The phosphorylated membrane estrogen receptor and cytoplasmic signaling and apoptosis proteins in human breast cancer.
BACKGROUND
Estrogens play a central role in breast cancer development, and the estrogen receptor-alpha (ERalpha) remains the single most important predictor of breast cancer prognosis. Therefore, it is crucial to elucidate pathways that may contribute to ER signaling in clinical specimens.


METHODS
Using extracts of fresh invasive ERalpha-positive invasive breast carcinomas, ductal carcinoma in situ, and normal glandular breast tissue, the authors performed Western blot analyses of the membrane-bound ER, 1 of its phosphorylated isoforms, and cytosolic fractions from the same specimens, examining associated proteins (Akt/mitogen-activated protein kinase pathways). Western blot analysis and immunocapture for the apoptosis and survival factors Bcl-2 agonist of death (BAD)/Bcl-2 and BAD/Bcl-xL were also performed.


RESULTS
To the authors' knowledge, this is the first study to report that ERalpha was phosphorylated in the plasma membrane fractions derived from patients' invasive breast carcinomas. This was associated with a predominance of phosphorylated BAD and a relative reduction in Bcl-2 compared with both normal tissue and ductal carcinoma in situ, although such studies in fresh tissue did not corroborate these findings. The authors also demonstrated that the BAD/Bcl-2 and BAD/Bcl-xL complexes characterized the invasive carcinoma state.


CONCLUSIONS
A phosphorylated form of the membrane ER was found to characterize the invasive cancer state. This was associated with a reduction in BAD/Bcl-2 and BAD/Bcl-xl. These data implicate the membrane ERalpha as the in vivo receptor responsible for transcription-independent cellular responses to estrogens.
Mintz
Paul J
PJ
Department of Biosurgery and Surgical Technology, Faculty of Medicine, Imperial College London, London, United Kingdom. p.mintz@imperial.ac.uk
Habib
Nagy A
NA
Jones
Louise J
LJ
Giamas
Georgios
G
Lewis
Jacqueline S
JS
Bowen
Rebecca L
RL
Coombes
R Charles
RC
Stebbing
Justin
J
D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis / Q000502:physiology*; D001940:Breast / Q000378:metabolism / Q000473:pathology; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism / Q000473:pathology; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000378:metabolism / Q000473:pathology; D002462:Cell Membrane / Q000378:metabolism / Q000473:pathology; D003593:Cytoplasm / Q000378:metabolism* / Q000473:pathology; D003600:Cytosol / Q000378:metabolism / Q000473:pathology; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D006801:Humans; D047468:Immunoprecipitation; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009361:Neoplasm Invasiveness; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D051025:bcl-Associated Death Protein / Q000378:metabolism*; D051020:bcl-X Protein / Q000378:metabolism*
D047628:Estrogen Receptor alpha; D004967:Estrogens; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; C494819:BAD protein, human; C494811:BCL2L1 protein, human; C506487:ESR1 protein, human