Cyr61, a member of the CCN family of genes, is an angiogenic factor. We have shown that it is overexpressed in invasive and metastatic human breast cancer cells and tissues. Here, we investigated whether Cyr61 is necessary and/or sufficient to bypass the 'normal' estrogen (E2) requirements for breast cancer cell growth. Our results demonstrate that Cyr61 is sufficient to induce MCF-7 cells to grow in the absence of E2. Cyr61-transfected MCF-7 cells (MCF-7/Cyr61) became E2-independent but still E2-responsive. On the other hand, MCF-7 cells transfected with the vector DNA (MCF-7/V) remain E2-dependent. MCF-7/Cyr61 cells acquire an antiestrogen-resistant phenotype, one of the most common clinical occurrences during breast cancer progression. MCF-7/Cyr61 cells are anchorageindependent and capable of forming Matrigel outgrowth patterns in the absence of E2. ERa expression in MCF-7/Cyr61 cells is decreased although still functional. Moreover, MCF-7/Cyr61 cells are tumorigenic in ovariectomized athymic nude mice. The tumors resemble human invasive carcinomas with increased vascularization and overexpression of vascular endothelial growth factor (VEGF). Our results demonstrate that Cyr61 is a tumor-promoting factor and a key regulator of breast cancer progression. This study provides evidence that Cyr61 is sufficient to induce E2-independence and antiestrogen-resistance, and to promote invasiveness in vitro, and to induce tumorigenesis in vivo, all of which are characteristics of an aggressive breast cancer phenotype.

In 1998, an estrogen receptor β (ERβ) knockout (KO) mouse was created by interrupting the gene at the DNA binding domain (DBD) with a neocassette. The mutant females were subfertile and there were abnormalities in the brain, prostate, lung, colon, and immune system. In 2008, another ERβ mutant mouse was generated by deleting ERβ exon 3 which encodes the first zinc finger in the DBD. The female mice of this strain were unable to ovulate but were otherwise normal. The differences in the phenotypes of the two KO strains, have led to questions about the physiological function of ERβ. In the present study, we created an ERβ exon 3-deleted mouse (ERβ-Δex3) and confirmed that the only observable defect was anovulation. Despite the two in-frame stop codons introduced by splicing between exons 2 and 4, an ERβ protein was expressed in nuclei of prostate epithelial cells. Using two different anti-ERβ antibodies, we showed that an in-frame ligand binding domain and C terminus were present in the ERβ-Δex3 protein. Moreover, with nuclear extracts from ERβ-Δex3 prostates, there was an ERβ-dependent retardation of migration of activator protein-1 response elements in EMSA. Unlike the original knockout mouse, expression of Ki67, androgen receptor, and Dachshund-1 in prostate epithelium was not altered in the ERβ-Δex3 mouse. We conclude that very little of ERβ transcriptional activity depends on binding to classical estrogen response elements (EREs).mouse model | nuclear receptors | targeted disruption | ventral prostate | AP-1

BackgroundUpregulation of estrogen receptor beta (ERβ) in breast cancer cells is associated with epithelial maintenance, decreased proliferation and invasion, and a reduction in the expression of the receptor has been observed in invasive breast tumors. However, proof of an association between loss of ERβ and breast carcinogenesis is still missing.MethodsTo study the role of ERβ in breast oncogenesis, we generated mouse conditional mutants with specific inactivation of ERβ and p53 in the mammary gland epithelium. For epithelium-specific knockout of ERβ and p53, ERβ F/F and p53 F/F mice were crossed to transgenic mice that express the Cre recombinase under the control of the human keratin 14 promoter.ResultsSomatic loss of ERβ significantly accelerated formation of p53-deficient mammary tumors. Loss of the receptor also resulted in the development of less differentiated carcinomas with stronger spindle cell morphology and decreased expression of luminal epithelial markers.ConclusionsOur results show that synergism between ERβ and p53 inactivation functions to determine important aspects of breast oncogenesis and cancer progression.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-017-0872-z) contains supplementary material, which is available to authorized users.