Characterization of epidermal growth factor-related proteins from human urinary chorionic gonadotrophin

A urinary chorionic gonadotrophin (hCG) preparation, mitogenic for ovarian carcinoma cells, was analysed by gel filtration through Sephadex G-100 Superfine. The resulting fractions were tested for hCG and for properties of the epidermal growth factor (EGF) by radioimmunoassays (RIA) in comparison with their ability to stimulate the growth of EFO-27nu ovarian carcinoma cells. The elution profile of the RIA activities for hCG corresponded to molecular weights of 12 and 71 kDa, whereas the mitogenic activity was found in peak fractions eluting at 7, 11 and 52 kDa, indicating the presence of mitogenic substances distinct from hCG or its beta-subunit. In comparison experiments, radiolabelled recombinant human EGF eluted at 7 kDa from the column. The profile of EGF immunoreactivity determined in the eluant fractions of hCG preparation A correlated with the mitogenic potential. Eluant fractions with growth-promoting activity competed with 125I-labelled EGF in binding to EFO-27nu cells; the inhibition of EGF binding was correlated with the mitogenic potential and the EGF immunoreactivity. We assume that the 7 kDa component of the gel filtration eluate corresponds to monomeric EGF; the high molecular weight mitogens may represent EGF precursor protein fragments of various molecular size classes.