Human chorionic gonadotropin beta-core fragment is directly produced by cancer cells

The present study was undertaken to investigate whether hCG beta-core fragment (hCGbeta cf) was directly produced by cancer cells. Fifteen cell lines, including four choriocarcinoma and five ovarian cancer cell lines, were tested, and immunoreactivity of hCGbeta cf was present in the culture media of five of the cell lines. It was also present in the culture media of Chinese hamster ovary (CHO) cells transfected with hCGbeta gene. In addition to hCGbeta cf, gel chromatography and Western blot analysis of the culture media showed the presence of an hCGbeta cf immunoreactive material with a molecular weight of approximately 40 kDa. In an in vivo study, hCGbeta cf immunoreactivity was detected in the sera of the mice transplanted with NaUCC-3 choriocarcinoma cells, although the ratios of hCGbeta cf/hCG and hCGbeta cf/free hCGbeta were lower than those in the culture medium. Incubation experiments of purified hCGbeta cf in the serum showed no substantial decrease in its values, ruling out the possibility that formation of a macromolecule with serum components may mask hCGbeta cf immunoreactivity in the serum. Taken together, these results indicate that hCGbeta cf immunoreactive materials are directly produced by cancer cells and hCGbeta cf is not a urinary metabolite of hCG or hCGbeta alone. Also, reduced levels of hCGbeta cf in the serum compared with that of intact hCG or free hCGbeta are likely due to its short half-life.