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Effect of Fbxo22 on ER and SRC-3 recruitment to the genomic loci

ABSTRACT: The agonistic/antagonistic bio-character of selective estrogen receptor modulators (SERMs) can have therapeutic advantages, particularly in the case of premenopausal breast cancers. Although the contradictory effects of these modulators have been studied in terms of cross-talk between estrogen receptor (ER)-coactivator dynamics and growth factor signaling, the molecular basis of these mechanisms is still obscure. We demonstrate here an unidentified series of regulatory mechanisms controlling cofactor dynamics on ER and SERM function whose activities require F-box protein 22 (Fbxo22). Skp, Cullin, F-box containing complex (SCF)Fbxo22 ubiquitylates lysine demethylase 4B (KDM4B) complexed with tamoxifen-bound ER, whose degradation releases steroid receptor coactivator (SRC) from ER. Depletion of Fbxo22 results in ER-dependent transcriptional activation via transactivation function 1 (AF1) function even in the presence of SERMs. In living cells, tamoxifen releases SRC and KDM4B from ER in a Fbxo22-dependent manner. SRC release by tamoxifen requires Fbxo22 on almost all ER-SRC-bound enhancer/promoters. Tamoxifen fails to prevent growth of Fbxo22-depleted ER-positive breast cancers both in vitro and in vivo. Clinically, a low level of Fbxo22 in tumor tissues predicts a poorer outcome in ER-positive/Human Epidermal Growth Factor Receptor Type 2 (HER-2)-negative breast cancers with high hazard ratios independently of other markers such as Ki-67 and node status. We propose that the level of Fbxo22 in tumor tissues defines a new subclass of ER-positive breast cancers for which patients SCFFbxo22-mediated KDM4B degradation can be a therapeutic target by the next generation of SERMs. We carried out the analysis using MCF-7 and Fbxo22-depleted MCF-7 cells. Cells were estrogen-starved for 72 hrs and subsequently stimulated for 2 hrs by E2 (10 nM) or E2 plus TAM. As a result, we identified a total of 12,645 and 23,216 enriched ER peaks in MCF-7 and Fbxo22-depleted MCF-7cells, respectively, in cells treated with E2, and 26,751 and 19,924 enriched ER peaks in MCF-7 and Fbxo22-depleted MCF-7cells, respectively, in cells treated with E2 plus 4-OHT.

ORGANISM(S): Homo sapiens

PROVIDER: GSE119702 | GEO | 2018/12/26

REPOSITORIES: GEO

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Project description:MCF-7:PF is a a new in vitro model of antihormone resistant breast cancer that exhibits the characteristics of acquired tamoxifen resistance in vivo. It is well known that estrogen (E2) induces apoptosis in long-term estrogen-deprived breast cancer cells, MCF-7:5C (PubMed References PMID:15862958, PMID:16333030). MCF-7:PF was derived from MCF-7:5C through inhibition of c-Src, which blocks E2-induced apoptosis, coverts E2 responses from apoptosis to proliferation. MCF-7:PF cell growth is stimulated by E2 and SERMS in an ERα-dependent manner. Abstract: A c-Src inhibitor blocks estrogen (E2)-induced stress and converts E2 responses from inducing apoptosis to stimulating growth in E2-deprived breast cancer cells. A resulting cell line, MCF-7:PF, is reprogrammed with features of functional estrogen receptor (ER) and over-expression of insulin-like growth factor-1 receptor beta (IGF-1Rβ). We addressed the question of whether the antiestrogenic selective ER modulator 4-hydroxytamoxifen (4-OHT) could target ER to prevent E2-stimulated growth in MCF-7:PF cells. Unexpectedly, 4-OHT stimulated cell growth in an ER-dependent manner. However, unlike E2, 4-OHT suppressed classic ER-target genes as does the pure antiestrogen ICI 182,780, even during growth stimulation. Chromatin-immunoprecipitation (ChIP) assay indicated that 4-OHT did not recruit ER or nuclear receptor coactivator 3 (SRC3) to the promoter of ER-target gene, pS2. Paradoxically, 4-OHT reduced total IGF-1Rβ but increased phosphorylation of IGF-1Rβ, which was responsible for the activation of the phosphatidylinositol-3 kinases (PI3K)/Akt signaling pathway. Mechanistic studies revealed that 4-OHT rapidly activated the non-genomic pathway through ER, but other membrane-associated proteins such as IGF-1Rβ and c-Src participated. Furthermore, 4-OHT was more potent than E2 to up-regulate membrane remodeling molecules and activated focal adhesion molecules to promote cell growth. Therefore, disruption of membrane-associated signaling completely abolished 4-OHT-stimulated cell growth, but not E2-stimulated cell growth. Despite continued suppression of classic ER-target genes, 4-OHT activated the complex network of cytoskeleton remodeling and extracellular matrix-related signaling which facilitated 4-OHT-stimulated cell growth. This study is the first to recapitulate a cellular model in vitro of acquired tamoxifen (TAM) resistance developed in athymic mice in vivo.

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Effect of Fbxo22 on ER and SRC-3 recruitment to the genomic loci

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