Primary human osteoblast-enriched (PHO) cultures derived from adult trabecular bone were analyzed to determine the presence or absence of transforming growth factor beta (TGF-β receptors. Saturation binding studies were performed with 125I-TGF-β in the absence or presence of 200-fold excess cold TGF-β Cross-linking experiments utilizing 125-I-TGF-β were performed to identify specific cell surface binding proteins for TGF-β The saturation binding studies demonstrated saturable binding for TGF-β on PHO cells. TGF-β was cross-linked to cell surface binding proteins of 50 to 110 KDa and a high molecular weight component. Thus, these receptors appear to be similar in affinity, number per cell, and molecular weight to those previously identified with other cell types. The potential biological effects of TGF-β on the growth of PHO cultures were evaluated by both 3H-thymidine incorporation and cell number determination. Growth of PHO cells in the presence of TGF-β resulted in an approximately two-fold stimulation in cell number as compared to control cells while the 3H-thymidine experiments demonstrated a two to four-fold increase in thymidine uptake in the presence of TGF-β Radiographic emulsion studies revealed that the alkaline phosphatase positive and negative cell populations were responsive to the TGF-β mitogenic stimulation. The cumulative findings of saturable binding, specific cell surface binding proteins, and biological effects suggest that functional TGF-β cell surface receptors are present on primary osteoblast-enriched cultures derived from adult human trabecular bone.
- Human osteoblasts
- Transforming growth factor beta