Abstract
We have examined the binding of human transferrin to cultured human choriocarcinoma cell lines and to detergent extracts of such cells. The results indicate the presence of a high-affinity saturable binding site (Ka = 4.25 x 10(8) M-1) that is specific for transferrin. This receptor has also been detected on three other human cell lines of different phenotypic origin, including Wil-2 (splenic lymphocytes of B-cell origin), RPMI-2650 (a quasi-diploid nasopharyngeal carcinoma), and WI-38 (embryonic lung fibroblasts). By using anti-human transferrin antiserum to immunoprecipitate the receptor-transferrin complex from detergent extracts of cells containing saturating levels of transferrin followed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, a single polypeptide of 90,000 daltons has been identified as a subunit of the putative transferrin receptor. The protein shows immunochemical identity and coelectrophoreses in sodium dodecyl sulfate gels with a cell surface glycoprotein subunit, previously identified in placental brush border membrane preparations, on all human cultured cell lines examined. These results suggest that the recent demonstration of transferrin dependence of maximal cell growth in culture [e.g., Hutchings, S.E. & Sato, G.H. (1978) Proc. Natl. Acad. Sci. USA 75, 901-904] is mediated through expression of this glycoprotein receptor.