Level of ETB receptor mRNA is down-regulated by endothelins through decreasing the intracellular stability of mRNA molecules.

Using ROS17/2 rat osteosarcoma cells as a model system, we examined the possibility that endothelin (ET)-induced down-regulation of ETB receptor was accompanied by a decrease in levels of ETB receptor mRNA. Northern blot analysis showed that low doses of ET-1 and ET-3 caused a transient decrease in ETB receptor mRNA in the cells. The maximum decrease in the levels of ETB receptor mRNA (80%) occurred after 2-4 h of exposure of the cells to ETs and was followed by a gradual recovery to control levels by 24 h. The effects were dose-dependent (EC50-1 nM), and ET-1 and ET-3 were almost equipotent in eliciting the response. The addition of either ionomycin, a Ca2+ ionophore, or phorbol dibutyrate, a protein kinase C activator, mimicked the effect of ETs. These results suggested that ETs-induced down-regulation of ETB receptor mRNA was mediated by the activation of ETB receptor and that it may have involved ETB receptor coupled second messenger pathways. We also showed that ETB receptor mRNA had a long intracellular life span which suggested that ETs-induced down-regulation of ETB receptor mRNA may have been due to a decrease in the stability of mRNA, rather than inactivation of the transcription of mRNA.