A murine osteosarcoma cell line with a potential to develop ossification upon transplantation

An osteosarcoma cell line has been established from a soft tissue tumor tha t occurred spontaneously in a BALB/c mouse. This cell line showed ossificat ion when transplanted into syngeneic mice. To examine the mechanism of bone formation, the expression of mRNAs for osteoblastic and chondroblastic mar kers and factors associated with ossification has been investigated, In cul ture, the cells exhibited a spindle shape in the growth phase, but had a po lygonal shape in the stationary phase, Reverse transcription-polymerase cha in reaction analysis showed that the cells expressed mRNAs for pro-alpha1(I ) chain of type I collagen, alkaline phosphatase, osteopontin, osteocalcin, and core binding factor al, suggesting differentiation into the stage of o steoblasts during the stationary phase. After transplantation, histological examination revealed small foci of pale blue material and basophilic netwo rks that were scattered in the tumor tissues at one week. The former staine d positive with alcian blue, suggesting a chondroid matrix. Pro-alpha1(II) chain of type II collagen mRNA was expressed at one week, A large Dart of t umors at two and three weeks consisted of basophilic networks, which staine d positive via von Kossa's method, indicating a calcified woven bone. In si tu hybridization analysis showed strong expression of osteopontin and osteo calcin mRNAs in tumor cells surrounding the hone matrix. Bone morphogenetic protein-6 and -7 mRNAs were detected in transplanted tumors, but not, in c ultured cells. These results suggest that the cell line has the properties of an osteoblastic lineage when cultured in vitro and has an ossifying abil ity through endochondral bone formation processes when transplanted in vivo .