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The E-Screen Assay: A Comparison of Different MCF7 Cell Stocks

Mercedes Villalobos, Nicolás Olea, José Antonio Brotons, María Fátima Olea-Serrano, J. Mariano Ruiz de Almodovar, and Vicente Pedraza

Laboratorio de Investigaciones Médicas, Universidad de Granada, 18071 Granada, Spain

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Abstract
MCF7 human breast cancer cells have been studied extensively as a model for hormonal effects on breast cancer cell growth and specific protein synthesis. Because the proliferative effect of natural estrogen is considered the hallmark of estrogen action, it was proposed that this property be used to determine whether a substance is an estrogen. The E-screen assay, developed for this purpose, is based on the ability of MCF7 cells to proliferate in the presence of estrogens. The aim of our study was to characterize the response of four MCF7 cell stocks (BUS, ATCC, BB, and BB104) and determine which of them performed best in the E-screen test. The four stocks assayed were distinguishable by their biological behavior. In the absence of estrogen, MCF7 BUS cells stopped proliferating and accumulated in the G ₀ /G ₁ phase of the cell cycle; estrogen receptors increased, progesterone receptors decreased, and small amounts of pS2 protein were secreted. Of all the MCF7 stocks tested, MCF7 BUS cells showed the highest proliferative response to estradiol-17ß: cell yields increased up to sixfold over those of nontreated cells in a 144-hr period. The differences between estrogen-supplemented and nonsupplemented MCF7 BUS cells were due mostly to G ₀ /G ₁ proliferative arrest mediated by charcoal dextran-stripped serum. MCF7 BUS cell stocks and others showing a similar proliferative pattern should be chosen for use in the E-screen test, or whenever a proliferative effect of estrogen is to be demonstrated. Key words : bisphenol-A, cell type-specific proteins, estrogen sensitivity, hormone receptors, MCF7 cell variants, p -nonylphenol. Environ Health Perspect 103:844-850 (1995)

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Address correspondence to N. Olea, Department of Radiology, University of Granada, 18071 Granada, Spain.

We thank A.M. Soto and C. Sonnenschein (Tufts University, Boston) for providing MCF7 BUS cells and for helpful discussions and G. Leclercq (Institut Jules Bordet, Brussels) for providing MCF7 BB cells. We thank M.A. Lucena for help with the flow cytometry studies and K. Shashok for improving the English of the manuscript. This work was supported by grant 94/1551 from the Fondo de Investigaciones Sanitarias, Spanish Ministry of Health. This work was reported in part at the meeting "Estrogens in the Environment III: Global Health Implications," held in Washington, DC, 9-11 January 1994.

Received 3 February 1995; accepted 25 May 1995.

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