Characterization of human chorionic gonadotropin in urine of patients with trophoblastic diseases by Western blotting using specific antibodies.

Human chorionic gonadotropin (hCG) from urine of patients with trophoblastic diseases was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by Western blotting using specific antibodies. Western blotting using anti-hCG beta carboxy-terminal peptide (CTP) revealed that the molecular weights of the beta subunits of the three molar hCG samples were identical to that of standard hCG beta, but those of choriocarcinoma hCG samples were individually different. In the five choriocarcinoma hCG samples, the beta subunits of three samples were apparently larger than standard hCG beta, while those of two samples were smaller than standard hCG beta but larger than desialylated standard hCG beta. These results suggest that structural changes of carbohydrates of hCG, which may be induced by malignant transformation of the trophoblast, can be observed as differences in molecular weight. In SDS-PAGE under nonreducing conditions. Western blotting using anti-hCG beta-CTP revealed a single band corresponding to hCG beta. Under reducing conditions with dithiothreitol (DTT), however, a second low-molecular-weight material (called here CTP') could be observed with anti-hCG beta-CTP. All five choriocarcinoma hCG samples were much more susceptible than standard hCG to cleavage of CTP' by DTT. We conclude that estimations of molecular weight and susceptibility to DTT reduction of urinary hCG by Western blotting using specific antibodies are useful in the diagnosis of choriocarcinoma.