Microtubule Dynamics Regulates the Level of Endothelin-B Receptor in Rat Cultured Astrocytes

Abstract: We investigated the effect of cytoskeleton modulators on endothelin-B (ET_B) receptor expression in rat primary cultured astrocytes. Northern blot analysis and a binding study revealed that colchicine and nocodazole, microtubule-disrupting agents, decreased the levels of both ET_B receptor mRNA and the number of ET-1 binding sites in quiescent astrocytes. Down-regulation of both ET_B receptor mRNA and the number of binding sites for ET-1 was also observed in quiescent astrocytes treated with taxol, a microtubule-stabilizing agent. In contrast, neither β-lumicolchicine, an inactive isomer of colchicine, nor cytochalasin D, a microfilament-disrupting agent, influenced ET_B receptor expression. The level of ET_B receptors in astrocytes was affected by the cell state, namely, proliferative, quiescent, or differentiated state. The order of ET_B receptor expression according to the cell state was proliferative state < quiescent state ? differentiated state induced by dibutyryl cyclic AMP. Also, in proliferative astrocytes and differentiated astrocytes, colchicine significantly down-regulated both ET_B receptor mRNA and the number of binding sites for ET-1. However, thymidine assay revealed that colchicine did not change quiescent astrocytes and differentiated astrocytes to a proliferative state. Furthermore, the increase in glutamine synthetase activity in differentiated astrocytes was not affected by colchicine. These results suggest that microtubule dynamics possibly regulates ET_B receptor expression in astrocytes without affecting the cell state.