| Abstract |
Culture systems have been of considerable value in examining the metabolic
effects of hormones on bone cells. However, even well-characterized
culture systems have heretofore been heterogeneous in terms of bone cell
types. In the current studies, we report further characterization of a
recently established, stable cell line isolated from mouse bone,
designated MMB-1. This cell line was established by cloning of spontaneous
transformants from primary osteoblast cultures, and was selected for its
ability to increase intracellular cAMP concentrations in response to PTH.
We have now shown that the cAMP response of the cells is similar to that
of primary osteoblasts in magnitude (10-15 fold elevation at maximal doses
of PTH); dose dependency (minimal PTH dose 3 ng per ml, maximal dose 300
ng per ml); and time course (peak elevation 5 min, return to baseline by
30 min). The MMB-1 cells also showed cAMP elevations in response to
osteoclast activating factor (OAF), epinephrine and prostaglandins, but
not to calcitonin, insulin or vitamin D metabolites. In each case where an
agent caused elevated cAMP, there was an associated increase in the
activity of cytoplasmic cAMP-dependent protein kinase, suggesting that
this enzyme may mediate the cAMP dependent effects of these hormones. In
addition to effects on cAMP, we studied other horm-one modulated
activities of MMB-1 cells: collagen synthesis was inhibited by PTH and OAF
but was stimulated by insulin; alkaline phosphatase activity was decreased
by PTH and OAF; and other synthetic activities associated with osteoblast
function were inhibited by the same agents. None of the hormone effects
seen in MMB-1 cells were detected in primary or several established lines
of fibroblasts or other cells. These data suggest that the MMB-1 cell line
retains a substantial fraction of the differentiated characteristics of
osteoblasts, and that the hormone control of these activities is
essentially identical to that in the normal osteoblast. The availability
of such a monoclonal, stable osteoblast cell line should materially aid
future studies of the regulation of bone cell function by hormones.
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