A distinctive form of human chorionic gonadotropin beta-subunit-like material produced by cervical carcinoma cells

The DoT and CaSki human cervical carcinoma cell lines ectopically produce material immunologically similar to the beta-subunit of human chorionic gonadotropin (hCG beta). Culture fluids were analyzed by gel filtration chromatography and radioimmunoassay (RIA) using (a) antiserum directed to conformation-specific (core-directed) determinants not involving the carboxyl-terminal peptide (CTP) in hCG beta purified from urinary hCG (i.e., standard hCG beta) or (b) antiserum directed to the CTP in standard hCG beta. CTP-directed RIA recognized a peak of hCG beta-like immunoreactive material that eluted in the same position as standard hCG beta. However, core-directed RIA recognized additional hCG beta-like material (i.e., ectopic beta-II), most of which eluted before standard hCG beta. CaSki cells were incubated with [3H]mannose, [3H]proline, and [3H] leucine, and the spent medium was immunoprecipitated and analyzed by gel electrophoresis. Several labeled peaks were detected in the lane from the anti-hCG beta X Sepharose immunoprecipitate, one of which corresponded in mobility to standard hCG beta, with two more intense components migrating at higher apparent molecular weights. Carboxypeptidase Y digestion released only 0.2 mol equivalents each of [3H]proline and [3H]leucine from the labeled CaSki material immunoprecipitated with anti-hCG beta X Sepharose, compared to 1 mol equivalent each in similar analysis of standard hCG beta. These findings were consistent with the absence of the 4-carboxy-terminal amino acids from 80% of the hCG beta-like immunoreactive material secreted by CaSki cells. The affinity purified ectopic beta-II failed to combine with standard hCG alpha under conditions in which combination of standard hCG beta with standard hCG alpha was essentially complete. Neither aggregation nor proteolytic degradation was the cause of failure of ectopic beta-II to combine with hCG alpha. We conclude that both the DoT and CaSki cervical carcinoma cell lines secrete a distinctive form of hCG beta-like material, ectopic beta-II. Lack of recognition by CTP-directed antisera and amino acid analysis suggest that ectopic beta-II may lack the CTP, despite its apparent larger size relative to standard hCG beta.