Estrogen receptor phosphorylation. Hormonal dependence and consequence on specific DNA binding.

We have shown that the 32P-phosphorylation of the nuclear estrogen receptor from human MCF-7 cells or the calf uterus is estrogen-dependent. Within 2 min of estradiol treatment the phosphorylation of the estrogen receptor from MCF-7 cells doubled, and increased 4-fold within 20-40 min of estradiol treatment. Progesterone was ineffective in stimulating the phosphorylation of the estrogen receptor. Phosphoamino acid analysis indicated that the estrogen-stimulated phosphorylation of the human or calf estrogen receptor occurred only on serine residue(s). Phosphotryptic peptide analysis of the human estrogen receptor by two-dimensional peptide mapping or reverse-phase high pressure liquid chromatography revealed that only a single tryptic peptide (site) was phosphorylated. Treatment of the estrogen receptor with potato acid phosphatase resulted in the dephosphorylation of the 32P-labeled estrogen receptor and a decrease of the receptor's affinity for specific DNA sequences. These data suggest that transcriptional activation by the estrogen receptor involves an estrogen-dependent phosphorylation of the receptor resulting in its increased affinity for specific DNA sequences.