Identification of gene regulation patterns underlying both E2- and tamoxifen-stimulated cell growth through global gene expression profiling in breast cancer cells [MCF-7]

A c-Src inhibitor blocks estrogen (E2)-induced stress and converts E2 responses from inducing apoptosis to growth stimulation in E2-deprived breast cancer cells. A reprogrammed cell line, MCF-7:PF, results with features of functional estrogen receptor (ER) and over-expression of insulin-like growth factor-1 receptor beta (IGF-1Rß). We addressed the question of whether the selective ER modulator 4-hydroxytamoxifen (4-OHT) could target ER to prevent E2-stimulated growth in MCF-7:PF cells. Selected expression of mRNA was measured through real-time RT-PCR. Global gene expression was analyzed by microarray and RNA-seq analysis. Unexpectedly, both 4-OHT and E2 stimulated cell growth in a concentration-dependent manner. Global gene expression analysis showed a remarkable overlap in genes regulated in the same direction by E2 and 4-OHT. Pathway enrichment analysis of the 280 genes commonly deregulated by 4-OHT and E2 revealed functions mainly related to membrane, cytoplasm, and metabolic processes. Further analysis of 98 up-regulated genes by both 4-OHT and E2 uncovered a significant enrichment in genes associated with membrane remodeling, cytoskeleton reorganization, cytoplasmic adapter proteins, cytoplasm organelles proteins, and related processes. 4-OHT was more potent than E2 to up-regulate some membrane remodeling molecules, such as EHD2, FHL2, HOMER3 and RHOF. In contrast, 4-OHT acted as an antagonist to inhibit expression of the majority of enriched membrane-associated genes in wild-type MCF-7 cells. Long-term selection pressure has changed the cell population responses to 4-OHT. Membrane-associated signaling is critical for 4-OHT-stimulated cell growth in MCF-7:PF cells. This study provides a rationale for the further investigation of targeted therapy for tamoxifen resistant patients. Overall design: Wild-type MCF-7 cells were treated with vehicle control (0.1% ethanol), E2 (10-9 mol/L) and 4-OHT (10-6 mol/L) respectively for 24 hours.

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Fan P, Cunliffe HE, Griffith OL, Agboke FA, Ramos P, Gray JW, Jordan VC