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.

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.

Demonstration of the transferrin receptor in human breast cancer tissue. Potential marker for identifying dividing cells.

A transferrin receptor was demonstrated in tumor tissue from 10 patients with breast carcinoma and one patient with breast sarcoma. Binding studies were conducted by measuring the amont of 1251-transferrin binding to microsomal preparations of the tumor tissue. Elevated levels of specific transferrin binding were found in the tumors with a range of 11-35% of bound transferrin, whereas microsomes prepared from non-neoplastic breast tissue samples bound only 2.3% and 2.4% of the transferrin. Scatchard analysis of binding studies conducted with tissues from a breast cancer and from a breast sarcoma indicate that the receptor has a Ka = 9.0 x 10(8)M. The binding site is specific for transferrin, as studies show that non-radioactive transferrin displaced labelled transferrin, while human IgG and human albumin did not. The receptor-transferrin complex was precipitated from a detergent extract of the breast sarcoma with antiserum to human transferrin. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the immunoprecipitate gave a polypeptide of M 90,000 daltons, which is of similar molecular weight found for the putative transferrin receptor in all of a series of human cultured cell lines previously examined.

Distribution and characterization of alpha hCG in the serum and tumor cytosol of patients with breast cancer.

Serum and tumor tissue from breast cancer patients were evaluated for the presence of alpha subunit of hCG, by means of the specific radioimmunoassay. Elevated serum levels occurred in 0/50 (0%) of normal female controls, 1/17 (6%) of patients with benign breast disease, 3/53 (6%) of patients with primary breast cancer, and 12/84 (14%) of patients with metastatic breast cancer. Cytosols from 10/56 (18%) primary tumors and 10/37 (28%) metastatic tumors were found to contain the alpha subunit. Comparison of serum and tumor cytosol levels in nine patients with metastatic disease showed a correspondence between elevated cytosol levels and elevated serum levels. No similar correspondence in 25 patients with primary disease was observed. Alpha subunit was isolated from one tumor cytosol and was characterized with respect to its immunochemical cross-reactivity and molecular weight as compared with native alpha subunit from hCG. For both parameters, the native and ectopic alpha subunit were found to be identical.

Demonstration of placental alkaline phosphatase in human breast cancer.

The screening of a series of 11 metastatic breast tumors for the presence of the placental isoenzyme of alkaline phosphatase (EC3.1.3.1) by RIA revealed one strong producer. The alkaline phosphatase of this tumor was characterized with respect to its immunochemical cross-reactivity, inhibition by L-phenylalanine and levamisole, subunit molecular weight (Mr) and isoelectric point (pl) in two-dimensional electrophoresis, and one-dimensional peptide map. In all parameters of the characterization, the tumor alkaline phosphatase, except for subunit molecular weight which was slightly lower (60,000 versus 64,000 for the placental isoenzyme). No strong placental alkaline phosphatase producers were found among 16 primary tumors examined by RIA. The screening of patients' sera for the placental alkaline phosphatase using RIA indicated elevated levels over post-menopausal controls in 20% of the metastatic patients. Only 3% of the primary patients had elevated serum levels. These results suggest that the placental isoenzyme of alkaline phosphatase may be a useful tumor marker for recurrent breast cancer.