A NATURALLY-OCCURRING BASICALLY CHARGED HUMAN FOLLICLE-STIMULATING-HORMONE (FSH) VARIANT INHIBITS FSH-INDUCED ANDROGEN AROMATIZATION AND TISSUE-TYPE PLASMINOGEN-ACTIVATOR ENZYME-ACTIVITY IN-VITRO

It is well known that deglycosylation of gonadotropins by enzymatic or chemical procedures or by deletion of sites for N-linked glycosylatio n produces antagonistic analogs which are able to interact strongly wi th the receptor and to inhibit binding of the wild-type hormone. In th e present study, we analyzed the antagonistic properties of a naturall y occurring basic follicle-stimulating hormone (FSH) charge isoform ob tained after high-resolution chromatofocusing of human anterior pituit ary glycoprotein extracts. Coincubation of increasing amounts of this isoform with a highly purified human pituitary FSH preparation or with recombinant human FSH at doses equivalent to their corresponding ED50 for estradiol and tissue-type plasminogen activator (tPA) production, inhibited FSH-induced estrogen production and tPA enzyme activity by cultured rat granulosa cells in a dose-dependent manner. These inhibit ory effects were apparently exerted at steps following 3',5'-cyclic ad enosine monophosphate (cAMP) formation and did not involve activation of the protein kinase C pathway since: (a) at low doses, this basic FS H isoform moderately increased FSH-induced cAMP production by cultured rat granulosa cells; (b) coincubation of the antagonist isoform with dibutyryl cAMP completely inhibited the effects of this cAMP analog on estrogen and tPA production; (c) the isoform was able to stimulate pr oduction of cAMP in a human fetal cell line expressing the recombinant human FSH receptor, and (d) the inhibitory effects of the isoform wer e not affected by staurosporine, a protein kinase C inhibitor. The eff ects of this isoform upon dibutyryl cAMP-induced estrogen and tPA prod uction were blocked by the addition of a highly specific antibody dire cted against human FSH, further demonstrating that the antagonistic ef fects observed were due to FSH-like molecules. In contrast to the inhi bitory effects exhibited by this basic FSH isoform, a more acidic FSH charge variant consistently acted as an agonist of pituitary and recom binant FSH on both estrogen production and induction of tPA enzyme act ivity. These results indicate that the anterior pituitary gland normal ly produces FSH isoforms which act as either agonists or antagonists o f FSH at the target cell level.