Molecular and cellular mechanisms of prostate cancer cell transendothelial migration and metastasis

Prostate cancer is the second leading cause of death in men in the United States. Mortality in these patients is not due to primary tumor growth, but rather from complications caused by metastasis to other organs. A step within metastasis, extravasation, involves cell lodgment or adherence in the microvasculature and subsequent migration of those cells across the endothelium into a secondary organ site, though, the molecular and cellular mechanisms remain largely obscure. The development of in vitro and in vivo models to recapitulate extravasation and metastatic disease are crucial for our understanding of this process. In vivo, we employed bioluminescence imaging to serially image the growth and distribution of a prostate cancer cell line, 22Rv1, after intracardiac injection. Tumors colonized multiple organ sites including bone, liver, and adrenal glands resembling the spectrum of prostatic metastases seen in patient autopsies. Using this model, we investigated the role of tumor derived endothelin-1 (ET-1) in prostate cancer metastasis by RNA interference knockdown in 22Rv1 cells and by administering pharmacological inhibitors of the endothelin receptors. Metastatic colonization and growth was significantly reduced after these treatments, but results were inconsistent. Further studies on the role of ET-1 in prostate cancer metastasis are warranted.;In an effort to mimic extravasation in vitro, we analyzed the transendothelial migration of PC-3 prostate cancer cells. We isolated a subpopulation of cells, TEM4-18, that crossed an endothelial barrier more efficiently, but were less migratory than parental PC-3 cells in other contexts. TEM4-18 cells were highly aggressive in vivo and exhibited characteristic molecular markers of an epithelial to mesenchymal transition (EMT), including upregulation of ZEB 1 and downregulation of integrin beta4 and laminin332. Silencing ZEB 1 in TEM4-18 cells resulted in reduced transendothelial migration and upregulation of laminin332 and integrin beta4. Further, exogenously supplied laminin332 restored TEM4-18 cell migration. Taken together, the data indicates that a mesenchymal phenotype facilitates transendothelial migration and suggests that EMT may underlie prostate cancer cell extravasation. Further, loss of laminin332 associated with the EMT phenotype suggests that this factor must be supplied by other cells in the tumor microenvironment to fully elaborate invasive potential of these cells.