Bone metastatic LNCaP-derivative C4-2B prostate cancer cell line mineralizes in vitro.

Prostate cancer frequently metastasizes to bone. However, unlike many other tumors that produce osteolytic lesions, prostate cancer produces osteoblastic lesions through unknown mechanisms. In the current study, we explored the ability and mechanism of an osteotropic prostate cancer cell line (C4-2B) to induce mineralization. C4-2B cells were grown in promineralization media. Mineral deposition was characterized using von Kossa staining, calcium retention, alizarin red staining, Raman spectroscopy, and electron microscopy. Expression of osteoblast-related proteins was determined by RT-PCR. The nuclear level of the bone-specific transcription factor Cbfa1 was determined using western analysis and the effect of inhibiting Cbfa1 function, using a "decoy" Cbfa1 response element oligo, on mineralization was determined. The studies demonstrated that C4-2B cells, but not its nonosteotropic parent cell line LNCaP, has an osteoblastlike phenotype including production of alkaline phosphatase, osteocalcin, osteonectin, bone sialoprotein, osteoprotegerin (OPG), and OPG ligand. Most importantly, the C4-2B cells produced hydroxyapatite mineral in vitro. Furthermore, C4-2B cells expressed high nuclear levels of the bone-specific transcription factor Cbfa1, compared to LNCaP cells, which accounts for their ability to produce bone-specific proteins. Inhibition of Cbfa1, using decoy DNA Cbfa1 response elements, abrogated the ability of C4-2B to produce mineral. Finally, we determined that C4-2B cells express bone morphogenic protein-7, a known inducer of Cbfa1 expression. These data demonstrate a novel mechanism through which prostate cancer cells may directly contribute to the osteoblastic component that characterize their skeletal metastatic lesions. Prostate 47:212-221, 2001.