The function and regulation of CD133 in human prostate cancer.

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Bibliographic Details
Author / Creator:Reyes, Edwin Ernesto.
Description:114 p.
Format: E-Resource Dissertations
Local Note:School code: 0330.
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Other authors / contributors:University of Chicago.
Notes:Advisor: Donald J. Vander Griend.
Thesis (Ph.D.)--The University of Chicago, Division of the Biological Sciences, and The Pritzker School of Medicine, Committee on Immunology, 2015.
Dissertation Abstracts International, Volume: 76-08(E), Section: B.
Summary:Many current therapies for metastatic castration-resistant prostate cancer (mCRPC) are aimed at AR signaling; however, resistance to these therapies is inevitable. To personalize CRPC therapy in an individual with clinical progression despite maximal AR signaling blockade, it is important to characterize the status of AR activity within their cancer. Biopsies of bone metastases are invasive and frequently fail to yield sufficient tissue for further study. Evaluation of circulating tumor cells (CTCs) offers an alternative, minimally invasive mechanism to characterize and study late-stage disease. The goal of our "quantitative characterization of androgen receptor protein expression and cellular localization in circulating tumor cells from patients with metastatic castration-resistant prostate cancer" study was to evaluate the utility of CTC interrogation with respect to the AR as a potential novel therapeutic biomarker in patients with mCRPC. We found inter-patient and intra-patient heterogeneity in expression and localization of AR. Increased AR expression and nuclear localization are associated with elevated co-expression of Ki-67, consistent with the continued role for AR in castration-resistant disease. Despite intra-patient heterogeneity, CTCs from patients with prior exposure to abiraterone had increased AR expression compared to CTCs from patients who were abiraterone-naive. Our ability to evaluate AR expression and function within tumor samples from patients with late-stage disease will likely be a critical component of the personalized management of advanced prostate cancer. Our study supports a molecularly diverse AR-centric pathobiology imparting castration-resistance.
We were also interested in studying non-AR markers that are associated with failure to AR-targeted therapies. The role of stem cells and cancer stem cells in mCRPC is an emerging idea that is implicated in disease progression. In the adult human prostate, CD133 (PROM1) expression is thought to mark rare prostate epithelial stem cells and malignant tumor stem/initiating cells. The goal of our "Growth kinetics of CD133-positive prostate cancer cells" study was two-fold: 1) to determine the growth conditions that led to changes in CD133 expression and proliferation, and 2) to determine if CD133 regulated these changes. Our results showed that the cell cycle distribution differs between CD133pos and CD133neg cells in all three human prostate cancer cell lines studied. CD133pos cells have a greater proportion of cells in G2 and proliferate faster than CD133neg cells. High cell density increases the percentage of CD133pos cells without changing CD133pos cell cycle progression. Treatment with the AR agonist R1881, or the anti-androgen MDV3100, significantly changed the percentage and proliferation of CD133pos cells. Finally, ectopic over-expression of CD133 had no effect on cell cycle progression. Contrary to our hypothesis, we demonstrated that CD133pos cells proliferate faster than CD133neg cells. This association of CD133 expression with increased cell proliferation is not directly mediated by CD133, suggesting that surface CD133 is a downstream target gene of an undefined pathway controlling cell proliferation.
Because we demonstrated that CD133 is associated with a more proliferative phenotype, the aim of our "increased proliferation in CD133-high circulating tumor cells from patients with metastatic castration-resistant prostate cancer" study was to determine if CD133 was associated with increased proliferation or changes in the androgen receptor (AR) expression or co-localization with the nucleus in CTCs from patients with mCRPC. We utilized ImageStreamX technology to capture and analyze CTCs for various markers associated with proliferation, including CD133, Ki-67, and the AR. Eighty-seven percent (24/31) of patient samples contain CTC that stain positive for CD133, and on average, 40.6% of presumptive CTCs are CD133-high (CD133high). Interestingly, CD133high CTCs have more Ki-67 protein expression compared to CD133-low (CD133low) CTCs, suggesting that CD133 high CTCs are more proliferative compared to their CD133low counterparts. Importantly, CD133high and CD133 low CTCs have similar levels of AR protein expression and cellular co-localization with the nucleus, implying that CD133 is an AR-independent marker of mCRPC proliferation. Our results suggested that CD133 or AR was not responsible for the cell proliferation phenotype in vitro or in CTCs, respectively. Before answering what is causing the CD133pos cells to be more proliferative, we wanted to discern the regulation of CD133 expression. Thus, we utilized a bioinformatics discovery approach.
Our results suggest that CD133 expression in patient tumors is associated with genes controlling cell proliferation. Single protein analysis of network (SPAN) identified that HOXA10 was amongst four genes implicated as potential mediators of CD133 expression. And our preliminary in vitro data suggests that over-expression of HOXA10 is sufficient to increase CD133 protein level. Thus, we hypothesize that CD133 itself may not play an active role in prostate cancer cell proliferation and pathogenesis; instead, CD133 may be up-regulated by HOXA10, a gene controlling proliferation