Human alpha fetoprotein enhances epidermal growth factor proliferative activity upon porcine granulosa cells in monolayer culture.

Alpha fetoprotein (AFP) is present at high concentrations in fetal fluids, certain neoplasias, and regenerating liver. Its physiological function remains largely unknown. Using a primary monolayer culture system, we investigated the proliferative activity of human (h) cord blood (CB) and highly purified AFP. hAFP, purified from hCB by Cibacron blue and immunoaffinity chromatography was homogeneous on SDS-PAGE and silver stain. Porcine granulosa cells from ovarian small follicles were cultured (25,000/cm2) for 2 days in medium (Ham's F-12:DMEM, 1:1) + 5% fetal calf serum (FCS) to facilitate attachment, followed by 6 days in medium containing: FCS, hCB or h amniotic fluid (1-20%)+/- EGF (10 ng/ml); or 0.25% plasma-derived serum (PDS) containing human low density lipoprotein (LDL, 25 ug/ml), +/- AFP (0.05-5 ug), and +/- EGF and IGF-I (10 ng/ml). In this system, single growth factors do not stimulate proliferation, a characteristic also exhibited by AFP. When combined with EGF, however, AFP dose-dependently increased proliferation to levels equal to that obtained with 10% FCS (2.3-fold increase vs PDS/LDL controls). When combined with EGF+IGF-I, AFP again dose-dependently increased proliferation to levels equal to that obtained with 10% FCS+EGF (6.7-fold increase vs controls). Purified human albumin used in place of AFP was not effective. TGF-a but not PDGF could replace the proliferative activity of EGF. These results suggest that AFP at physiological levels, although not itself mitogenic, can enhance the mitogenic activity of EGF and TGF-a and may function to modulate growth factor-mediated proliferation during development and neoplasia.