Regulation of cytoskeletal protein organization and expression in human granulosa cells in response to gonadotropin treatment.
The organization and expression of the major cytoskeletal protein systems and of several cytoskeleton-associated proteins were analyzed in human granulosa cells obtained from preovulatory follicles in the course of an in vitro fertilization program. The cells were cultured in medium containing 5% fetal calf serum in the absence or presence of gonadotropins. Within several hours after the addition of hCG to cultured human granulosa cells, the cells acquired a rounded and aggregated morphology with numerous thin and long processes. Cells cultured without the gonadotropin had a flat and extended morphology on the substrate, with a well developed stress fiber system and numerous large vinculin-containing adhesion plaques. The [35S]methionine-labeled protein pattern of hCG-treated cells obtained by two-dimensional isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a 7- to 10-fold decrease in the synthesis of vinculin and the nonmuscle tropomyosin isoforms, and a 2- to 4-fold decrease in the synthesis of alpha-actinin and actin, without a comparable change in alpha- and beta-tubulin synthesis. In the absence of gonadotropins, human granulosa cells synthesized both the intermediate filament (IF) protein vimentin and cytokeratin-type IF proteins 8 and 18 and, to a lesser extent, cytokeratins 7 and 19. By immunofluorescence, both type of IF networks were detected in untreated cells, while hCG-treated cells synthesized and contained only vimentin-type IF networks. Thus, maintenance of the steroidogenic capacity in the presence of gonadotropins in human granulosa-luteal cells involves specific changes in cell shape and in both the organization and the expression of the microfilament and IF systems.