Studies on the synthesis and secretion of transthyretin by the human hepatoma cell line Hep G2

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Abstract
Transthyretin (TTR) is a circulatory protein which plays an important role in the transport of both thyroid hormone and retinol. Hep G2 cells, a human hepatoma-denved cell line. have been used extensively in studies of protein secretion by liver cells. The original description of this cell line indicated that this line, unlike primary hepatocytes, does not secrete TTR. We now report studies which reexamine the ability of Hep G2 cells to synthesize and secrete TTR. For this purpose, total RNA was isolated from Hep G2 cells grown on both uncoated and collagen-coated plastic plates and was examined for TTR expression by Northern blot analysis. TTR mRNA was found to be present m nearly equal amounts in Hep G2 cells cultured in either condition. When Hep G2 cells were cultured in [35S]jmethionine-containing medium, the cells were found both to synthesize and to secrete immunoprecipitable [35S]SJTTR. Hep G2 cells were found, by sensitive and specific radioimmunoassay, to contain 142 ± 91 ng TTR/106 cells and to secrete TTR into the medium at a nearly constant rate for at least 24 h after medium change. Our data demonstrate that Hep G2 cells do synthesize and secrete TTR and suggest that this cell line might be useful for studies of the secretion of TTR