Regulation of the production of plasminogen activators by bone resorption enhancing and inhibiting factors in three types of osteoblast-like cells.

Production of proteolytic enzymes by osteoblasts is considered to be important for the initiation of osteoclastic bone resorption. We examined the production of tissue-type (tPA) and urokinase-type plasminogen activator (uPA) activity by three types of osteoblast-like cells (normal rat osteoblasts, rat and human osteosarcoma cells) using a quantitative spectrophotometric assay and a qualitative gel overlay technique. All 3 types of cells released both types of PA-activity into the medium, but normal rat osteoblasts released uPA probably in an inactive form. Treatment with different concentrations of the bone resorbing factors bovine Parathyroid Hormone [1-84], synthetic human Parathyroid Hormone-Like Protein [1-34]. Prostaglandin E2, Interleukin-1 beta, Tumor Necrosis Factor alpha and 1,25-dihydroxyvitamin D3 increased in general the production of both PA's by all three cell types. However, there were differences in the relative potencies of these factors. In contrast, Transforming Growth Factor beta, which inhibits bone resorption, decreased PA-activity in osteoblast-like cells. In all three types of cells, under control as well as under stimulated conditions, a high molecular weight form of PA was demonstrated by the gel overlay technique, most likely a complex of tPA with the PA-inhibitor PAI-1. The uniform increase in production of PA's by osteoblast-like cells in response to bone resorbing factors and its decrease by TGF beta supports the notion that PA's are involved in bone resorption. The exact mechanism however, remains to be elucidated.

Modulation of the production of a parathyroid hormone-like protein in human squamous carcinoma cell lines by interaction with fibroblasts.

Normal human keratinocytes as well as human squamous cell carcinomas produce a parathyroid hormone-like protein (PLP). However, PLP production by these cells is not a constant phenomenon. Since nothing is known about factors which regulate the production of PLP, in vitro studies were performed with normal keratinocytes and squamous carcinoma cell lines in order to establish conditions under which PLP production may vary. PLP was measured as cyclic AMP production in parathyroid hormone target cells (osteoblasts) which could be inhibited by a parathyroid hormone antagonist. The presence of PLP was confirmed using a radioimmunoassay specific for PLP. Results from the bioassay correlated very well with the data obtained by radioimmunoassay for PLP. The results confirm that human squamous carcinoma cells and normal keratinocytes produce PLP. PLP production appeared to be very sensitive to modulation of coculture of squamous carcinoma cells with fibroblasts. The effect of fibroblasts was not mediated by an effect on squamous carcinoma cell viability. Murine transformed fibroblasts (3T3 cells) as well as human normal foreskin fibroblasts were equally effective in inducing PLP production in these cells. The fibroblastic factor was apparently present in a soluble form in the coculture system which prevented direct cell-cell contact but allowed communication through the medium. Nevertheless, conditioned medium from 3T3 cells failed to induce PLP production by squamous carcinoma cells. This suggests a more complicated interaction between the two cell types than a one way message from fibroblasts to keratinocytes. Production of PLP by a number of squamous carcinoma cell lines was variable and not evidently correlated with the ability of these carcinoma cells to differentiate. Production of parathyroid hormone-like protein not only is the expression of a disturbed metabolism of a specific cell type but also reflects the cell-cell interaction in tumor tissue.