pp90rsk1 regulates estrogen receptor-mediated transcription through phosphorylation of Ser-167.

The estrogen receptor alpha (ER), a member of the steroid receptor superfamily, contains an N-terminal hormone-independent transcriptional activation function (AF-1) and a C-terminal hormone-dependent transcriptional activation function (AF-2). Here, we used in-gel kinase assays to determine that pp90rsk1 activated by either epidermal growth factor (EGF) or phorbol myristate acetate specifically ...
phosphorylates Ser-167 within AF-1. In vitro kinase assays demonstrated that pp90rsk1 phosphorylates the N terminus of the wild-type ER but not of a mutant ER in which Ser-167 was replaced by Ala. In vivo, EGF stimulated phosphorylation of Ser-167 as well as Ser-118. Ectopic expression of active pp90rsk1 increased the level of phosphorylation of Ser-167 compared to that of either a mutant pp90rsk1, which is catalytically inactive in the N-terminal kinase domain, or to that of vector control. The ER formed a stable complex with the mutant pp90rsk1 in vivo. Transfection of the mutant pp90rsk1 depressed ER-dependent transcription of both a wild-type ER and a mutant ER that had a defective AF-2 domain (ER TAF-1). Furthermore, replacing either Ser-118 or Ser-167 with Ala in ER TAF-1 showed similar decreases in transcription levels. A double mutant in which both Ser-118 and Ser-167 were replaced with Ala demonstrated a further decrease in transcription compared to either of the single mutations. Taken together, our results strongly suggest that pp90rsk1 phosphorylates Ser-167 of the human ER in vivo and that Ser-167 aids in regulating the transcriptional activity of AF-1 in the ER.
Mesh Terms:
Animals, COS Cells, Catalysis, Chromosomal Proteins, Non-Histone, Cricetinae, DNA-Binding Proteins, Epidermal Growth Factor, Furylfuramide, Histone Chaperones, Humans, Leucine Zippers, Phosphorylation, Protein Kinases, Receptors, Estrogen, Receptors, Interferon, Ribosomal Protein S6 Kinases, 90-kDa, Serine, Transcription Factors, Transcription, Genetic, Tumor Cells, Cultured
Mol. Cell. Biol.
Date: Apr. 01, 1998
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