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Effect of Growth on the Estrogen Receptor Levels in MCF-7 Cells¹

Department of Biochemistry, Wayne State University School of Medicine, Detroit, Michigan 48201

MCF-7 cells have been shown to contain estrogen receptor in several cell fractions following homogenization: nuclei, microsomes, and cytosol. The amount of 17ß-estradiol-binding capacity found in each cellular compartment dependent on the inclusion of detergent in homogenization buffers and on the use of 0.25 M sucrose in the nuclear washes. 17ß-Estradiol receptor (E₂R) associated with nuclei (whole nuclei exchange assay, 0.6 M KCI soluble, and that found on membranes sheared from crude nuclear pellets by centrifugation in 0.25 M sucrose buffer) displayed a dissociation constant (K_d) of 0.77 ± 0.01 (S.D.) nM (n = 7). K_ds of the cytoplasmic (microsomes and soluble) receptors were determined to be 0.33 ± 0.10 nM (n = 9). Exchangeable ligand on partially purified nuclei assumed its highest level in MCF-7 cells during logarithmic growth in serum-containing media (0.8 pmol/µg DNA) but declined after the culture reached confluence (0.2 pmol/µg DNA). Seventy-five % of the nuclear E₂R declined linearly after feeding MCF-7 cells in logarithmic growth phase an estrogen- and serum-free medium (t_v2 3.5 days). Another class of salt-extractable nuclear receptor (0.2 pmol/µg DNA) persisted in postconfluent cultures whether fed estrogen (serum-containing media) or not (serum-free media). This residual binding capacity remained in nuclei of MCF-7 cells for an extended period of time. MCF-7 cells demonstrated functionality of E₂R throughout their growth phases as evidenced by the replenishment of cytosolic E₂R and the induction of progesterone receptor when given 17ß-estradiol.

¹ Supported in part by NIH Grant CA-22828 from the National Cancer Institute.

² To whom requests for reprints should be addressed.

³ Present address: Clinical Chemistry Department, Veterans Administration Hospital, Ann Arbor, MI 48105.

⁴ Present address: Innovative Research of America, P. O. Box 5688, Rockville, MD 20855.

Received 8/29/83. Accepted 5/17/84.