Phosphorylation of Ser211 in the Chicken Progesterone Receptor Modulates Its Transcriptional Activity

The chicken progesterone receptor has been shown to be phosphorylated in vivo at four major sites. Previous studies have shown that mutation of one of the hormone-dependent phosphorylation sites, Ser530, to alanine decreases the transcriptional activity of the receptor under conditions where ligand is limited. Here, we present evidence for the functional significance of another phosphorylation site, Ser211. Mutation of Ser211 to alanine results in a decrease in the transcriptional activity of the receptor and affects the phosphorylation-dependent decrease in mobility of the receptor in SDS-polyacrylamide gel electrophoresis. The degree of reduction in transcriptional activity is dependent on both the cell type and the reporters used in the studies but is independent of hormone concentration, suggesting that phosphorylation at Ser211 regulates the activity of the receptor through a mechanism distinct from Ser530 phosphorylation.