purified by the SRR2 reporter will exhibit distinct molecular mechanisms underlying their differential phenotypes. Firstly, we show that Y-box binding protein-1 (YB-1), another oncogenic transcription factor, negatively regulates Sox2 expression in ER+ RU and RR cells. Consequentially, loss of YB-1 induced increased Sox2 activity only in the RR cells, providing the RR cells with the unique ability to maintain tumourigenic capacity in the absence of YB-1. Secondly, using chromatin immunoprecipitation and a human genome-wide promoter microarray chip (ChIP-chip), we found a largely mutually exclusive profile of gene promoters bound by Sox2 in the ER+ RU and RR cells. Sox2 was bound to 1830 and 456 unique gene promoters in the RU and RR cells respectively, with only 62 overlapping gene promoters. Intriguingly, Sox2 was bound to many stem cell- and cancer-associated genes only in RR cells, mediating the enhanced stem-like, tumourigenic phenotype in RR cells. Thirdly, we observed that triple negative breast cancer (TNBC) cells also exhibited heterogeneous activation of the SRR2 reporter and were comprised of RU and RR cell subsets. Similar to the ER+ BC cells, RR cells showed enhanced tumourigenic capacity in vitro and in vivo, particularly within the CD44High/CD24- TNBC cells. Unlike ER+ cells, however, Sox2 was not a major contributor to the SRR2 activity. Fourthly, we discovered that Myc is a novel transcriptional activator the SRR2 reporter in the RR TNBC cells, and contributes to the RR stem-like, tumourigenic phenotype, providing a therapeutic opportunity. Taken together, ER+ and ER- BC cells exhibit heterogeneous response to the SRR2 enhancer reporter, and the SRR2 reporter is an invaluable tool to distinguish cells with differential tumourigenic properties and distinct Sox2 and Myc molecular mechanisms that can be exploited for novel targeted therapies in the treatment of BC patients.
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- Graduation date
- Fall 2015
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.