Endothelin-1 modulates calcium signaling by epidermal growth factor, α-thrombin, and prostaglandin E1 in UMR-106 osteoblastic cells

Abstract

Local factors play an important role in the regulation of bone metabolism. The homologous and heterologous desensitization of responses to these factors may be crucial in the modulation of bone cell signaling. In this study, the effects and interactions of endothelin-1 (25 nM), alpha-thrombin (0.9 microM), epidermal growth factor (40 nM), prostaglandin E1 (5 microM), and prostaglandin F1 alpha (5 microM) were examined on calcium signaling in UMR-106 rat osteoblastic osteosarcoma cells. Intracellular calcium was measured using fluo-3 fluorescent dye. All agents elicited calcium transients at these concentrations and showed homologous desensitization to their repeated administration. Preincubation for 60 minutes with 500 microM monodansylcadaverine and 30 minutes or 24 h preincubation with 0.5 microM indomethacin did not affect homologous desensitization, suggesting that neither the internalization of receptors nor prostaglandins are involved in this event. Pretreatment for 3 minutes with 2 microM 4 beta-phorbol-12 beta, 13 alpha-dibutyrate significantly reduced the calcium elevations elicited by the first application of these compounds, whereas an inactive phorbol, 12,13-didecanoate, had no effect. Pretreatment for 4 minutes with 0.5 microM forskolin decreased the calcium signal response to PGE1 only. Pretreatment with endothelin-1 for 3 minutes significantly decreased the calcium signals elicited by epidermal growth factor and alpha-thrombin. Prior administration of endothelin-1 significantly increased prostaglandin E1-stimulated calcium transients, whereas prostaglandin F1 alpha responses were not affected. Preincubation with indomethacin did not alter any of the interactions. Responses to endothelin-1 were not significantly altered by 2-3 minutes pretreatment with the other factors, nor was there cross-desensitization among the other factors. The results could indicate that endothelin-1 has a unique and specific role in the modulation of bone cell signaling.

Inositol trisphosphate receptor gene expression and hormonal regulation in osteoblast-like cell lines and primary osteoblastic cell cultures

“…(2) Inducers of resorption, including PTH, PTH-related peptide, endothelins, prostaglandins, bradykinin, leukotriene B 4, and thrombin, all stimulate phosphoinositide turnover and mobilization of intracellular calcium in osteoblasts. (9,(15)(16)(17)(18)…”

“…(13,14) Estrogens and other chronic inhibitors of bone resorption may exert their effects on osteoblasts by regulating specific signal transduction pathways. Acute bone resorbing agents includingPlH, PlH-related peptide, endothelins, prostaglandins, bradykinin, leukotriene B 4, and others rapidly stimulate phosphoinositide turnover and mobilization of intracellular calcium in osteoblasts, suggesting that the phosphoinositide is an important signal transduction system in these cells, (9,(15)(16)(17)(18) This suggestion is substantiated by the observation that raising intracellular calcium in osteoblasts and osteoblastic osteosarcoma cells stimulates the secretion of IL_6. (19,20) Also, pretreatment of osteoblast-like UMR-106 cells with calcitonin or 1,25-dihydroxyvitamin D 3 (1,25(OHhD 3) selectively inhibits the release of calcium from intracellular stores induced by the bone resorbing agents PTH and prostaglandin E 2.…”