The role of phosphorylation in human estrogen receptor function

Area of Science:

• Molecular biology
• Endocrinology
• Cancer research

Background:

• The human estrogen receptor (hER) is a key regulator of gene expression.
• Phosphorylation at serine 118 (Ser118) has been implicated in hER transactivation.
• The precise role of Ser118 phosphorylation in hER function requires further elucidation.

Purpose of the Study:

• To investigate the functional significance of hER phosphorylation at Ser118.
• To determine the impact of Ser118 phosphorylation on hER transcriptional activity, hormone binding, and DNA binding.
• To analyze the phosphorylation pattern of a Ser118 mutant hER in different cell types.

Main Methods:

• Site-directed mutagenesis of hER at Ser118 to alanine.
• Yeast and cell-free transcription assays to measure transcriptional activity.
• Hormone binding assays and electrophoretic mobility shift assays (EMSAs) for DNA binding.
• Western blot analysis to assess phosphorylation patterns in COS-1, Sf9, and HeLa cells.

Main Results:

• Mutation of Ser118 to alanine resulted in a 30-40% decrease in hER-dependent transcription.
• The Ser118 mutation did not affect the binding affinity of hER for estradiol or an estrogen response element (ERE).
• The mutant hER exhibited an altered phosphorylation pattern in COS-1 and Sf9 cells, but not in HeLa cells.

Conclusions:

• Phosphorylation of hER at Ser118 plays a significant role in regulating its transcriptional activity.
• Ser118 phosphorylation is important for transactivation but not for hormone or DNA binding.
• Cell-specific differences exist in the phosphorylation patterns of the hER mutant.