THYROXINE-BINDING GLOBULIN SYNTHESIS BY HEPATOCARCINOMA CELLS IN CONTINUOUS CULTURE - EFFECT OF PHYSIOLOGICAL CONCENTRATIONS OF THYROXINE

Thyroxine-binding globulin (TBG) synthesis and secretion were demonstrated in a continuous cell culture line, NCLP-6-E, of Rhesus monkey hepatocarcinoma cells. The cells survived and grew normally for up to 5 days in the absence of serum, thus permitting study of TBG production in chemically defined media. TBG was identified by its ability to bind thyroxine (T4) and immunoelectrophoresis, and quantitated by radioimmunoassay. TBG accumulation in the media was linear for up to 48 h. Physiological concentrations of T4 induced a biphasic response in TBG secretion. There was a progressive increase in TBG accumulation from 10-14M-10-11M T4. TBG accumulation decreased from the maximum at T4 greater than 10-10M, and was depressed below control at T4 greater than 10-8M. These results indicate that T4 regulates the synthesis and secretion of TBG in hepatocarcinoma cells in culture.