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

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