Immunological and physiological analysis of human breast cancer progesterone receptor heterogeneity, following KCl dissociation and size exclusion chromatography

Measurement of insulin-like growth factor (IGF)-II binding to purified IGF binding proteins 1-6: comparison of charcoal adsorption and high performance size exclusion chromatography

Insulin-like growth factor (IGF) binding to IGF binding proteins is commonly assessed by adsorbing free IGF to albumin-coated charcoal and quantitating bound IGF in the supernatant, but the validity of this technique has been questioned and many variations have been described. We compared the measurement of binding affinity and capacity of purified IGFBPs 1-6 for IGF-II using charcoal adsorption and Superdex G75 high performance size exclusion chromatography (HPSEC) to separate free and bound 125I-IGF-II. Optimal HPSEC recovery and resolution was obtained for IGFBP-1 and IGFBP-6 with low salt buffer (0.1 M sodium phosphate, pH 7.4), whereas phosphate buffer supplemented with 0.5 M NaCl was optimal for IGFBPs 2-5. Measurement of binding of 125I-IGF-II to IGFBPs 3-5 using the charcoal assay was also increased by the use of high salt buffer. Under optimal conditions, charcoal measurements of 125I-IGF-II binding to IGFBPs 1-5 were consistently lower than HPSEC measurements. By competitive binding using unlabeled IGF-II, the binding affinity of each of the IGFBPs for IGF-II was the same using both methods. Similarly, binding affinities as measured by charcoal assay were not affected by buffer composition. Differences in total binding obtained using the two methods and under different conditions were therefore due to differences in binding capacity. Charcoal adsorbs 15% of cross-linked 125I-IGF-II:IGFBP complexes which may partially explain the lower binding capacity for IGFBPs 1-5 determined by charcoal adsorption. Charcoal adsorption and HPSEC, therefore, are both valid methods for the measurement of binding affinities of IGFBPs for IGF-II, but assay conditions must be validated prior to measurement of binding capacity.

Evolution of immunoreactivity of monoclonal antibodies H222 and/or D547 used in the detection of breast cancer estrogen receptors. Varying reactivity of receptor isoforms

From 1984 to 1990, human breast cancer estrogen receptors have been measured both by a radioligand assay (RLA[3H]estradiol) and by an enzyme immunoassay (Abbott ER-EIA kit). The ratio EIA/RLA results increased continuously from 1.04 (1984) to 1.87 (1990), and this evolution was consistent with the last trial of the E.O.R.T.C. receptor study group (Trial 1989-II, EIA/RLA = 2.5). Dilution studies of cytosols with the current ER-EIA kits showed an important parallelism defect of the standard curve, the final result of cytosols (fmol/mg protein) obtained from the upper part of the curve (between 100 and 500 fmol/ml) being 1.5 to 2 times higher than the results obtained from readings of the lower part of the standard curve (between 0 and 50 fmol/ml). Chromatographic experiments were carried out during 1986 and the measures of binding sites by RLA and of immunoreactive sites by EIA on chromatographic fractions were compared. Identical results were obtained with EIA and RLA, either on polymeric forms of the estrogen receptor, or on monomeric forms obtained after dissociation by 0.4 M KCl. The same experiments performed during 1990 showed that, in the chromatographic fractions, the concentration of immunoreactive sites was twice as large as that of ligand-binding sites, detected by tritiated estradiol. Furthermore, the detection of polymeric and monomeric receptor isoforms by monoclonal antibodies varied, and was increased by the presence of KCl (0.4 M) and/or bovine serum albumin (BSA) (1 mg/ml) in the cytosol. These findings showed that the large differences between enzyme immunoassay and ligand-binding assay results currently observed were due to differential reactivity of monoclonal antibodies for the estrogen receptor standard provided in the ER-EIA kits and for the estrogen receptor present in cytosols from human breast cancers, suggesting modifications of immunoreactivity of the monoclonal antibodies actually provided in the ER-EIA kits.