Ligand-independent activation of oestrogen receptor alpha by caveolin-1.
Expression of caveolin-1 in the human mammary adenocarcinoma cell line MCF-7 causes ligand-independent concentration of oestrogen receptor alpha (ERalpha) in the nucleus, and potentiates ligand-independent and ligand-dependent transcription from an oestrogen response element-driven reporter gene. Furthermore, caveolin-1 co-immunoprecipitates with ERalpha [Schlegel, Wang, Katzenellenbogen, Pestell and Lisanti (1999) J. Biol. Chem. 274, 33551-33556]. In the present study we show that caveolin-1 binds directly to ERalpha. This interaction is mediated by residues 82-101 of caveolin-1 (i.e. the caveolin scaffolding domain) and residues 1-282 of ERalpha. The caveolin-binding domain of ERalpha includes the ligand-independent transactivation domain, activation function (AF)-1, but lacks the hormone-binding domain and the ligand-gated transactivation domain, AF-2. In co-transfection studies, caveolin-1 potentiates the transcriptional activation of ERalpha(1-282), a truncation mutant that has intact AF-1 and DNA-binding domains. Since AF-1 activity is regulated largely by phosphorylation we determined that co-expression with caveolin-1 increased the basal phosphorylation of ERalpha(1-282), but blocked the epidermal growth factor-dependent increase in phosphorylation. Indeed, caveolin-1 interacted with and potentiated the transactivation of an ERalpha mutant that cannot be phosphorylated by extracellular signal-regulated kinase (ERK)1/2 [ERalpha(Ser(118)-->Ala)]. Thus caveolin-1 is a novel ERalpha regulator that drives ERK1/2-independent phosphorylation and activation of AF-1.
Schlegel
A
A
Department of Molecular Pharmacology, The Albert Einstein Cancer Centre, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
Wang
C
C
Pestell
R G
RG
Lisanti
M P
MP
D000818:Animals; D019556:COS Cells; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005786:Gene Expression Regulation; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D008024:Ligands; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation / Q000235:genetics*
C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D008024:Ligands; D011960:Receptors, Estrogen; D015534:Trans-Activators; D005982:Glutathione Transferase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases