EXTRAHEPATIC EXPRESSION OF FIBRINOGEN BY GRANULOSA-CELLS - POTENTIAL ROLE IN OVULATION

Granulosa cells from ovarian follicles were shown to express and secre te fibrinogen under the control of FSH. Conditioned medium was collect ed from granulosa cell cultures and found to contain FSH-dependent 50- kilodalton (kDa) and 93- to 95-kDa proteins. N-Terminal microsequence analysis identified these proteins as fibrinogen beta- and gamma-chain s, respectively. Proteins migrating at 93 and 95 kDa contain identical gamma-chain sequences at the N-terminal, suggesting differential proc essing of fibrinogen. These fibrinogen chains were specifically detect ed with antifibrinogen antibodies in immunoblot and immunoprecipitatio n analysis. Fibrinogen gamma-chain mRNA was detected in granulosa cell s by polymerase chain reaction analysis, confirming fibrinogen gene ex pression by these cells. Fibrinogen secretion by granulosa cells was m easured by a competitive enzyme-linked immunosorbent assay. Granulosa cells treated with FSH (100 ng/ml) secreted 2-3 times more fibrinogen than untreated cells. These data show that fibrinogen, a major product of the liver, is also a secretory product of granulosa cells. This pr ovides a novel extrahepatic site of fibrinogen expression. As hepatic parenchymal cells normally maintain high circulating levels of fibrino gen, the local production of fibrinogen in the ovary is anticipated to have specialized functions. Locally produced fibrinogen may be import ant in the clotting process following tissue rupture at ovulation. In addition, fibrinogen fragments may be involved in the mechanism of ovu lation by increasing the activity of tissue-type plasminogen activator to control the proteolytic activity required for ovulation.