Endothelin-induced cytoskeletal actin re-organization in cultured astrocytes: inhibition by C3 ADP-ribosyltransferase.

Abstract

We investigated signal transduction mechanisms of endothelin (ET) receptor-mediated actin re-organization of rat cultured astrocytes. Staining of filamentous actin (F-actin) showed that stress fibers were a prominent cytoskeletal actin structure in protoplasmic astrocytes. A treatment with 0.5 mM dibutyryl cAMP (DBcAMP) caused cytoplasmic retraction and disappearance of stress fibers of astrocytes. A subsequent addition of 1 nM ET-3 after the DBcAMP treatment expanded the cytoplasm and stimulated stress fiber formation. ET-1, sarafotoxin S6b, and [Ala1,3,11,16]-ET-1 had similar effects. Pre-treatment with 0.1 microgram/ml pertussis toxin (PTX) and chelation of cytosolic Ca2+ did not affect astrocytic stress fiber formation by ET-3. ET-3 stimulated stress fiber formation in stellate astrocytes induced by 50 microM ML-9, 20 microM W-7, and 5 microM cytochalasin B (CB). Cytoplasmic microinjection of C3ADP-ribosyltransferase of C. botulinum (C3 enzyme), which impairs the interaction between rho proteins and the effectors, prevented ET-3-induced stress fiber formation and cytoplasmic expansion in DBcAMP-and CB-treated cells. Effects of ET-1 and sarafotoxin on stress fiber formation were also prevented by C3 enzyme. On the other hand, injection of C3 enzyme did not affect increase in cytoplasmic Ca2+ levels induced by ET-3. These results suggest that rho proteins are involved in the ET receptor-mediated actin re-organization of astrocytes.