Transfilter bone induction by Chinese hamster ovary (CHO) cells transfected by DNA encoding bone morphogenetic...

This study was undertaken to identify the factor responsible for classical transfilter bone induction by a murine osteosarcoma. Chinese hamster ovary (CHO) cells were transfected with the complementary DNA (cDNA) for bone morphogenetic protein-4 (BMP-4) that was purified from a murine (Dunn) osteosarcoma. Diffusion chambers were filled with the cells expressing the gene for BMP-4 and implanted subcutaneously into the flanks of ICR strain nude mice. Ectopic transfilter bone formation was seen consistently on the outer surfaces of the cellulose acetate membranes of chambers containing transfected cells at three weeks after implantation. Bone was not observed on chambers loaded with nontransfected CHO cells. The transfected CHO cells were inoculated into nude mice to form tumors, which were then homogenized, defatted, and bioassayed also in the ICR, nu/nu mice. The cell-free implants consistently elicited new bone and marrow within three weeks, whereas the control implants consisting of nontransfected tumor were not osteoinductive. These experimental results suggest that BMP-4 is one of the molecules responsible for the transfilter bone induction by vital Dunn osteosarcoma cells reported by Heiple and for the ectopic bone induction after implantation of devitalized, freeze-dried Dunn osteosarcoma tissue described originally by Amitani.