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Ectopic β-Human Chorionic Gonadotropin Production by a Human Hepatoma Cell Line (FOCUS): Isolation and Immunochemical Characterization^*

MEHMET OZTURK, DOMINIQUE BELLET, KURT J. ISSELBACHER and JACK WANDS

Gastrointestinal Unit, Massachusetts General Hospital, and the Department of Medicine, Harvard Medical School (M.O., K.J.I., J. W.) Boston, Massachusetts 02114
the Departement de Biologie Clinique, Institut Gustave-Roussy (D.B.) 94805 Villejuif, France

Address all correspondence and requests for reprints to: J. R. Wands, M.D., Gastrointestinal Unit, Massachusetts General Hospital, Boston, Massachusetts 02114.

Abstract

We have established a human hepatocellular carcinoma cell line designed FOCUS that produces and secretes the β-subunit of hCG. In the study of βhCG production by FOCUS cells, we have developed and employed a series of monoclonal immunoradiometric assays (IRMAs) that detect epitopes unique to βhCG, hCG, hCG, and sequence-specific regions of the carboxyl-terminal peptide of βhCG. The cells secrete approximately 15 ng /ihCG/lO⁶ cells and per 24 h; however, we were unable to detect either hCG or the a-subunit. The ectopic jtfhCG was subsequently affinity purified from the culture medium and partially characterized by sodium dodecyl sulfatepolyacrylamide gel electrophoresis and autoradiography. The mol wt of ectopic βhCG was approximately 35,000 daltons. Immunochemical analysis of ectopic βhCG by sequence-specific monoclonal antibodies revealed that epitopes corresponding to amino acid sequences 109–115, 121–145, 134–140, and 139–145 of the carboxyl-terminal peptide were present. FOCUS cells also demonstrate an intracytoplasmic localization of βhCG by immunoperoxidase- staining techniques. Taken together, these findings suggest that FOCUS cells produce and secrete only βhCG and that thus far, its physical properties appear indistinguishable from those of the native subunit. This unique cell line will be useful to study βhCG gene(s) regulation as well as the mechanisms of ectopic βhCG production and secretion. (Endocrinology 120: 559–566, 1987)

Footnotes

^* This work was supported in part by Grants AA-20666, HD-20469, and CA-35711 from the NIH.

Recipient of a research fellowship from Association pour la Recherche sur le Cancer.

Recipient of Research Career Scientist Development Award AA-00048 from the NIH.

Received March 20, 1986.