title: The role of growth factor receptor pathways in human breast cancer cells adapted to long-term estrogen deprivation.
abstract: To study the long-term effects of estrogen deprivation on breast cancer, MCF-7Ca human estrogen receptor-positive breast cancer cells stably transfected with human aromatase gene were cultured in the steroid-depleted medium for 6 to 8 months until they had acquired the ability to grow. Proliferation of these cells (UMB-1Ca) was accompanied by increased expression of human epidermal growth factor receptor 2, increased activation of AKT through phosphorylation at Ser473 and Thr308, and increased invasion compared with parental MCF-7Ca cells. Estrogen receptor expression was also increased 5-fold. Although growth was inhibited by the antiestrogen fulvestrant, the IC50 was 100-fold higher than for parental MCF-7Ca cells. Aromatase inhibitor letrozole also inhibited growth at 10,000-fold higher concentration than required for MCF-7Ca cells, whereas anastrozole, exemestane, formestane, and tamoxifen were ineffective at 100 nmol/L. Growth of UMB-1Ca cells was inhibited by phosphatidylinositol 3-kinase inhibitor wortmannin (IC50 approximately 25 nmol/L) and epidermal growth factor receptor kinase inhibitor gefitinib (ZD 1839; IC50 approximately 10 micromol/L) whereas parental MCF-7Ca cells were insensitive to these agents. Concomitant treatment of UMB-1Ca cells with the signal transduction inhibitors and anastrozole and tamoxifen restored their growth inhibitory effects. These studies show that estrogen deprivation results in up-regulation of growth factor signaling pathways, which leads to a more aggressive and hormone refractory phenotype. Cross-talk between ER and growth factor signaling was evident as inhibition of these pathways could restore estrogen responsiveness to these cells.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland Baltimore, Baltimore, Maryland 21201, USA.
authors.forename: Gauri J
authors.initials: GJ
authors.lastname: Sabnis
authors.forename: Danijela
authors.initials: D
authors.lastname: Jelovac
authors.forename: Brian
authors.initials: B
authors.lastname: Long
authors.forename: Angela
authors.initials: A
authors.lastname: Brodie
mesh_terms: D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D018450:Disease Progression; D004789:Enzyme Activation; D004967:Estrogens / Q000172:deficiency* / Q000502:physiology; D006801:Humans; D009361:Neoplasm Invasiveness; D009376:Neoplasms, Hormone-Dependent / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D020239:Receptor Cross-Talk / Q000502:physiology; D011960:Receptors, Estrogen / Q000502:physiology*; D017978:Receptors, Growth Factor / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D015854:Up-Regulation
chemical_list: D004967:Estrogens; D011518:Proto-Oncogene Proteins; D011960:Receptors, Estrogen; D017978:Receptors, Growth Factor; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt