Estrogen receptor alpha binds to peroxisome proliferator-activated receptor response element and negatively interferes with peroxisome proliferator-activated receptor gamma signaling in breast cancer cells.
OBJECTIVE
The molecular mechanisms involved in the repressive effects exerted by estrogen receptors (ER) on peroxisome proliferator-activated receptor (PPAR) gamma-mediated transcriptional activity remain to be elucidated. The aim of the present study was to provide new insight into the crosstalk between ERalpha and PPARgamma pathways in breast cancer cells.


METHODS
Using MCF7 and HeLa cells as model systems, we did transient transfections and electrophoretic mobility shift assay and chromatin immunoprecipitation studies to evaluate the ability of ERalpha to influence PPAR response element-mediated transcription. A possible direct interaction between ERalpha and PPARgamma was ascertained by co-immunoprecipitation assay, whereas their modulatory role in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway was evaluated by determining PI3K activity and AKT phosphorylation. As a biological counterpart, we investigated the growth response to the cognate ligands of both receptors in hormone-dependent MCF7 breast cancer cells.


RESULTS
Our data show for the first time that ERalpha binds to PPAR response element and represses its transactivation. Moreover, we have documented the physical and functional interactions of ERalpha and PPARgamma, which also involve the p85 regulatory subunit of PI3K. Interestingly, ERalpha and PPARgamma pathways have an opposite effect on the regulation of the PI3K/AKT transduction cascade, explaining, at least in part, the divergent response exerted by the cognate ligands 17beta-estradiol and BRL49653 on MCF7 cell proliferation.


CONCLUSIONS
ERalpha physically associates with PPARgamma and functionally interferes with PPARgamma signaling. This crosstalk could be taken into account in setting new pharmacologic strategies for breast cancer disease.
Bonofiglio
Daniela
D
Department of Pharmaco-Biology, University of Calabria, Cosenza, Italy.
Gabriele
Sabrina
S
Aquila
Saveria
S
Catalano
Stefania
S
Gentile
Mariaelena
M
Middea
Emilia
E
Giordano
Francesca
F
Andò
Sebastiano
S
D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism*; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D020218:Response Elements / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077154:Rosiglitazone; D015398:Signal Transduction; D045162:Thiazolidinediones / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D025521:Tumor Suppressor Proteins / Q000187:drug effects / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology
D004958:Estradiol; D047628:Estrogen Receptor alpha; D008024:Ligands; D047495:PPAR gamma; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D000077154:Rosiglitazone; D045162:Thiazolidinediones; D013936:Thymidine; D025521:Tumor Suppressor Proteins; D014665:Vasodilator Agents; C494918:AKT1 protein, human; C494929:PTEN protein, human