['Osteoprotegerin (OPG) expression participates in the pathophysiology of osteoblastic metastasis in prostate cancer.', 'We investigated whether the expression of OPG of PC-3 prostate cancer cells grown in 3-D collagen gels is stimulated by co-culture with MG-63 osteoblast-like cells. The expression of Runx2 (Cbfa1) and OPG were assessed by reverse transcription-polymerase chain reaction and Western blot analysis.', 'OPG and Runx2 were expressed in both PC-3 and MG-63 cells. OPG expression was remarkably enhanced in PC-3 cells grown in co-culture with MG-63 cells in a time-dependent manner. Runx2 expression of PC-3 cells was not altered by their co-culture with MG-63 cells. OPG expression of PC-3 cells was altered neither by insulin-like growth factor I (IGF-1), transforming growth factor beta1 (TGFbeta1), interleukin 6 (IL-6) nor by dexamethasone and zoledronic acid exogenously added to PC-3 cells.'] Do mG-63 osteoblast-like cells enhance the osteoprotegerin expression of PC-3 prostate cancer cells?