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Characterization of the Estrogen Receptor in Two Antiestrogen-resistant Cell Lines, LY2 and T47D¹

Laboratoire de Génétique Moléculaire des Eucaryotes du CNRS, Unité 184 de Biologie Moléculaire et de Génie Génétique de l'INSERM, Institut de Chimie Biologique, Faculté de Médecine, 11, rue Humann, 67085 Strasbourg Cédex, France

Drug resistance occurs frequently during breast cancer treatment with antiestrogens. Since antiestrogen action is mediated by the estrogen receptor (ER), we have examined both the structural and functional properties of the ER present in two breast cancer cell lines, LY2 and T47D, which proliferate rapidly in the presence of antiestrogens. The ER function in LY2 cells was indistinguishable from that of the parental tamoxifen-sensitive MCF-7 cells as assessed by estrogen regulation of two endogenous genes and estrogen-regulated transcription in a transient transfection system. RNase protection assays, sensitive enough to detect single base pair mismatches, showed that the sequence of the coding region of ER of LY2 and T47D cells was wild type. Thus the ER appears to be normal in two independently isolated breast cancer cell lines whose growth is resistant to the inhibitory effect of antiestrogens. Moreover by conducting the cell proliferation studies in a phenol red-free medium, we have demonstrated that the antiestrogen resistance of LY2 and T47D cells corresponds in fact to an estrogen-independent growth.

¹ The present work was supported by grants from the CNRS, the INSERM (CNAMTS), the Ministère de la Recherche et de l'Enseignement Supérieur, the Fondation pour la Recherche Médicale, the Ligue Nationale Française contre le Cancer and the Association pour la Recherche contre le Cancer.

² Present address: Institut de Recherches Cliniques de Montréal, Montréal, Québec H2W 1R7, Canada. To whom requests for reprints should be sent.

Received 7/ 7/89. Revised 10/10/89. Accepted 10/16/89.

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