Angiogenesis, Metastasis, and the Cellular Microenvironment Loss of TGF-b Responsiveness in Prostate Stromal Cells Alters Chemokine Levels and Facilitates the Development of Mixed Osteoblastic/Osteolytic Bone Lesions

Loss of TGF-b type II receptor (TbRII, encoded by Tgfbr2) expression in the prostate stroma contributes to prostate cancer initiation, progression, and invasion.We evaluated whether TbRII loss also affected prostate cancer bone metastatic growth. Immunohistologic analysis revealed that TbRII expression was lost in cancer-associated fibroblasts in human prostate cancer bone metastatic tissues. We recapitulated the human situation with a conditional stromal Tgfbr2 knockout (Tgfbr2-KO) mouse model. Conditioned media from primary cultured Tgfbr2-KOor control Tgfbr2-flox prostatic fibroblasts (koPFCMorwtPFCM, respectively) were applied toC4-2B prostate cancer cells before grafting the cells tibially.We found that koPFCMpromoted prostate cancer cell growth in the bone and development of early mixed osteoblastic/osteolytic bone lesions. Furthermore, the koPFCM promoted greater C4-2B adhesion to type-I collagen, themajor component of bonematrix, compared to wtPFCMtreated C4-2B. Cytokine antibody array analysis revealed that koPFCM had more than two-fold elevation in granulocyte colony-stimulating factor and CXCL1, CXCL16, and CXCL5 expression relative to wtPFCM. Interestingly, neutralizing antibodies of CXCL16 orCXCL1were able to reduce koPFCM-associatedC4-2B type-I collagen adhesion to that comparable with wtPFCM-mediated adhesion. Collectively, our data indicate that loss of TGF-b responsiveness in prostatic fibroblasts results in upregulation of CXCL16 and CXCL1 and that these paracrine signals increase prostate cancer cell adhesion in the bone matrix. These microenvironment changes at the primary tumor site can mediate early establishment of prostate cancer cells in the bone and support subsequent tumor development at the metastatic site. Mol Cancer Res; 1–10. 2012 AACR.