Research Summary: The mechanism by which the prostate cancer cells colonize the bone environment and develop resistance to prevent or treat prostate cancer bone metastasis is critical to increase the survival rate of advanced prostate cancer patients. Annexin A2 (AnxA2) protein is overexpressed in metastatic prostate tumors and promotes cell migration and invasion by activating plasminogen and cleaving extracellular matrix. AnxA2 plays a critical role in hematopoietic stem cell localization to the marrow niche. AnxA2 serves as an adhesion molecule and regulates osteogenic differentiation, yet the molecular mechanisms remain unclear. We hypothesize that PTEN loss or mutation causes the increased translocation of AnxA2 to the outer cell surface which promotes prostate tumor metastasis to bone. The rationale for this hypothesis is based on our findings that demonstrated the higher expression of cell surface AnxA2 in PTEN null or mutated prostate cancer cell lines compared to wild-type PTEN prostate cancer cell lines because of increased phosphorylation of AnxA2 at Tyr-23 in PTEN null or mutated prostate cancer cell lines. The goal of the proposed study is to establish the correlation between PTEN loss and increased cell surface expression of AnxA2 in prostate cancer. In addition, we will establish that AnxA2 is an important phenomenon for prostate tumor bone metastasis. The proposed work will enhance our understanding on the role of cell surface AnxA2 in prostate cancer bone metastasis and could potentially be used as an important therapeutic target. The proposed work will provide the stepping stones for the development of a novel targeted therapy that may translate into an effective treatment regimen against advanced prostate cancer.