BASEMENT-MEMBRANE INCREASES G-PROTEIN LEVELS AND FOLLICLE-STIMULATING-HORMONE RESPONSIVENESS OF SERTOLI-CELL ADENYLYL CYCLASE ACTIVITY

On a basement membrane substrate, Sertoli cells in culture have been shown to assume a phenotype similar to that of the in vivo differentiated cells. Sertoli cells from 10-day-old rats were cultured on plastic and on different extracellular matrix substrates [laminin, a reconstituted basement membrane (Matrigel), and a synthetic laminin peptide containing the arginine-glycine-aspartic acid (RGD) tripeptide sequence] to investigate the effects of the extracellular matrix on FSH responsiveness. Both laminin and Matrigel markedly enhanced the cAMP response to FSH and cholera toxin, indicating modifications at the level of guanine nucleotide-binding regulatory (G) proteins. Furthermore, Sertoli cells grown on either of these two substrates responded to physiological levels of FSH (25-50 ng/ml), whereas pharmacological levels of FSH (500 ng/ml) were required for cells grown on either plastic or on the RGD-containing laminin peptide. Immunoblotting of Sertoli cell plasma membranes with antibodies directed against the alpha-subunit of the stimulatory G-protein (Gs-alpha) of adenylyl cyclase indicated that Sertoli cell culture on either laminin or Matrigel increased the amounts of Gs-alpha. These results were further confirmed by immunoprecipitating the Gs-alpha protein from the particulate fraction of [S-35] methionine metabolically labeled Sertoli cells. However, Northern blot analysis using a cDNA probe for Gs-alpha did not demonstrate changes in gene expression when Sertoli cells were grown on the various substrates. Immunofluorescent studies revealed that the Gs complex of adenylyl cyclase was preferentially located at the base of the Sertoli cells at the site of contact with the extracellular matrix. These data suggest that culture of epithelial Sertoli cells on basement membrane substrates enhances the Gs complex of adenylyl cyclase and the cAMP response to FSH, consistent with the more differentiated morphology and function of the cells.