ELF5 suppresses estrogen sensitivity and underpins the acquisition of antiestrogen resistance in luminal breast cancer.

We have previously shown that during pregnancy the E-twenty-six (ETS) transcription factor ELF5 directs the differentiation of mammary progenitor cells toward the estrogen receptor (ER)-negative and milk producing cell lineage, raising the possibility that ELF5 may suppress the estrogen sensitivity of breast cancers. To test this we constructed inducible models of ELF5 expression in ER positive luminal breast cancer cells and interrogated them using transcript profiling and chromatin immunoprecipitation of DNA followed by DNA sequencing (ChIP-Seq). ELF5 suppressed ER and FOXA1 expression and broadly suppressed ER-driven patterns of gene expression including sets of genes distinguishing the luminal molecular subtype. Direct transcriptional targets of ELF5, which included FOXA1, EGFR, and MYC, accurately classified a large cohort of breast cancers into their intrinsic molecular subtypes, predicted ER status with high precision, and defined groups with differential prognosis. Knockdown of ELF5 in basal breast cancer cell lines suppressed basal patterns of gene expression and produced a shift in molecular subtype toward the claudin-low and normal-like groups. Luminal breast cancer cells that acquired resistance to the antiestrogen Tamoxifen showed greatly elevated levels of ELF5 and its transcriptional signature, and became dependent on ELF5 for proliferation, compared to the parental cells. Thus ELF5 provides a key transcriptional determinant of breast cancer molecular subtype by suppression of estrogen sensitivity in luminal breast cancer cells and promotion of basal characteristics in basal breast cancer cells, an action that may be utilised to acquire antiestrogen resistance

ELF5 drives lung metastasis in luminal breast cancer through recruitment of Gr1+ CD11b+ myeloid-derived suppressor cells

During pregnancy, the ETS transcription factor ELF5 establishes the milk-secreting alveolar cell lineage by driving a cell fate decision of the mammary luminal progenitor cell. In breast cancer, ELF5 is a key transcriptional determinant of tumor subtype and has been implicated in the development of insensitivity to anti-estrogen therapy. In the mouse mammary tumor virus-Polyoma Middle T (MMTV-PyMT) model of luminal breast cancer, induction of ELF5 levels increased leukocyte infiltration, angiogenesis, and blood vessel permeability in primary tumors and greatly increased the size and number of lung metastasis. Myeloid-derived suppressor cells, a group of immature neutrophils recently identified as mediators of vasculogenesis and metastasis, were recruited to the tumor in response to ELF5. Depletion of these cells using specific Ly6G antibodies prevented ELF5 from driving vasculogenesis and metastasis. Expression signatures in luminal A breast cancers indicated that increased myeloid cell invasion and inflammation were correlated with ELF5 expression, and increased ELF5 immunohistochemical staining predicted much shorter metastasis–free and overall survival of luminal A patients, defining a group who experienced unexpectedly early disease progression. Thus, in the MMTV-PyMT mouse mammary model, increased ELF5 levels drive metastasis by co-opting the innate immune system. As ELF5 has been previously implicated in the development of antiestrogen resistance, this finding implicates ELF5 as a defining factor in the acquisition of the key aspects of the lethal phenotype in luminal A breast cancer

ELF5 drives lung metastasis in luminal breast cancer through recruitment of Gr1+ CD11b+ myeloid-derived suppressor cells

During pregnancy, the ETS transcription factor ELF5 establishes the milk-secreting alveolar cell lineage by driving a cell fate decision of the mammary luminal progenitor cell. In breast cancer, ELF5 is a key transcriptional determinant of tumor subtype and has been implicated in the development of insensitivity to anti-estrogen therapy. In the mouse mammary tumor virus-Polyoma Middle T (MMTV-PyMT) model of luminal breast cancer, induction of ELF5 levels increased leukocyte infiltration, angiogenesis, and blood vessel permeability in primary tumors and greatly increased the size and number of lung metastasis. Myeloid-derived suppressor cells, a group of immature neutrophils recently identified as mediators of vasculogenesis and metastasis, were recruited to the tumor in response to ELF5. Depletion of these cells using specific Ly6G antibodies prevented ELF5 from driving vasculogenesis and metastasis. Expression signatures in luminal A breast cancers indicated that increased myeloid cell invasion and inflammation were correlated with ELF5 expression, and increased ELF5 immunohistochemical staining predicted much shorter metastasis–free and overall survival of luminal A patients, defining a group who experienced unexpectedly early disease progression. Thus, in the MMTV-PyMT mouse mammary model, increased ELF5 levels drive metastasis by co-opting the innate immune system. As ELF5 has been previously implicated in the development of antiestrogen resistance, this finding implicates ELF5 as a defining factor in the acquisition of the key aspects of the lethal phenotype in luminal A breast cancer

