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.This work was supported by grants from the Congress Directed Medical Research Program (BC995364 and DAMD17-01-1-0241), Cure Cancer Australia Foundation, NHMRC Australia (projects 1047149, Fellowships 1058356, 481310, 1043400), the Australian Research Council Discovery Project (DP110102288), Princeton University, NIH grant 1R01GM110161-01 (AK), Sidney Kimmel Foundation for Cancer Research (AK), Burroughs Wellcome Foundation (AK), Banque Nationale de Paris-Paribas Australia and New Zealand, Mostyn Family Foundation, Cue Clothing Co., Estee Lauder Australia, RT Hall Trust and Fellowships (ECF-13-08 and ECF-16-022) from the National Breast Cancer Foundatio

Single-cell transcriptomics reveals involution mimicry during the specification of the basal breast cancer subtype

Basal breast cancer is associated with younger age, early relapse, and a high mortality rate. Here, we use unbiased droplet-based single-cell RNA sequencing (RNA-seq) to elucidate the cellular basis of tumor progression during the specification of the basal breast cancer subtype from the luminal progenitor population in the MMTV-PyMT (mouse mammary tumor virus-polyoma middle tumor-antigen) mammary tumor model. We find that basal-like cancer cells resemble the alveolar lineage that is specified upon pregnancy and encompass the acquisition of an aberrant post-lactation developmental program of involution that triggers remodeling of the tumor microenvironment and metastatic dissemination. This involution mimicry is characterized by a highly interactive multicellular network, with involution cancer-associated fibroblasts playing a pivotal role in extracellular matrix remodeling and immunosuppression. Our results may partially explain the increased risk and poor prognosis of breast cancer associated with childbirth.</p

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

The androgen receptor interacts with GATA3 to transcriptionally regulate a luminal epithelial cell phenotype in breast cancer.

BACKGROUND: The androgen receptor (AR) is a tumor suppressor in estrogen receptor (ER) positive breast cancer, a role sustained in some ER negative breast cancers. Key factors dictating AR genomic activity in a breast context are largely unknown. Herein, we employ an unbiased chromatin immunoprecipitation-based proteomic technique to identify endogenous AR interacting co-regulatory proteins in ER positive and negative models of breast cancer to gain new insight into mechanisms of AR signaling in this disease. RESULTS: The DNA-binding factor GATA3 is identified and validated as a novel AR interacting protein in breast cancer cells irrespective of ER status. AR activation by the natural ligand 5α-dihydrotestosterone (DHT) increases nuclear AR-GATA3 interactions, resulting in AR-dependent enrichment of GATA3 chromatin binding at a sub-set of genomic loci. Silencing GATA3 reduces but does not prevent AR DNA binding and transactivation of genes associated with AR/GATA3 co-occupied loci, indicating a co-regulatory role for GATA3 in AR signaling. DHT-induced AR/GATA3 binding coincides with upregulation of luminal differentiation genes, including EHF and KDM4B, established master regulators of a breast epithelial cell lineage. These findings are validated in a patient-derived xenograft model of breast cancer. Interaction between AR and GATA3 is also associated with AR-mediated growth inhibition in ER positive and ER negative breast cancer. CONCLUSIONS: AR and GATA3 interact to transcriptionally regulate luminal epithelial cell differentiation in breast cancer regardless of ER status. This interaction facilitates the tumor suppressor function of AR and mechanistically explains why AR expression is associated with less proliferative, more differentiated breast tumors and better overall survival in 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

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

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

The effects of inducible expression of mutant and wild type <i>Oas2</i> in T47D cells.

<p><b>(A</b>) pHUSH ProEx expression vector used to express either mutant (mt) or wild type (wt) mouse <i>Oas2</i> in T47D cells in response to doxycycline (DOX). <b>(B</b>) relative expression of mt and wt <i>Oas2</i>. <b>(C</b>) Western blot showing induction of mouse OAS2 (m) running just below endogenous human OAS2 protein, with both bands above a non-specific band (nsb). <b>(D</b>) Sensitivity of the cells lines to poly I:C (pl:C) with and without DOX induction of mt and wt <i>Oas2</i>. <b>(E</b>) Effect of mt and wt <i>Oas2</i> on adherent cell number after 72h. (<b>F</b>) Cell detachment (numbers of live cells in supernatant fraction) caused by mt <i>Oas2</i>. <b>(G</b>) Effects of mt or wt <i>Oas2</i> on replating of T47D cells in a 4 hour trypsin only replating assay after 48h of DOX. <b>(H</b>) Expression of β1 integrin (β1), E-cadherin (EC) and β-actin (βa) in response to induction of mt or wt <i>Oas2</i>. <b>(I</b>) apoptotic response to induction of mt or wt <i>Oas2</i>. Data represents the average of 7 independent experiments. <b>(J</b>) cell-cycle-phase distribution at the indicated times following induction of mt or wt <i>Oas2</i>. Data represents the average of 5 independent experiments. <i>*</i>p<0.01. ANOVA 4I and J. <b>(K)</b> <i>Oas2</i> expression in parental (p) normal mouse mammary HC11 cells or in cells constitutively expressing mt or wt <i>Oas2</i>. <b>(L)</b> Effect of wt or mt Oas2 on beta Casein in HC11s after 72 hours of prolactin (Prl) and Dexamethasone (Dex) stimulation. <b>(M)</b> Effect of mt or wt <i>Oas2</i> expression on cell death at 96 hours in HC11 cells after transient transfection. All data are representative of 3 independent experiments in response to 72h of DOX except otherwise specified. Paired t-tests 4B,E,F, G, L and M.</p