The role of actin in changes of cell shape and steroidogenesis in mouse Y-1 cells stimulated by ACTH--immunocytochemical studies.

We investigated the immunocytochemical localization of two kinds of representative cytoskeletal proteins (tubulin and actin) and the morphology of Y-1 mouse adrenal tumor cells under ACTH stimulation at the light and electron microscopic levels. After ACTH stimulation, Y-1 cells showed the rounding-up phenomenon and increased steroidogenesis. Meanwhile, actin was accumulated near the cell membrane and formed filaments. Electron microscopically, stress fibers disappeared with ACTH administration. However, changes in the tubulin localization (main element of the microtubules) were not conspicuous. Cytochalasin B which blocks formation of actin filaments induced rounding-up of Y-1 cells and inhibited increases of steroid synthesis induced by ACTH. Colchicine caused disappearance of the microtubule-organizing center, but the shape of Y-1 cells was not changed. These results suggested that actin-filaments may be the main filament involved in the changes of cell shape and the increased steroidogenesis induced by ACTH.