Heterogeneity of the Human Chorionic Gonadotropin α-Subunit Secreted by Cultured Choriocarcinoma (JEG) Cells*

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Abstract
The cultured human choriocarcinoma cell line, JEG-clone 3, secretes substantial quantities of both biologically active hCG and an immunoreactive α-subunit (JEG-α). This study is concerned with a comparative characterization, using RIA, of the chromatographic properties (via gel exclusion and isoelectric focusing) of JEG-α and standard urinary hCG-α. Most of the molecules comprising the JEG-α fraction have an apparent molecular weight greater than that of hCG-α. Both hCG-α and JEG-α exhibit heterogeneity on electrofocusing. However, JEGa contains a major component with an isoelectric pH (pi) of 4.8; this is a minor component, if present at all, in hCG-α. The JEGa pi 4.8 component chromatographs with an apparent molecular weight greater than hCG-α, while a minor JEG-α pi 7.0 component chromatographs with an apparent molecular weight similar to that of the standard. Heterogeneity is expected in the carbohydrate moieties of the glycoprotein hormone subunits. Results of studies on the incorporation of 14C- and 3H-labeled amino acids into JEG-α suggest that heterogeneity also exists in the protein moiety of JEG-α. An interesting possibility is that the form(s) of JEG-α with larger apparent molecular weight represents a precursor of the α-subunit used to form hCG.