A mutation in the viral sensor 2’-5’-oligoadenylate synthetase 2 causes failure of lactation

We identified a non-synonymous mutation in Oas2 (I405N), a sensor of viral double-stranded RNA, from an ENU-mutagenesis screen designed to discover new genes involved in mammary development. The mutation caused post-partum failure of lactation in healthy mice with otherwise normally developed mammary glands, characterized by greatly reduced milk protein synthesis coupled with epithelial cell death, inhibition of proliferation and a robust interferon response. Expression of mutant but not wild type Oas2 in cultured HC-11 or T47D mammary cells recapitulated the phenotypic and transcriptional effects observed in the mouse. The mutation activates the OAS2 pathway, demonstrated by a 34-fold increase in RNase L activity, and its effects were dependent on expression of RNase L and IRF7, proximal and distal pathway members. This is the first report of a viral recognition pathway regulating lactation

Effects of OAS2 mutation on global patterns of gene expression in the mammary gland.

<p>Whole mouse mammary glands from homozygous <i>Oas2</i> mutant (mt) or wild type (wt) animals were profiled using Affymetrix MTA arrays. Differential gene expression was ranked by the limma t-statistic and this was used as the input for gene set enrichment analysis to identify functional signatures. The enrichment-map plug in for Cytoscape was used to visualize the results. Each node represents a gene set and the expression of genes comprising the leading edge of some of these sets is shown as heat maps of the t-statistic. Labels indicate the function of the clustered gene sets. Gene expression in mt animals is compared with wt animals at 2dpp (node center color) or 18dpc (node edge color). Red indicates enrichment of expression the gene set and blue suppression of expression.</p

<i>ELF5</i> expression in normal breast and breast cancer.

<p><i>ELF5</i> expression in the UNC337 breast cancer cohort according to subtype. Top panel shows combined results with statistical analysis (thick black line, median;, box, interquartile range 25%–75% of points; whiskers, 1.5× interquartile range; crosses, individual tumors). Bottom panel <i>ELF5</i> expression in all individual tumor and normal samples. Basal and normal had significantly higher expression of ELF5.</p

Enzymatic properties of mutant OAS2.

<p><b>(A</b>) Details of the mutation in <i>Oas2</i> showing the ENU-induced SNP changing isoleucine to asparagine. <b>(B)</b> RNAseL activity measured as the abundance of RNase L-specific cleavage of tRNA-His-36 (upper panel) or rRNA (lower panel) at day 18 of pregnancy (d18pc) and two days post partum (2dpp). <b>(C</b>) Representative denaturing PAGE separating 2-5A species of different molecular weights synthesized in a cell free system by mutant (mt) or wild type (wt) mouse OAS2, in response to activation by different concentrations of the double-stranded RNA mimic polyI:C. <b>(D</b>) quantification of the data in panel C. <b>(E</b>) western blot demonstrating similar OAS2 protein input to the assay above.</p

Effects of knockdown of RNASEL, IRF7 and IRF3 on the effects of inducible expression of either mutant (mt) or wild type (wt) mouse <i>Oas2</i> in T47D cells.

<p><b>(A-G)</b> Provide the context of RNase L knockdown. <b>(A-C</b>) Demonstration of Doxycycline (DOX)-inducible expression of wt or mt <i>Oas2</i> in T47D cells, and effective knock-down of RNASEL (RNaL) in mt or wt expressing T47D cells by quantitative PCR (<b>B</b>) or western blot (<b>C</b>). <b>(D)</b> Effect of the induction of mt or wt OAS2 on RNase L activity <b>(E)</b> Effects of induction of mt and wt <i>Oas2</i> expression on apoptosis. <b>(F)</b> Effects of these treatments on interferon gamma protein production. <b>(G</b>) effects of these treatments on GM-CSF production. <b>(H</b>) Demonstration of effective knockdown of IRF7. <b>(I)</b> Effects of knockdown of IRF7 on mutant or wild type <i>Oas2</i>-driven apoptosis. <b>(J)</b> Demonstration of knockdown of IRF3. <b>(K)</b> Effects of knockdown of IRF3 on mutant or wild type <i>Oas2</i>-driven apoptosis.</p

Taqman probes used for quantitative PCR indicating gene name, probe ID number and species specificity.

<p>Taqman probes used for quantitative PCR indicating gene name, probe ID number and species specificity.</p