Binding Analysis of the Estrogen Receptor to Its Specific DNA Target Site in Human Breast Cancer

The estrogen receptor (KR) is a nuclear protein with a hormone- and a DNA-binding domain. \\e examined the DNA binding of KR in MCK- 7 cells and 79 primary breast cancers by gel mobility shift assay using as a probe the estrogen response element (KRK). The mobility shift assay showed saturable, specific binding of IK to KRK in crude, high molar extracts containing 2:4 mg/ml protein. Nonspecific binding was reduced by increasing concentrations of poly(deoxyinosidylate · deocoxycytidylate) and shortening of the KRK probe from 35 to 15 base pairs. In the presence of Mg:+ the KR-KRK complex formation was hormone depend ent at 22°Cbut not at 37°C.In the absence of Mg;+ estradiol was not necessary for KR-KRK complex formation. Correlation of the mobility shift assay with the hormone-binding (K;) assay showed agreement in 55 of the 79 tumors. Both assays were positive (E;+/KRK+) in 35 cases and both were negative (E2-/ERE+) 20 cases. In 11 tumors the hormonebinding assay was positive and the mobility shift assay negative (I + KRK-),suggesting an alteration of the DNA-binding domain. In 13 cancers the hormone-binding assay was negative and the mobility shift assay positive (Kj-/ERK+) suggesting an alteration of the hormonebinding domain. By performing both hormone- and DNA-binding assays of KR and the hormone-binding assay of progesterone receptor (PR), we found the following subgroups of breast cancer: (a) E2+/ERE+/PR+, (b) E2+/ERE+/PR-, (c)E2+/ERE-/PR+, (d)E2+/ERE-/PR-, (e)E2-/ERE+/PR+, (f)E2+/ERE+/PR-,(g)E2-/ERE-/PR-. The simulta neous determination of 17/3-estradiol and KRK binding may provide a better definition of the KR status of individual tumors and prove useful in refining endocrine therapy of patients with breast cancer.