Adaptive mechanisms induced by long-term estrogen deprivation in breast cancer cells.
Clinical observations suggest that human breast tumors can adapt in response to endocrine therapy by developing hypersensitivity to estradiol. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided evidence that long-term deprivation of estradiol causes adaptive hypersensitivity. The enhanced responses to estradiol do not involve mechanisms acting at the level of transcription of estrogen regulated genes. We found no evidence of hypersensitivity when examining the effects of estradiol on regulation of c-myc, pS2, progesterone receptor, several ER reporter genes or c-myb in hypersensitive cells. On the other hand, deprivation of breast cells long term was found to up-regulate a separate pathway whereby the estrogen receptor co-opts a classical growth factor pathway and induces rapid non-genomic effects. Through this pathway, estradiol caused rapid activation of mitogen-activated protein (MAP) kinase. In exploring the mechanisms mediating this event, we found that estradiol binds to cell membrane associated estrogen receptors and causes phosphorylation of Shc, an adaptor protein usually involved in growth factor signaling pathways. ERalpha was found to complex with Shc under these conditions. In turn, Shc bound Grb-2 and Sos which resulted in the activation of MAP kinase. The pure antiestrogen, ICI 182,780, blocked several steps in the rapidly responding ER alpha, Shc, MAP kinase pathway. These non-genomic effects of estradiol produced biologic effects by activating Elk and by inducing morphologic changes in cell membranes. Using confocal microscopy, we demonstrated that estradiol caused a rapid alteration in membrane ruffling, the formation of pseudopodia and translocation of ER alpha to regions contiguous with the cell membrane. These morphologic effects could be blocked with a pure anti-estrogen. We conclude that long-term estradiol deprived cells utilize both genomic (transcriptional) and rapid, non-genomic estradiol induced pathways. We postulate that synergy between these two pathways acting at the level of the cell cycle is responsible for adaptive hypersensitivity.
Song
R X
RX
Department of Medicine, University of Virginia Health Sciences System, Charlottesville, VA, USA.
Santen
R J
RJ
Kumar
R
R
Adam
L
L
Jeng
M-H
MH
Masamura
S
S
Yue
W
W
D000222:Adaptation, Physiological; D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D018929:Cell Culture Techniques / Q000379:methods; D002455:Cell Division / Q000187:drug effects; D004342:Drug Hypersensitivity; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D006133:Growth Substances / Q000502:physiology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011960:Receptors, Estrogen / Q000502:physiology; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D004967:Estrogens; D006133:Growth Substances; D011506:Proteins; D011960:Receptors, Estrogen; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D004958:Estradiol; D020928:Mitogen-Activated Protein Kinases