Purified human alpha fetoprotein inhibits growth factor-stimulated estradiol production by porcine granulosa cells in monolayer culture.

Abstract

Purified alpha fetoprotein (AFP) synergizes with transforming growth factor alpha (TGF alpha) and insulin-like growth factor I (IGF-I) to enhance proliferation of porcine granulosa cells (pGC) in primary culture, suggesting a role for AFP in the modulation of growth factor-mediated cell growth. TGF alpha stimulates basal estrogen production by pGC and is in fact more potent than FSH in these cells. In this study, we investigated the effects of AFP on growth factor-stimulated estradiol (E2) production by pGC. Basal production of E2 was not altered by the addition of AFP. AFP dose-dependently inhibited TGF alpha-stimulated E2 production with statistically significant inhibition observed with 2.5 micrograms/ml. We have previously shown that the mitogenic effects of AFP are maximized with TGF alpha+IGF-I. E2 production was even more sensitive to AFP inhibition when the two growth factors were combined. Human serum albumin (HSA; 10 micrograms/ml) was without effect. AFP did not interfere with the E2 RIA, affect the uptake of or display specific in vitro binding of the androgen substrate. Furthermore, human AFP and HSA did not exhibit specific in vitro binding of E2, in contrast to purified rat AFP (positive control). These data indicate that physiological concentrations of purified AFP significantly and dose-dependently inhibit growth factor-stimulated E2 production by pGC in culture. Since AFP is known to increase TGF alpha+IGF-I mediated cell growth, these data suggest that AFP may be inhibiting the differentiated function (steroidogenesis) of pGC while enhancing the proliferation of these cells.

Biological Role of Alpha-Fetoprotein in the Endocrinological Field: Data and Hypotheses

“…The results obtained by Keel et al [49][50][51] showing that, depending on the nature of the associated growth factors, AFP can act on cell multiplication or differentiation are particu larly interesting. Nevertheless, the role of the various fatty acids bound to AFP must now be evaluated in these experiments considering the results of Bandhyopadyay [53] indicating that fatty acids intervene to potentiate the effect of some growth factors.…”

“…2. Two possible mechanisms by which AFP regulates cell multiplication and differen tiation either by its ligands acting together with growth factors [53] or by AFP itself interacting with growth factors [49][50][51][52].…”

“…Recently, very interesting studies on the differentiation and multiplication of estro gen-producing and estrogen-sensitive cells have been published [49][50][51]. These studies in two apparently independent domains are an example of how a multidomain synthesis can aid in revitalizing our thinking and our exper imental strategies to better understand the biological roles of AFP.…”

“…The studies of Keel et al [49][50][51] show that transforming growth factor a stimulates basal estradiol production by porcine granulosa cells (Pgc) in culture. Physiological concentra tions of purified AFP significantly and dosedependently inhibit growth-factor-stimulated estradiol production by Pgc.…”

Mapping of Structure-Function Peptide Sites on the Human Alpha-fetoprotein Amino Acid Sequence

“…It may be of interest that a PDGF receptor-like sequence has been detected on the first domain of HAFP and IGF sites were found on domain II and III ( Figure 5H). Subsequent use of the granulosal cell cultures seemed to indicate that, while HAFP was capable of growth factor-enhanced growth of these cells in vitro, HAFP also inhibited the steroidogenic function of E2 production (Keel et al, 1992). It was later demonstrated that HAFP actually inhibited the FSHstimulated E2 production in the porcine granulosa cells (Keel, 1993).…”