Mutation of Serines 104, 106, and 118 Inhibits Dimerization of the Human Estrogen Receptor in Yeast

Abstract

Ligand‐dependent dimerization and phosphorylation participate in regulating transcriptional activation of the estrogen receptor‐α (ER). We investigated the role of serines 104, 106, and 118 located in the activation function‐1 (AF‐1) domain of ER in ligand‐induced receptor dimerization. These serines, previously documented as important sites for transactivation, were mutated to alanine, and yeast genetic systems were used to determine their effect on receptor dimerization and transcriptional activity. The serine to alanine mutants resulted in 50–80% decreased dimerization in response to 17β‐estradiol, while having modest effects on ER‐mediated transactivation. We further demonstrated that ER expressed in yeast became hyperphosphorylated in the presence of estradiol, most likely at a site(s) different than the serines under investigation. Ligand‐induced phosphorylation was inhibited by U0126 indicating that the ER was phosphorylated via the MAPK pathway. Taken together, these data indicate that serines 104, 106, and 118 are important for ligand‐dependent ER dimerization, and that MAP kinase mediated phosphorylation may be important for ER function, in yeast model systems.

• Estrogen receptor
• Phosphorylation
• Dimerization
• MAP kinase
• Transactivation
• Yeast two‐hybrid

Acknowledgments

The authors would like to thank Dr. Mark Dudley (Quintiles, Inc., Kansas City, MO), Dr. Randal Morris, and Emma Lou Cardell (University of Cincinnati College of Medicine) for critically reading this manuscript. We also thank Matthew Sheeler for his technical assistance in preparing the mutant ERs.

This work was supported by funds from NIH/NICHD training grant (T32 HD07463‐05), (T32 CA59268), and ROICA72039.