| Authors |
Chen D., Chen H., Feng J.Q., Windle J.J., Koop B.A., Harris M.A., Bonewald L.F., Boyce B.F., Wozney J.M., Mundy G.R., Harris S.E. |
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| Abstract |
The object of this study was to develop new murine osteoblast-like cell
lines for studying bone cell differentiation. In an attempt to develop
cell lines representing a specific stage in osteoblast differentiation, we
utilized transgenic mice. Immortalized osteoblastic cells were isolated
and cloned from the calvaria of a transgenic mouse containing a 2.6-kb
fragment of the rat osteocalcin promoter driving the expression of SV40
large T antigen. Two clonal cell lines, OCT-1 and OCT-2, were
characterized. T-antigen expression by these two cell lines was confirmed
using T-antigen antibody. Cell lines were tested for their responsiveness
to parathyroid hormone (PTH), prostaglandin B2 (PGE2), 1,25-
dihydroxyvitamin D3 (1,25D3), bone morphogenetic protein-2 (BMP-2),
transforming growth factor beta (TGF-beta), and retinoic acid. Their
capacity to produce mineralized bone nodules and to express type I
collagen, alkaline phosphatase (ALP), and osteocalcin at the mRNA level
was also evaluated. Osteocalcin expression was found to be very low: OCT-1
and OCT-2 cells injected into nude mice subcutaneously over the surface of
calvaria caused osteosarcomas in 10 and 6 weeks, respectively. Significant
new bone formation was associated with the tumors. OCT-1 and OCT-2 cells
have different response profiles to BMP-2, retinoic acid, PTH, and PGE2.
These results demonstrate that OCT-1 and OCT-2 are cells representative of
different stages of osteoblast differentiation. They have low levels of
osteocalcin expression and may offer a tool to study the role of
osteocalcin in bone formation and mineralization.
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