Plasminogen activator is associated with the extracellular matrix of ovarian granulosa cells

Follicle-stimulating hormone (FSH) increases the activity of a cell-associated, tissue-type plasminogen activator (tPA) during the initial hours of granulosa cell development. In order to determine the cellular localization of tPA, granulosa cells were labeled with [35S]methionine for 4 h and detergent-solubilized proteins were immunoprecipitated and analyzed by polyacrylamide gel electrophoresis. FSH stimulated the synthesis of a Mr 70,000 PA in granulosa cells that was specifically immunoprecipitated by tPA antibodies. Subcellular fractionation of granulosa cells indicated that the newly biosynthesized tPA was present in a 100,000 X g membrane fraction with minimal tPA in the cytosolic, nuclear, and secreted compartments. Isolation of the extracellular matrix (ECM) synthesized by granulosa cells revealed that the membrane-associated tPA induced by FSH was present in the basement membrane. Deposition of tPA into the ECM increased with time and the enzyme exhibited a low turnover rate of greater than 4 h at this site. The ECM-associated tPA was functionally active as determined by fibrin autography and approximately 95% of the PA activity observed in intact, plated cells was localized to the ECM. When the attachment of cells and deposition of ECM were reduced by maintaining granulosa cells in suspension culture, 40% of the newly synthesized tPA was released instead of being cell-associated. The addition of increasing quantities of anti-tPA IgG or unlabeled tPA minimally depleted the biosynthesized enzyme from the cells, indicating that tPA tightly interacted with the ECM. These results indicate that FSH regulates the biosynthesis of a tPA that is preferentially localized to the ECM region of granulosa cells.(ABSTRACT TRUNCATED AT 250 WORDS)