Estrogens are not required for prolactin induced growth of MCF-7 human breast cancer cells

MCF-7 human breast cancer cells in continuous culture respond to the growth promoting activity of prolactin. Within 3 days of addition to culture medium in the presence of charcoal stripped fetal bovine serum which is depleted of bovine lactogens and estrogens, prolactin at 250 ng/ml promotes a 2- to 3-fold increase in cell number. When phenol red, which is a weak estrogen agonist, is also eliminated from the medium, the cells respond to prolactin to the same extent. When cells are grown for two generations in the presence of lactogen free, phenol red free, charcoal stripped serum, the prolactin induced response is even greater. Human and ovine prolactins are equipotent. The ability of the cells to bind lactogenic hormones remains unaltered by elimination of phenol red from the growth medium. These data indicate that prolactin alone is a mitogen for human breast cancer cells in long-term culture.