Transferrin receptor is inversely correlated with estrogen receptor in breast cancer.

The transferrin receptor (TfR) has been identified as a marker for proliferation in cells in culture and can be accurately quantitated by specific radioimmunoassay. This study directly quantifies levels of TfR and compares them to levels of estrogen receptor (ER) and progesterone receptor (PgR) in biopsy material obtained from patients with infiltrating ductal carcinoma of the breast. A comparison of ER and TfR levels displayed an exponential distribution which was log-normalized to yield a linear inverse relationship (r = -.44). Although ER was strongly correlated with PgR, there was no correlation pattern between TfR and PgR. Multiple regression analysis indicated that 73% of ER levels could be predicted by a combination of the other two markers, PgR (representing degree of differentiation) and TfR (representing growth rate). Transferrin receptor levels were also found to be correlated (p less than .05) with menopausal status, with tumors from premenopausal patients exhibiting higher levels, whereas the opposite pattern was shown for estrogen receptor levels (p less than .02). Neither steroid receptor nor transferrin receptor levels were correlated to stage of disease or presence of nodal involvement. Addition of TfR level as an independent marker for proliferation may facilitate the decision-making process in the treatment of individual cases of carcinoma of the breast.

Monoclonal antibodies to a purified human transferrin receptor.

BALB/c mice were injected with an affinity-chromatography-purified placental transferrin receptor preparation. Spleen cells were fused with NS-1 myeloma cells. Sixteen hybrids producing monoclonal antibodies specific for the transferrin receptor and two hybrids specific for transferrin were identified by radioimmunoassay (RIA). Five hybrids were selected for cloning on the basis of antibody specificity and affinity. None of the antibodies inhibited the binding of transferrin to K562 cells. The binding of antibody ID9 to K562 cells was partially inhibited by transferrin or a polyclonal goat anti-transferrin receptor antiserum. Of the five antibodies, two (IIB6 and IIB2) reacted only with the purified receptor and solubilized cells and not with whole cells. The other three antibodies, when tested with normal human cells and leukaemia and tumour cell lines, showed identical reaction patterns. The antibodies precipitated a glycoprotein from K562 cells with an apparent molecular weight of 94,000, estimated from sodium dodecyl sulphate-polyacrylamide gel electrophoretograms run under reducing conditions, and a molecular weight of 188,000 when run under unreduced conditions. All antibodies have a high affinity with Ka values ranging from 1.44 X 10(9) to 3.56 X 10(10) (l/mol). The antigen precipitated by all five antibodies showed identical peptide maps after partial proteolytic digestion.

Radioimmunochemical measurement of the transferrin receptor in human trophoblast and reticulocyte membranes with a specific anti-receptor antibody.

A radioimmunoassay was developed to directly assay the presence of transferrin receptors in human tissues. Antisera developed in a goat against purified human placental transferrin binding protein was purified by fractional sodium sulfate precipitation and adsorption against Sepharose-bound transferrin to remove trace anti-transferrin activity. The antisera immunoprecipitates a Mr 94,000 peptide on 125I-iodinated syncytial trophoblast membranes from placentae. This polypeptide has been identified previously as the transferrin binding protein of the placenta [Wada, H. G., Hass, P. E. & Sussman, H. H. (1979) J. Biol. Chem. 254, 12629-12635]. A standard curve using purified 125I-iodinated placental transferrin receptor and various amounts of the purified noniodinated receptor is sensitive from 5 to 900 ng. A reticulocyte-enriched membrane ghost preparation (5% reticulocyte) gives a value of 9.5 micrograms of receptor per mg of protein. Normal erythrocyte membrane ghosts show binding (0.57 micrograms of receptor per mg of protein) proportional to the amount of reticulocytes normally present in blood (0.5-1.0%). In other tissues in which the transferrin receptor binding has been reported, purified syncytial trophoblastic membranes are found to have 34.5 micrograms of receptor per mg of protein, and BeWo cells, a choriocarcinoma cell line, are found to have 15.7 micrograms of receptor per mg of protein. In contrast, normal breast tissue, which has no demonstrated transferrin binding, contains only 0.18 micrograms of receptor per mg of protein by this method.