title: Estrogen utilization of IGF-1-R and EGF-R to signal in breast cancer cells.
abstract: As breast cancer cells develop secondary resistance to estrogen deprivation therapy, they increase their utilization of non-genomic signaling pathways. Our prior work demonstrated that estradiol causes an association of ERalpha with Shc, Src and the IGF-1-R. In cells developing resistance to estrogen deprivation (surrogate for aromatase inhibition) and to the anti-estrogens tamoxifen, 4-OH-tamoxifen, and fulvestrant, an increased association of ERalpha with c-Src and the EGF-R occurs. At the same time, there is a translocation of ERalpha out of the nucleus and into the cytoplasm and cell membrane. Blockade of c-Src with the Src kinase inhibitor, PP-2 causes relocation of ERalpha into the nucleus. While these changes are not identical in response to each anti-estrogen, ERalpha binding to the EGF-R is increased in response to 4-OH-tamoxifen when compared with tamoxifen. The changes in EGF-R interactions with ERalpha impart an enhanced sensitivity of tamoxifen-resistant cells to the inhibitory properties of the specific EGF-R tyrosine kinase inhibitor, AG 1478. However, with long term exposure of tamoxifen-resistant cells to AG 1478, the cells begin to re-grow but can now be inhibited by the IGF-R tyrosine kinase inhibitor, AG 1024. These data suggest that the IGF-R system becomes the predominant signaling mechanism as an adaptive response to the EGF-R inhibitor. Taken together, this information suggests that both the EGF-R and IGF-R pathways can mediate ERalpha signaling. To further examine the effects of fulvestrant on ERalpha function, we examined the acute effects of fulvestrant, on non-genomic functionality. Fulvestrant enhanced ERalpha association with the membrane IGF-1-receptor (IGF-1-R). Using siRNA or expression vectors to knock-down or knock-in selective proteins, we further demonstrated that the ERalpha/IGF-1-R association is Src-dependent. Fulvestrant rapidly induced IGF-1-R and MAPK phosphorylation. The Src inhibitor PP2 and IGF-1-R inhibitor AG1024 greatly blocked fulvestrant-induced ERalpha/IGF-1-R interaction leading to a further depletion of total cellular ERalpha induced by fulvestrant and further enhanced fulvestrant-induced cell growth arrest. More dramatic was the translocation of ERalpha to the plasma membrane in combination with the IGF-1-R as shown by confocal microscopy. Taken in aggregate, these studies suggest that secondary resistance to hormonal therapy results in usage of both IGF-R and EGF-R for non-genomic signaling.
authors.affiliation: Department of Internal Medicine, University of Virginia School of Medicine, 450 Ray Hunt Dr., Charlottesville, VA 22903, USA.
authors.forename: Robert X-D
authors.initials: RX
authors.lastname: Song
authors.forename: Yuchai
authors.initials: Y
authors.lastname: Chen
authors.forename: Zhenguo
authors.initials: Z
authors.lastname: Zhang
authors.forename: Yongde
authors.initials: Y
authors.lastname: Bao
authors.forename: Wei
authors.initials: W
authors.lastname: Yue
authors.forename: Ji-Ping
authors.initials: JP
authors.lastname: Wang
authors.forename: Ping
authors.initials: P
authors.lastname: Fan
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Santen
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D066246:ErbB Receptors / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047628:Estrogen Receptor alpha; D004967:Estrogens; D000077267:Fulvestrant; D004958:Estradiol; D066246:ErbB Receptors; D017526:Receptor, IGF Type 1; D020928:Mitogen-Activated Protein Kinases