Interferon as a modifier of estrogen receptors.

Interferon (IFN-alpha) increased estrogen receptor (ER) activity in human breast cancer tissue, human uterus (endometrium), and rabbit uterus. The optimum response was obtained with three different doses of IFN-alpha 10, 100, and 1000 U per ml. Escalation of the dose up to 5000 U per ml did not increase further ER activity. Cytosol fractions with zero or low binding activity (below 10 fm per mg) did not respond to IFN-alpha treatment. Addition of antibodies against IFN-alpha resulted in abrogation of IFN-alpha effect. Use of recombinant IFN-alpha or highly purified lymphoblastoid IFN-alpha showed similar effects on ER. The mechanism of the augmentation effect of ER activity by IFN-alpha is not clear. The increase of ER activity may have important clinical applications if the same is obtained in vivo.