ESTROGENIC AND ANTIESTROGENIC REGULATION OF ESTROGEN-RECEPTOR IN MCF-7 BREAST-CANCER CELLS - COMPARISON OF IMMUNOCYTOCHEMICAL DATA WITH BIOCHEMICAL MEASUREMENTS

Data from immunocytochemical assessment of estrogen receptor (ER) regu lation in MCF-7 cells under estrogenic and anti-estrogenic stimulation were compared with those obtained by enzyme immunoassay (Abbott ER-EI A), Similar trends were observed, although ER level variations were le ss marked when assessed immunocytochemically. We confirmed reports of ER disappearance in the presence of estrogens (Es; E-2 and DES) and pu re anti-estrogens (AEs; RU 58,668 and ICI 164,384) as well as its incr ease with partial AEs (4-OH-TAM and RU 39,119), E-2-induced ER down-re gulation was partly blocked by actinomycin D (AMD), okadaic acid (OK) and cycloheximide (CHX) when assessed by these 2 methods. Down-regulat ion by pure AEs was not impeded by CHX, indicating that: they operate differently from Es (i.e., transformation of ER to a form sensitive to constitutive degradation activity), In situ pre-labeling of the cells with [H-3]TAZ indicated that all investigated ligands eliminate pre-e xisting ER through binding to newly synthetized receptors, since [H-3] TAZ co-valently associates with ER; Eland RU 58,668 were more effectiv e than 4-OH-TAM in this regard. CHX blocked ER disappearance even in t he presence of pure AEs, which is in contrast to the data established with cells not pre-exposed to [H-3]TAZ. Nuclear location of [H-3]TAZ-E R complexes may explain this discrepancy, since pure AE-ER complexes w ere reported to be incapable of nuclear translocation, (C) 1998 Wiley- Liss, Inc.