The goal of this project was to address whether the stem cell and cancer stem cell marker CD133 plays a role in the development of hormone-resistant prostate cancer. We have stably expressed CD133 in a series of prostate cancer cell lines, and stable surface expression has been documented using western blotting and flow cytometry. Our ongoing in vitro characterization suggests that CD133 expression may promote cell growth, and we are actively testing whether CD133 expression promotes cell colonogenicity and androgen-resistance. Using the cells and tumor tissue from our first Aim, we are currently working with the University of Chicago Immunohistochemistry core to develop a reliable and robust staining protocol for CD133 using appropriate controls. We have also obtained and scanned six prostate tissue microarrays so that when a staining protocol is ready we can stain and analyze. In short, the work is progressing as anticipated and no major scientific obstacles have been encountered which require revision of the work proposed. Our work has shown and will move forward to document that the stem cell gene CD133 functions to promote prostate cancer cell growth. We are now engaged in testing whether CD133 expression modulates prostate cancer cell responses to androgen regulation. We are excited about the work as it is progressing and anticipate having ample data for future proposals and publications.