Pregnancy-associated plasma protein-A is the insulin-like growth factor binding protein-4 protease secreted by human ovarian granulosa cells and is amarker of dominant follicle selection and the corpus luteum.

Insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs), and IGFB P proteases are important in ovarian function. IGFs stimulate granulosa ste roidogenesis, an effect that is inhibited by IGFBP-4 and augmented by IGFBP -4 proteolysis. We have recently identified the IGFBP-4 protease in human o varian follicular fluid (FF) as pregnancy-associated plasma protein-A (PAPP -A). In the current study, we identify the IGFBP-4 protease secreted by cul tured human ovarian granulosa cells as PAPP-A, based on specific immunoinhi bition and immunodepletion of the IGFBP-4 protease activity with PAPP-A pol yclonal antibodies and immunorecognition by PAPP-A monoclonal antibodies in ELISA. PAPP-A was barely detectable in conditioned media (CM) from granulo sa derived from less than or equal to 9 mm androgendominant follicles, but was secreted by cultured granulosa from system in human ovary estrogen-domi nant follicles greater than or equal to 9 mm, coincident with dominant foll icle selection, and by luteinizing granulosa. PAPP-A levels in CM from the latter did not change in response to IGF-II or hCG (100 ng/mL). A naturally occurring inhibitor of PAPP-A, preform of eosinophil major basic protein ( proMBP), was detected by ELISA in estrogen-dominant follicular fluid FF, bu t not in CM from granulosa or luteinizing granulosa cells treated with IGF- II (0-200 ng/mL), FSH (0-100 ng/mL) or hCG (0-100 ng/mL), suggesting an alt ernative source (other than granulosa) for proMBP, compared to PAPP-A. The data demonstrate granulosa cells as a source of PAPP-A in human ovary and s uggest that PAPP-A is a marker of ovarian follicle selection and corpus lut eum formation. In addition the data suggest complex regulation of this syst em in human ovary.