Abstract
Human breast cancer cells in tissue culture (MCF-7) were pretreated with the antiestrogen nafoxidine to arrest cellular proliferation and then were given estradiol to release this block and stimulate DNA synthesis and cell division. During this period of growth stimulation intracellular proteins, labeled by a double isotope method, were analyzed on SDS-polyacrylamide gel electrophoresis. Estradiol directly increases the rates of synthesis of specific proteins which migrate on SDS-gels at molecular weights of 24,000 and 36,000. Nafoxidine-pretreatment alone does not induce these same proteins, and no changes in the rates of specific protein synthesis occur in cells grown on control medium for the same length of time as on estradiol. Induced synthesis of these proteins is observed only during the period of estrogen stimulation of cell proliferation following pretreatment with nafoxidine. We do not detect induction when cells are incubated with estradiol without antiestrogen-pretreatment. Since rescue of antiestrogen growth inhibition is also the only condition under which MCF-7 cell division can be reproducibly stimulated by estrogen, these proteins may be related to estrogen effects on cellular proliferation.
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