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

BACKGROUND. Prostate cancer frequently metastasizes to bone. However, unlik e many other tumors that produce osteolytic lesions, prostate cancer produc es osteoblastic lesions through unknown mechanisms. In the current study, w e explored the ability and mechanism of an osteotropic prostate cancer cell line (C4-2B) to induce mineralization. METHODS. C4-2B cells were grown in promineralization media. Mineral deposit ion was characterized using von Kossa staining, calcium retention, alizarin red staining, Raman spectroscopy, and electron microscopy. Expression of o steoblast-related proteins was determined by RT-PCR. The nuclear level of t he bone-soecific transcription factor Cbfa1 was determined using western an alysis and the effect of inhibiting Cbfa1 function, using a "decoy" Cbfa1 r esponse element oligo, on mineralization was determined. RESULTS. The studies demonstrated that C4-2B cells, but not its nonosteotro pic parent cell line LNCaP, has an osteoblastlike phenotype including produ ction of alkaline phosphatase, osteocalcin, osteonectin, bone sialoprotein, osteoprotegerin (OPG), and OPG ligand. Most importantly, the C4-2B cells p roduced hydroxyapatite mineral in vitro. Furthermore, C4-2B cells expressed high nuclear levels of the bone-specific transcription factor Gbfa1, compa red to LNCaP cells, which accounts for their ability to produce bone-specif ic proteins. Inhibition of Cbfa1 using decoy DNA Cbfa1 response elements, a brogated the ability of C4-2B to produce mineral. Finally, we determined th at C4-2B cells express bone morphogenic protein-7, a known inducer of Cbfa1 expression CONCLUSIONS. These data demonstrate a novel mechanism through which prostat e cancer cells may directly contribute to the osteoblastic component that c haracterize their skeletal metastatic lesions. Prostate 47:212-221, 2001. ( C) 2001 Wiley-Liss, Inc.