Background. B-lymphoma Moloney murine leukemia virus insertion region-1 (Bmi-1) acts as an oncogene in various cancer such as non-small cell lung cancer, colon cancer, gastric cancer, bladder cancer and nasopharyngeal cancer (NPC). / Methods. Immunohistochemistry was performed to evaluate Bmi-1 expression in 252 breast cancer samples. The correlations were analyzed between Bmi-1 expression and clinicopathologic parameters, including age, tumor size, lymph nodal involvement, distant metastasis, clinical stages, hormone receptor (ER, PR) and Human Epidermal Growth Factor Receptor 2 (HER-2). The overall survivals were compared by Kaplan-Meier analysis based on Bmi-1 expression. / Results. Bmi-1 expression was significantly increased in primary cancer tissues than in matched adjacent non-cancerous tissues ( P<0.001). Only 35.9% (14 of 39) of adjacent non-cancerous tissues displayed high expression compared with 72.2% (182 of 252) in primary cancer tissues. Among adjacent non-cancerous tissues, no Bmi-1 staining signal was detected in 30.8% (12 in 39) samples. Only 28.2% (11 in 39) samples showed nucleus staining and the remaining 41.0% (16 in 39) samples exhibited cytoplasm staining. Of those cancer tissues, however, 75.4% (190 in 252) was stained in the nucleus and 24.6% (62 in 252) located in the cytoplasm. The elevated Bmi-1 expression was correlated with advanced clinicopathologic classifications (T, N, M) and clinical stages (P<0.001, respectively). A high level of Bmi-1 expression displayed unfavorable overall survival ( P<0.001). The overall survival rate, assessed by the Kaplan-Meier method, was 85.1% (57 in 67) in low Bmi-1 expression group, whereas it was only 59.9% (103 in 172) in high Bmi-1 expression group. In addition, Bmi-1 serves as a high risk for breast cancer and the relative risk increased almost four fold in patients with high Bmi-1 expression compared with that with low Bmi-1 expression by univariate Cox regression analyses. After the adjustment of the confounding factors, Bmi-1 was still found to predict the poor survival (P=0.042), which indicated Bmi-1 was an independent prognostic factor. The overexpression of Bmi-1 increased the mobility and invasiveness in 76N-TERT and MCF-10A, concurrent EMT-like molecular changes, the stabilization of Snail protein and the activation of Akt/GSK3beta pathway. Consistent with these observations, the repression of Bmi-1 in MDA-MB-435S remarkably attenuated the cellular mobility, invasiveness and transformation, as well as tumorigenesis and spontaneous lung metastases in nude mice. In addition, the repression of Bmi-1 reversed the EMT markers and inhibited the Akt/GSK3beta/Snail pathway. However, ectopic Bmi-1 alone was not able to lead to the phenotype of HMECs. Additionally, discordant mRNA expression levels of Bmi-1 and E-cadherin were detected between primary cancer tissues and matched adjacent non-cancerous tissues. The mRNA level of Bmi-1 was strongly up-regulated in breast cancer tissues compared with paired non-cancerous tissues ( P=0.001), whereas the mRNA level of E-cadherin was markedly down-regulated (P=0.042). Furthermore, there was a converse correlation between Bmi-1 and E-cadherin expression at the transcriptional level ( P=0.041). (Abstract shortened by UMI.) / Guo, Baohong. / Adviser: Kung, Hsiang Fu. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 161-183). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

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Self-renewal is central to the expansion of normal and cancerous stem cells. Its understanding is therefore critical for future advances in transplantation-based therapies and cancer treatment. Although the molecular machinery controlling stem cell self-renewal remains poorly defined, a number of genes important to this process have recently been identified. Two prominent genes in this group are Hoxb4 and Bmi1. Members of our group led the way to demonstrate important regulatory functions of these genes in hematopoietic stem cell (HSC) self-renewal and expansion. / The major goal of my thesis project is to dissect mechanisms that regulate self-renewal of HSCs. Our starting hypothesis was that HSC activity is regulated by complementary and independent self-renewal mechanisms: self-renewal of expansion and self-renewal of maintenance (Chapters 1-2). In order to further verify this theory, we have analyzed the genetic interaction between Hoxb4 and Bmi1. While Hoxb4 overexpression triggers HSC expansion, Bmi1 proper expression is essential to sustain long-term stem cell activity. We have also demonstrated that Hoxb4 and Bmi1 regulate distinct gene targets, likely suggesting a complementary and independent function for these two regulators in HSC activity (Chapter 3). / The second part of this thesis highlights efforts that were made in order to get a better understanding of self-renewal mechanisms. We have identified potential new regulators of stem cell activity by characterizing a stem cell leukemia population (Chapter 4) and by assessing the expression of asymmetrical distributed factors (Chapter 5) and selected nuclear factors of the Hematopoietic Stem Cell Nuclear Factor Database (Chapter 6) in stem cell-enriched sub-fractions. / This project will lead to a better understanding of the cellular basis regulating self-renewal of both normal and cancer stem cells and potentially to the future identification of new self-renewal determinants.