Effects of dioxin and estrogen on collagenase-3 in UMR 106-01 osteosarcoma cells

Since estrogen is important in preventing osteoporosis in postmenopausal women and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an estrogen antagonist in reproductive tissues, we investigated the effects of 17β-estradiol (E₂) and TCDD on collagenase-3 secretion using parathyroid hormone (PTH)-stimulated UMR 106-01 cells, a rat osteoblastic osteosarcoma cell line. Whereas E₂ or TCDD had no effect on UMR cells in the absence of PTH, cells grown in the presence of 10^-7 M PTH, which induces a dramatic 30-fold increase in collagenase-3 secretion, surprisingly demonstrated a further stimulation of collagenase-3 secretion in the presence of TCDD or E₂. However, the potentiating response was biphasic; i.e., at higher concentrations of E₂ or TCDD, there was no enhancement of the PTH effect. PTH induces multiple effects on UMR cells, including inducing collagenase-3 mRNA transcription and regulating its extracellular abundance through a specific receptor and endocytosis. Thus, we investigated the ability of TCDD or E₂ to stimulate the induction of collagenase-3 mRNA using Northern analysis. As previously reported, PTH dose dependently induced collagenase-3 mRNA after 4 h of treatment. There was little effect of TCDD or E₂ on PTH-induced levels of collagenase-3 mRNA. These data could not account for the final effects on secreted collagenase-3. We postulated that low concentrations of E₂ and TCDD may downregulate the collagenase-3 endocytotic two-step receptor-mediated process that includes the LDL-receptor-related protein to enhance the effects of PTH. However, this was not the case. Therefore, we conclude that low concentrations of TCDD and estrogen alter translation or secretion of PTH-stimulated collagenase-3. (C) 2000 Academic Press.